SU1319144A1 - Device for redundant protection of tap-changing transformer - Google Patents

Abstract

The invention relates to electrical engineering, in particular to relay protection of power transformers, which are connected by tapping to a power line, and is a backup protection. The purpose of the invention is to increase the sensitivity and simplify the design. A current transformer 11 is installed on the power end of the power line, the secondary winding of which is connected to the reacting organ 12, designed as a balanced relay 13, which through time relay 17 acts on the circuit breaker 18. In the circuit of the transformer I to be installed, 1 sat is saturating the reactor 3, shunted by a diode 4 and counter-thyristor 5, between the anode and the control, whose electrode includes a resistor 6 and a second diode 7. To the control electrode of the thyristor 5 through the current transformer 10, the potential ometr 9 and the rectifier bridge. 8, a signal is proportional to the current in the circuit of the forbidden transformer 1. With a short circuit (short-circuit), transformer 1 saturates the transformer 1, which leads to disruption of the current in line 2, which in turn triggers a balanced relay 13. With a duration A short circuit, which exceeds protection time 1, triggers the time relay 17 for switching off the switch 18, which ensures redundancy protection of the transformer 1 in case of its failure. 1 il. CO with co 4

Description

The invention relates to electrical engineering, in particular, to devices for relay protection of power transformers connected by tap-off to a power line.

The purpose of the invention is to increase the sensitivity and reinforcement of the structure.

The drawing shows a schematic diagram of a device for back-up protection of a tapping transformer.

The device contains a transformer 1, connected by tapping to the power line 2. A saturating reactor 3, clamped by the first diode 4 and the countercurrent thyristor 5, is connected in series with one of the windings of the auxiliary transformer 1, and the chains containing the resistor 6 and the second diode 7 are connected between the anode and the control electrode and the rectifier output circuit bridge 8, the input circuit of which is connected to a potentiometer 9 installed at the output of the current trapformer 10, made in the form of a transreactor. A current transformer II is installed on the power supply cable of the power supply, the secondary winding of which is connected to the reacting organ 12, designed as a balancing relay 13, the windings of which are bounded by capacitors 14 and connected via multidirectional diodes 5 and 16. The executive contacts of the balancing relay (not shown) act on the start of the relay 17 time, the contacts of which are included in the disconnecting circuit of the switch 18.

The device works in the following way.

In the normal loading mode of a transformer 1, the voltage taken from the secondary winding of the transreactor 10 and supplied through a potentiometer 9 and rectifier 8 to the control electrode of the thyristor 5 is less than the voltage caused by the flow of current through the reactor 3, therefore diode 7 open and due to the flow of current through the diode 7 and the resistor 6, the thyristor 5 opens to shunt the reactor 3. In the second half-period the shunting of the reactor 3 occurs by the diode 4, B the result of the sinusoidal load current of the transformer 1 is not a pair of y-1 oidal- iy. The equality of the currents of both half-periods does not cause the operation of the balanced relay 13 and the switching off of the switch 18, since the installation of the balanced relay 13 is rebuilt from the unbalance of the normal operation mode.

When k. 3. Transformer I, due to a significant increase in current, leads to the insertion of reactor 3 with an increase in voltage on it to a lesser extent than on the secondary winding of transreactor 10; Due to the closure of the thyristor 5, the reactor 3 is shunted by diode 4 only in one half-cycle of the sinusoid re 0

current, and in the other half period reduces the amount of current to. C. by an amount proportional to the ratio of the resistance of the reactor and the rest of the circuit. When the difference between the positive and negative half-cycle currents in line 2 from the current transformer 11 through diodes 15 and 16, different currents flow into the windings of the balanced relay 13, which cause it to trip. When the duration of the short circuit exceeds the time of protection of the transformer 1, the time relay 17 trips the switch 18, which ensures redundancy of the protection of the transformer 1 in case of its failure.

Resistor 6 sets the required value of the control current for opening the thyristor 5. To select the threshold for changing the operating mode of the thyristor 5 from an open state to a closed state depending on

0, the primary current of the circuit uses a potentiometer 9, by which the blocking voltage level is changed.

The capacitors 14 of the balance relay 13 stabilize the currents in its windings for

c the possibility of comparing them with the difference in the time of flow in half the period of the observed frequency. Since in the normal mode the sinusoid current does not have distortions, in case of overloads, different types of k. 3. The equality of the positive and negative half-period currents is preserved, therefore a balanced relay can have a high sensitivity. With non-linearity of the load, the distortion of the sinusoid of the fundamental frequency by multiple harmonics also does not change the indicated difference of the currents. Ne is changing

5 this difference is also observed with full-wave rectification, therefore, almost everywhere, the difference in the currents of both half-periods is absent in all cases.

Since the current transformer 11 and the circuits connected to it operate in the same mode for the positive and negative half-periods, the unbalance level can reach a value less than the absolute error of the current transformers 11 in the measurement mode. Taking into account the difference between the specified error, the setpoint of the balanced relay 13 is selected, in relation to which the ratio of the resistance of the reactor 3 in the saturation mode and the rest of the kc circuit is chosen, which is mainly determined by the resistance

0 transformer 1.

Claims (1)

Invention Formula A backup protection device for a tamping transformer containing a current transformer installed at the supply end of the transmission line, the secondary winding of which is connected to the reacting element from a time relay to you 0 during timed contacts of which are included in the disconnecting circuit of a power line switch, a current transformer mounted on a tapping transformer, the secondary winding of which is connected to a current shape distortion unit, is a rectifying bridge, characterized in that, in order to increase sensitivity and simplify the design , a saturable reactor, a thyristor, a resistor, four diodes, two capacitors and a balanced pejie are additionally introduced, while the current shape distortion unit is made in the form of a saturating reactor, shunted by the first diode and an oppositely connected thyristor, and connected to the primary winding of the back-up transformer of the same phase on which the current transformer of the power supply line of the transmission line is installed, between the anode and the control electrode of the thyristor includes a circuit of a series-connected second diode and a resistor and an output circuit of a rectifying bridge, the input circuit of which is connected to a potentiometer connected to the secondary winding a current transformer installed on a tapping transformer and made in the form of a transreactor, the reacting organ is made in the form of a balanced relay with two windings, in series with which the third and fourth diodes are oppositely directed, respectively, and the windings themselves are bridged by capacitors.