SU1403195A1 - Transformer differential protection device - Google Patents

Abstract

The invention relates to electrical engineering. The purpose of the invention is to increase the speed of differential protection of the transformer by reducing the time: blocking from magnetizing current surges. The goal is achieved by fixing the difference between the times of voltage on the low-voltage side and the current in the differential transformer protection circuit. By the difference of these times, the fact that the transformer is energized is determined, while in order to exclude the false operation of the protection of the transformer, the actuator of the transformer is shunted. Moreover, in order to increase the speed of protection of a transformer, shunting is only fulfilled if there is a current in the differential protection circuit exceeding a certain setpoint, and when current flows in the differential circuit of the differential circuit through zero, the bypass of the transformer protection actuator is removed. 2 Il. (/; with

Description

about

00 WITH

&one

The invention relates to electrical engineering and is intended for use in the differential current protection of power transformers and auto-transformers.

The aim of the invention is to increase the speed of differential protection of the transformer by reducing the blocking time from inrush current |

i FIG. 1 shows a block diagram of the proposed device; in fig. 2 - diagrams illustrating the operation of the device

The device contains an intermediate current transformer 1 connected by an input to a differential protection circuit | and an output to the input of a rectifying bridge 2, an intermediate voltage transformer 13 connected by an input to the voltage transformer on the underside of the protected transformer, the output of which is connected to you - 1 mbsta 4, to the outputs of high-voltage bridges 2 and 4 are connected | expensive elements 5 and 6, the output of poro-IroBoro element 5 is connected through the element HE 7 and the element 8 delay with the first input of the element AND 9, another INPUT th element 10 is connected to the delay. The output of the element And 9 is connected via a delay element 1 1 to the input of the semiconductor switch 12 connected at the input of the switching bridge 13, to the output of which the protection actuator 14 is connected. I Consider the operation of the device when turning on the transformer at idle (Fig. 2a) and during internal damage (Fig. 1b)

When the transformer is idled, the current in the differential protection circuit is absent until its magnetic core is saturated. In the absence of a differential current, a signal appears at the first input of the AND circuit. After 1-2 ms after switching on the transformer, a signal appears at the second input of the logic circuit 9, Which leads to the appearance of a signal at the Output of this circuit. Scheme 1 Delay Starts to gain time. If the current circuit signal tio does not appear within 4-5 ms, then a signal is sent to the control electrode of the thyristor 12 (time t). In this case, the thyristor shunts the input of the relay, which causes the protection to be blocked.

When the power transformer magnetic circuit is saturated in the differential protection circuit, an unbalance current appears, a potential difference arises at the terminals of the differential relay, which leads to the opening of the thyristor 12, which then shunts the differential relay 14. There is a signal on the control electrode of the thyristor through delay circuit 8 during the time t after the occurrence of the differential current.

When the power transformer comes out of the current, the current of the differential circuit becomes zero and the differential relay 14 is decoupled. Thus, the protection is ready for operation immediately after the transition of the current flow curve through zero.

In case of internal damage in the formatter, the current in the differential circuit appears simultaneously with the voltage on (if the closing phase corresponds to the maximum value of the aperiodic component in the short circuit current, then the threshold value reaches the current only after 1-2 ms) we And 9 signal is zero, and, therefore, there is no signal at the control electrode of the thyristor. In this case, the differential relay operates without delay.

The device assumes a phase-by-phase execution, therefore it allows to provide -selective protection in such a complex mode, when a magnetizing current rush occurs in two phases, and a short circuit occurs in the third.

Claims (1)

Invention Formula A device for differential protection of a transformer, comprising intermediate current and voltage transformers with leads for connection to the circuit to be protected; The secondary windings of which are connected to a full-wave rectifier, a semiconductor key with an actuator at the output, characterized in that, in order to improve performance by reducing the blocking time at inrush currents, three delays and two threshold elements, and the output is logical