SU838876A1 - Device for pulse protection of converting bridge - Google Patents

Description

The invention relates to relay protection and emergency automation and can be used to protect converter bridges.

A device for the differential protection of the Converter bridge, containing protective current transformers, a multiphase rectifier and a DC sensor having a core with a rectangular magnetization characteristic [1].

The disadvantage of this device is the low reliability due to the possibility of saturation of current transformers,

Closest in technical essence to the proposed device is the pulse protection of the converter bridge from valve switching failures, containing phase current transformers, to the secondary windings of which switching sensors are connected, the outputs of the latter through the pulse matching unit and logic element AND are connected to the output organ, and a blocking organ connected to a DC transformer installed in the rectified circuit of the converter bridge [2].

However, this device does not protect the converter bridge when the latter on the existing short circuit due to the fact that in this mode of operation is carried blocking current, which is intended for ^s eliminate false protection device operations at input of the converter bridge in operation when currents occur simultaneously in two phases.

The purpose of the invention is to increase the reliability of the device when you turn on the bridge to the existing short circuit.

This goal is achieved by the fact that the device is additionally equipped with an OR element and a pulse selector in duration, the input of which is connected to the output of the pulse matching unit, and the output to the first input of the OR element connected to the second input of the AND element, and the output of the blocking organ is connected to the second input element OR.

²⁰ In FIG. 1 shows a structural electrical diagram of the proposed device;

in FIG. 2 and 3 are diagrams explaining the principle of operation of the device.

The device contains phase current transformers 1, sensors 2 switching, transformer 3 DC, blocking body 4, block 5 matching pulses, element And 6, selector 7 pulses in duration, element OR 8 and the output unit 9.

The conversion bridge consists of valves 10-15 and is connected to the load 16.

The scheme works as follows.

When the converter bridge is idling as a result of applying the maximum reverse voltage, a breakdown occurs, for example, of valve 12. A two-phase short circuit begins to develop only after the supply of control pulses to the fans 10 and 11 (Fig. 3).

At the output of the sensors 2 switching (Fig. 1) phases A and B during the time Θό - in; there are signals (U2A and U2B) obtained as a result of differentiation of currents passing through valves 12 and 10, but limited in amplitude. The voltages ДГА and Ugg are supplied to the input of the coincidence unit 5, made in such a way that, as a result of the supply of signals from two opposite sensors 2 of the switching, an impulse for protection operation appears at the output of the coincidence unit 5. The duration of the coincidence signal in this mode at the output of the coincidence unit is ^ Since the current does not flow through the current transformer 3, but closes through the valves 10, 12 and 14 of the cathode group, there is no signal at the output of the blocking organ 4, which reliably blocks the protection. After a time determined by the setting of t pulses of the 7 pulses in duration, the output of the last signal appears through the element OR 8 to the second input of the element And 6, at the first input of which there is a signal U _s from the output of coincidence unit 5. As a result of the coincidence of these signals, the output unit 9 and the entire protection are triggered.

When the bridge is put into operation in normal mode (Fig. 2), the current occurs simultaneously in two phases A and B. However, using the time delay t B0, the protection is blocked, which is also carried out using the selector 7 pulses in duration, since the signal duration coincidence U _s is equal to y. By selecting the setpoint for the operation of the pulse selector in duration within '

I <cst?

where y is the angle of switching valves, determined from the expression y = arc cos [cosd + cozy ₀ -1] - where is the control angle;

Yo - switching angle at ci = 0, you can detach from false positives when entering the bridge into operation.

In the normal operating mode, the pulses from the switching sensors 2 are supplied to the coincidence unit 5 with a shift ψ (Fig. 2), which excludes the operation of the pulse selector 7 in duration and protection in general.

Using the difference in the shape of the currents during internal damage and during normal operating conditions of the converter bridge, which is expressed after differentiating the currents in different durations, by introducing the OR logic element and the pulse selector in duration into the device, it can improve the reliability of the device when the converter bridge is connected to an existing short circuit.

Thus, the application of the invention improves the reliability of the protection of the Converter bridge as a whole.

Claims (2)

(54) DEVICE FOR PULSE PROTECTION OF THE CONVERSION BRIDGE The device contains phase current transformers 1, switching sensors 2, direct current transformer 3, blocking organ 4, unit 5 of pulses matching, element AND 6., pulse selector 7, duration, element OR 8 and output block 9. The converter bridge consists of valves 10-15 and is connected to the load 16. The circuit operates as follows. When the converter bridge is in idle mode, as a result of application of the maximum reverse voltage, breakdown occurs, for example, valve 12. A two-phase short circuit begins to develop only after the supply of control pulses to internals 10 and 11 (Fig. 3). At the output of switching sensors 2 (Fig. 1) of phases L and B during the time Ey - 61 there are signals (Angle and U2B), obtained as a result of differentiation of currents passing through gates 12 and 10, but limited in amplitude. The voltages UaA and are fed to the input of the coincidence unit 5, designed in such a way that, as a result of signals from the two opposite sensors 2 of the switching, the output of the coincidence unit 5 is a pulse to activate the protection. The duration of the coincidence signal in this mode at the output of the coincidence unit is equal. Since no current flows through the current transformer 3, but closes through the cathode group valves 10, 12 and 14, there is no signal at the output of the locking member 4, which reliably blocks protection. After a time determined by the setpoint tijt of the pulse selector 7, at the output of the last, a signal arrives through the element OR 8 to the second input of the element 6, the first input of which contains the signal Us from the output of the coincidence unit 5. As a result of the coincidence of these signals, the output unit 9 and the entire protection act. When the bridge is put into operation in the normal mode (Fig. 2), the current occurs simultaneously in two phases A B. However, using the time delay t VO, protection is blocked, which is also carried out using the pulse selector 7 in duration, since the duration The match signal Us is j. By choosing the triggering setpoint of the pulse selector by duration within, rxU.e y is the angle of valve switching, determined from the expression at arccos coso (+ cosjfo - 1 - "t, where dL is the control angle; io is the angle of switching at ci О, in the normal operating mode, the pulses from the switching sensors 2 arrive at a block 5 coinciding with the shift (Fig. 2), which eliminates the triggering of the pulse selector 7 in terms of duration and protection in general. currents during internal damage during normal operating conditions of the converter bridge, which is expressed after differentiating the currents in different durations, by introducing the OR logic element and the pulse selector into the device, the device can increase the reliability of the device when the converter bridge is turned on for an existing short circuit. reliability of protection of the converter bridge as a whole. The invention The device for pulse protection of the converter bridge, containing phase current transformers, to the secondary windings of which are connected switching sensors, the outputs of which are connected to the first input of the element I connected to the output unit and the blocking device connected to the transformer , characterized in that, in order to increase reliability, it is equipped with an OR element and a pulse selector in terms of duration, the input of which is connected to the output of the unit is the same and pulses, and the output is to the first input of the OR element connected to the second input of the AND element, and the output of the blocking organ is connected to the second input of the OR element. Sources of information taken into account in the examination 1.Glukh EM, Zelenov V.E. Protection of semiconductor converters. M., “Energie, 1970, p. 116-117. 2. Impulse protection of the converter bridge against valve switching impairments. Lime universities. “Electromechanics, 1976, No. 2, p. 218-222. W yes l s // CF one Ul.l Oahus