US2288331A - Circuit breaker testing apparatus - Google Patents

Description

Jun 30, 1942. w F SKEATS 2,288,331

CIRCUIT BREAKER TESTING APPARATUS Filed Aug. 13, 1940 4 .22 h 2 Inventor: Wilfred F. Slmaaig His Attorn Patented June 30, 1942 UNITED STATES PATENT OFFICE cmcurr BREAKER. TESTING APPARATUS Wilfred F. Skeats, Lansdowne, Pa., assignor to General Electric Company, a corporation of New York Application August 13, 1940,Serial No. 352,392

14 Claims.

improved, simply operating, synthetic circuit for testing circuit breakers under conditions simulating the conditions of short circuit at rated apparent power as they occur in actual operation.

It is another object of my invention to provide an improved arrangement for testing circuit breakers in which the recovery voltage is built up with great rapidity after current zero in the test breaker.

It is a further object of my invention to provide improved apparatus of the foregoing character having a simple arrangement which determines very promptly and accurately when current zero in the test breaker has occurred and which automatically synchronizes with this current zero the application to the test breaker of a voltage surge simulating a recovery voltage transient as the circuit interrupting device being tested is opened.

Other objects and advantages of my invention will become apparent as the description proceeds.

ment is such that both circuit breaker units clear together or such that the tested breaker clears slightly earlier so that itwill be subjected to the full recovery voltage while clearing its current.

The foregoing arrangement may be modified by connecting an inductance in the circuit between one terminal of the high current power source and the auxiliary breaker or between the auxiliary breaker and the breaker under test. A further modification may be made by connecting an auxiliary resistance element in series circuit relation with a spark-gap across the terminals of the breaker under test. The inductance element aids in rapid extinction of the residual current flowing through the auxiliary breaker after current zero in the test breaker so that the build-up of voltage at the point between the two breakers is not unduly delayed. The insertion of the resistance element and the sparkgap provides the desired overshoot, as will be explained hereinafter.

The invention will be understood more readily from the following detailed description when considered in connection with the accompanying drawing and those features of the invention which are believed to be novel and patentable are pointed out in the appended claims;- In the drawing Fig. 1 is a circuit diagram representing schematically one embodiment of my invention, and Figs. 2 and 3 are modified circuit diagrams of embodiments of my invention.

Referring now to Fig. 1, I have shown schematically a current interrupting device or a circuit breaker unit H which is to be tested-connested in series with an auxiliary interrupting device or circuit breaker unit I! across a suitable high current source, such as a generator in the form of an alternator I 3. If desired, a threepole switch I 4 may be employed, two poles of which are interposed between the alternator I3 and the two circuit breakers. Ordinarily, it is desirable that the circuit breaker units II and H be similar for reasons which hereinafter appear. The current source [3 is of such capacity as to supply the full current at which it is desired to test the breaker. It will be understood that circuit interrupting devices, such as II and I2, are ordinarily provided with operating mechanisms which are electrically controlled and the same control means for use in protecting electrical circuits under commercial use of circuit breakers are used for causing the circuit breakers H and 12 to open as soon as the short circuit is produced.

4 These arrangements, however, are well known to those skilled in the art, are not a part oi. my invention, and, therefore, are omitted for the sake of simplicity in the description and drawing.

In order that thedevice I I may be tested under conditions simulating actual operating conditions with a high recovery voltage, I provide a high voltage at point IT. This voltage is connected to the test breaker terminals I9 and 20 through a series impedance 2| which in this instance comprises a resistance element. For reasons of safety and to provide a fixed reference point, the points i6, 20 and I8 are grounded at 24. The voltage applied to the high potential terminal II should be of such a phase relation that it is near its crest value at the time of current zero in the high current circuit which includes the test breaker II. In other words, the voltage across the terminals l1 and [8 should lead the current flowing through the breaker H by approximately degrees, since this is the approximate phase in the art and a more detailed description or illustration thereof is regarded as unnecessary. In Fig. 2, I have shown a modification in which a resistance element It and a spark-gap 31 are considerations being that it be a voltage source of correct phase angle and of low regulation to the load imposed by the impedance element 2|.

However, because of the convenience and simplicity made possible, I prefer to supply the high voltage from the polyphase alternator II which is employed for sending the high current through the two breakers.

It will be appreciated that the normal frequency recovery voltage is relatively high in comparison with the voltage which might be obtained directly from the phases of the alternator 13 which are connected to the circuit terminals l5 and It. In order to produce such a recovery voltage without drawing appreciable power from the alternator II, I employ a step-up transformer having a primary winding 26 and a secondary winding 21. The primary winding 26 is connected to the ground connection 24 and terminal l8 and to the unused terminal 28, these terminals being connected respectively to one: of the used phases and the unused phase of the alternator I! through the breaker I4. I wish to point out that an autotransformer may be employed instead of the transformer 25, if desired. As explained hereinbefore it is desired that the high voltage supplied to the breaker under test shall be' near its crest value at the time of current zero in the test breaker. To this end I provide a phase shifting device comprising preferably a resistor 29 and a capacitor 30 which are connected in series circuit relation across the high potential winding 21. The simulated recovery voltage is obtained by connecting the high side terminal l1 and the grounded terminal I. acros the capacitor '30. By properly corrdinating the sizes of the resistor 29 and the capacitor 30 in conjunction with the transformer 25 the voltage across the capacitor may be made to lead the current through the breaker II by approximately 90 degrees.

It will be understood that for obtaining records of tests on an oscillograph 3| suitable oscillograph attachments are provided, such as a current shunt or a transformer 32 in series with the breaker elements, a potential transformer element 33 connected across the breaker terminals l9 and 20, and a second shunt or current transformer 34 connected in the circuit of the breaker II under test and the capacitor element 30.

Also, in general it may be found very useful, if not absolutely necessary, to employ a cathode ray oscillograph for examining the behavior of the voltage at the high voltage terminal of the connected in series circuit relation across the breaker terminals l9 and 20. Also, an inductance element 38 is connected between the terminal I! of the alternator l3 and the generator side of the auxiliary breaker l2. This latter element may also be employed in the arrangement of Fig. 1.

In Fig. 3, I have shown a further modification ,of Figs. 1 and 2which includes the inductance element 38 of Fig. 2 and in which the resistance element 3' and spark-gap 31 of Fig. 2 are omitted. and the function of these latter elements performed by including in the impedance element an inductance I! in addition to a resistance element 2|. The inductance element 39 is located between the auxiliary breaker unit and the unit under test, and in the illustrated embodiment it is shown connected between the auxiliary unit and point l9.

The primary considerations governing the nature of the impedance element connected between points I! and I! of the several figures are first, that the voltage at point ll should be near its crest value at the time of current zero in the high current circuit which includes the test breaker, and second, that in order to obtain a high recovery rate a finite current should be flowing through this impedance element at the time of current zero in the high current circuit. These considerations are best met if this element is a pure resistance as shown in Fig. l, but the deleterious effect of a moderate deviation from this condition, as by the introduction of a small amount of reactance will be relatively very small.

When testing the interrupting ability of the circuit breaker ll, both breakers II and I 2 are first closed. Consider now the operation of the system as illustrated in Fig. 1 for applying to the test breaker a recovery voltage immediately after a current zero. Current of the desired magnitude is applied from the alternator I! to the auxiliary breaker l2 and the test breaker H. in series by closing the breaker H. At the same time an alternating voltage is supplied from the alternator l3 or any other suitable auxiliary source to the primary winding 26 of the transformer 25. The application of power to the auxiliary transformer sets up a voltage at point ll which by manipulation of the circuit can be made to have any desired phase relation with respect to the current through the breakers H and i2. If the current through the breakers II and I2 has no direct current component the most severe breaker under test. Thus I have shown -a suitable potentiometer 33a for connecting the defleeting plates of such an oscillograph to the test breaker. There may also be provided an attachment for recording motion of the breaker mechanism or contacts and possible attachments for recording other conditions. Such oscillographs and attachments, however, do not constitute a part of my invention and relate to recording the results of the test rather than to the arrangement or method of subjecting the breaker to the test. Furthermore, such osciliographs and attachments are well known to those skilled conditions will usually be obtained when the voltage at H leads the current through the breakers by degrees so that the voltage crest occurs at current zero of the test breaker. In some cases it may be found desirable to increase the current through the breakers by the employment of a displaced wave rather than a symmetrical wave and in such event it may still 'be desired that the voltage be at its crest value at the time of current zero. This may be brought about for the current zero after the major loop by reducing somewhat the angle of lead of the voltage at point ll.

While there is voltage at point l1 and the breakers II and I2 are still closed and even after the breaker contacts have been separated by the operating mechanism, up to the time that the are drawn between the opening contacts is broken and the current reduced to zero, the

' breakers.

' zero is reached. with the current through the resistance 2| leading the breaker current, upon opening of the breakers, the current through the test breaker will reach zero a short time before the current through the auxiliary breaker, the current through the auxiliary breaker at this time being equal to the instantaneous value of the current through the resistance II. This current is so low that in many cases it may be expectedcto be easily and promptly extinguished in the auxiliary breaker arc. When this occurs the entire current through the resistance 2i, having no other place to flow, flows into the small stray capacitance of the circuit connection I! between the auxiliary breaker and the test breaker. to raise very rapidly the voltage at the common point I! between the two breakers until that voltage becomes substantially equal to the voltage of the capacitor 30 corresponding to the voltage at the point I1, the rate of this rise in voltage being governed by the magnitude of the resitsance 2| and the capacitance of the point between the two breakers, together with some effect from the characteristics of the current circuit which will be explained hereinafter. From that time on the voltage at the point l9 between the two breakers remains equal to the voltage at H except for the drop in potential across the resistance 2i, usually negligible, which will be caused by the' charging current for the stray capacitance of the connection between the two breakers. When this voltage'has been maintained in this way for two or three cycles the test may be considered complete.

From the foregoing description of the operation it will be noted that the test breaker II has sufferedthe passage of a high current which it interrupted by an arc and that very promptly after this interruption the voltage across the test breaker rose rapidly to the voltage at the point I I thereafter being maintained at the voltage of point I! until the completion of the test. This is rather a good approximation of the duty of the breaker I I in a normal interruption of the current which initially flowed through it at a circuit voltage equal to that at point l1. However, it may fall short of this in two respects. The residual current which was spoken of as flowing through the auxiliary breaker I2 after current zero in the test breaker II may not be extinguished as rapidly as desired. Such a condition will delay the build-up of voltage at the point I9 between the two breakers and consequently reduce the severity of the test. Also, in the interruption of many circuits the voltage across the breaker rises during the transient immediately following interruption to an instantaneous value which may be approximately twice as high as the normal crest value of applied voltage across the breaker. .This rise above the crest value of applied voltage is referred to here- This current then starts immediately in as overshoot. The circuit as described in connection with Fig. 1 does not include features providing for such a rise or overshoot. It is to meet such conditions as the foregoing that the arrangements of Figs. 2'and 3 have been devised.

In the apparatus of Figs. 1, 2 and 3, just before current zero, for proper polarity relationship, the

- polarity of the voltage at the capacitor 30 should be opposite to that of the current flowing through.

the test breaker, by virtue of the fact that in the latter part of a loop of current in an inductive circuit the voltage is of opposite polarity to the current which it produces. This being so, and the voltage across the capacitor 30 and at point II being higher than the voltage at I3, current will tend to flow through the auxiliary breaker after interruption in the same direction which it has been flowing during the last half cycle. This may mean that the current in the auxiliary breaker will be reduced almost to zero and then continue at a low value without reaching zero for about a quarter of a cycle. If this occurs, the voltage at the point I9 between the two breakers will be dissipated by conduction through the auxiliary breaker and only normal generator voltage will appear at this point. This state of ail'airs may continue fora good' fraction of a cycle, or, as I have found in some cases, it may continue only for a number of microseconds, the current inthe auxiliary breaker eventually going out of its own accord. In the latter situation, although the voltage at the point I9 between the two breakers eventually does reach its proper value, there is some delay in its rise, so that even this conditionis prejudicial to the truesignificance of the test. I

The foregoing situation may be controlled by causing the voltage on the generator side of the auxiliary breaker, as represented by the connection 35, to rise initially at a rate approximately equal to that at which it is desired to have the voltage rise at the point I9 between the two breakers. If the voltage on the generator side 35 catches up with the voltage on the other side I 9 of the auxiliary breaker for a brief instant during the rising period, the current through the auxiliary breaker will automatically be reduced to zero at this time and will, therefore. have a very good chance of becoming extinguished permanently. It may not be necessary, however, to cause the voltage on the generator'side of the auxiliary breaker to catchup completely with the voltage at point I9 between the two breakers,

as merely reducing the current flow and the voltage across the auxiliary breaker to a low value will tend to cause the arc in the auxiliary breaker to become extinguished of its own accord.

It is for the purpose of causing the voltage to rise rapidly on the generator side of the auxiliary breaker that I introduce in the arrangement of Fig. 2 the inductance element 38 in the connection 35 between the generator or alternator I3 and the auxiliary breaker element I2, the inductance element being so located that the capacitance to ground of the connection 35 between the auxiliary breaker and the inductance will be as low as possible.

A complete description of the arrangement of Fig. 2 is unnecessary for a full understanding of the invention in view of the foregoing description of the operation of Fi 1.- The circuit of Fig. it behaves in the same way as that of Fig. 1 up to the time when the current reaches zero in the test breaker I I and the first difierence is with reference to the residual current through the auxiliary breaker II. On account of the reactance supplied by the inductive reactance element 38 the major 'part of this residual current must flow into the capacitance to ground of the circuit connection 35 between the auxiliary breaker and the reactor element 38. Current will also tend to flow to this point through the reactor element, and the polarity of these two currents will be such that their effect in increasing the voltage to ground at connection 35 will be additive. Thus, .the voltage at this point or at the generator side of the auxiliary breaker rises rapidly and, in order to maintain current flow through the auxiliary breaker 12, the voltage at the point l5 between the two breakers must also rise rapidly so that the stray capacitance from this point to ground will draw a relatively high current. This will drain some and perhaps all of the current through the auxiliary breaker l2, thu assuring prompt interruption whether this current zero can be attained before the voltage difference across the reactance 38 is reduced to zero. A mathematical analysis indicates that this can be done if the following equations are satisfied:

where i=current through impedance element between points" and l9.

- E=instantaneous generated voltage in high ourof this residual current. The possibility of the delay in the build-up of voltage across the test breaker ll after current zero which was mentioned as a shortcoming of the circuit of Fig. 1 is thus eliminated in the arrangement of Fig. 2.

The reactance element 38 will also be efiective for bringing the current through the auxiliary breaker to zero immediately after extinction of the arc in the breaker ll if it is placed between auxiliary breaker "and the point I 9 as shown in the alternative arrangement of Fig. 3. The

action of this elementwhen so located may be mined by the voltage at IT and the impedance between points l1 and I9, and inasmuch as neither of these is subject to rapid change, this current will be substantially constant over a period of microseconds. At the instant of current zero in unit II, a current substantially equal to that flowing from I! to ID will be flowing from H) through the reactance 38. This current is in opposition to the voltage across that circuit, and sincethe circuit consists primarily of an inductance this current will be subject to rapid decay and eventual reversal involving passage through zero at the time of reversal which will provide an opportunity for are extinction in the breaker unit I2. It will be obvious, however, that this changein the current through reactor 38 must be accompanied by a rise in voltage at H and consequently a reduction in voltage across the .unit 38. Indeed the voltage at I 9 is normally expected to rise eventually to a value equal to that at I! which is considerably higher than that at breaker l2. At this time, unless the arc in breaker "has been extinguished so that a high potential difierence can be maintained across the contacts of breaker II, the voltage across thereactance unit 38 will have reversed. If this is allowed to occur, the inductance 38 can no longer be relied upon to bring the current through the unit I! to zero. v

I am thus confronted with a situation which is initially favorable to producing a current zero in the breaker unit I 2, but which is rapidly changing in adverse manner,- and the question is rent source. C=effective stray capacitance at point l9. L0=inductance of high current source. L=inductance of reactor 38.

The foregoing is a slightly less exacting condition under most circumstances than that involved in bringing about current zero in the breaker unit It with the inductance 38 located between the high current source and the auxiliary breaker unit I 2.

As stated hereinbefore, a second short-coming of the simple circuit of Fig. 1 is that it provides no overshoot, as do circuits commonly encountered in practice, that is, upon interruption of the circuit the instantaneous value of the recovery voltage does not exceed the crest value of the applied voltage. It is to meet this condition that I have provided in the arrangement of Fig. 2, the resistance element 38 which is connected from the point l9 between the two breakers through the sphere-gap 31 to ground.' In this arrangement, the voltage across the capacitor 30 and at the point I! is set slightly higher than the crest value of the recovery transient for which it is desired to test, and the sphere-gap 31 is set to break down at the crest value of the recovery characteristic.

Taking up the operation from the point at which the arcs in the two breaker units have been extinguished, then, the voltage at the point l9 between the two breakers rises along an exponential curve approaching the voltage of capacitor 30 corresponding to the voltage at point l1. Before this voltage is quite attained, however, the sphere-gap 31 breaks down, and the voltage at the point I9 between the two breakers falls exponentially to a value determined by the relative magnitudes of the resistances 2| and 36. From that time on this voltage will maintain its proper ratio to the capacitor voltage as the lat ter goes through its cyclic variations. It will thus be seen that the two resistances 2| and 36 act as a potentiometer, maintaining the voltage at the point I 9 between the two breakers equal to some fraction of the voltage at point I! rather than equal to the voltage at IT itself. If the voltage at I! is made enough in excess of that for which it is desired to test the breaker H to compensate for the reduction of voltage in the potentiometer, the result will be a. test at the voltage finally maintained at the point Is between the two breakers with an overshoot corresponding to that allowed by' the sphere-gap. Thus the overshoot which was lacking in the circuit of Fig. 1 has been supplied.

It has been stated hereinbefore that the primary factors determining the character of the impedance element which is connected between the points H and 19 are the desirability of having the voltage at I1 near its crest value at the ever, in Fig. 3 I haveinserted some series react ance in the form of an inductance element 40 in circuit with a resistor element 2|. Withthe addition of inductance as at 40, it will be appreciated that the circuit consisting of the resistance 2|, the inductance 40, and the stray capacitance from point I9 to ground, having both inductance and capacitance, may be oscillatory and if a large value of inductance is introduced at 40 and an appreciable change of current suddenly impressed on the circuit at l9, this oscillation may reach a very high magnitude. The events taking place at interruption amount substantially to suddenly impressing on the circuit a current equal to that flowing at the time through the resistance 2| which might easily be sufficient to give rise to an oscillation of very high amplitude. The amplitude of this oscillation can becontrolled, however, by properly proportioning the magnitude of the inductance 40. It may be shown, for example, that if this inductance is made equal to about 3R C where R is the resistance of the unit 2| and C is the stray capacimentarilv at quite a low value.

tance at point IS, an overshoot to approximately double the crest value of the applied voltage will be obtained under ideal conditions. If it is desired to simulate a circuit condition for comparatively low overshoot, a lower value of inductance would be suitable.

The foregoing arrangement may be found to be quite beneficial in introducing oscillations and overshoot into the voltage recovery curve, which will cause it to simulate more closely the voltage recovery conditions associated with a normal operation without serious sacrifice in the phase relationship and the recovery rate conditions mentioned above. This simple feature thus permits elimination of the resistor element 36 and the spark-gap 31.

I have thus provided a synthetic circuit breaker testing circuit which eliminates the difliculty of automatically synchronizing the application of the recovery voltage with the passage of the current to zero as the circuit interrupting device being tested is opened. The apparatus automatically determines very promptly when the current zero has occurred, and applies a surge or recovery voltage transient within a few microseconds after that time. In the present arrangement, the recovery rate may be made quite high since at the time of current zero in the breaker, current is already established in that part of the circuit which supplies the high voltage. While the recovery rate is subject to certain conditions with reference to the current circuit, the inductance involved here is very low and as a result the recovery rate of this circuit may be very high.

It is not necessary that both the auxiliary breaker and the breaker under test shall have extremely positive interrupt-characteristics. By this I refer to the requirement that these breakers will or will not interrupt at a given current zero regardless of whether the recovery voltage resulting is that for which the test is being made or a very much lower one. While this requirement is present in some degree in the circuit of the present invention, its severity is greatly reduced because interruption by the breaker under test will in some respects tend to encourage interruption by the auxiliary breaker at the same current zero, and similarly failure of the test breaker to interrupt at a given current zero will encourage failure of the auxiliary breaker to interrupt at the same current zero. This is explained as follows: The breaker under test will always reach its current zero slightly ahead of the other breaker and will have initially a higher recovery rate applied to it, while the voltage across the auxiliary breaker is maintained mo- Should the gap of the test breaker break down, however, a voltage equal to that which the generator circuit has attained after the opening of the breakers is immediately thrown across the auxiliary breaker. During the early part of the recovery transient,

this will greatly increase the voltage across theauxiliary breaker and thus tend to favor a break down of its gap, although during the latter part of the recovery transient, this would of course not be true. Under certain conditions, therefore, the auxiliary breaker has a tendency to clear its part of the circuit when the test breaker clears, and ,to restrike when the test-breaker restrikes, carrying an additional half cycle of current at the end of which the circuit will operate in the same manner as before, and the breaker will have another chance to clear against full voltage. This is an extremely valuable characteristic since the clearing of the auxiliary breaker either a half cycle before or a half cycle after the test breaker vitiates the test.

I have herein shown and particularly described certain embodiments of my invention and certain methods .of operation embraced therein for the purpose of explaining its principle and showing its application but it will be obvious to those skilled in the art that modifications and variations are possible and I aim, therefore, to cover all such modifications and variations as fall within the scope of my invention which is defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

I. An arrangement for. testing circuit breaker units comprising in combination with a unit to be tested, an auxiliary circuit breaker unit, a high current source, a high voltage source for applying a simulated recovery voltage to the breaker unit under test, a resistance element, means connecting said circuit breaker units in series circuit relation to said high current source, means connecting said resistance element between said high voltage source and the high voltage terminal of the breaker unit under test, and means associated with the circuit of said high voltage source and said breaker under test whereby the desired overshoot may be obtained in said recovery voltage.

2. An arrangement for testing circuit breaker units comprising in combination with a unit to be tested an auxiliary circuit breaker unit, a high current source of alternating current, an inductive reactance element, means connecting said circuit breaker units and said inductive reactance element in series to said high current source, said inductive reactance element tending to reduce to zero the current through the auxiliary breaker immediately after extinction of the arc in the circuit breaker unit to be tested, a source of high potential, an impedance element, means connecting said impedance element between said high potential source and the high voltage termi nal of the breaker unit under test.

3. An arrangement for testing circuit breaker units comprising in combination with a unit to be tested. an auxiliary circuit breaker unit, a

' source of- -relatively high alternating current, a

high voltage terminal of the breaker unit under test.

4. An arrangement for testing circuit breaker units comprisingin combination with a unit to be tested, an auxiliary circuitbreaker unit, a polyphase alternating current generator for providing a high current, a high potential transformer having relatively low and high potential windings, an inductive reactance element, means connecting said circuit breaker units and said reactance element in series circuit realtion with at least one phase of said generator, means connecting the low potential winding in circuit with an unused phase of said generator, a phase shifting device connected to the high potential winding of said transformer, an impedance element comprising a resistance unit, means connecting said impedance element and a portion of said phase shifting device in series circuit relation across the breaker unit under test, and means associated with the circuit including the br'eaker unit under test and said phase shifting device for obtaining the desired overshoot in the simulated recovery voltage obtained from said phase shifting device.

5. An arrangement for testing circuit breaker units comprising in combination with a unit to be tested, an auxiliary circuit breaker unit,

a high current source of alternating current, an inductive reactance element, means connecting said circuit breaker units and said inductive reactive element in series to said high current source, said reactance element being connected between said high current source and the terminal of said auxiliary breaker 'unit nearest said current source, a source of high potential, .an impedance element including a resistance, means connecting said impedance element between said high potential source and the high voltage terminal of the breaker unit under test.

6. An arrangement for testing circuit breaker units comprising in combination with a unit to be tested, an auxiliary circuit breaker unit, a source of alternating current, said circuit breakerunits being connected in series across said current source, a source of relatively high potential alternating current, a phase shifting device connected to said source, a resistance element, said Ill necting said circuit breaker units and said in ductive reactance element in series to said current source, said reactance element being connected between said current source and the terminal of said auxiliary breaker unit nearestsaid current source, a source of high potential, an impedance phase shifting device including a capacitor, said phase shifting device being connected to said high potential source, an impedance element, and means connecting said impedance element and said capacitor in across the breaker unit under test.

8. An arrangement for testing circuit-breaker units at rated kilovolt amperes without the expenditure of a corresponding amount of power, said arrangement comprising in combination with the circuit breaker unit to be tested, an auxiliary circuit breaker unit, a source of alternating current, an inductive reactance element, means connecting said circuit breaker units and said inductive reactance, element in series to said current source, said reactance element being connected between said current source and the terminal of said auxiliary breaker unit nearest said current source, a source of high potential, said high potential having a leading phase relation with respect to said current source, a resistance element connected between said high potential source and the high voltage terminal of the breaker unit under test, asecond resistance element and a spark-gap, and means connecting said second resistance element and said sparkgap in series across the breaker unit under test.

9. An arrangement for testing circuit breaker units comprising in combination with a unit to be tested, an auxiliary circuit breaker unit, a polyphase alternating current generator for providing a high current, a high potential transformer having relatively low and high potential windings, an inductive reactance element, means connecting said circuit breaker units and said reactance element in series circuit relation with at least one phase of said generator, said reactive element being connected between on of said gen,-

erator terminals and the terminal of said auxiliary breaker unit nearest said generator, means connecting the low potential winding in circuit with an unused phase of said generator, a phase shifting device connected to the high potential winding of said transformer, an impedance element comprising a resistance unit, means connecting said impedance element and a portion of said phaseshifting device in series circuit relation across the breaker unit under test, and

=means associated with the circuit including the breaker unit under test and-said phase shifting device for obtaining the desired overshoot in the simulated recovery voltage obtained from said phase shifting device.

10. An arrangement for testing circuit breaker units comprising in combination with a unit to be tested an auxiliary circuit breaker unit, a high current source of alternating current, an inductive reactance element, means connecting said circuit breaker units and said inductive reactance element in series to said high current source, said reactancev element being connected between said auxiliary breaker and the breaker unit under test, a source of high potential, an impedance element, means connecting said impedance element between said high potential source and the high voltage terminal of the breaker unit under test.

11. An arrangement for testing circuit-breaker units comprising in combination with a unit to series be tested, an auxiliary circuit breaker unit, a relatively high current source, a relatively high voltage source, an impedance element comprising a resistance and an inductance, means connecting said circuit breaker units in series circuit relation to said high current source, and means connecting said impedance element between said high voltage source and the high voltage terminal of the breaker unit under test.

12. An arrangement for testing circuit breaker units at rated kilovolt amperes without the ex penditure oi a corresponding amount of power, said arrangement comprising in combination with the circuit breaker unit to be tested, an auxiliary circuit breaker unit, a source of alternating current, an inductive reactance element, means connecting said circuit breaker units and said inductive reactance element in series to said current source, said reactive element being connected between said auxiliary breaker and the breaker unit under test, a source of high potential, an im-" pedance phase shifting device including a capacitor, said phase shifting device being connected to said high potential source, a resistance element, and means connecting said resistance element and said capacitor in series across the breaker unit under test.

13. An arrangement for testing circuit breaker units at rated kilovolt amperes without the expenditure of a corresponding amount of power, said arrangement comprising in combination with the circuit breaker unit to be tested, an auxiliary circuit breaker unit, a source of alternating current, an inductive reactance element,

means connecting said circuit breaker units and said inductive reactance element in series to said current source, said reactance element being connected between said auxiliary breaker and the breaker unit under test, a source of high potential for applying a simulated recovery voltag to the breaker unit under test, said high potential having a leading phase relation with respect to said current source, a resistance connected between said high potential source and the high voltage terminal of the breaker unit under test,.

and means associated with the circuit of said high potential'source and said breaker under test for causing said recovery voltage instantaneously to exceed the crest value of the voltage applied from said high potential source.

14. An arrangement for testing circuit breaker units comprising in combination with a unit to be tested, an auxiliary circuit breaker unit,- a polyphase alternating current generator for providing a relatively high alternating current, a high potential transformer having relatively low and high potential windings, said breaker units being connected in series to at least one phase of said generator, said low potentialwinding of said transformer being connected in circuit with an unused phase of said alternator, a phase shifting device connected to the highpotential winding of said transformer, an impedance device including an inductance unit and a resistance unit and means connecting said impedance device and a portion of said phase shifting device across the breaker unit under test.

WILFRED F. SKEATS.

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