SU1272398A1 - Device for protection of reactor of static thyristor compensator of reactive power against internal damage - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to methods for protecting reactors installed in static thyristor compensators (STK) for controlling reactive power in networks of 35-1150 kV against all types of internal damage. The aim of the invention is to increase the sensitivity of the protection. This goal is achieved by measuring the first time interval from the moment of switching on the thyristor in the circuit of the protected reactor to the moment the voltage goes across the reactor through zero in block 3, then the second time interval from block interval until the thyristor mentioned above switches off and when block 6 is triggered, the reactor is turned off if the time difference (the first and second time intervals exceed the specified value. 6 Il.

Description

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00 The invention relates to electrical engineering, in particular, to methods for protecting reactors installed in static thyristor compensators (STK) for regulating reactive power in networks of 35-150 kV against all types of internal damage. The purpose of the invention is to increase the sensitivity of protection. It is known that with internal coil damage to the reactor, its impedance decreases. In this case, the inductive component of the resistance decreases, and the active component can significantly increase. However, in the STK scheme with an unchanged turn-on angle of the thyristor switches and the closure of a small number of turns of the reactor, the integral current value may not change, since an increase in the current amplitude is compensated by a decrease in its flow time. The latter is due to a decrease in the reactor time constant. FIG. 1 shows the diagrams explaining the essence of the known method; in fig. 2 - voltage and current of the STK reactor; in fig. 3 - curves of currents and voltages of the reactor at different values of the angle of the reactor; in fig. 4 is a block diagram for implementing the method; in fig. 5 and 6 are diagrams showing the flowchart. FIG. 1 t / is the voltage on the JCC; / i and ia are the currents of the operational and damaged reactors, respectively; a is the turning on angle of the thyristor key STK; t to t is the current flow time, respectively, of the serviceable and damaged reactors; I is the area corresponding to an increase in the current integral 12 due to a decrease in the impedance of the damaged reactor; II is the area corresponding to the decrease in the duration of the current flow in the damaged reactor. The essence of the method is explained in FIG. 2-6. Consider the voltage and current of the STK reactor, the circuit of which is shown in FIG. 2, where Q is a switch; R - reactor and VT thyristor key. A special control circuit generates signals, upon arrival of which, the thyristor switch VT is turned on. A transient process in the reactor circuit R begins, and at the moment the current passes through zero, the thyristor switch is turned off and remains locked until the control signal is received in the next half period. Voltage voltage in the network (Xsmco we obtain the ratio for current and voltage at the reactor and g /. / Fokl - (OGt g-15sh () - 5gp (vk-fr) if | b, 1.,. () .W ) ,, SP) Q Grotl, O5L) Up (i), if / 1 (2) ... 1 2.U) where n is the number of the half-talk under consideration) (, period (, 2, ...); r | ) on and fotkl - the angles of switching on and off of the thyristor switch, respectively, in the nth half period; fr is the angle of the reactor; ZP - reactor impedance Tr - time constant of the reactor (P, -} Analysis of relations (1) and (2) shows the following: the time between the time of switching on the thyristor VT (current occurrence) and the time of voltage transition at the reactor through zero is the first time interval (l-iJ) Bo) / a), at a given switching angle a | svk does not depend on the value of the angle of the reactor (); the duration of the second time interval A / 2 (TJ) OTM-l) / (o at this switching angle decreases with decreasing reactor angle, as photocl / fr). Figure 3 shows the curves of the currents and voltages of the reactor at different values ; constructed in accordance with ratios (1) and (2), moreover, fr1, fr2, Frz (numbering of currents / pi, / p2, 1rz, voltages Upl, UpZ, Up3, turn-off angles ;, lj) oTM2, a |) off and the second time intervals A / 2.1, .2, A / 2.3 corresponds to the numbering of the angles Фр1, фр2, фрз). The high sensitivity of the method is due to the fact that the moment when the transition current reaches zero (the moment the thyristor switch is turned off) and, consequently, the duration of the second time interval is largely determined by the value of the constant time of the reactor. The nominal angle of the reactors 500-1150 kV is 89.8-89.9, and the time constant (tr Jaф / η) is 1-1.8 s. In this case, the difference in the durations of the first and second time intervals, calculated from relations (1) and (2), is 20 µs. It is known that with internal damage to the reactor, including winding closures, there is an increase in the active component of its resistance, resulting in the angle of the reactor and its time constant

reduced. For example, when the reactor angle is reduced by only 1 °, which corresponds to the closure of 1-2 turns of the winding, the reactor time constant decreases by a factor of 7-10, which gives a difference in the durations of the first and second time intervals of more than 190 µs.

Thus, the excess of the duration of the first time interval over the second for a given time is a reliable indication of internal damage to the reactor, ensuring its high sensitivity of the suture.

The proposed method can be implemented quite simply on known functional elements, for example, in accordance with the simplified block diagram shown in FIG. 4. The operation of the flowchart is illustrated in diagrams in FIG. 5 and 6 in the normal mode with a working reactor and in the mode of internal damage to the reactor.

The block diagram (Fig. 4) consists of a voltage sensor 1 at the reactor, a rectangular voltage driver 2, a unit 3 comparing the durations of rectangular signals of different polarities, a key 4 with a working input connected to the output of the unit 3 comparing and controlling The upper input of the control signal generator 5 for controlling the key 4, as well as the threshold output element (block) 6.

Plot numbers in FIG. 5 and 6 corresponds to the numbering of the blocks in FIG. four.

Unit 2 forms rectangular signals of standard amplitude from the reactor voltage. Comparison unit 3 generates a voltage proportional to the difference in the durations of rectangular pulses of different signs, for example, by integrating them. Key 4 is in the open state and allows the signal to flow to its working input from unit 3 if there is an enable signal at the control input. Unit 5 generates an enable signal when the thyristor switch is turned off in the circuit of the reactor being encrypted (in dead-time pauses, when / ,, 0). The output unit 6 is triggered and sends a command to shut down the reactor if the output signal of the comparison unit 3 to the empty pause of the reactor circuit exceeds a predetermined level (setpoint).

In the normal mode (Fig. 5), the duration of the first A / 1 and the second time intervals is almost the same, so the voltage at the output of the comparison unit 3 to the time of turning off the switch key is close to zero and the output unit does not operate.

When an internal damage occurs in the reactor (Fig. 6), the duration of the first time interval AL is longer than the duration of the second time interval () - If by the time the thyristor switch is turned off, the output voltage of the comparison unit 3 exceeds the setpoint of the output unit 6, the latter triggers and issues a command to shutdown reactor.

The use of the proposed method 0 makes it possible to increase the sensitivity of the protection of the STK reactor against internal damage.

Claims (1)

Invention Formula The method is protected from internal damage to the reactor of a static thyristor compensator of reactive power, which consists in measuring the parameters of the monitored signal in the time interval of an open thyristor switch, comparing them with the setpoint and disconnecting the reactor if the measured signal does not match the specified one, characterized in that in each half-cycle of the industrial frequency, the first time interval is measured from the moment the thyristor was turned on in the circuit of the protected reactor to the moment p Transfer the voltage across the reactor to zero, then measure the second time interval from the end of the first time interval to the moment when the thyristor is turned on, and turn off the reactor if the difference between the durations of the first and second time intervals exceeds the specified value. - // „IP .. bnl. ti otnl. 3 Watnl. 2 VomXA 1 A Dump 5 .tr t Stadnab J. Jl t FIG. 6