SU955321A1 - Device for directional ptotection against grounding in ac network - Google Patents

Description

(54) DEVICE FOR DIRECTED PROTECTION AGAINST LOCKING TO EARTH IN AC NETWORK

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This invention relates to electrical engineering and is intended to protect an insulated neutral network from single-phase earth faults.

The known directional protection against single-phase earth faults reacts to the direction of the zero-sequence power, which is a zero-sequence power direction relay connected by one input to the zero-sequence current filter (FTNP), and the second input to the zero-sequence voltage filter (TFTV). The protection action is based on the fact that the zero-sequence current on the damaged line is lagging in phase, and on intact lines it is ahead of the zero-sequence voltage of 90 ° in phase. The device makes it possible to determine a damaged connection with any number of outgoing lines 1.

 However, such protection does not allow an operational check of its operability during the operation | 1. At the same time, modern protection devices should have elements that provide

the possibility of testing the operability in the operating mode without performing any work on the preparation of the testing scheme.

It is also known to have a ground fault protection device containing current sensors and zero sequence voltage, a power direction relay with an actuator on the output, a control button, a switch, capacitors and resistors, an alternating current source.

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Using the control button, the switch, the capacitors, signals are simulated at the input of the power direction relay that correspond to the response conditions, which makes it possible to partially control the performance of the device during its operation 2.

However, the control elements of the device is not carried out in sufficient detail.

The purpose of the invention is to increase reliability by expanding the volume of elements of the device monitored during operation.

The goal is achieved by the fact that in a device for directional protection against

A ground-fault current in the AC network containing a zero-sequence current transformer, the secondary winding of which is connected to the first input of the power direction relay, a zero-sequence voltage filter, the output of which through the closed contacts of the control button is connected to the second input of the power direction relay, the output of which is connected to the executive body, switch, capacitor, resistor and AC source, zero sequence current transformer contains additional winding, Connecting to the output of the switch, the input of which via a capacitor and controlling open contacts connected to an AC power source button, which is also connected through a control button open contacts and a resistor to the second input direction of the power relay.

The drawing shows a diagram of the device.

The device comprises a zero-sequence current transformer 1, the secondary winding 2 of which is connected to the first input of the power direction relay 3. Additional winding 4 of the transformer 1 through the switch 5, the capacitor 6 and the control button 7 is connected to the AC source 8. The zero-sequence voltage filter 9 is connected via the control button 7 to the second input of the power direction relay 3, to the output of which the actuator 10 is connected. The AC source 8 via the control button 7 and the resistor 11 is connected to the second input of the power direction relay 3.

In the absence of a ground fault at the output of the current transformer 1 and the voltage filter 9, there are no components of the current and zero sequence voltage. The protection circuit is open.

When a ground fault occurs in a monitored network, the inputs of the relay 3 of the power direction receive signals corresponding in amplitude and phase to the current and to the zero-sequence voltage in the controlled connection. Depending on the phase ratio of the signals at the input of the relay 3, it works or does not work, switching the circuit of the executive body 10 To test the protection operability, they act on the control button 7, press the button and thereby change the state of its contacts.

In this case, the disconnecting contacts of the button 7 disconnect from the second input of the relay 3 the output clips of the filter 9. The closing contacts of the button 7 connect the terminals of the AC source 8 to the second input of the relay 3 through a resistor 11 and to the terminals of the additional winding 4 through a capacitor 6.

Thus, to the input terminals of the relay 3 of the power direction, the signals are shifted in phase relative to each other by 90 °, corresponding to the current and the zero-sequence voltage. The resistance value of the resistor 11 regulates the level of the signal simulating the zero-sequence voltage, and the capacitance of the capacitor 6 regulates the level of the signal simulating the zero-sequence current.

To test the protection in case of damage in its own zone and outside its zone, switch 5 serves to change the phase of the signal imitating the zero-sequence current by 180 ° with the same phase of the signal imitating the zero-sequence voltage. In principle, the same effect can be achieved by connecting said switch 5 to a circuit connecting the second input of the power direction relay 3 to the terminals of the AC source 8.

The device allows periodic testing of operability, including a transformer, and thereby increase the reliability of protection against earth faults.

Claims (2)

1. USSR author's certificate number 541232, cl. H 02 H 3/16, 1978. 2. USSR author's certificate According to application no. 2572610/07, cl. H 02 H 3/16, 1978.