SU989649A1 - Device for current protection of zero sequence from short-circuiting in network with grounded neutral - Google Patents

Description

The invention relates to electrical engineering and is intended to protect electrical installations from a ground fault in a network with a grounded neutral.

A zero-sequence current protection with acceleration when the line is turned on is known, which includes a current relay, a time relay, an acceleration relay, and a switching element fl.

However, the triggering setting of the current relay must be rebuilt from the inrush current of the power transformer, which reduces the sensitivity of the protection.

It is also known a protection device comprising a zero-sequence current sensor and zero-sequence current relays connected to it and a blocking device against magnetizing current surges. The zero-sequence current relay acts on the executive body through the time element, as well as through the accelerator relay contact and element I, to the second input of which the output of the blocking element from the inrush current is connected.

Exclusion of the blocking body from the chain, according to which the protection operates in the normal, not accelerated mode

Improves the reliability of protection performance.

However, in the on-off switch mode of the protected line, for a short circuit (when the protection accelerates), because of the longer time of the blocking device action compared to the current relay, there can be a delay in switching off the short circuit when

10, the short circuit current is large and contains a large aperiodic component, from which the measuring current transformer can be saturated. In this case, the secondary current circuit

15 may, in transient mode, contain signs of a surge current of magnetization of power transformers: a second harmonic in the current pause, an aperiodic compound, and the blocking organ at Bpewt

20 transient does not allow protection to open the circuit breaker.

The aim of the invention is to increase speed.

The goal is achieved by

Claims (2)

25 that the device for current protection of a zero-sequence earth fault in a network with a zemglemenny neutral, containing series-connected zero-sequence current sensors, a sensitive current relay, an acceleration relay, a logic element And an actuator, and a time relay, on between the output of the sensitive current relay and the second input of the executive body, and the body blocking the rms of the magnetizing current surges, connected by the input to the output of the specified Zero current sensor In addition, a logical element IL and an additional current relay are connected between the output of the zero sequence current sensor and the first input of the OR element, the second input of which is connected to the output of the blocking device from surges, magnetizing current, and the output element I. The drawing shows the functional diagram of the device. The device contains a zero-sequence current sensor 1, the output of which is connected to the blocking organ from inrush current magnetization 2 and sensing current relay 3. Time relay 4 and acceleration relay 5 are connected to the output of sensing current relay 3. Acceleration relay 5 through a logic element And b It is connected with the executive unit 7. Additional current 8 is connected to the input of the logical element OR 9. The device operates as follows. If a short circuit occurs on the line during operation, the sensitive current relay 3 is triggered. The line is turned off with a time delay of time 4. When the line loaded on the power transformer is turned on, components of a zero sequence in the magnetizing current may appear. Sensitive relay, current 3 is triggered, but the protection does not disconnect the line, because time delay of time relay 4 is longer than the duration of the inrush of the magnetizing current, and in the acceleration circuit the actuation is blocked by block 2. When the switch is turned on for a short circuit, for example unresolved shorting, with automatic restarting in case the current of the zero sequence of the circuit is not greater than the maximum inrush current of the magnetizing current (not more than 6-8 times greater than rated current), the blocking device from surges of magnetization 2 triggers quickly enough, because the secondary current is distorted weakly, in this case the auxiliary current relay 8 does not work, and the accelerated shutdown of the switch proceeds besides it through the element OR 9, element And 6 and executive body 7. If the zero-sequence current is greater than the maximum surge current –– magnetization current (greater than 6–8 nominal currents), the blockage blocking from the inrush of the magnetizing current 2 can delay the switch-off switch , Since the form of the second current can be distorted when the measuring current transformer is aperiodic component of the current. In this case, the device operates in addition to blocking organ 2 from the additional current relay 8, which operates without slowing down through the OR element 9 and element 6. The use of the device reduces damage to the high-voltage equipment of the substations when the switch is turned on for a short circuit due to the fast switch-off in this mode. Claims. A device for current protection of zero sequence from ground short circuit in a network with grounded neutral, containing in series connected zero-sequence current sensor, sensitive current relay, acceleration relay, logic element And and the actuator, as well as a time relay connected between the output of the sensitive the current relay and the second input of the actuator, and the blocking device from inrush current magnetization, connected by the input to the output of the specified current sensor, zero sequence and, characterized in that, in order to increase the speed, the logical element OR and the additional current relay included between the output of the mentioned data point are introduced into it. zero sequence current and the first input of an OR gate, the second input of which is connected to the output of the blocking device against magnetizing current surges, and the output to the second input of the logic element I. Sources of information taken into account in the examination 1, Guidelines for relay protection , issue. 2, SEI, 1961G76, fig. 2 2. USSR author's certificate No. 547898, cl. H 02 H 3/16, 1975. Of I Of