SU1444915A1 - Device for protecting step-down transformer with single-end supply - Google Patents

Abstract

The invention relates to the field of electrical engineering, namely to relay protection of transformers. The purpose of the invention is to increase the sensitivity of the device. The goal is achieved by the signal that the primary current changes from the current transformer 1 through the industrial frequency filter 5, the first signal converter 6 and the first differentiating element 7 is fed through the BAN 16 element to the threshold element 17, which, when the setpoint is reached through the output unit 18, turns off the transformer . Signals to the prohibiting inputs of the BAND 16 are applied: when the load current from the current transformer 2 increases, when the magnetizing current rush from the high harmonics filter 8, when the transformer ratio from the switching unit is adjusted 11. 1 cp f-ly, 2 ill. with (L

Description

O / pcl

4; ik 4ib

cl

The invention relates to electrical engineering, namely, relay protection of transformers, and can be used to protect transformers with one-sided power, for example, lowering block transformers, generator-transformer units, short-circuit generators.

The aim of the invention is to increase the sensitivity of the device.

FIG. 1 shows a block diagram of a device for protecting a step-down transformer with a single-sided power supply; figure 2 - structure on the block circuit of the brake signal.

The device for protection of a step-down transformer with one-way power supply contains current transformers 1 and 2, the first 3 and second 4 matching intermediate transformers, the frequency filter 5, the first signal converter 6, the first differentiating element 7, the harmonics filter 8, the second signal converter 9, the second differentiating element 10 block

11-amp switch, block

12 brake signal, third converter 13 signals, third differentiating element 14, rectifier 15, block 16 BAN, threshold element 17, output block 18. Block

} 2 brake signal contains key

19 and one-shot 20.

The device works as follows.

In normal operation, under the action of the load current in the secondary windings of transformers 1 and 2 currents flow, which in intermediate transformers 3 and 4, respectively, are transformed into voltage. From the output of the first intermediate transformer 3., the alternating sinusoidal voltage flows through industrial frequency filter 5 in which the first harmonic is extracted from the voltage to the signal converter 6, where the alternating current is transformed into a constant voltage. The first differentiating element 7 only passes the variable component of the voltage and therefore there is no signal at the enable input of block 16 BAN.

From the output of the second intermediate transformer 4, the alternating current voltage is supplied to the third transformer.

the signal diverter 13, in which the alternating current voltage is also converted into a constant, since the third differentiating element 14 also passes only the variable component of the voltage, then the third prohibitive input of the block 14 is FORBID connected through the actuator 15 to the output of the differentiating element 14, no signal.

With an increase in the load current and external short circuits in the power circuit, the aperiodic component of the current appears and therefore a change in level occurs at the outputs of the signal converters 6 and I3. voltages from lower values to large ones, - as a result, short voltage pulses appear at the outputs of the first and third differentiating elements 7 and 14. However, at the output of block 16, the BANNER remains zero potential, since the voltage from the output of the third differentiating element 14 through the rectifier 15 is supplied to the blocking input of the block.

If a short circuit occurs in a power transformer and a voltage pulse is generated only at the output of the first differentiating element 7, then the enable input of the block 16. A PREMED signal is given leading to the triggering of the latter. From the output of block 16, the BANNING voltage is applied to the threshold element 17, which is a zero-level crossing detector, and from the output of the latter, a signal with a fixed amplitude is fed to the output block 18, from the output of which the voltage is applied to the switching circuit of the switching device. To eliminate false positives of protection during inrush magnetization, a filter of 8 higher harmonics, a converter of 9. signals and a differentiating element 10 are introduced into the device circuit. At inrush currents, aperiodic composition appears in the power circuit, and the current containing the first and higher current harmonics, as a result of which short voltage pulses appear at the outputs of the first and second differentiating elements 7 and 10. However, the blocking of block 16 does not occur because the output is differentiated.3

The element IO is fed to its locking input. Block 12 generates a brake signal in the mode of switching the voltage control device under load (BPN). This block works as follows. When switching the switch I1, a signal starts, which triggers the single-vibrator 20. At the moment of switching the on-load tap-changer, a current surge occurs from the power side of the transformer in the power circuit, resulting in the output of block 6 a signal arriving at the power input of switch 19 of block 12. At Since the one-shot 20 of the one-shot 20, the key 19 is unlocked and a brake signal prohibiting the switching-off of the switching apparatus is applied to the second prohibiting input of the 16 BANCH block 16. The time of the one-vibrator is chosen by a large time constant of the differentiating element 7 to avoid false operation of the protection. The transmitter 15 is designed to cut the negative polarity signal that occurs at the output of the differentiating element 14 when the voltage level at the output of the signal converter 13 goes from a large value to less. To eliminate the false triggering of the protection, the time constant of the second 10 and third 14 differentiating elements is chosen somewhat longer than the time constant of the first differentiating element 7,

The proposed device for protection of a step-down transformer with a single-sided power supply can also be used to protect a transformer containing several secondary windings. In this case, a current transformer is installed on each secondary winding, and an intermediate transformer, a signal converter, a differentiation element and a miniature are added to the device circuit. Thus, the number of prohibiting inputs of the BAN block is correspondingly increased.

Claims (2)

1. Device for protection step-down transformer with unilateral supply, containing intended for installation at the terminals of the power 44915 transformers are current transformers, the secondary windings of which are connected to the inputs of matching intermediate transformers, the output of the first intermediate transformer is connected to the inputs of industrial frequency filters and harmonics, whose outputs are connected to the inputs of the first and 10 second signal converters, respectively, the first differentiating element whose input is connected to the output the first converter of signals, the block of the anti-phase switch 15, the input terminals of which are connected to the control winding with sludge transformer, the third signal converter, the input of which is connected to the output of the second intermediate transformer, element BAN, threshold element, output block, different. In order to increase the sensitivity, two 25 differentiating elements were additionally introduced, a brake signal block, a rectifier, the output of the first differentiating element is connected to the enable input of the BAN block, the input of the second differentiating element is connected to the output of the secondary signal converter, and the output is connected to the first prohibitory input of the BANCH block, the output of the first brake signal block is connected to the output of the first signal converter, the second input of which is connected to the output of the anti-switching switch unit And the code is -, - with the second prohibiting input of the BANCH unit, the output of the third 0 signal converter through the third differentiating element and the rectifier are connected to the third prohibiting input of the BANGE block, the output through the threshold element 5 is connected to the input of the output unit, 2., The device of claim 1, about tl, which is that the block of the brake signal is designed as a one-shot and a key, the power input of the key is connected to the output of the first signal converter, and the output is to the second prohibition the entrance 5 of the BANNER block i the one-shot input is connected to the output of the anti-phase switch unit, and the output is connected to. control key input. From block 6 W H5lok16 O / p5loko and 20 FIG. g