SU792461A1 - Transformer differential protection device - Google Patents

Description

The invention relates to a technique of relay protection of power systems, namely to relay protection of transformers and autotransformers. Devices for differential protection (DZ) of a transformer are known, in which the build-up in the rush current of the magnetizing current (bt, k) is provided by braking the second harmonic of the differential current 1. The closest technical essence to the proposed device is for the DZ transformer, in which braking at btc is performed by a signal proportional to the amplitude of the second harmonic of the differential current. The working signal of this device is proportional to the amplitude of the first harmonic differentially About current fSj. The disadvantage of such devices for remote sensing is that they may have a reduced sensitivity during internal short circuits (short-circuit) in the 6.THJ mode when the transformer windings are subject to strong dynamic effects and the likelihood of internal The decrease in sensitivity is explained by the presence of a brake signal in the second harmonic, the content of which varies in relation to the first harmonic in the differential current, and the protection is coarsened to different degrees. In order to provide a high protection capability, the response characteristic of a DZ should be located as close as possible to the point characterizing the bt. The aim of the invention is to increase the sensitivity of the device to internal short circuits arising in modes bp, by reducing the deceleration rate of the response characteristic depending on the intensity of the first and second harmonics of the differential current. This goal is achieved by the fact that a device for a DZ transformer contains measuring current transformers installed on the protected object, the secondary windings of which are included differentially according to the circuit for circulating currents, receiving blocks, one of which is included in the differential current circuit, and the others obtomatszh protected transformer included in the circuit currents of the shoulders, the unit operating signal, the pro-normal amplitude of the first harmonic, and the first block of the brake signal. proportional to the amplitude of the second harmony, the inputs of which are connected to the output of the differential current sensing unit, the second block of the brake signal at external short circuits, whose inputs are connected to the outputs of all specified sensing units, the comparison unit, on the working input of which the output of the working unit is connected signal and the brake inputs are connected to the outputs of both blocks of brake signals, and the output unit, the output of which is connected to the transformer disconnecting circuits, is additionally equipped with second - and third blocks as compared to and, the TIME element, the MEMORY TIME element, the NOT element and two NAND elements, the working input of the second comparison unit is connected to the output of the first brake signal unit, and the brake input is connected to the output of the operating signal unit; the working input of the third comparison unit is connected to the output of the block the operating signal, the first brake input is connected to the output of the first brake signal unit, and the second brake input is connected to the output of the second brake signal unit, the output of the second comparison unit is connected through successively TIMED and TIME MEMORY elements to one of the inputs of the First NAND element to another input of which is connected to the third comparison block. The output of the first AND NN element is connected to one input of the second AND NONE element, to the other input of which is NOT connected the output of the first comparison unit, and the output of the second element are NOT connected to the input of the output unit. FIG. 1 shows a functional diagram of the device; figure 2 shows the response characteristics of the comparison blocks and the characteristic of b.c. torus transformation (for single phase impulse). FIG. 1 designates a protected transformer 1, measuring current transformers 2.3, sensing unit 4 differential current} sensing units 5.6 shoulder currents, unit 7 operating signal, first unit 8 and second unit 9 T-signals, first unit 10, second unit 11 and third comparison unit 12; element 13 TIME element 14 TIME MEMORY, element 15 NOT, first element 16 and second element 17 NAND, output block 18. In FIG. 2, the characteristic is bt. single-phase transformer 19: response characteristics 20,21,22 of the first, second and third comparison units, respectively} zones 23,24,25, located respectively between response characteristics 20 and 22, response characteristics 22 to 21 to between the abscissa axis and response characteristic 21. FIG. 2 The following letter designations are accepted: - the amplitude value of the first harmonic, b.c. effective value of network voltage; total resistance of the network and transformer at bp -, I7 - amplitude value. second harmonic btn - base single phase b.n. - the angle corresponding to the flow time b.n. for the period gsgmin - - (S.EMIN. ci.MHH 1 1C.5.MIN minimum relative values of processing of the comparison blocks. Measuring current transformers 2.3 are included on all sides of the protected transformer 1, their secondary windings are connected differentially along the circuit to current circulation. The receiving current 4 is included in the differential current circuit and is intended for galvanic isolation of circuits.

secondary windings of trans (bformers 2.3 current n circuits of a DZ device, as well as to convert current transformer signals into signals with parameters required for a DZ device. E take blocks 5, 6 are included in shoulder current circuits | their assignment is similar to a sensing unit 41

To the output of the sensing unit 4 is connected to the unit 7 of the working signal R blocks 8.9 brake signals. Block 7 is designed to form a working signal proportional to the amplitude of the first harmonic of the differential current. Block 8 is designed to form in bt mode. brake signal proportional to the amplitude of the second harmonic of the differential current. Block 8 is connected to sensing units 4, 5,6 and is intended for forming

brake at external short circuit sigalaal proportional to, for example, the difference between the arithmetic and the modulus of the hermetic sum of shoulder currents. In the established modes of btn or kz, the signals in the blocks of 7.8 and 9 are straightened and smoothed voltages with a slight ripple.

The operating inputs of the first unit 10 and the third comparison unit 12 are connected to the output of the operating signal unit 7, and their two brake inputs to the outputs of the brake signal units 8.9.

The working input of the second comparator unit 11 is connected to the output of the brake signal unit 8, and the brake input to the output of the operating signal unit 7.

Comparisons 10,11,12 consist of a series-connected totalizer and a reacting element. The blocks of the summation make the summation of the inputs to the working worker to the brake signals and at their predetermined ratios. provide at the output a discrete signal of a certain sign - a signal of a logical unit (hereinafter referred to as a signal). The zero value of the voltage at the output of the adder of the comparison unit corresponds to the specified value of the ratio of the input voltage,

At a certain polarity of the deviation of the output voltage of the adder from the zero level, the responding element of the comparison unit is triggered and a signal is produced at the output.

The output of the second comparison unit 11 is connected via a series-connected element 13 TIME and element 14 MEMORY TIME to one of the inputs

the first element 1B AND-NOT, to another input of which is connected to the output of the third unit 12 of the comparison. The TIME element 13 is characterized by the fact that when a signal occurs at its input, signal 1 at its output appears after a certain predetermined time. Element 14 TIME OF MEMORY is characterized by the fact that during the disappearance of its input signal 1, its output signal 1 disappears after a certain predetermined time,

The output of the first element 16 AND-NOT is connected to one of the inputs of the second element 17 AND-NOT, to the other input of which through the element 15 is not connected the output of the first block 10 of the comparison. The code of the second element 17 AND-NOT connected to the input of the output unit 18,

It is known that undamped bt. a single-phase transformer with a piece-linear approximation of the magnetization characteristic is expressed by the following formula;

.

Sun-3,

 cos -cosCtijt-nk)

 eight

ig - induction of transformer saturation8 - residual induction:

R

 .- amplitude value of induction; GU CoWS

circular frequency voltage

mains,

the number of BITs in the winding and core of the transformer magnetic core

initial angle of the voltage vector upon switching on.

denotes J CO &tk;

AT

will get

and

  A-cos ()

) A-cosCo-by) a)

.

It can be seen from (1) that the shape of the current depends on the values of L and o, and the amplitude depends, in particular, on the network resistance. The first and second harmonics bt, and. functions of the value of A or base of the broth J), and

D

A -cos-2Characteristics 19 b; t, n. a one-phase transformer, the delightful 7 () dependence was built with a change in J) from 0 to 4 rad., which corresponds to real conditions. At 2) 4: b.t.i. single-phase transformer in comparison with other types of btn. The second harmonic content is characterized by a minimum relative to the first harmonic. This mode is calculated to select the maximum slope of the DZ response characteristic. At attenuation b.n. J decreases and the point characterizing the bp, moves along the characteristic 19 to the origin. To ensure build-up, the response characteristic of the DZ should be located above the point characterizing the bp. Consider the phenomena occurring in a transformer in a mode of operation. Internal damage occurs — a short wiring of an insignificant part of the winding turns. As studies show, the occurrence of damage has practically no effect on the damping rate of the bp, the magnitude of the second harmonic decreases slightly. {Zelichina first harmonic increases depending on the number of locked turns. The known device for a DZ transformer (2) has a response characteristic 20 (see Fig. 2). It can be seen from FIG. 2 that when the value of D changes, the content of the second harmonic with respect to the first harmonic in the differential current changes and the protection is deformed to varying degrees. In the proposed device, the sensitivity of the DZ in the mode btn. This is achieved by reducing the braking coefficient of the response characteristic depending on the ratio of the first and second harmonics of the differential current. When finding a point b.n. in zones 23 and 24, DZ has a response characteristic of 20, and when attenuating, it has a bt. and the transition point b.n. in zone 25, the characteristics of srabat shan 22, in the modes of b.t.n. the signal at the output of block 9 of the braking signal is insignificant, since theoretically the difference between the arithmetic and geometric sums of the arm currents is zero. At the same time, each of the comparison units (BS) has a corresponding response characteristic: S.BU 1C.2. MINI 2t lc.3.5Cl2 lc.3. tlch ,, III -1 2s.z..g. . t t where; i 0.3. 11. C. - values of currents, operation of the comparison units, different amplitudes of the first and second harmonics of the differential current: b. f, (i j. y rtj, - braking coefficients. Figure 2 shows the relative positioning of the response characteristics of the comparison blocks (the response areas are shaded). Neglecting the minimum values of the comparison accumulation currents, you can write the required ratios for the deceleration ratios: 7Г / I К " The "DZ deceleration factors are determined by comparison units 10 and 12. The comparison unit 11 serves to fix the predetermined ratio of the first n, the second harmonic of the differential current and give a signal for a change in the deceleration coefficient of the DZ. The operation 2O of the operation of the comparison unit 10 should be located above the characteristic 19 of the syphonic-phase btn. At the same time, the remote sensing is built in the computational mode with the minimum second harmonic content in the bt. characteristic 21 of the operating unit of the 11-block comparison It is advisable to position it in such a way that it crosses the characteristic of 19 bp in the range of 2.5–3.5. In this case, the teller sensitivity is ensured in b. for a great time. The characteristic22 of the srabatshan of the block 12 is compared to be located near the angle 21 of the characteristic 21, but does not cross it. In the presence of supply voltage and the absence of currents in the sensing units

4,5,6 at the outputs of the blocks 10,11,12 of the comparison, there are signals of logical zero (B, hereinafter referred to as signal O), at the inputs of the element 16 AND-NEO, at the inputs of the element 17 I-HE-1,

and at its output, Oh, Output Block 18 does not work.

In the single-phase b mode, the so-called one, which is characterized by a point located in zone 23 (see Fig.2), the signal at the output of comparison unit 12 is changed compared to the original mode: see becomes equal to 1, but this does not change signals at the outputs of the elements 16, 17.

After some time, b, t. decays, J7 decreases and the point characterizing the bt n. moves to zone 24. When

When entering the zone, the signal at the output of the comparator unit 12 becomes pa (Om), which corresponds to the initial mode. Then the point characterizing btn goes to zone 25, and signal 1 appears first on the top of the comparator unit 11, and after a predetermined time determined by the element 13 TIME at the first input of the element 16 AND-NOT,

At the end of the transition process, Ph.D. the reactive element of the comparator unit 11 is returned and the signal Of is restored at the first input of the element 16 to AND-NO.

If in the mode of btn. Characterized by a point located in zone 23, an internal short-circuit appears. and the reacting element of the comparator unit 10 is triggered, then a signal O appears at the second input of the element 17 AND-N and an output appears at its output 1. The output unit 18 operates and gives a command to disconnect the protected transformer 1 from the power sources.

BOLI mode b.n., characterized by a point located in zone 25, there is an internal short-circuit. and the reacting element of the comparator unit 12 is triggered, then 1 appears at the second input of the element 16 AND-NOT, and from its first input the signal 1 does not disappear during the time determined by the element 14 MEMORY TIME, although at the moment of the considered short-circuit. At the output of the comparison unit 13, a signal O appears. At the same time, at the output of the element 16 AND-NO, O appears, and at the output of the element 17 IS-HE1-1, the output block 18 is triggered. F3 of the considered mode is bt, the braking coefficient DZ is determined by block 12

comparison, therefore, the sensitivity of the proposed device to internal damage is significantly higher than that of the prototype.

If, in a normal steady state, an internal KS problem occurs. and reacting elements of blocks 10 and 12 are triggered, the signal at the second input of element 17 will NOT take the value O, and will not change at the first input of this element. In this case, a signal 1 appears, at the output of the element 17, AND-NO, and triggers the output block 18.

The value of the time element

13 TIME is in the order of a millisecond and is selected from the condition of excluding the false work of the DZ with a fast transfer process. from zone 23 to zone 24, when due to the finite return time of the reacting element of the comparison unit 12 and the prompt response of the reacting element of the comparison unit 11, the appearance of signals 1 on both inputs of the It.i AND-NOT element is possible.

Value (element time

14B MEMORY OF THE MEMORY takes about ten milliseconds and is selected according to the condition of ensuring reliable operation of the output unit L8. and, as a result, reliable disconnection of the transformer 1 from the power sources.

The proposed device, depending on the ratio and the 15th harmonic in the differential current, provides two braking coefficients, which significantly increases the protection of the DZ in the modes of bp.

Sensitivity DZ mode b.n. rises. This makes it possible to speed up the breakdown of the transformer, reduce its destruction and reduce repair costs.

Claims (2)

Invention Formula A device for differential protection of a transformer containing measuring current transformers installed on the protected object, the secondary windings of which are included differentially according to the circuit for the circulation of currents, reproducing blocks, one of which is connected to the differential current circuit, and the others are equal to the number of windings of the protected transformer, included in the circuit of the shoulder currents . the first harmonics, and the first block of the brake signal proportional to the amplitude of the second harmonic, whose inputs are iodine & luchny to the output BocrtpitelUKidibuJer o block of differential current, the second block of the brake signal for external short circuits x, the inputs of which are connected to the outputs of all indicated sensing blocks EFFICIENCY INPUT which is connected to the output of the operating signal block, and the brake inputs are connected to the outputs of both blocks of brake signals, and the output block,. the output of which is connected to ceggs from the transformer's key, characterized in that, in order to increase the sensitivity to internal short circuits m occurring in the flow modes of the magnetizing current inrush of the protected transformer by: y1y {the deceleration of the deceleration rate of the response characteristic depending on the ratio of the first and the second harmonic of the differential current, the second to the third comparison block, the TIME element, the MEMORY TIME element, the NOT element and two NAND elements, the working input the second comparator block is connected to the high-speed stroke of the first brake signal block, and the brake input is connected to the output of the operating signal block, the operating input of the third comparison unit is connected to the output of the operating signal unit, the first brake input is connected to the first code of the brake skgnal unit, and the brake input is connected to the output of the second brake signal unit, the output of the second comparator block connected through series-connected elements TIME and TIME of MEMORY to one of the inputs of the first NAND element, to the other input of which the output of the third comparison unit is connected, the output of the first element NAND connected En to one of the inputs of the second element AND-NOT, to the other input of which through the element the output of the first comparison unit is NOT connected, and the output of the second element is connected to the input of the output unit Sources of information taken into account in the examination l. US Patent No. 314459О, class, 317-138, 19649 2. Ul1shitsky EM, Mayorov VD. Development and research of a differential relay on an operational amplifier h.- Lime universities Electromechanics, 1975, No. 7, p.784-790. f / S OirtK / tiS- Vftytf / c.min / faw //