SU542289A1 - Device for differential protection of power transformer - Google Patents

Description

the protected zone due to the increased EFFICIENCY in the secondary current of the second harmonic used in the device of the interlock system.

The prototype of the invention is a device for differential protection of a power transformer, containing sensors of phase and differential currents, to the outputs of which, via the operating and brake circuits, is connected a reacting organ consisting of a forward die and a logical logical chain HE-HE-B 3. This protection uses the principle of inhibition on the second harmonic of the current and the time-pulse principle based on a comparison for the duration of the pauses.

The disadvantages of protitopes are;

1. A significant increase in the response time of the protection at short-circuit. in the protected zone with the aperiodic component in the primary current, which leads to the naxing of the TT magnetic circuits in a transient mode. Such a mode is possible even with short-circuit currents that do not exceed the differential cut-off trigger threshold. In addition, the presence of the second harmonic in the distorted secondary current transients leads to additional deceleration (desensitization) of protection.

2. Incorrect operation of the protection in the presence of periodic inrush currents of magnetization, since in the circuits with real TTs the shape of the unbalance current curve can be close to sinusoidal. A similar situation arises when the generator-transformer unit is turned on in the network by the self-synchronization method. The duration of pauses in these cases may not exceed the corresponding values for a short wiring in the protected zone.

The purpose of the invention is to increase reliability and selectivity. This goal is achieved by the fact that in each phase the input of the first element of one logical chain is connected to the output of a positive-polarity pulse generator and to the input of the second element of the second logical chain, and the input of the first element of the second logical chain is connected to the output of the magnetic driver of a negative field current to the input of the second element is NOT the first logical chain, and the outputs of all logical chains of the three phases are connected to the blocking inputs of the starting organs through the logical organ OR. This makes it possible to increase the sensitivity of the protection by ensuring reliable

blocking it in case of external short circuits and all types of inrush current of the power transformer.

The drawing shows a block diagram of the device. On both sides of the protected object 1, there are current transformers 2 and 3, the secondary windings of which are connected through a phase-matching starting elements 4 to a differential circuit. Differential current sensors 5 are included in the differential circuit of each phase. Shapers 6 and 7 of continuous pulses from half-wave current are connected to the outputs of the differential current sensors

and negative polarities. The outputs of the formers 6 and 7 are connected respectively to the inputs of two logical chains NOT-IN-NOT-IN (8,9,10,11 and 12, 13,14,15) and to the second inputs of the elements

NOT opposite chains - 14 and 10. The outputs of all logical chains of the three phases through the circuit OR 16 are connected to the blocking inputs of the starting bodies 4, The device operates as follows. In the normal mode, the starting organs 4 and the formers of 6.7 pulses are rebuilt according to the setting from the unbalance operating currents. Current transformers 2 and 3 are selected so that in the steady state external short-circuit mode. their fullness did not exceed 10%.

When the protected transformer is turned on under voltage or when the voltage is restored to the whole network, the set of current transformers corresponding to the switched winding measures the magnetizing current of the power transformer. The current flows through the differential circuit through the sensors 5 and

starting organs 4. If the current values exceed the setpoint of operation 4 and 5, then in those phases where the current is unipolar, only one of the two drivers 6 or 7 and the corresponding logical chain 8-11 or 12-15 will work. On

elements 8.9, 10 (12, 13, 14) a memory circuit is implemented. The trigger time setting 9 (13) (memory time) is chosen to be about 15 ms, taking into account

overlap the largest pause between two adjacent whitefish: ala current of one polarity.

The signal from the .10 (14) output goes to the second time element 11 (15), where

there is a delay of 20 ms. Such a time is chosen, in view of the need to check the absence of a current pulse of reverse polarity arriving at the DOR memory reset input (14) from the

Waddle of opposite polarity. With you -

move 11 (15) ci-gnal through the scheme OR (16) enters the blocking starting organs (4) of all three phases. The intrinsic response time of the trigger units (4) must be greater than the setting of elements 11 (15).

In those phases where the current is double-polar, both transducers 6 and 7 work alternately, but there is no output at 11 and 15 S1tgnals, so. how both logical chains periodically interlock, i.e. The memory is periodically reset from the formers of opposite polarities.

Since there is always a unipolar unbalance current in at least one phase when the magnetizing current is thrown, the protection will be blocked. The same takes place with external short circuits with aperiodic component in the primary current and when the generator-transformer unit is switched on to the network by the self-synchronization method. In these cases, at least in one of the phases of the differential circuit, there will always be a unipolar current and the protection will be blocked.

In case of short circuits in the protected zone, the current in the differential circuit in all tr phases is always two-polar, even in a transient mode and saturates the current transformers, therefore, the starting elements are not blocked, and the protection acts on tripping.

The device allows transformer protection built up from all kinds of possible unbalance with a response current of 0.15 - 0.2 of the rated transformer current. At the same time, the protection is quite sensitive in case of damage to the transformer winding (short circuit of one turn). The protection time does not exceed 20-25 ms,

The device can be used to protect generators and generator-transformer blocks. The economic feasibility lies in the fact that eliminating improper shutdowns of protected objects, resulting in damage.

associated with interruptions in the energy supply of consumers.

Formula 3 o b riet

a V.

Device for differential 3aiL-.ity power transformer, top-oashe. current transducers of all terminals, the secondary windings of which are connected through a phase-matching triggering organ and potential current sensors into a differential circuit, the drivers of right angle pulses from the current differential positive and negative fields and the logical chains NE-B-NP-B characterized in that, in order to increase reliability and selectivity, in each phase, the input of the first element Hi of one PS-B-IB-B logic circuit is connected to the output of the KMpyjiv generator of positive polarity and to the input; the second element is NOT the second logical chain, and the input of the first e.pement — a second loop of the second logical chain — is connected to; M; connected to the blocking inputs of the trigger organs through the logical organ OR.

Sources of information taken into account in the examination:

1. Polkov V. Ye., Trotsenko A. A. - Device for protection of a two-winding transformer. Auth. side jV 393793, class H O2 H 3/28, 7/04. Inventory of inventions NO 33, 1973

2.Rote K. and others. Relays to protect generators, transformers and tires in the power grid of the GDR. Lime universities of the USSR. Electromechanics, 1974 № 9, p.1O48- lO5l

3.Dmitrenko A.M., Differential protection of transformers and autotransformers. Electricity, 1975 № 2, p. 1-9 (prototype).

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