CA1079347A - Saturating time-delay transformer for overcurrent protection - Google Patents
Saturating time-delay transformer for overcurrent protectionInfo
- Publication number
- CA1079347A CA1079347A CA263,181A CA263181A CA1079347A CA 1079347 A CA1079347 A CA 1079347A CA 263181 A CA263181 A CA 263181A CA 1079347 A CA1079347 A CA 1079347A
- Authority
- CA
- Canada
- Prior art keywords
- load
- winding
- current
- electrode
- crowbar
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
- H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
- H02H9/021—Current limitation using saturable reactors
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/02—Details
- H02H3/021—Details concerning the disconnection itself, e.g. at a particular instant, particularly at zero value of current, disconnection in a predetermined order
- H02H3/023—Details concerning the disconnection itself, e.g. at a particular instant, particularly at zero value of current, disconnection in a predetermined order by short-circuiting
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H33/00—High-tension or heavy-current switches with arc-extinguishing or arc-preventing means
- H01H33/02—Details
- H01H33/59—Circuit arrangements not adapted to a particular application of the switch and not otherwise provided for, e.g. for ensuring operation of the switch at a predetermined point in the ac cycle
- H01H33/596—Circuit arrangements not adapted to a particular application of the switch and not otherwise provided for, e.g. for ensuring operation of the switch at a predetermined point in the ac cycle for interrupting dc
Abstract
ABSTRACT OF THE DISCLOSURE
Electrical loads connected to d-c supplies are pro-tected from damage by overcurrent in the case of a load fault by connecting in series with the load a saturating transformer that detects a load fault and limits the fault current to a safe level for a period long enough to correct the fault or else disconnect the power supply.
Electrical loads connected to d-c supplies are pro-tected from damage by overcurrent in the case of a load fault by connecting in series with the load a saturating transformer that detects a load fault and limits the fault current to a safe level for a period long enough to correct the fault or else disconnect the power supply.
Description
~CD7~347 .. . . . .. ... ...... .... .
SA'rURATING TIME--DELAY T:E~\NSFORMEX FOR OYE~¢CURRENT PROTECTION
' BACKGROUND OF THE INYENTION
This invention relates to the protection of d-c ~
electrical loads from damaging overcurrent~ In particular ,' it applies to circuits where a breakdown,of insulation in ,;
the load causes a sudden large increase in current. Such an increase is characteristic of a faulk in a high-voltage tube or a high-voltage accelerating skructure.
, Electrical loads that are connecked to high-voltage d-c;power supplies are frequently sub~ect to a risk of destruction by delivery of so,me of the power from the supply to portions of the load in excessi~e quantities as a result of a~ault. ~This~is especially krue of high-voltage ac~cel~erating structures connected t,o high-volkage power supplie~s,~alt'hough almost any load that is connected to a d-c~power~supply~is capable,of being damaged, ak least " locally, by ~ault currents~. However, the threat of electrioal-breakdown~is greatest in those electrical loads ~ Ot~ 3~
that are connected to power supplies at relatively high voltage, of the order of kilovolts. It is customary to protect such loads from damage by the use o~ a crowbar.
This is a controllable short circuit that can be placed across the output terminals of the power supply to short out the load and thereby bypass the electrical energy that would otherwise be delivered ln an excessive amount to the load. The crowbar is often a gas tube such as an ignitron, a solid-state device such as a sillcon-controlled rectifier ~SCR), or a triggered spark gap. A control signal ~or the crowbar is derived from a sensor o~ load current, load voltage or both, and the presence of a damaging fault is caused to generate a signal that operates khe crowbar. With the output of the supply shorte~, the load is relieved o~
the excess electrical energy that would otherwise have been delivered to it and the overcurrent protective mechanisms normally built into the circuit will trip to prevent damage to the power supply.
The arrangement ~ust described has one ma~or dis-29 advantage.~ This is the fact that the signal required to operate the crowbar results from the application of damaging currents to the load. It frequently happens that the load ,:: : :.
is damaged~before the orowbar can be applied. Even in cirou~stances when the load is not immediately dama8ed by the excessive current, it remains true that the load is caused~ to carry current beyond its normal operating range :::
in order to tr~ip the crowbar. A ~ault current that may be ~ as muoh as several orders o~ magnitude larger than normal ; ~ - 2 -~;:: :
~ ' , . . ., . : , , , . . . :
93~'7 load currents thus passes for a period of time through the load. It would clearly be desirable to have a protective mechanism whose operation did not requ-Lre damaging currents.
It is an ob;ect of the present inventlon to provide a better means o~ protecting d-c electrical loads ~rom damage due to overcurrents.
It is a further ob~ect of the present invention to provide a means o~ overcurrent protection ~or d-c electrical loads that does not require the passage o~ damaging currents through the load to operate the protection.
Other ob~ectæ will become apparent in the course of a detailed description o~ the invention.
SUMMARY OF THE INVENTION
A d-c electrical load is protected from damage due to oYercurrent by an apparatus comprising a saturating trans-~ormer that has a primary winding connected in series with the load. A seoond winding carries a bias current which magnetizes in opposition to the primary current and which, : ` :
together with the load current, established in the core ; of the trans~ormer a net flux level that is in saturat1on but near the knee~ of the B-H curve. A load fault causes the prlmary cu:rrent to ~lncrease to a value tha~ brings the ~ ~ .. .;
core out of saturation, thereby generating an opposin~ emf that llmita the ~ourrent increase. When the core comes out of saturat1on~a signal ls generated that can be used to trlgger a crowbar to disconnect the circuit from the power supply.~ This slgnal may be taken from the second ~: :
. , ... ': . : :; ' . . : .
. . . ~ .~ .
~L07~3~
winding or from a third winding added for this purpose.
A crowbar time delay may be interposed between the sensing winding and the crowbar to delay operation of the crowbar and thus avoid the interruption Or service from unsustained arcs. The triggering winding may also operate a spark gap placed in series with a chargecl capacitor that is discharged through the load to clear the f`ault and restore normal operation of the circuit.
BRIEF DESCRIPTION OF THE DRA~INC7S
10 Fig. 1 is a circuit diagram of an apparatus for the practice of the present invention.
Fig. 2 is a typical hysteresis or B-H curve for the core of the transformer of the present invention.
Fig. 3 is a time plot o~ currents and voltages in the circuit of Fig. 1.
Fig. 4 is a circuit diagram of an alternate embodi-ment of the present invention, appearing with ~ig. 1.
; DETAILED DESCRIPTION OF THE INVENTION
Fig. 1 is a circuit diagram of an apparatus for the practice of the present invention. In Fig. 1~ load 10 is an electrical load that is sub~ect to damage in the event of , a fault in the load. Examples of such electrical loads include high-voltage accelerating structures and high-voltage , vacuum tubes. Load 10 is connected to form a series circuit .
with primary winding 11 of transformer 12 and d-c power .
supply 14. Bridge rectifiers 16 and three-phase transformer :~
18 are connected through contactor 20 and circuit breaker 22 to an a-c power line to comprise d-c power supply 14. A
_ 4 0 ..
. . .. : , - - .. ~. . ,; ., . . - , .. . . .
~al7~3~7 crowbar 24 is connected across the terminals o~ power supply 14 to apply a short circuit across power supply 14 and thereby af~ord protection to load 10. Current detector 26 is placed in series with crowbar 24 to provide a signal to trip circuit breaker 22 to disconnect the a-c power line from trans~ormer 18 and thereby protect power supply 14 against damage. Alternatively, circuit breaker 22 may trip normally under the influence o~ an overcurrent through circuit breaker 22.
Circuits such a5 that of Fig. 1 in which a power supply 14 supplies a load 1-0 with a crowbar 24 placed to protect load 10 are well known in the art. The crowbar 24 is typically triggered either by sensing a drop in the voltage across load 10 or an increase in the current through load 10. Each of these means of triggering requires that load 10 carry a current that is substantially beyond its normal operating current in order to trigger crowbar 24. The present invention avoids~ that disadvantage as ~ollows.
Trans~ormer 12 o~ the present invention includes a winding 28 that generates an input to a time delay circuit 30 to trigger crowbar 24. Trans~ormer 12 also generates a back ; em~ that opposes the inorease in load current that would otherwise result ~rom~a ~ault in load 10. The point of operation is set by the current in blas windlng 32. This is a d-c~current~ that~is~ supplied by bias supply 34 ~hrough resistor 36. The~combination of capacitor 40 and inductor~42 forms a filter to isolate bias supply 34 ~rom ; ~:: ~ : ~ , :
~ pulses~generated in bias~winding 32 by changes in load :: : : -, : : :
~ - 5 -~ :: .
.
93~'7 current through transformer 12. In trans~ormer 12 primary winding 11 must be sized to carry load current and also insulated su~ficiently to withstand the voltages applied to load 10. Core 46 of trans~ormer 12 sustains the ~lux that establishes magnetic coupling among primary winding 11, winding 28 and bias winding 32.
Understanding of the operation o~ the present invention will be aided by reference to Fig. 2 which is an ideallzed version o~ a B-H curve o~ the core 46 of trans~ormer 12 of Fig. 1. Fig. 2 is idealized for ease of drawing and refer-ence, but the idealization of the characteristics is not signi~icant to the description of the invention. The curve of Fig. 2 is the ma~or hysteresis loop for the material. It is the curve of magnetic ~lux density B as a ~unction of magnetizing force H, also called the B-H curve~ This curve is obtained by cycling the magnetizing force on a closed loop of the material in an amount su~ficient to cause the material to go into saturatlon alternately in the positive and negative directionsO This is indicated in ~ig. 2 by the cycllng between point 50 and point 52, The meaning of the term "major hysteresis loopl' is that the application of ; larger amounts of magnetlzing force in either direction will not chan~e the cur~e on which the material returns .:.
; when the magneti~lng ~orce ls reduced. This is in contrast to the minor hysteresis loops which are obtained by cycling the magnetlzlngr force;at Yalues that place the state of the ., material inside the area bounded by curves 53, 54, 55, and 56. Curves 54 and 56 are shown as straight and slightly :
....
1~7~'7 sloped vertical lines. The presence of an air gap in the core would give curves 54 and 56 a finite value of slope, equal for both~ and would facilitate manufacture of the transformer 12 of Fig. l, but would not otherwise a~fect this invention. The invention is practiced by ad~usting the voltage of bias supply 34 o~ Fig. l or the resistance of resistor 36 of Fig. l to set current i2 at a value that produces in core 46 of Fig. l a state of saturation at point 50 of Fig, 2. This saturation is then reduced to point 58 ~y the passage of load current through primary winding ll of Fig. l. The result of the two opposing effects in core 46 is to place point 58 in saturation but close to the knee of the curve of Fig. 2 which is indi-cated by point 60. The sharpness of the knee at point 60 is a function of the particular material o~ which core 46 is made, and ls also a ~unc~ion of the scale to which the curve of Fig. 2 is drawn. However, saturation in the curve of Fig. 2 is unambiguous and it is necessary that point 58 be in the region of saturation of the core. It follows from inspection of Fig. 2 that, with the current i2 in bias ~ winding 32 held constant, variations in the load current ; ~ through primary winding ll will cause corresponding motion of point 58 along the cur~e. Because point 58 is in a rsglon of saturatlon, these changes in location cause essentially no change in magnetlc ~lux in core 46 and hence no lnduced smf across primary winding 11. However, lf the current through prlmary winding 11 increases suf~iciently ~to oause the nst magnetic flux in the core to pass point :, ~ .
. ~ :~; :. : : .
'7~
60 and start up curve 54s then the transformer enters a region in which B, and hence the magnetic flux, ls changing.
This change o~ magnetic flux in a given period of time will generate an emf in primary winding 11 which will oppose the direction of current increase according to Lenz's law. The opposition takes the form o~ an emf e = -n d(phl)/dt that appears across primary winding 11 in a sense to subtract from or oppose the power supply voltage. Thls opposing em~
will protect load 10 of Fig. 1 by keeping the load current at a value that will place the core in some portion of curve 54 for a time equal to that needed to move the length of curve 54. Point 62 is one such point. At the same time, the increase in flux llnkages that was associated with the development of the back emf across primary winding 11 will also generate a voltage across signal winding 28 that can be used either directly or through a time delay such as time-delay circult 30 to trigger crowbar 24. This triggering has thus taken place without the necessity ~or a damaging overcurrent in load 10 of Fig. 1.
:
Fig. 3 is a time plot of currents and voltages in the ; clrcuit of Fig. 1. The tlme scale of Fig. 3 is a function of the values of voltages, currents and the load in the circuit, but marker 64 1s placed to show the time of 50 to 100 microseconds that is typical of a wide range o~
applications. ~Four time intervals are shown in Fig. 3, , characterized as follows. Interval 66 is a period of normal operation. Inter~al 68 is a period of time during which an undes'ired arc exists in load 10 of Fig. 1.
~ .
:
l~V~3~7 Interval 70 is a tlme period in which the arc has gone out and the circuit is returning to the normal operating condition. Interval 72 is a period of normal currents and voltages again. These interva:Ls and the values of current and voltage associated with them are best understood by referring to the corresponding points on Fig. 2 as follows.
During interval 66, current curve 74 i5 at a constant value representing the normal load current. Load voltage curve 76 is at a constant value which differs from the source voltage only by the small amount of the amplitude of d-c voltage drop of transformer voltage curve 78.
Associated with these values of load current and load voltage is an operating point 58 on the B-H curve o~ Fig. 2, marked in parentheses on Fig. 3. Interval 66 ends when a short circuit develops in load 10 of Fig. 1. The load current immediately begins a rapid rise which is associated with a motion of the operating point in Fig. 2 ~rom point 58 to point 60. During this change~ the flux in core 46 is hardly changing. ~herefore, the supply voltage is divided between the voltage drop across the transformer leakage inductance and that across the arc. As soon as the load current has reached point 60 of Fig. 2, a~ a value shown in parentheses in Fig. 3, the core enters the st~eply rising ~ .
port;ion of the hysteresis loop, curve ~4. This portion is characterized by a high magnetizing inductance. Point 60 ~ :
o~ Fig. 2 is ~cnown as the knee of the hysteresis loop.
Past point 60~ the steeply~rising portion3 curve 54, is associated in Fig. 3 with a relatively constant portion of , ~ . . , :, -; ,. . . . .
~93~
the curve for load current 74~ an abrupt rise in the curve of transformer voltage 78 and a correspondingly abrupt drop in load voltage curve 76. Once the knee o~ the B-H curve is turned, trans~ormer winding 11 behaves like an inductor and the flux change in the core causes essentially all of the load voltage to appear across the prirnary o~ trans~
~ormer 12. In some cases, this abrupt drop in the arc -voltage together with the limit imposed by transformer 12 on the maximum value of load current will cause the ~ault to extinguish itself. The curves of Fig. 3 are drawn under the assumption that this has happened at the end o~ interval 68. The time at the end o~ interval 68 is associated in Fig. 2 with poink 62 on the B-H curve, as indicated in parentheses in Fig. 3. It can be seen that point 62 in Fig. 2 is on the rising portion o~ the hysteresis curve.
Restora~ion of normal operating conditions begins with a drop in the load ourrent and occurs in three stages.
The first stage is an abrupt drop in a short interval that is associated in Fig. 2 with rapid passage along a minor hysteresis loop to point 80 on the B-H curve or ma~or hysteresis loop of the ma~erial. Next the current is nearly constant, showing only a slight decrease, while the , ~ .
-~ ~ core is taken from point 80 to point 82. Thls corresponds to interval 70 in Fig.~ 3, in which the values corresponding to points 80 and~82 are shown in parentheses. Finally, on ~ -passing~again~into the region of saturation past point 82, the current drops abruptly to its normal operating level as the core returns to point 58. This is interval 72 in : :
,:
..... . ,. . . . . . ,.. ,~ :.
. .
~793~7 Fig. 3. Transformer voltage curve 78 is readily derivable from Fig. 2 by associating the changes with each interval.
Thus, during interval 66, the voltage across transformer 12 is constant at the low value, nearly zero, representing the IR drop across the transformer. A change in the con-ditions of the circuit that cause the operatlng point o~
the core to move at the saturatlon level represents very little change in the voltage across the primary transformer 12~ since the flux ls changing very little in saturation, and the voltage is proportional to the time rate o~ change of magnetic flux. However, when the condition of the core is past point 60 and is in region 54 of Fig. 2, then the current, which is proportional to H, is changing very slightly while the flux~ which is proportional to B, is changing rapidly. Thus, the trans~ormer voltage achieves a high value and, in general, will drop almost ail of ~he supply voltage. The passage in Fig. 2 ~rom point 62 to 58 represents a return of stored magnetic energy ~rom core 46 of transformer 12 so that the voltage across primary 2Q winding 12 becomes negative during this interval. Once this energy has been returned, allowing return of the core to point 58, the voltage across primary wlnding 4ll of trans~ormer 12 drops again to the low value representing the IR drop acrQss the transformer.
The;sloping lines in all the curves of Fig. 3 repre sent straight-:Line approximations to c~rves that are essentially exponentials with L/R time constants that are long compared t;o the time scale shown. The exact shape o~
:
- , ~ , - ; , -. , , ., .. ,. ~ , . . .......... . . - . .
- . , , ~: , : , , , : , .
~7~3~L~
these curves is less important than their relative magnitude and direction of increase or decrease and they are therefore idealized as straight lines. However~ one thing should be noted from a comparison o~ the curves of Figs. 2 and 3: the apparatus of the present invention will protect a load only as long as operation is maintalned on curve 54 of Fig. 2. In other words, operation must not be allowed to pass point 84 of Fig. 2, which is represented as the terminus o~ a dashed line in Fig. 3. Accordingly, it i5 useful to set a time delay to operate a crowbar within a time that is less than the length o~ time interval 86, the time from point 60 to point 84. This is facilitated by the fact that the flux change in core 46 is associated wlth the rise in transformer voltage curve 78 after point 60 and this flux change is available to trigger the time-delay circuit 30 of Fig. 1. The length of time interval 86 is directly proportional to the total change in flux linkages in the primary winding and inversely proportional to the voltage of the power supply. If the circuit quenches automatically as illustrated in Fig. 3 3 then the portion . .
~ of Fig. 2 between polnts 62 and 80 will generate in signal ~ .
winding 28 an impulse that can be used to reset the crowbar time~delay and prevent the ~opera~ion of crowbar 24 of Fig. 1.
If the arc does not quench automatically before the pre-determlned tlme;o~the~tlme-delay circuit, then orowbar 24 will~be triggered to short the power supply and protect the load. The;design of crowbar time-delay circult 30 is a routine matter of using counters or flip-~lops to time the ~'793~'~
desired waiting period before triggering the crowbar 24.
Fig. 4 is a circuit diagram of an alternate embodimento~ the present invention. Fig. 4 is similar to Fig. 1 in that a load 10 is connected through a trans~ormer 12 to a high-voltage power supply 14. A crowbar 24 is connected across the terminals of high-voltage power supply 14 to protect load 10 from the effects of damaging overvoltages.
Transformer 12 includes a primary winding 11, a signal winding 28 and a bias winding 32. As with Fig. 1~ bias winding 32 is connected to bias supply 34 through a series-parallel combination o~ resistor 36, capacitor 40 and inductor 42 to filter pulses in bias winding 32 to protect bias supply 34. In the embodiment of Fig. 4, signal winding 28 serves two functlons. The first, as in Fig. 1, ls to trigger crowbar 24, either directly or as shown in Fig. 4 through a time-delay circuit 30. The other ~unction of signal winding 28 is to sense an overload in the same way that was explained with re~erence to the circuit of Fig. l and to initiate a ~urther protective response for load 10. This is accomplished by connecting ~; a triggered hi.gh-voltage spark gap 90 in series with a capaoltor 91 across load 10. Capacitor 91 is charged through resistor 92 by power supply 93 to a d-c voltage ~-that is low in comparlson with the normal operating voltage across load 10. Trigger electrode 911 is disposed ln spark .
gap 90 to initiate conduction across spark gap 90 in response to a signal fram slgnal wlnding 28. When this happens~ the energy stored ln capacitor 91 will discharge and drive :
:
7~34~
current through the fault in load 10 in a direction opposite to the flow of fault current. By thls means, the net current in load 10 goes through zero and the arc is quenched. Normal operation of the circuit o~ Fig. 4 comprises quenching the arc by means o~ the triggered spark gap 90 and the quenching energy from capacitor 91.
However, if the arc is not quenched or i~ the arc restrikes before the circuit of Fig. 4 has been restored to steady-state conditions, then the signal from time-delay trigKer circuit 30 will cause crowbar 24 to operate and short out power supply 14 before time interval 86 has elapsed, thus protecting the load against damage.
The nature of load 10 in Figs. 1 and 4 has been des-cribed herein as a high-voltage load. While the present invention has particular utility in application to struc-tures such as accelerating tubes, Cockro~t-Walton generators, and other structure designed to support high voltages, its use is not limited to such structures. The saturating time-delay ~ransformer lZ o~ F1gs. 1 and 4 can equally as well 20 be used to protect loads at lower voltages, of the order of -hundreds o~ volts or less.~ This extends the choice o~
elements to be used for crowbar 24 which includes ignltrons, thyratrons, SC~'s, transistors, vacuum tubes, and any of a number o~ other elements meeting the requirement that they : : : ~ : : . ..
sustain the operatlng voltage of power supply 14 with very 11ttle~current unlesæ~tr1ggered, in which case they must sustain the short circuit current of power supply 14.
Trans~ormer 12 has a primary winding that must be capable .
~75~3~L~7 of carrying the load current ln load 10 and must be capable o~ supporting the load voltage of powe:r supply 14. The bias winding 32 and signal wincling 28 can be designed ~or relatively low voltage. Signa] winding 28 is primarily a pulse winding and must be designed to provide adequate response to pulses induced by rapid change in the ~lux in core 46 of Figs. 1 and Ll. Other requirements of the circuits of Figs. 1 and 4 are design choices depending on the parameters of the source and load. For example, one such design choice allows the designer to combine the functions of the bias winding and the signal windlng into a single winding. In thls case, the signal used to trigger the crowbar and, if used, the spark gap is obtained by connecting across the terminals of the bias winding before the ~ilter network. This is an obvious possibility, although not a likely choice because of the typical para-meters to be expected in such a circuit.
The following example will make this clear. Consider the problem of protecting with a time delay of 50 micro-secpnds a load designed to carry 10 amperes at 200 kilovolts.
.
Suppose there i9 avallable a core in which the saturation level of flux density is 17 kiloGauss~ and assume a primary winding comprising 100 turns. The core area would then be 294 square centimeters, obtained as follows. The change of flux denslty is from saturation in one direction to satura- ~ -tion in the o~her so that the net change is 2 x 17 -kiloGauss = 34 kiloGauss and this change takes place in at most 50 microseconds. From Faraday's Law, the cross-~;
.. . . . . . ......... .. . . . . ......... . . .
: ' , , ' ' 1~793~'~
sectional area o~ the core is thus the ratio of the product of voltage and time to the product of turns and change in flux density. Substitution of the values above gives 294 square centimeters or a square cross section approximately 17.2 cm on a side. During normal operation, the magneto-motive force (mmf) of the load current is 100 turns x 10 amperes = 1000 ampere~turns. This value of mmf represents the distance between points 50 and 58 in Fig. 2. The value of mmf supplied by the bias windlng must equal this amount plus an additional amount sufficlent to move the core to point 58. A routine calculation of the amount of core necessary to provide a cross section of 17.2 square centimeters and enough core window to support a primary o~
100 turns insulated ~or 200 kilovolts results in a median core length of approximately 160 cm. A typlcal value o~
the magnetic field strength at saturation is 2 amperes/cm. ' The product of this magnetic field strength and the mean length shows that 320 ampere turns are necessary to put the core into saturation at point 58. Thus, the bias winding must produce the sum Or 1000 and 320 ampere turns or 1320 ampere turns. A two-turn coil will produce this with a current of 660 amperes. ~With this current ~lowing in the :
bias winding, the core would be placed in operation a~
point 58 o~ Fig. 2. Slight ~ariations in this value of current enable the motion of point 58 to the l,eft or right to make a read~ ad~ustment of the sensitivity of triggering.
It will be reme~mbered that triggering takes place only when the current through the primary is increased sufficiently "
~,, ~L~7~33~'7 to move the primary ampere turns from point 58 to and past point 60. It should also be evident that the voltage ratings necessary for both the primary and bias coils are evident from this design approximationO Thus each primary turn must be insulated from the next by an amount sufficient to with-stand the ratio 200 kilovolts/100 turns or 2 kilovolts per turn. The bias winding will be sub~ected to a step down of 100:2 on 200 kilovolts, or a voltage of 4 kilo~olts~
The foregoing calculations make it evident that in situations where 4 kv is too high a voltage for the crowbar trigger circuit, it will be easier to use separate windings for the bias winding and the signal winding. However, this is a matter o~ design convenience rather than necessity, as the signal ~ufficient to trigger a crowbar is available at the terminals of the bias winding and could be so used. It should also be evident that the indicated use of more than one ignitron as a crowbar is a matter as well of design requirements. If the voltage rating capaclty of the power supply exceeds that of the ignitrons readily available, then it is a simple matter to place additional ignitrons in series to support the load voltage or ln parallel to carry the load current. In such a case, it is an equally simple matter to add other signal windings to the transformer to control these ignitrons if they are to be controlled directly. In the alternative, one signal winding can be - connected~to a single time-delay circuit whic~ can then be u9ed to trigger a plurality Or ignitrons via separate ; tri8ger circuits.
., , . ~ . . . ~ .
. ~ ~ . .
- . ~ .,
SA'rURATING TIME--DELAY T:E~\NSFORMEX FOR OYE~¢CURRENT PROTECTION
' BACKGROUND OF THE INYENTION
This invention relates to the protection of d-c ~
electrical loads from damaging overcurrent~ In particular ,' it applies to circuits where a breakdown,of insulation in ,;
the load causes a sudden large increase in current. Such an increase is characteristic of a faulk in a high-voltage tube or a high-voltage accelerating skructure.
, Electrical loads that are connecked to high-voltage d-c;power supplies are frequently sub~ect to a risk of destruction by delivery of so,me of the power from the supply to portions of the load in excessi~e quantities as a result of a~ault. ~This~is especially krue of high-voltage ac~cel~erating structures connected t,o high-volkage power supplie~s,~alt'hough almost any load that is connected to a d-c~power~supply~is capable,of being damaged, ak least " locally, by ~ault currents~. However, the threat of electrioal-breakdown~is greatest in those electrical loads ~ Ot~ 3~
that are connected to power supplies at relatively high voltage, of the order of kilovolts. It is customary to protect such loads from damage by the use o~ a crowbar.
This is a controllable short circuit that can be placed across the output terminals of the power supply to short out the load and thereby bypass the electrical energy that would otherwise be delivered ln an excessive amount to the load. The crowbar is often a gas tube such as an ignitron, a solid-state device such as a sillcon-controlled rectifier ~SCR), or a triggered spark gap. A control signal ~or the crowbar is derived from a sensor o~ load current, load voltage or both, and the presence of a damaging fault is caused to generate a signal that operates khe crowbar. With the output of the supply shorte~, the load is relieved o~
the excess electrical energy that would otherwise have been delivered to it and the overcurrent protective mechanisms normally built into the circuit will trip to prevent damage to the power supply.
The arrangement ~ust described has one ma~or dis-29 advantage.~ This is the fact that the signal required to operate the crowbar results from the application of damaging currents to the load. It frequently happens that the load ,:: : :.
is damaged~before the orowbar can be applied. Even in cirou~stances when the load is not immediately dama8ed by the excessive current, it remains true that the load is caused~ to carry current beyond its normal operating range :::
in order to tr~ip the crowbar. A ~ault current that may be ~ as muoh as several orders o~ magnitude larger than normal ; ~ - 2 -~;:: :
~ ' , . . ., . : , , , . . . :
93~'7 load currents thus passes for a period of time through the load. It would clearly be desirable to have a protective mechanism whose operation did not requ-Lre damaging currents.
It is an ob;ect of the present inventlon to provide a better means o~ protecting d-c electrical loads ~rom damage due to overcurrents.
It is a further ob~ect of the present invention to provide a means o~ overcurrent protection ~or d-c electrical loads that does not require the passage o~ damaging currents through the load to operate the protection.
Other ob~ectæ will become apparent in the course of a detailed description o~ the invention.
SUMMARY OF THE INVENTION
A d-c electrical load is protected from damage due to oYercurrent by an apparatus comprising a saturating trans-~ormer that has a primary winding connected in series with the load. A seoond winding carries a bias current which magnetizes in opposition to the primary current and which, : ` :
together with the load current, established in the core ; of the trans~ormer a net flux level that is in saturat1on but near the knee~ of the B-H curve. A load fault causes the prlmary cu:rrent to ~lncrease to a value tha~ brings the ~ ~ .. .;
core out of saturation, thereby generating an opposin~ emf that llmita the ~ourrent increase. When the core comes out of saturat1on~a signal ls generated that can be used to trlgger a crowbar to disconnect the circuit from the power supply.~ This slgnal may be taken from the second ~: :
. , ... ': . : :; ' . . : .
. . . ~ .~ .
~L07~3~
winding or from a third winding added for this purpose.
A crowbar time delay may be interposed between the sensing winding and the crowbar to delay operation of the crowbar and thus avoid the interruption Or service from unsustained arcs. The triggering winding may also operate a spark gap placed in series with a chargecl capacitor that is discharged through the load to clear the f`ault and restore normal operation of the circuit.
BRIEF DESCRIPTION OF THE DRA~INC7S
10 Fig. 1 is a circuit diagram of an apparatus for the practice of the present invention.
Fig. 2 is a typical hysteresis or B-H curve for the core of the transformer of the present invention.
Fig. 3 is a time plot o~ currents and voltages in the circuit of Fig. 1.
Fig. 4 is a circuit diagram of an alternate embodi-ment of the present invention, appearing with ~ig. 1.
; DETAILED DESCRIPTION OF THE INVENTION
Fig. 1 is a circuit diagram of an apparatus for the practice of the present invention. In Fig. 1~ load 10 is an electrical load that is sub~ect to damage in the event of , a fault in the load. Examples of such electrical loads include high-voltage accelerating structures and high-voltage , vacuum tubes. Load 10 is connected to form a series circuit .
with primary winding 11 of transformer 12 and d-c power .
supply 14. Bridge rectifiers 16 and three-phase transformer :~
18 are connected through contactor 20 and circuit breaker 22 to an a-c power line to comprise d-c power supply 14. A
_ 4 0 ..
. . .. : , - - .. ~. . ,; ., . . - , .. . . .
~al7~3~7 crowbar 24 is connected across the terminals o~ power supply 14 to apply a short circuit across power supply 14 and thereby af~ord protection to load 10. Current detector 26 is placed in series with crowbar 24 to provide a signal to trip circuit breaker 22 to disconnect the a-c power line from trans~ormer 18 and thereby protect power supply 14 against damage. Alternatively, circuit breaker 22 may trip normally under the influence o~ an overcurrent through circuit breaker 22.
Circuits such a5 that of Fig. 1 in which a power supply 14 supplies a load 1-0 with a crowbar 24 placed to protect load 10 are well known in the art. The crowbar 24 is typically triggered either by sensing a drop in the voltage across load 10 or an increase in the current through load 10. Each of these means of triggering requires that load 10 carry a current that is substantially beyond its normal operating current in order to trigger crowbar 24. The present invention avoids~ that disadvantage as ~ollows.
Trans~ormer 12 o~ the present invention includes a winding 28 that generates an input to a time delay circuit 30 to trigger crowbar 24. Trans~ormer 12 also generates a back ; em~ that opposes the inorease in load current that would otherwise result ~rom~a ~ault in load 10. The point of operation is set by the current in blas windlng 32. This is a d-c~current~ that~is~ supplied by bias supply 34 ~hrough resistor 36. The~combination of capacitor 40 and inductor~42 forms a filter to isolate bias supply 34 ~rom ; ~:: ~ : ~ , :
~ pulses~generated in bias~winding 32 by changes in load :: : : -, : : :
~ - 5 -~ :: .
.
93~'7 current through transformer 12. In trans~ormer 12 primary winding 11 must be sized to carry load current and also insulated su~ficiently to withstand the voltages applied to load 10. Core 46 of trans~ormer 12 sustains the ~lux that establishes magnetic coupling among primary winding 11, winding 28 and bias winding 32.
Understanding of the operation o~ the present invention will be aided by reference to Fig. 2 which is an ideallzed version o~ a B-H curve o~ the core 46 of trans~ormer 12 of Fig. 1. Fig. 2 is idealized for ease of drawing and refer-ence, but the idealization of the characteristics is not signi~icant to the description of the invention. The curve of Fig. 2 is the ma~or hysteresis loop for the material. It is the curve of magnetic ~lux density B as a ~unction of magnetizing force H, also called the B-H curve~ This curve is obtained by cycling the magnetizing force on a closed loop of the material in an amount su~ficient to cause the material to go into saturatlon alternately in the positive and negative directionsO This is indicated in ~ig. 2 by the cycllng between point 50 and point 52, The meaning of the term "major hysteresis loopl' is that the application of ; larger amounts of magnetlzing force in either direction will not chan~e the cur~e on which the material returns .:.
; when the magneti~lng ~orce ls reduced. This is in contrast to the minor hysteresis loops which are obtained by cycling the magnetlzlngr force;at Yalues that place the state of the ., material inside the area bounded by curves 53, 54, 55, and 56. Curves 54 and 56 are shown as straight and slightly :
....
1~7~'7 sloped vertical lines. The presence of an air gap in the core would give curves 54 and 56 a finite value of slope, equal for both~ and would facilitate manufacture of the transformer 12 of Fig. l, but would not otherwise a~fect this invention. The invention is practiced by ad~usting the voltage of bias supply 34 o~ Fig. l or the resistance of resistor 36 of Fig. l to set current i2 at a value that produces in core 46 of Fig. l a state of saturation at point 50 of Fig, 2. This saturation is then reduced to point 58 ~y the passage of load current through primary winding ll of Fig. l. The result of the two opposing effects in core 46 is to place point 58 in saturation but close to the knee of the curve of Fig. 2 which is indi-cated by point 60. The sharpness of the knee at point 60 is a function of the particular material o~ which core 46 is made, and ls also a ~unc~ion of the scale to which the curve of Fig. 2 is drawn. However, saturation in the curve of Fig. 2 is unambiguous and it is necessary that point 58 be in the region of saturation of the core. It follows from inspection of Fig. 2 that, with the current i2 in bias ~ winding 32 held constant, variations in the load current ; ~ through primary winding ll will cause corresponding motion of point 58 along the cur~e. Because point 58 is in a rsglon of saturatlon, these changes in location cause essentially no change in magnetlc ~lux in core 46 and hence no lnduced smf across primary winding 11. However, lf the current through prlmary winding 11 increases suf~iciently ~to oause the nst magnetic flux in the core to pass point :, ~ .
. ~ :~; :. : : .
'7~
60 and start up curve 54s then the transformer enters a region in which B, and hence the magnetic flux, ls changing.
This change o~ magnetic flux in a given period of time will generate an emf in primary winding 11 which will oppose the direction of current increase according to Lenz's law. The opposition takes the form o~ an emf e = -n d(phl)/dt that appears across primary winding 11 in a sense to subtract from or oppose the power supply voltage. Thls opposing em~
will protect load 10 of Fig. 1 by keeping the load current at a value that will place the core in some portion of curve 54 for a time equal to that needed to move the length of curve 54. Point 62 is one such point. At the same time, the increase in flux llnkages that was associated with the development of the back emf across primary winding 11 will also generate a voltage across signal winding 28 that can be used either directly or through a time delay such as time-delay circult 30 to trigger crowbar 24. This triggering has thus taken place without the necessity ~or a damaging overcurrent in load 10 of Fig. 1.
:
Fig. 3 is a time plot of currents and voltages in the ; clrcuit of Fig. 1. The tlme scale of Fig. 3 is a function of the values of voltages, currents and the load in the circuit, but marker 64 1s placed to show the time of 50 to 100 microseconds that is typical of a wide range o~
applications. ~Four time intervals are shown in Fig. 3, , characterized as follows. Interval 66 is a period of normal operation. Inter~al 68 is a period of time during which an undes'ired arc exists in load 10 of Fig. 1.
~ .
:
l~V~3~7 Interval 70 is a tlme period in which the arc has gone out and the circuit is returning to the normal operating condition. Interval 72 is a period of normal currents and voltages again. These interva:Ls and the values of current and voltage associated with them are best understood by referring to the corresponding points on Fig. 2 as follows.
During interval 66, current curve 74 i5 at a constant value representing the normal load current. Load voltage curve 76 is at a constant value which differs from the source voltage only by the small amount of the amplitude of d-c voltage drop of transformer voltage curve 78.
Associated with these values of load current and load voltage is an operating point 58 on the B-H curve o~ Fig. 2, marked in parentheses on Fig. 3. Interval 66 ends when a short circuit develops in load 10 of Fig. 1. The load current immediately begins a rapid rise which is associated with a motion of the operating point in Fig. 2 ~rom point 58 to point 60. During this change~ the flux in core 46 is hardly changing. ~herefore, the supply voltage is divided between the voltage drop across the transformer leakage inductance and that across the arc. As soon as the load current has reached point 60 of Fig. 2, a~ a value shown in parentheses in Fig. 3, the core enters the st~eply rising ~ .
port;ion of the hysteresis loop, curve ~4. This portion is characterized by a high magnetizing inductance. Point 60 ~ :
o~ Fig. 2 is ~cnown as the knee of the hysteresis loop.
Past point 60~ the steeply~rising portion3 curve 54, is associated in Fig. 3 with a relatively constant portion of , ~ . . , :, -; ,. . . . .
~93~
the curve for load current 74~ an abrupt rise in the curve of transformer voltage 78 and a correspondingly abrupt drop in load voltage curve 76. Once the knee o~ the B-H curve is turned, trans~ormer winding 11 behaves like an inductor and the flux change in the core causes essentially all of the load voltage to appear across the prirnary o~ trans~
~ormer 12. In some cases, this abrupt drop in the arc -voltage together with the limit imposed by transformer 12 on the maximum value of load current will cause the ~ault to extinguish itself. The curves of Fig. 3 are drawn under the assumption that this has happened at the end o~ interval 68. The time at the end o~ interval 68 is associated in Fig. 2 with poink 62 on the B-H curve, as indicated in parentheses in Fig. 3. It can be seen that point 62 in Fig. 2 is on the rising portion o~ the hysteresis curve.
Restora~ion of normal operating conditions begins with a drop in the load ourrent and occurs in three stages.
The first stage is an abrupt drop in a short interval that is associated in Fig. 2 with rapid passage along a minor hysteresis loop to point 80 on the B-H curve or ma~or hysteresis loop of the ma~erial. Next the current is nearly constant, showing only a slight decrease, while the , ~ .
-~ ~ core is taken from point 80 to point 82. Thls corresponds to interval 70 in Fig.~ 3, in which the values corresponding to points 80 and~82 are shown in parentheses. Finally, on ~ -passing~again~into the region of saturation past point 82, the current drops abruptly to its normal operating level as the core returns to point 58. This is interval 72 in : :
,:
..... . ,. . . . . . ,.. ,~ :.
. .
~793~7 Fig. 3. Transformer voltage curve 78 is readily derivable from Fig. 2 by associating the changes with each interval.
Thus, during interval 66, the voltage across transformer 12 is constant at the low value, nearly zero, representing the IR drop across the transformer. A change in the con-ditions of the circuit that cause the operatlng point o~
the core to move at the saturatlon level represents very little change in the voltage across the primary transformer 12~ since the flux ls changing very little in saturation, and the voltage is proportional to the time rate o~ change of magnetic flux. However, when the condition of the core is past point 60 and is in region 54 of Fig. 2, then the current, which is proportional to H, is changing very slightly while the flux~ which is proportional to B, is changing rapidly. Thus, the trans~ormer voltage achieves a high value and, in general, will drop almost ail of ~he supply voltage. The passage in Fig. 2 ~rom point 62 to 58 represents a return of stored magnetic energy ~rom core 46 of transformer 12 so that the voltage across primary 2Q winding 12 becomes negative during this interval. Once this energy has been returned, allowing return of the core to point 58, the voltage across primary wlnding 4ll of trans~ormer 12 drops again to the low value representing the IR drop acrQss the transformer.
The;sloping lines in all the curves of Fig. 3 repre sent straight-:Line approximations to c~rves that are essentially exponentials with L/R time constants that are long compared t;o the time scale shown. The exact shape o~
:
- , ~ , - ; , -. , , ., .. ,. ~ , . . .......... . . - . .
- . , , ~: , : , , , : , .
~7~3~L~
these curves is less important than their relative magnitude and direction of increase or decrease and they are therefore idealized as straight lines. However~ one thing should be noted from a comparison o~ the curves of Figs. 2 and 3: the apparatus of the present invention will protect a load only as long as operation is maintalned on curve 54 of Fig. 2. In other words, operation must not be allowed to pass point 84 of Fig. 2, which is represented as the terminus o~ a dashed line in Fig. 3. Accordingly, it i5 useful to set a time delay to operate a crowbar within a time that is less than the length o~ time interval 86, the time from point 60 to point 84. This is facilitated by the fact that the flux change in core 46 is associated wlth the rise in transformer voltage curve 78 after point 60 and this flux change is available to trigger the time-delay circuit 30 of Fig. 1. The length of time interval 86 is directly proportional to the total change in flux linkages in the primary winding and inversely proportional to the voltage of the power supply. If the circuit quenches automatically as illustrated in Fig. 3 3 then the portion . .
~ of Fig. 2 between polnts 62 and 80 will generate in signal ~ .
winding 28 an impulse that can be used to reset the crowbar time~delay and prevent the ~opera~ion of crowbar 24 of Fig. 1.
If the arc does not quench automatically before the pre-determlned tlme;o~the~tlme-delay circuit, then orowbar 24 will~be triggered to short the power supply and protect the load. The;design of crowbar time-delay circult 30 is a routine matter of using counters or flip-~lops to time the ~'793~'~
desired waiting period before triggering the crowbar 24.
Fig. 4 is a circuit diagram of an alternate embodimento~ the present invention. Fig. 4 is similar to Fig. 1 in that a load 10 is connected through a trans~ormer 12 to a high-voltage power supply 14. A crowbar 24 is connected across the terminals of high-voltage power supply 14 to protect load 10 from the effects of damaging overvoltages.
Transformer 12 includes a primary winding 11, a signal winding 28 and a bias winding 32. As with Fig. 1~ bias winding 32 is connected to bias supply 34 through a series-parallel combination o~ resistor 36, capacitor 40 and inductor 42 to filter pulses in bias winding 32 to protect bias supply 34. In the embodiment of Fig. 4, signal winding 28 serves two functlons. The first, as in Fig. 1, ls to trigger crowbar 24, either directly or as shown in Fig. 4 through a time-delay circuit 30. The other ~unction of signal winding 28 is to sense an overload in the same way that was explained with re~erence to the circuit of Fig. l and to initiate a ~urther protective response for load 10. This is accomplished by connecting ~; a triggered hi.gh-voltage spark gap 90 in series with a capaoltor 91 across load 10. Capacitor 91 is charged through resistor 92 by power supply 93 to a d-c voltage ~-that is low in comparlson with the normal operating voltage across load 10. Trigger electrode 911 is disposed ln spark .
gap 90 to initiate conduction across spark gap 90 in response to a signal fram slgnal wlnding 28. When this happens~ the energy stored ln capacitor 91 will discharge and drive :
:
7~34~
current through the fault in load 10 in a direction opposite to the flow of fault current. By thls means, the net current in load 10 goes through zero and the arc is quenched. Normal operation of the circuit o~ Fig. 4 comprises quenching the arc by means o~ the triggered spark gap 90 and the quenching energy from capacitor 91.
However, if the arc is not quenched or i~ the arc restrikes before the circuit of Fig. 4 has been restored to steady-state conditions, then the signal from time-delay trigKer circuit 30 will cause crowbar 24 to operate and short out power supply 14 before time interval 86 has elapsed, thus protecting the load against damage.
The nature of load 10 in Figs. 1 and 4 has been des-cribed herein as a high-voltage load. While the present invention has particular utility in application to struc-tures such as accelerating tubes, Cockro~t-Walton generators, and other structure designed to support high voltages, its use is not limited to such structures. The saturating time-delay ~ransformer lZ o~ F1gs. 1 and 4 can equally as well 20 be used to protect loads at lower voltages, of the order of -hundreds o~ volts or less.~ This extends the choice o~
elements to be used for crowbar 24 which includes ignltrons, thyratrons, SC~'s, transistors, vacuum tubes, and any of a number o~ other elements meeting the requirement that they : : : ~ : : . ..
sustain the operatlng voltage of power supply 14 with very 11ttle~current unlesæ~tr1ggered, in which case they must sustain the short circuit current of power supply 14.
Trans~ormer 12 has a primary winding that must be capable .
~75~3~L~7 of carrying the load current ln load 10 and must be capable o~ supporting the load voltage of powe:r supply 14. The bias winding 32 and signal wincling 28 can be designed ~or relatively low voltage. Signa] winding 28 is primarily a pulse winding and must be designed to provide adequate response to pulses induced by rapid change in the ~lux in core 46 of Figs. 1 and Ll. Other requirements of the circuits of Figs. 1 and 4 are design choices depending on the parameters of the source and load. For example, one such design choice allows the designer to combine the functions of the bias winding and the signal windlng into a single winding. In thls case, the signal used to trigger the crowbar and, if used, the spark gap is obtained by connecting across the terminals of the bias winding before the ~ilter network. This is an obvious possibility, although not a likely choice because of the typical para-meters to be expected in such a circuit.
The following example will make this clear. Consider the problem of protecting with a time delay of 50 micro-secpnds a load designed to carry 10 amperes at 200 kilovolts.
.
Suppose there i9 avallable a core in which the saturation level of flux density is 17 kiloGauss~ and assume a primary winding comprising 100 turns. The core area would then be 294 square centimeters, obtained as follows. The change of flux denslty is from saturation in one direction to satura- ~ -tion in the o~her so that the net change is 2 x 17 -kiloGauss = 34 kiloGauss and this change takes place in at most 50 microseconds. From Faraday's Law, the cross-~;
.. . . . . . ......... .. . . . . ......... . . .
: ' , , ' ' 1~793~'~
sectional area o~ the core is thus the ratio of the product of voltage and time to the product of turns and change in flux density. Substitution of the values above gives 294 square centimeters or a square cross section approximately 17.2 cm on a side. During normal operation, the magneto-motive force (mmf) of the load current is 100 turns x 10 amperes = 1000 ampere~turns. This value of mmf represents the distance between points 50 and 58 in Fig. 2. The value of mmf supplied by the bias windlng must equal this amount plus an additional amount sufficlent to move the core to point 58. A routine calculation of the amount of core necessary to provide a cross section of 17.2 square centimeters and enough core window to support a primary o~
100 turns insulated ~or 200 kilovolts results in a median core length of approximately 160 cm. A typlcal value o~
the magnetic field strength at saturation is 2 amperes/cm. ' The product of this magnetic field strength and the mean length shows that 320 ampere turns are necessary to put the core into saturation at point 58. Thus, the bias winding must produce the sum Or 1000 and 320 ampere turns or 1320 ampere turns. A two-turn coil will produce this with a current of 660 amperes. ~With this current ~lowing in the :
bias winding, the core would be placed in operation a~
point 58 o~ Fig. 2. Slight ~ariations in this value of current enable the motion of point 58 to the l,eft or right to make a read~ ad~ustment of the sensitivity of triggering.
It will be reme~mbered that triggering takes place only when the current through the primary is increased sufficiently "
~,, ~L~7~33~'7 to move the primary ampere turns from point 58 to and past point 60. It should also be evident that the voltage ratings necessary for both the primary and bias coils are evident from this design approximationO Thus each primary turn must be insulated from the next by an amount sufficient to with-stand the ratio 200 kilovolts/100 turns or 2 kilovolts per turn. The bias winding will be sub~ected to a step down of 100:2 on 200 kilovolts, or a voltage of 4 kilo~olts~
The foregoing calculations make it evident that in situations where 4 kv is too high a voltage for the crowbar trigger circuit, it will be easier to use separate windings for the bias winding and the signal winding. However, this is a matter o~ design convenience rather than necessity, as the signal ~ufficient to trigger a crowbar is available at the terminals of the bias winding and could be so used. It should also be evident that the indicated use of more than one ignitron as a crowbar is a matter as well of design requirements. If the voltage rating capaclty of the power supply exceeds that of the ignitrons readily available, then it is a simple matter to place additional ignitrons in series to support the load voltage or ln parallel to carry the load current. In such a case, it is an equally simple matter to add other signal windings to the transformer to control these ignitrons if they are to be controlled directly. In the alternative, one signal winding can be - connected~to a single time-delay circuit whic~ can then be u9ed to trigger a plurality Or ignitrons via separate ; tri8ger circuits.
., , . ~ . . . ~ .
. ~ ~ . .
- . ~ .,
Claims (9)
1. An apparatus for protecting an electrical load con-nected to a d-c supply from damage from overcurrent in case of a load fault comprising:
(a) a transformer having a primary winding, a secondary winding, and a ferromagnetic core capable of main-taining inductive coupling between the primary winding and the secondary winding, the primary carrying the load current and the ferromagnetic core in magnetic saturation from mag-netic flux set up in the ferromagnetic core by the load current;
(b) a bias supply connected electrically to the secondary winding and supplying a current to the secondary winding in a direction to saturate the ferromagnetic core, the current in the secondary winding producing an mmf greater in magnitude and opposite in direction to the mmf produced by the load current, the net mmf placing the saturation of the core at a value near the knee of the B-H curve and in in saturation;
(c) a filter connected between the bias supply and the secondary winding to isolate the bias supply from the pulses generated in the secondary winding by changes in load current through the primary winding;
(d) a crowbar connected across the d-c supply; and (e) a time-delay circuit connected to the crowbar and to the transformer and responsive to changes in the trans-former that indicate a fault to apply a delayed triggering sig-nal to the crowbar after a predetermined time interval, there-by making the crowbar a short circuit and protecting the load
(a) a transformer having a primary winding, a secondary winding, and a ferromagnetic core capable of main-taining inductive coupling between the primary winding and the secondary winding, the primary carrying the load current and the ferromagnetic core in magnetic saturation from mag-netic flux set up in the ferromagnetic core by the load current;
(b) a bias supply connected electrically to the secondary winding and supplying a current to the secondary winding in a direction to saturate the ferromagnetic core, the current in the secondary winding producing an mmf greater in magnitude and opposite in direction to the mmf produced by the load current, the net mmf placing the saturation of the core at a value near the knee of the B-H curve and in in saturation;
(c) a filter connected between the bias supply and the secondary winding to isolate the bias supply from the pulses generated in the secondary winding by changes in load current through the primary winding;
(d) a crowbar connected across the d-c supply; and (e) a time-delay circuit connected to the crowbar and to the transformer and responsive to changes in the trans-former that indicate a fault to apply a delayed triggering sig-nal to the crowbar after a predetermined time interval, there-by making the crowbar a short circuit and protecting the load
2. The apparatus of claim 1 wherein the time-delay circuit is resettable to prevent the triggering of the crowbar upon receipt of a signal indicating that the fault has been clear-ed during the time interval to which the time-delay circuit is set.
3. The apparatus of claim 1 wherein the time-delay cir-cuit is connected to the secondary winding of the transformer.
4. The apparatus of claim 1 comprising in addition a signal winding of the transformer coupled inductively through the ferromagnetic core to the primary winding and the second-ary winding, the signal winding further coupled to the time-delay circuit to initiate a time-delayed triggering of the crowbar.
5. The apparatus of claim 4 comprising in addition:
(a) a triggered spark gap having two gap electrodes and a trigger electrode;
(b) a capacitor connected to one of the two gap electrodes and to one side of the load, the other of the gap electrodes connected to the other side of the load to form a closed circuit of the first gap, the second gap, the capacitor and the load, the triggering electrode of the triggered spark gap connected to the transformer and responsive to a signal therefrom to trigger the triggered gap into conduction; and (c) a power supply connected across the capacitor to charge the capacitor to a voltage that is opposite in sense to the load voltage, whereby a current flows through the load in opposition to the load current when the gap is triggered into conduction.
(a) a triggered spark gap having two gap electrodes and a trigger electrode;
(b) a capacitor connected to one of the two gap electrodes and to one side of the load, the other of the gap electrodes connected to the other side of the load to form a closed circuit of the first gap, the second gap, the capacitor and the load, the triggering electrode of the triggered spark gap connected to the transformer and responsive to a signal therefrom to trigger the triggered gap into conduction; and (c) a power supply connected across the capacitor to charge the capacitor to a voltage that is opposite in sense to the load voltage, whereby a current flows through the load in opposition to the load current when the gap is triggered into conduction.
6. The apparatus of claim 1 wherein the crowbar is an ignitron.
7. The apparatus of claim 1 wherein the crowbar is a silicon-controlled rectifier.
8. The apparatus of claim 1 wherein the crowbar is a spark gap.
9. The apparatus for protecting from damage by over-current an electrical load that is supplied with a load voltage by a d-c supply, the apparatus comprising:
a transformer having a primary winding, a bias winding, and signal winding, the windings all coupled inductively to each other by a ferromagnetic core, the primary winding connected in series with the d-c supply and the load to form a series circuit, the core in magnetic saturation when carrying a load current in a normal amount;
an ignitron connected across the d-c supply, the ignitron having an ignitor electrode to trigger conduction;
a time-delay circuit connected to the signal winding and the ignitor electrode and responsive to a signal from the signal winding to effect a time-delayed triggering of conduction of the ignitron;
a bias supply connected to the filter to establish a bias current in the bias winding in a sense to saturate the core in opposition to the normal load current and to leave the core in saturation near the knee of the B-H curve;
a triggered spark gap having a first electrode, a second electrode, and a triggering electrode, the first electrode connected to a first terminal of the electrical load, the triggering electrode connected to the signal winding to initiate conduction from first electrode to the second electrode in response to a signal from the signal winding;
a capacitor connected to the second electrode and to a second terminal of the electrical load to form with the electrical load, the first electrode, and the second electrode a simple series circuit; and a d-c power supply connected in parallel with the capacitor to charge the capacitor to a voltage that is opposite in sense to the load voltage and smaller in magnitude than the load voltage.
a transformer having a primary winding, a bias winding, and signal winding, the windings all coupled inductively to each other by a ferromagnetic core, the primary winding connected in series with the d-c supply and the load to form a series circuit, the core in magnetic saturation when carrying a load current in a normal amount;
an ignitron connected across the d-c supply, the ignitron having an ignitor electrode to trigger conduction;
a time-delay circuit connected to the signal winding and the ignitor electrode and responsive to a signal from the signal winding to effect a time-delayed triggering of conduction of the ignitron;
a bias supply connected to the filter to establish a bias current in the bias winding in a sense to saturate the core in opposition to the normal load current and to leave the core in saturation near the knee of the B-H curve;
a triggered spark gap having a first electrode, a second electrode, and a triggering electrode, the first electrode connected to a first terminal of the electrical load, the triggering electrode connected to the signal winding to initiate conduction from first electrode to the second electrode in response to a signal from the signal winding;
a capacitor connected to the second electrode and to a second terminal of the electrical load to form with the electrical load, the first electrode, and the second electrode a simple series circuit; and a d-c power supply connected in parallel with the capacitor to charge the capacitor to a voltage that is opposite in sense to the load voltage and smaller in magnitude than the load voltage.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/642,045 US4054933A (en) | 1975-12-18 | 1975-12-18 | Saturating time-delay transformer for overcurrent protection |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1079347A true CA1079347A (en) | 1980-06-10 |
Family
ID=24574954
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA263,181A Expired CA1079347A (en) | 1975-12-18 | 1976-10-12 | Saturating time-delay transformer for overcurrent protection |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4054933A (en) |
| JP (1) | JPS5278049A (en) |
| CA (1) | CA1079347A (en) |
| DE (1) | DE2657594A1 (en) |
| FR (1) | FR2335976A1 (en) |
| GB (1) | GB1566289A (en) |
Families Citing this family (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4156264A (en) * | 1977-08-10 | 1979-05-22 | Rca Corporation | High power protection apparatus |
| US4232351A (en) * | 1979-01-03 | 1980-11-04 | The United States Of America As Represented By The United States Department Of Energy | High-voltage crowbar circuit with cascade-triggered series ignitrons |
| US4346421A (en) * | 1979-07-02 | 1982-08-24 | Sangamo Weston, Inc. | Fault detector |
| US4358808A (en) * | 1981-05-18 | 1982-11-09 | The United States Of America As Represented By The United States Department Of Energy | High energy overcurrent protective device |
| US5136453A (en) * | 1990-04-04 | 1992-08-04 | Oliver Bernard M | Method and means for suppressing geomagnetically induced currents |
| DE4418518A1 (en) * | 1994-05-27 | 1995-11-30 | Philips Patentverwaltung | Power generator with a transformer |
| US5559658A (en) * | 1994-09-06 | 1996-09-24 | Eldec Corporation | Solid-state high voltage crowbar circuit |
| US6066979A (en) * | 1996-09-23 | 2000-05-23 | Eldec Corporation | Solid-state high voltage linear regulator circuit |
| US6008549A (en) * | 1999-03-19 | 1999-12-28 | Eldec Corporation | Solid-state high voltage switch and switching power supply |
| US6577479B1 (en) * | 2000-08-28 | 2003-06-10 | The Regents Of The University Of California | Arc suppression circuit |
| SE530248C2 (en) * | 2006-08-25 | 2008-04-08 | Powerwave Technologies Sweden | Active lightning protection |
| EP2495745A1 (en) * | 2011-03-04 | 2012-09-05 | ABB Technology AG | Current-rise limitation in high-voltage DC systems |
| EP3522194B1 (en) | 2018-01-31 | 2021-04-14 | General Electric Technology GmbH | Switching apparatus |
Family Cites Families (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2571027A (en) * | 1950-03-09 | 1951-10-09 | Rca Corp | Electron tube protective system |
| US2971130A (en) * | 1956-01-10 | 1961-02-07 | Ite Circuit Breaker Ltd | Electro-dynamic switching device |
| US2910626A (en) * | 1956-01-18 | 1959-10-27 | Rca Corp | Protective system |
| US2949568A (en) * | 1956-07-13 | 1960-08-16 | Ite Circuit Breaker Ltd | Protection of parallel connected d.-c. sources |
| US2971146A (en) * | 1957-02-20 | 1961-02-07 | Ite Circuit Breaker Ltd | Instantaneous trip for rectifier protection |
| US2928956A (en) * | 1959-01-07 | 1960-03-15 | Martin L Jones | Electronic overload protection for pulsed systems |
| US3267331A (en) * | 1963-05-15 | 1966-08-16 | Leonard J Melhart | Capacitor trigger and fault circuit |
| US3601657A (en) * | 1968-10-31 | 1971-08-24 | Avco Corp | Overvoltage protective device |
| US3569784A (en) * | 1968-11-21 | 1971-03-09 | Atomic Energy Commission | Solid state crowbar circuit |
| US3671810A (en) * | 1969-09-18 | 1972-06-20 | Singer Co | Saturated core transient current limiter |
| US3564339A (en) * | 1969-10-31 | 1971-02-16 | Kms Ind Inc | Circuit for rapid shutoff of electrochemical machining apparatus |
| US3660721A (en) * | 1971-02-01 | 1972-05-02 | Gen Electric | Protective equipment for an alternating current power distribution system |
| US3936702A (en) * | 1972-02-24 | 1976-02-03 | Micro Devices Corporation | Electrical protection means |
| US3867669A (en) * | 1974-01-11 | 1975-02-18 | Yakov Lvovich Krasik | Power source with a sparkproof output |
-
1975
- 1975-12-18 US US05/642,045 patent/US4054933A/en not_active Expired - Lifetime
-
1976
- 1976-10-12 CA CA263,181A patent/CA1079347A/en not_active Expired
- 1976-12-06 GB GB50723/76A patent/GB1566289A/en not_active Expired
- 1976-12-16 FR FR7637953A patent/FR2335976A1/en active Granted
- 1976-12-17 JP JP51151050A patent/JPS5278049A/en active Pending
- 1976-12-18 DE DE19762657594 patent/DE2657594A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| FR2335976B1 (en) | 1982-10-29 |
| GB1566289A (en) | 1980-04-30 |
| DE2657594A1 (en) | 1977-06-30 |
| US4054933A (en) | 1977-10-18 |
| FR2335976A1 (en) | 1977-07-15 |
| JPS5278049A (en) | 1977-07-01 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1079347A (en) | Saturating time-delay transformer for overcurrent protection | |
| US4425596A (en) | Electric circuit breaker | |
| US3619721A (en) | Triggered vacuum gap keep-alive circuit | |
| US20140005053A1 (en) | Current-rise limitation in high-voltage dc systems | |
| US4567424A (en) | Reactive power compensator with capacitor and capacitor discharge circuit | |
| US3863109A (en) | Short circuit sensing device for electromagnetic induction apparatus | |
| EP0563904B1 (en) | Vacuum circuit breaker | |
| US5390064A (en) | Current limiters in power utility applications | |
| EP0415179B1 (en) | Differential protective relay apparatus | |
| US3676737A (en) | Ground-fault detector using square hysteresis loop reactor core | |
| Yamaguchi et al. | Mechanical arcless dc circuit breaker by current zero operation | |
| JPH0581973A (en) | Dc circuit breaker | |
| Novak et al. | Sensitive ground-fault relaying | |
| US4305108A (en) | Three-phase time overcurrent detector | |
| Shein et al. | Domains of ferroresonance occurrence in voltage transformers with or without damping reactors | |
| SU907654A1 (en) | Device for limiting overvoltages and short-circuiting currents at high-voltage substation | |
| JPS6331418A (en) | Circuit breaker | |
| EP0107359A2 (en) | Alternating current limiting type semiconductor current circuit breaker | |
| SU913516A1 (en) | Current limiting device | |
| RU2069434C1 (en) | Ground fault protective device for three-phase line | |
| Csida et al. | An improved method for determining line discharge through potential transformers | |
| SU553692A2 (en) | Conductorless AC contactor | |
| SU864423A1 (en) | Device for limiting short-circuiting currents and overvoltages at high-voltage substation | |
| Marbury et al. | New series capacitor protective device | |
| SU1074672A1 (en) | Power supply for d.c.arc welding |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |