RU2265941C1 - Protection device for low-voltage automatic switch - Google Patents

Abstract

FIELD: power engineering, in particular, relay protection devices.

SUBSTANCE: device has three current transformers, enabled into each phase of protected network, three measuring resistors, enabled in star-shaped circuit, power and bearing displacement current source, executing organ, three two-semi-period bridge rectifiers, OR element, three two-input AND-NOT elements, two three-input AND elements and comparator.

EFFECT: higher stability of activation, speed of operation, operation comforts settings.

1 dwg, 1 tbl

Description

The invention relates to the electric power industry, in particular to relay protection devices.

Known protection devices that provide protection with increased sensitivity to currents of single-phase earth faults, containing current transformers in all phases and in the neutral (or on the ground conductor of the power source), a semiconductor control unit and a shutdown electromagnet [1, 2, 3].

Their disadvantage is the need for a special zero-sequence current transformer, which is not always acceptable in conditions of limited dimensions of circuit breakers and electrical installations.

A device is known [4], free from this drawback. It contains three current transformers included in each phase of the protected network, three measuring resistors connected by a star with a zero output to the secondary windings of current transformers, an actuator, a zero sequence current filter, an RC circuit, two operational amplifiers, and a power source , the input of the zero sequence current filter is connected to the secondary windings of the current transformers, the zero point of the zero sequence current filter is connected to the zero terminal of the transformer current through two opposite directional diodes, as well as to the input of the first operational amplifier, the same input of the first operational amplifier is connected to a power source, which is also a reference bias current source, an RC circuit resistor is connected to the output of the first operational amplifier, the capacitor of which is connected to the input the second operational amplifier, included with its output to the executive body.

The disadvantages of this device include:

- instability of the response current associated with temperature changes in the parameters of the RC circuit, which can reach 30% of the nominal value of the setpoint;

- the need to pre-charge the capacitor of the RC circuit before the occurrence of a single-phase circuit current.

These disadvantages are eliminated in the device [5], which contains current transformers, a zero-sequence current filter, a bias current source, which is both a power source, two operational amplifiers, an RC timing circuit, an actuator, an amplitude detector, a comparator and a diode, and a transformer output current is connected to the input of the filter of currents of zero sequence, the output of the filter is to the input of the first operational amplifier, the output of which is connected to the resistor of the RC chain, the common point of the resistor and the capacitor is connected to the input of the second operational amplifier, its output is connected to the input of the executive body, the input of the amplitude detector is connected to the output of the filter, the output of the amplitude detector is connected to one input of the comparator, the second input of which is connected to the bias current source, the output of the comparator to one of the isolation outputs diode, the second output of which is connected to the common point of the resistor and capacitor of the RC circuit.

Common disadvantages of devices [4, 5] include:

- the need to comply with a certain phasing of current transformers, which creates inconvenience in production and operation;

- dependence of the tripping current on the frequency of the supply network, due to the fact that the setting of the tripping current is determined by the time during which the current exceeds the setting and during which the capacitor of the RC circuit is charged;

- insufficient performance due to the fact that the device responds to only one of the half-waves of current in the protected network;

- lack of voltage control at the output of the power source and its sufficiency for the actuator to operate;

- they work not only with single-phase faults, but also with phase imbalance, which is not always acceptable.

Closest to the proposed device is [4].

The objective of the proposed device is to eliminate the above-mentioned disadvantages of the device [4].

The solution to this problem is ensured by the fact that in a device containing three current transformers included in each phase of the protected network, three measuring resistors included by a "star", a power source, which is also a source of the reference bias current, and an actuator, secondary windings of current transformers are connected to the diagonals of the alternating current of three half-wave bridge rectifiers, the second terminals of the measuring resistors are connected respectively to one of the nodes of the diagonals of the direct current of the bridge frames, the second nodes of the DC diagonals of bridge rectifiers are combined, the common points of the measuring resistors and rectifiers are connected respectively to the three inputs of the three-input OR element and to the first inputs of the three two-input AND elements, the first input of the first AND element is NOT connected to the second input of the second AND element -NOT, the first input of the second AND-NOT connected to the second input of the third AND-NOT element, the first input of the third AND-NOT connected to the second input of the first AND-NOT, the outputs of the three AND-NOT connected are connected to the inputs of the first three-input element And, the output of the OR element is connected to the first input of the comparator, the second input of which is connected to a power source, the output of the first three-input element And and the output of the comparator are connected respectively to the first and second inputs of the second three-input element And, the third input of the second three-input And and the actuator is connected to the power source, and the output of the second three-input element And is connected to the actuator.

The structural diagram of the proposed device is shown in the drawing. It contains current transformers 1 included in each phase of the protected network, three measuring resistors 2 connected by a star, a power supply 3, which is also a source of the reference bias current, and an actuator 4. The secondary windings of current transformers 1 are connected to three diagonals of alternating current half-wave bridge rectifiers 5. The second terminals of the measuring resistors 2 are connected respectively to one of the nodes of the DC diagonals of the bridge rectifiers 5. The second nodes of the DC diagonals of the bridges 5 rectifiers combined. The common points of the measuring resistors 2 and rectifiers 5 are connected respectively to the three inputs of the OR element 6 and to the first inputs of the three AND-NOT elements 7. The first input of the first element 7.1 is connected to the second input of the second element 7.2, the first input of the second element 7.2 is connected to the second input of the third element 7.3, the first input of the third element 7.3 is connected to the second input of the first element 7.1. The outputs of elements 7.1, 7.2, 7.3 are connected to the inputs of the first 8 three-input element I. The output of the three-input element OR 6 is connected to the first input of the comparator 9, the second input of which is connected to the power source 3. The output of the first 8 three-input element And and the output of the comparator 9 are connected respectively to the first and second inputs of the second three-input element I. The third input of the second 10 element And and the actuator 4 are connected to the power source 3. The output of the second 10 element And is connected to the actuator 4.

In the normal mode of the protected network, when the current flows in all three or in any two phases, the corresponding resistors 2.1, 2.2, 2.3 - voltage proportional to the current. The largest of these voltages is selected by the OR element 6, supplied to the input of the comparator 9 and compared with the voltage supplied to the second - inverting input of the comparator 9 from the power source 3. If the current in the network is lower than the current setting of the protection against single-phase circuits, the largest of the voltages across the resistors 2, selected by the OR element 6 and received at the input of the comparator 9, is lower than the voltage at the inverse input of the comparator 9, and at the output of the comparator 9 is a low level voltage that is supplied to one of the inputs of the three-input element And 10.

If the voltage at the output of the power source 3 is sufficient for the actuator 4 to operate, at the second input of the element And 10 is a high level voltage; if the output voltage of the source 3 is not enough for the actuator 4 to operate, there is a low level at the input of element 10. In conditions when at least one of the inputs of element 10 is a low level voltage, its output also has a low level voltage, and the actuator does not work.

The states of the inputs and outputs of elements 7 and 8, depending on the mode of the protected network, are shown in the table, which shows that a high level voltage at the output of element 8 and the connected input of element 10 can only be in single-phase mode and in the absence of current in all phases . But in the absence of current in all phases at the input of element 10 associated with the output of comparator 9, the voltage is low, so the actuator 4 will not operate.

Thus, the actuation of the executive body 4 is possible only when three conditions are satisfied:

- the supply voltage is sufficient to actuate the executive body 4;

- current flows only in one of the phases of the protected network;

- the magnitude of this current exceeds the setpoint for the operation of protection against single-phase short circuits.

The proposed device eliminates the instability of the operating current associated with temperature changes in the parameters of the timing RC circuit, because she is absent from him.

For the same reason, the need for pre-charging the capacitor of the RC circuit and the dependence of the tripping current on the frequency are excluded.

The voltage polarity across the measuring resistors is not related to the phasing of current transformers, as it is the same for any connection of the beginnings and ends of their windings and does not depend on the direction of currents in the phases of the protected network.

The device responds to both half-waves of current in the protected network, which improves performance.

The device provides control of the magnitude of the voltage at the output of the power source and its sufficiency for actuator actuation, which increases the reliability of the work.

The device does not work during phase imbalance, but only in single-phase mode.

Thus, the proposed device eliminates all the noted disadvantages of the devices [4, 5], i.e. solves the problem.

Table Inputs and outputs of elements Status of inputs and outputs in the presence of current in phases ABC AB Sun CA A IN FROM No current Inputs 7.1 1,1 1,1 0.1 1,0 1,0 0.1 0,0 0,0 Inputs 7.2 1,1 1,0 1,1 0.1 0,0 1,0 0.1 0,0 Inputs 7.3 1,1 0.1 1,0 1,1 0.1 0,0 1,0 0,0 Output 7.1 0 0 1 1 1 1 1 1 Output 7.2 0 1 0 1 1 1 1 1 Output 7.3 0 1 1 0 1 1 1 1 Inputs 8 0, 0, 0 0, 1, 1 1, 0, 1 1, 1, 0 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 Output 8 0 0 0 0 1 1 1 1

SOURCES OF INFORMATION

1. Low-voltage circuit breakers of the Sace Emax series. ABB Technical Catalog 604019/011, March 2002, p. 18, 29, 82, 114.

2. Circuit breakers - low voltage disconnectors for currents from 800 to 6300 A Masterpact Merlin Gerin. Graupe Schneider Catalog, 1997, p. 23, 76.

3. A.S. USSR No. 519807, H 02 H 3/08, 1976

4. A.S. USSR No. 807425, H 02 H 3/08, 1981

5. Patent No. 2091948, H 02 H 3/08, 1997.

Claims (1)

A protection device for a low-voltage circuit breaker containing three current transformers included in each phase of the protected network, three measuring resistors connected by a "star", a power source and a bias reference current, and an actuator, characterized in that the secondary windings of the current transformers are connected to alternating diagonals current of three half-wave bridge rectifiers, the second terminals of the measuring resistors are connected respectively to one of the nodes of the DC diagonals of the half-wave bridge rectifiers, the second nodes of the DC diagonals of half-wave rectifiers are combined, the common points of the measuring resistors and half-wave bridge rectifiers are connected respectively to the three inputs of the three-input OR element and to the first inputs of the three two-input AND elements, the first input of the first two-input AND element is NOT connected the second input of the second two-input element AND NOT, the first input of the second two-input element AND NOT connected to the second input of the third two-input element AND, per the output of the third two-input AND-NOT element is connected to the second input of the first two-input AND-NOT element, the outputs of three two-input elements AND are NOT connected to the inputs of the first three-input AND element, the output of the three-input OR element is connected to the first input of the comparator, the second input of which is connected to the source power supply, the output of the first three-input element And and the output of the comparator are connected respectively to the first and second inputs of the second three-input element And, the third input of the second three-input element And and executive n are connected to the power source, and the output of the second AND gate trehvhodovogo connected to the actuator body.