SU754564A1 - Method of preventing switching -on of line switch at short-circuiting in line - Google Patents

Description

The method relates to the protection of electrical equipment and can be used, for example, at traction converter stations.

Known methods of preventing the inclusion of a linear switch during a short circuit in the line by testing it with a pulsed voltage or high frequency voltage, measuring the direct and alternating current residual resistance (1] and [2].

In the first case, it is necessary to reckon with the radio interference and the inductive-capacitive component of the resistance of the network and rolling stock, which affect the test result. In the second case, the circuit for measuring the resistance on direct current does not allow distinguishing the short circuit resistance from the resistance of the included traction motors; the alternating current circuit must have a special transformer. In addition, in both cases, the test is performed on voltage and power, ^ other than operating conditions. Connection directly to the measuring resistance as an actuating element of the voltage relay. does not provide the required feelings *

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security, which leads to failure of protection.

Of the known methods for preventing the re-activation of a linear 5 switch, the closest in technical essence to the proposed method is the method [3], according to which for this purpose a half-wave voltage of a low transformer with a primary and secondary voltage of 220/36 V is used. To increase the sensitivity of the circuit, a magnet amplifier in the relay mode is used as an actuating element. The load resistance is included in the primary circuit of the transformer and, by the voltage drop across it, determine the state of the line before it is turned on again.

The presence of a special transformer and magnetic amplifier makes the installation rather cumbersome. A low test voltage due to contamination and oxidation of the wires is not always sufficient to trigger the protection, and an increase in the test voltage leads to an increase in the power of the installation.

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754564

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The aim of the invention is to increase the reliability of work, increase the reliability of monitoring the state of the line while reducing the installed capacity.

This is achieved by the fact that, at the point where the linear switch is prevented from turning on, there is a short circuit in the line, which means that after switching the switch to the line, test one-half-period voltage is obtained, the flowing current is measured and, if this current exceeds the specified value, the switch-off is prohibited linear switch, as a test voltage using a gradually increasing voltage, formed from the specified half-wave by gradually reducing the firing angle iristornogo key and according to the level of the test voltage changed the setting flowing current measuring element.

Ya FIG. 1 is a block diagram illustrating a method for preventing a linear switch to be turned on during a short circuit on a line; figure 2 - the form of the test voltage.

The block diagram contains a simplified representation of a converter unit with a power circuit: a star — two reverse stars with a balancing reactor 1, a thyristor 2, a current sensor 3 with automatically: changing operation setpoint, a thyristor control system, a current sensor and a unit, 4 switching on the linear switch, load 5, linear switch 6, block 7 of switching and turning on the line switch, disconnectors 8, 9. Output 10 of block 4 of the line switch is connected with block 7 of turning off and turning on the line switch.

To complete the work (see Fig. 2), it should be added that the test voltage is automatically adjusted from zero to working by applying 2 control pulses 11 to the thyristor with a control angle from 180 to 90 el. hail, from one phase of the converter transformer.

To provide a limited-response characteristic with a cut-off, the current sensor setpoint is automatically changed by a signal 12 for each thyristor control angle. The circuit starts working immediately on a signal from output 10 of block 4 from being disconnected due to a short circuit in the line circuit breaker line. If it "feels" the presence of a short circuit of the signal .13 already at some intermediate voltage 0 is _used, then its operation will occur cyclically, starting from I) · 0 to I) · Itsssch. At is10

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In the event of a short circuit, the control system sends a signal 14 to enable the linear circuit breaker to turn on, after which the entire circuit returns to its initial state, i.e. the thyristor 2 is locked and the line switch 6 is turned on.

The use of a controlled operating voltage for testing a line excludes the failure of protection in the case of a metallic short circuit in the line due to the insufficient power of the source of the probing impulse of contaminants and the oxidation of wires, which is the case when testing with a reduced voltage of a regulated value. This eliminates unwanted mode in the line when the voltage is applied to a short-circuited network, which worsens its condition, causing a burned out contact of wires and damage to elements of the contact network.

In addition, by applying the phase test of a converter transformer supplied to the line through a thyristor as a source, it can significantly reduce the installed capacity of the installation.

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Claims (1)

Claim The way to prevent the linear switch from turning on for a short circuit in the line is that after disconnecting the switch, a half-wave test voltage is applied to the line, the flowing current is measured, and if this current exceeds the specified value, the linear switch is prohibited from turning on I have the fact that, in order to increase reliability by increasing the reliability of monitoring the state of the line, gradually increasing voltage is used as a test voltage Noe of said half-wave by gradually decreasing the firing angle of the thyristor switch in accordance with the level of the test voltage changed the setting flowing current measuring element.