US3511999A - Light responsive continuously tested tripping device for electric circuit breaker - Google Patents

Description

May 12, 1970 ELECTRIC CIRCUIT BREAKER Filed MW. 2, 1966 TESTED TRIPPING DEVICE FOR 2 Sheets-Sheet 1 Fa i i P 3 I 2o L i N J; a. I

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TRIPPING DEVIC May 12, 1970 E FOR LIGHT RESPONSIVE CONTINUOUSLY TESTED ELECTRIC CIRCUIT BREAKER 2 Sheets-Sheet 2 Filed NOV. 2, 1966 United States Patent Office Int. Cl. I-l01j31/50 U.S. Cl. 250-214 6 Claims ABSTRACT OF THE DISCLOSURE A monitoring circuit for checking photo-electric trip ping devices in high voltage lines including a photoelectrically controlled switch and a disabling device operable to prevent switching in the absence of current in the high voltage line.

This invention relates to photo-electric control devices for tripping a high-voltage circuit-breaker.

The constant endeavour to reduce the tripping time of high-voltage circuit-breakers has led designers to consider replacing the conventional hydraulic, pneumatic or hydro-pneumatic devices by a photo-electric device. In such a photo-electric device the space separating the parts of the breaker which are at the high-voltage potential of the line or power circuit in which the circuit breaker is inserted from the parts which are at or near earth potential is bridged by a light beam. The beam is emitted by a light source which is usually formed by flash tube at earth potential which discharges in a gaseous medium. The flash at earth potential is turned on or ignited when the breaker is to be tripped or opened for instance in case of a major fault in the power circuit, and the light beam emitted by the flash is conducted by a light guide to the high-voltage region of the circuit breaker to trigger a photo-electric cell, which controls in turn an electromagnetic tripping device such as a relay, for example by means of a controlled rectifier, such as an SCR.

Generally, these photo-electric control devices are combined with a conventional control used for the normal opening and closing of the circuit breaker, and are intended to function only in the case of a major fault on the power system because of their short response time. In the case of a high-voltage circuit-breaker having a plurality of breaking or switching elements which are electrically connected in series for each pole, each breaking element generally has its own tripping device, and it is obvious that it is necessary to avoid the tripping of only a single breaking element in the case of a major fault on the power circuit, such as a short circuit. This condition has given rise to the design of testing devices capable of detecting the proper operating state of the tripping circuit of all breaking elements. In this way, a tripping order can be avoided if one of the tripping circuits of one .of the breaking elements is not in its normal proper operating condition in which it is capable of responding correctly to the given order. Known testing 3,511,999 Patented May 12, 1970 devices of this kind test the various tripping circuits only immediately prior to the transmission of a tripping order. It is obvious that such a test needs time, however short this time may be, and that this does not allow the' immediate execution of such a tripping order.

It is an object of the present invention to solve this problem by eliminating this preliminary test, through carrying out a continuous testing of the tripping circuits.

The invention will be further described, by way of example, with reference to the accompanying drawings, showing embodiments thereof, and in which:

FIG. 1 shows the diagram of a photo-electric tripping device for one pole of a high-voltage circuit-breaker comprising a single breaking point; and

FIG. 2 shows a part of a photo-electric tripping device for a circuit breaker having per pole two breaking elements which are electrically connected in series.

In FIG. 1, the parts of the tripping device shown inside the rectangle T are located in a control panel disposed on the ground and at or near earth potential. The parts at the potential of the high-voltage line L of the power system in which the circuit breaker is installed are shown inside the rectangle P.

At ground level, a source of electrical energy 10 may be connected to the terminals of the filament of a flash tube 11 (forming the flash or light source) through the contacts of a fault relay 12 and through a gate circuit 13. The gate circuit 13 is shown diagrammatically and may comprise essentially an SCR, or any other suitable known switching device which does not form part of the invention.

The gate circuit 13 is controlled by a photo-electric cell 14 capable of gating on the gate when it is illuminated under the conditions mentioned further below, and of gating off, that is to say, of interrupting the circuit connecting the source 10 to the light source 11, in the case that the device 14 is not illuminated. The flash 11 may direct a light beam through a light guide 15 onto a photo-electric cell 16 located to the live part P of the circuit-breaker.

The opening of the moving contact of the breaking element, shown diagrammatically at 17, is controlled by a suitable electromagnetic tripping device or control relay having a coil 18. A source of electric energy is formed by a capacitor 19, supplied directly by the high-voltage line L through a current transformer 20 and a rectifier bridge 21. SCRs 22, 23 in anti-parallel connection serve to limit the voltage at the terminals of the bridge 21, when the line current is too high, and resistors 24, 25, connected to the control electrodes of the diodes 22, 23, energize the same. The capacitor 19 is connected to the coil 18 through an SCR 26 or another controlled valve means or solid state switch whose control electrode may be excited if the cell 16 is illuminated and triggered; this cell is connected on the other side to one terminal of the capacitor 19 through a resistor 27. A lamp or other light source 28 is connected in series with a current limiting resistor 29, and the whole assembly is connected in parallel to the main terminals of the SCR 26. A capacitor 30 of lower capacity than the capacitor 19 is connected between the cathode of the SCR 26 on the one hand, and

the junction of the resistor 29 and the lamp 28 on the other hand. The latter can illuminate the cell 14 through a second light guide 31 bridging the space between the parts under high voltage and those at earth potential, and which may possibly be the same as, or be combined with, the first guide 15 to form a single unit. Lenses 32, 33 and 34 enable the beams passing through the guides 15 and 31 to be focussed.

All the breaking elements of the circuit-breaker are equipped with a device according to the drawing, but certain parts shown in the rectangle T may be common to different breaking elements of one or more poles, as explained with reference to FIG. 2. In this figure, the rectangles P and P show the high potential regions of two breaking points of the same pole of a circuit breaker. For the sake of simplification, there are shown only the two lamps 28, 28' and the two photo- electric devices 16 and 16 but each rectangle P and P of FIG. 2 actually contains all the elements of the rectangle P of FIG. 1. The single flash 11 illuminates through two guides 15, 15 two cells 16, 16' of two breaking points 17, 17' mounted in series on the line L. The gate circuit 13 is common to the two breaking points and is controlled by the two cells 14, 14'. In all cases, the absence of energizing by illumination of a single cell 14 has the result that no flash 11 can function.

The arrangement of FIG. 1 as shown functions as follows:

With the main contacts 17 of the breaker point of a breaker pole being closed, the conductor L carries a current which charges the capacitor 19 across the transformer 20 and the bridge 21. If the circuit of the coil 18 is not broken and if the SCR 26 is not short-circuited, a normal OFF-state voltage appears at the main terminals of the latter and the detecting lamp 28 lights up. The cell 14 is therefore illuminated and unblocks the flash 11 by enabling the gate circuit 13. I

The proper functioning of the SCR 26 is thus checked, but for reasons of safety it is advisable to double or triple this element to provide two or three parallel SCRs.

It should be noted that the monitoring or testing system is capable of detecting the most frequent fault of an SCR, namely its short-circuiting. In fact, in this case, no voltage can appear at the terminals of the light source 28, so that the cell 14 is not triggered and cannot enable the gate circuit 13 which now blocks the flash 11.

The optical transmission is effected by means of tubes made of glass or Plexiglas which may be Water-tight, filled with an inert gas and having an inner diameter of the order to 10 to 20 millimeters.

If the tripping circuit is in its proper operating condition and a tripping order is given by the relay 12, in case of fault of the high-voltage circuit, the light source 28 illuminates the cell 14 so that the flash 11 may be energized and send a light beam onto the cell 16 of the pole, causing the turning ON of the SCR 26 and the discharge of the capacitor 19 across the coil 18. The breaker contacts 17 open and the fault on the high voltage circuit is eliminated.

As may be seen from FIG. 2, if a single one or both of the cells 14 or 14' are not illuminated owing to a fault in the corresponding high voltage parts of the tripping circuit of the breaking points 17 and 17', an order for tripping or opening of the breaking points 17 and 17 given by the relay 12 cannot pass through the gate circuit 13 so that no breaker element can receive the tripping order.

The lamp 28 which remains generally illuminated has a low light output. It has been found that this type of lamp needs a certain time for reaching its full light output after a voltage has been applied thereto. In order to prevent the illumination of the cell 14 from being too weak under these circumstances immediately after the closure of the circuit-breaker to unblock the Cir flash 11 without delay, and thus to avoid that a tripping order is not carried out in the case of closure of the circuit-breaker in case of a fault on the high-voltage system, in spite of the good state of the tripping circuits, the capacitor 30* has been provided which enables the application of an overvoltage to the lamp 28 for a few moments after it has been energized. The cell 14 now is sufficiently illuminated at the closure of the circuitbreaker to enable the ultra-rapid tripping immediately after the closure of the circuit-breaker.

Obviously, the described embodiments may be modified in many ways without departing from the principle of the invention. For example, the cell 16 may be combined with the SCR 26 by using a photothyristor.

What I claim is:

1. A light responsive continuously tested tripping device for a breaking element of a circuit breaker, comprising:

(a) a first light source,

(b) energizing means for electrically energizing said first light source in response to a tripping order,

(c) first photo-electric means responsive to the light emitted by said first light source,

(d) control means for operating said breaking element,

(e) electronic switching means controlled by said first photo-electric means, said electronic switching means being operatively connectetd to said control means to operate said control means in response to the triggering of said first photo-electric means by the light emitted by said first light source,

(f) sensing means for continuously detecting the presence of a normal OFF-state voltage across said electronic switching means, and

(g) inhibiting means for rendering inoperative said energizing means in response to the disappearance of said normal OFF-state voltage.

2. The device of claim 1, in which said sensing means further comprises a second light source energized by said normal voltage, said inhibiting means being controlled by second photo-electric means responsive to the light emitted by said second light source.

3. The device of claim 2, in which said inhibiting means comprise an electronic gate circuit gating said first light source and electrically controlled by the output voltage of said second photo-electric means.

4. The device of claim 2 for tripping of a breaking element of a circuit breaker inserted in a high-voltage power line, wherein said first photo-electric means and said second light source are located in the high voltage region of the circuit breaker, said first light source and said second photo-electric means being located in a lowvoltage region at or near earth potential.

5. The device of claim 2 further comprising means for applying a transient overvoltage to said second light source at the moment of appearance of said normal voltage.

6. A light responsive continuously tested tripping device for at least a pair of series connected breaking elements of a circuit breaker, comprising:

(a) first light emitting means responsive to a tripping order,

(b) first and second photo-electric means responsive to the light emitted by said first light emitting means,

(c) first and second control means for respectively operating said breaking elements,

(d) first and second electronic switching means respectively controlled by said first and second photoelectric means and operatively connected respectively to said first and second control means to operate said control means in response to the triggering of said first and second photo-electric means by the light emitted by said first light emitting means,

(e) second and third light emitting means respectively 5 6 energized by the normal OFF-state voltages of said first and second electronic switching means, erences Clted (f1 tillilrdragtti fourthtiphoto-eletctit;J meags respoinsivg UNITED STATES PATENTS o e 1 res ec ve emi e sai secon an third ligfit emitfing and Y 3,2 9,154 9/196 M rm 4 (g) inhibiting means controlled by sald third and fourth photo-electric means so that said first light RALPH NILSON Pnmary Exammer emitting means can only be energized when both M. ABRAMSON, Assistant Examiner said third and fourth photo-electric means are triggered by the light emitted respectively by said sec- 10 0nd and third light emitting means energized by 317 124 the normal OFF-state voltage of respectively said first and second electronic switching means.

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