RU195895U1 - BODY FOR RELAYING RELAY PROTECTION DEVICES AGAINST NON-SELECTIVE ACTIONS IN TRANSITION MODES AT CURRENT SATURATION OF CURRENT TRANSFORMERS IN UNDAMAGED PHASES - Google Patents

Abstract

The invention relates to electrical engineering and the electric power industry and can be used at power plants and substations of distribution and intersystem networks of electric power systems to ensure the correct functioning of high-speed relay protection devices (URZ) in transient asymmetric short circuits (SC) when the magnetic cores of current transformers (CT) are turned on into intact phases. The technical result obtained by using the utility model is to ensure URZ operation and selectivity in accordance with the requirements of the dynamic stability of the electric power system, safety and reliability of power supply. The problem is solved by using the detuning body of relay protection devices against non-selective actions in transient conditions when current transformers are saturated in undamaged phases (UNF). The proposed UNF has two inputs and one way out. The UNF includes a relay (comparator) of the integrated (average rectified or effective) value of the phase voltage and a coincidence logical element I. The input of the specified relay is the first input of the UNF and is connected to the output of the integrated voltage value meter. The output of the specified relay is connected to the first (inverse) input of the logical element of coincidence I. The second (direct) input of the logical element of coincidence AND is the second input of the UNF and is connected to the output of the starting element of the URZ. The output of the AND gate is the output of the UNF and is connected to the output circuits of the residual current transformer. Thanks to the use of the utility model, incorrect operation of the residual current transducer with asymmetrical short-circuit out of range is eliminated due to saturation of CT magnetic circuits included in undamaged phases. At the same time, high-speed protection in case of short circuit in the protection zone is preserved.

Description

The utility model relates to electrical engineering and the electric power industry and can be used at power plants and substations of distribution and intersystem networks of electric power systems to ensure the correct functioning of high-speed relay protection devices (URZ) in transient modes of asymmetric short circuits (short circuit) when the magnetic cores of current transformers (CT) are saturated, included in intact phases.

The relevance of this task is explained by the cases that have occurred in practice of tripping of power supply protection devices of power plants and substations with external single-phase and two-phase short circuits that are not included in the protection zone.

There is a known option to prevent the non-selective operation of differential busbar shields (DZSh) with external asymmetrical short-circuit by connecting microprocessor DZSh to TT with individual phase and zero conductors (On ensuring the necessary accuracy of protective current transformers in transient conditions / Kuzhekov S.L., Degtyarev A.A. , Cherednichenko K.V. - Electric stations, 2015, No. 5. P. 53-60).

The advantage of the option is its radicalism: the possibility of saturation of CTs in intact phases is excluded, since there is no common neutral conductor of a group of CTs connected to a star. The implementation of the option is possible if the CT group can be connected to the current inputs of the protection terminal by six conductors. The event is advisable for new construction or reconstruction of electric power facilities. Under operating conditions, the implementation of the option is usually impossible, as this requires replacement of the relay protection terminal.

There is also a known option, which consists in reducing the resistance of the neutral conductors in the secondary CTs connected to a star by connecting additional conductors of the control cable parallel to the neutral conductors (Analysis of the non-selective actions of the differential busbar protection with external single-phase short circuits with saturation of the current transformer in the undamaged phase / C .L. Kuzhekov, A. A. Degtyarev, N. A. Doni, A. A. Shurupov, A. A. Petrov, L. N. Kostarev, I. A. Koshelkov. - Relay protection and automation, 01 / March 2019 .-- S. 28-36).

The essence of the option is to create conditions under which the TT in the damaged phase is saturated sooner than in the undamaged. This eliminates the possibility of saturation of the CT in the intact phase.

The disadvantage of this technical solution is the need to connect in parallel to the existing neutral conductor a large number of cores of control cables. The calculation showed that in some cases it is necessary to connect 7 additional cores, which is difficult to implement in practice.

It is also possible to replace used CTs with similar devices with an increased transformation ratio (for example, instead of CTs with a rated secondary current of 5 A, CTs with the same rated primary current, but having a rated secondary current of 1A, can be used). The event is advisable for new construction or reconstruction of electric power facilities. In operating conditions, the implementation of the option is problematic, since it is necessary to dismantle the existing ones and replace them with new TTs.

A variant of the technical solution of the problem is also known: the introduction of a time delay for the operation of the residual current protection (Analysis of the non-selective action of the differential disaster (in the undamaged phase) with external single-phase short circuit / S.L. Kuzhekov, A.A. Degtyarev, L.N. Kostarev. - Collection of reports Technical Conference .-- Cheboksary: Publishing House of the Chuvash University, 2019. -. P. 72-75).

This option is the most easily implemented measure in the field. For example, for a DZSH, the indicated time delay must be no less than the sum of the response time of the main (or high-speed backup protection steps, if it is greater) of the overhead lines (OHL) protection connected to the busbars and the total time for the circuit breaker with the drive to trip. The response time of most overhead protection, for example, manufactured by NPP EKRA LLC, is not more than 25 ms. The total tripping time of a 110 kV SF6 circuit breaker with a drive does not exceed 35 ms. Thus, the delay time for the operation of the remote sensing device must be at least 60 ms. Given the slowdown in the operation of the overhead line protection, the indicated time delay can be more than 100 ms, which is not always acceptable under the conditions of the dynamic stability of the electric power system, as well as the requirements of electrical and fire safety.

The task underlying the utility model is to exclude incorrect tripping of residual current transformers when asymmetrical faults are out of range due to saturation of CT magnetic circuits included in undamaged phases.

The technical result obtained by using the utility model is to ensure the speed and selectivity of the URZ in accordance with the requirements of the dynamic stability of the electric power system, safety and reliability of power supply.

The problem is solved by using the body detuning relay protection from non-selective actions in transient conditions when the saturation of current transformers in undamaged phases (UNF).

The proposed UNF has two inputs and one output. The UNF includes a relay (comparator) of the integrated (average rectified or effective) value of the phase voltage and a coincidence logical element I. The input of the specified relay is the first input of the UNF and is connected to the output of the integrated voltage value meter. The output of the specified relay is connected to the first (inverse) input of the logical element of coincidence I. The second (direct) input of the logical element of coincidence AND is the second input of the UNF and is connected to the output of the starting element of the URZ. The output of the AND gate is the output of the UNF and is connected to the output circuits of the URZ.

The proposed UNF can be used in a variety of high-speed DRM. In FIG. Figure 1 shows, as an example, the connection of a UNF to a phase-A device.

In FIG. 1 the following notation is accepted:

PO _A - start-up body of the phase A DSS;

IN _A - measuring the integral value of voltage U _A in phase A;

ReleU _A - relay (comparator) of phase A voltage. At the output of this element, logic signal 1 (true) appears when the following inequality is fulfilled:

U _A > 0.8⋅U _nom ,

U _nom - nominal effective value of voltage in phase A;

And - a logical element of coincidence with two inputs: the first is inverse, the second is direct;

VODZSh _A - output organ DZSh phase A.

Elements that are part of the proposed UNF can be performed, for example, in microprocessor-based DZSh devices manufactured by various Russian companies (NPP EKRA LLC, NPP Relatika LLC, RADIUS Avtomatika CJSC, etc.), as well as abroad .

It is convenient to analyze the operation of the device using the example of differential tire protection in three characteristic modes:

- good condition of the object of protection, i.e. there are no damages on it;

- external (with respect to the protection device) asymmetrical short circuit;

- asymmetrical short circuit on the protected object.

Symmetric (three-phase) fault is not considered, since with it all phases of the protected object are damaged.

The device with the proposed authority works as follows.

Good condition of the protection object. The start-up protective element of software _A is in an unused state, its output has a logic signal 0. The voltage U _A at the output of IN _A exceeds the threshold of the relay (comparator) of the phase voltage ReleU _A. The relay (comparator) of the phase voltage ReleU _A is in the tripped state, at its output there is a logic signal 1. The output signal of the AND gate is equal to zero. The proposed UNF- _A body is not operational.

External (with respect to the protection device) asymmetrical short circuit. When the CT magnetic circuit is included in the circuit of the undamaged phase, the starting protection element PO _A in this phase is triggered. A logic signal 1 occurs at its output. The voltage in the undamaged phase exceeds the threshold of the relay (comparator) of the phase voltage ReleU _A. The relay (comparator) of the phase voltage ReleU _A is in the tripped state, at its output there is a logic signal 1. At the output of the logic element AND, the signal is absent due to the presence of logic signal 1 at its inverse input. As a result, the non-selective action of the protection does not occur.

Asymmetrical short circuit on the protected object. The start-up protection organ of software _A in the damaged phase is triggered, a logical signal 1 appears at its output. The integrated voltage value U _A in this phase decreases and falls below the threshold of the relay (comparator) of the phase voltage ReleU _A. A logical signal 0 appears at the output of the specified relay. At the output of a logical element AND, a logical 1 appears and the object protection is triggered. A certain delay in the operation of the protection, not exceeding 10 ms, is due to the return time of the relay (comparator) of the phase voltage ReleU _A.

The proposed device has the following set of properties that none of the known devices of the same purpose have:

1 Elimination of malfunctioning of relay protection devices in transient modes of asymmetrical short-circuit out of range during saturation of current transformers included in undamaged phases.

2 Providing, without special delay, the shutdown of the damaged element of the electric power system during short-circuit in the coverage area.

3 No need to reduce the resistance of the neutral conductor in the secondary circuits of the CT connected to the star, for example, by connecting in parallel to the latter additional conductors of the control cable.

4 No need to connect microprocessor relay protection devices to CTs with individual phase and neutral conductors.

5 No need to replace CTs with a rated secondary current of 5A by CTs with a rated secondary current of 1 A.

6 Low cost, since the proposed body is a program element, for the implementation of which additional electromagnetic, electronic and other components are not required.

The specified set of properties is explained by the use of an additional feature - control of the voltage level of the intact phase.

Claims (2)

An organ for detuning relay protection devices against non-selective actions in transient conditions when current transformers are saturated in intact phases, having two inputs and one output, characterized in that it includes a comparator of the integrated phase voltage value, the input of which is connected to the first input of the organ connected to the output measuring the integral value of the phase voltage, and the logical element of coincidence AND, the inverse input of which is connected to the output of the specified relay, and the direct input is connected to the second input of the body connected to the output of the starting element of the relay protection device, and the output of the logical element And is the output of the organ and connected to the output circuits of the relay protection device. .

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