SU1660093A1 - Device for protection against single-phase-to-ground short-circuit in network with insulated neutral - Google Patents

Description

The invention relates to electrical engineering and is intended for relay protection of electrical networks. The aim of the invention is to increase the selectivity and the expansion of the use of the device. When a ground fault occurs, for example, at the connection I of the EMF induced by the resulting current in the secondary

the current transformer 2 will have more EMF induced by the resulting current in the secondary winding of current transformer 3, because the primary windings of transformer 2 flow the sum of short-circuit currents and magnetic bias, and the primary windings of transformer 3 - their difference, which is determined by the direction of the main and additional windings . At the output of the organ 8 of the signal comparison modulo, a signal appears that triggers the response of the reacting element 11 when it exceeds the response setpoint. Executive authority 12 disables the bay switch. Thus, the comparison of two signals of one connection ensures the independence of the protection against changes in monitored signals in a wide range and increases the selectivity of the action of protection. 1 il.

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The invention relates to electromechanics, in particular to devices for protection against single-phase earth fault in a network with insulated neutral.

The purpose of the invention is to increase the selectivity and the expansion of the use of the device.

The drawing shows a schematic diagram of a device for protection against single-phase earth fault.

The device for protection against earth fault contains 1 primary 2 and additional 3 zero-sequence current transformers (TTPC) installed at connection, with two primary windings - 4 and 5 main windings and 6 and 7 additional, modulo signal comparison authority (OSSM) 8 connected through converters 9 and 10 current - rectified voltage (PTVN) to the secondary windings of TNTP 2 and 3, the reactive element (RE) 11, the input of which is connected to the OSSM 8 output, the executive body (IO) 12, whose input through the coincidence element 13 is connected to exits RE 11i starting body (PO) 14, connected to the output of the transformer 15 voltage zero-sequence (TNNP). Additional windings of TNCS 2 and 3 are fed through a CS-circuit 16 from the secondary winding of TNNP 15 connected in an open triangle pattern, while the additional winding 6 is included according to the main winding 4 of the TNCF 2, and the additional winding 7 is opposite to the main winding 5 of the TCTP 3 PTVN 9 (10) converts the zero-sequence current into rectified (smoothed) voltage. OSSM 8 compares two signals in absolute value (module) and can be made in the form of a semiconductor circuit pa of operational amplifiers, transistors, etc. The signal at the output of the circuit appears only when the signal at the output of the HTVN 9 is larger than the output signal of the HTVN 10 The ER 11 can be performed using an amplifier, a comparator, a time-measuring element and a Schmitt trigger.

The device works as follows.

In the absence of a single-phase earth fault in the network, the ER 11, IO 12 and SW 14 are in the initial state. When a single-phase earth fault occurs at the protected connection 1, for example, a zero-sequence voltage appears at the K1 point on the secondary winding of the TNNP 15, under the influence of which it triggers. Software 14, and current-flow magnetization begins to flow through the additional windings 6 and 7 . Due to this current, the mode of operation of transformers 2 and 3 is translated into the steeper part of the magnetization characteristic. Through the main windings 4 and 5 of the current transformers 2 and 3 flows the total capacitive current of the entire network - the earth fault current directed from the busbars to the connection (with the selected positive direction of the currents). The electromotive force (EMF) induced by the resulting current in the secondary winding of TTPC 2 is greater than the EMF induced by the resulting current in the secondary winding of TTPC 3, as the primary current flowing through the primary windings of TTPC 2 is equal to the sum of the short-circuit and bias current, and. through the primary windings of TTPD 3 - their difference (with a given inclusion of the main and additional windings). Since the EMF module at the output of the secondary winding ΤΪΗΠ 2 is larger than the EMF module at the output of the secondary winding of the TTPC 3. then a signal appears at the OSSM 8 output and, accordingly, at the input of the ER 11. When the value of this signal exceeds the threshold (setpoint) of the operation of ER 11, the latter switches to the opposite state ,. As a result, IO 12 is activated, which acts to disconnect the connection switch 1.

When an external circuit to earth, for example, on the tires of the supply substation at point K2, primary windings 4 and 5 and additional 6 and 7 flow, respectively, their own capacitive current of connection 1 directed to the tires, and bias current. Due to the fact that its own capacitive current has a direction opposite to the direction of the earth fault current, the resulting current, equal to the sum of its own capacitive current and bias current, flows through the primary windings of the TNTP 3, and the primary windings of the TNTP flow through the primary windings 2 the resulting current flows. equal to the difference of the own capacitive current and bias current. The module of the resulting current flowing through TTPD 3. exceeds the module of the resulting current flowing through TTPC 2. With this ratio between the resulting primary currents, the signals at the OSSM 8 output do not appear and the device does not come into action.

Thus, in the proposed device the differences of two signals of one connection are compared, that

ensures the independence of work from the change in the amplitudes of the currents zero succession5

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tension in a wide range, which expands the scope of the device; the possibility of using the device to protect single power lines; increased selectivity and sensitivity, the device does not respond to unbalance signals, due to increased load currents or self-starting currents of electric motors. Therefore, there is no need to tune out these signals. The device does not come into effect when external ground faults occur, for example, on substation buses or in the supply distribution network.

The proposed device can be implemented on a modern element base and made individually for each connection. Its use increases the reliability of the protection against earth fault, which contributes to reducing the number of unjustified disconnections of consumers and improving the reliability of power supply.

Claims (1)

Claim. Device for protection against single-phase earth fault in the network with insulated neutral, containing a voltage transformer zero sequence, the output of which is connected to the starting body, the zero-sequence current transformer with an additional primary winding connected via an HC circuit to the output of the voltage transformer zero sequence and included in accordance with the primary primary winding, the comparison unit modulo, whose input through the converter current - rectified voltage is connected to the output of the zero-sequence current transformer. the executive body connected by the input to the output of the coincidence element, the input of which is connected to the output of the modulatory signal unit through the reacting element and to the output of the starting organ, characterized in that, in order to increase the selectivity and expand the field of use of the device, it is equipped with an additional current transformer zero sequences with an additional primary winding connected in opposite with the main primary winding and fed through the specified PC circuit from the voltage transformer zero sequence, while the output of the additional current transformer of the zero sequence through the newly introduced converter current - rectified voltage is connected to the newly entered input of the signal comparison unit modulo.