SU1585854A1 - Three-phase current relay - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to relay protection of electrical installations against short-circuit currents. The aim of the invention is to increase the sensitivity to the mode with an increased one of the phase currents. The relay contains three phase modulators of phase currents 1, 2, 3, a block for extracting the sum of phase currents 4, a block for allocating the largest of the phase currents 5, a comparison block 7 and two comparators 8 and 14. With a three-phase symmetric short circuit (SC) at the output of the compare block 7 has a negative signal, and with an asymmetrical short circuit - a positive one. This leads to increased sensitivity in single-phase asymmetrical short-circuits. 1 il.

Description

The invention relates to electrical engineering, in particular to a three-phase current relay, and can be used for relay protection of electrical installations.

The purpose of the invention is to increase the sensitivity to the mode with increased one

from phase currents.

The drawing is a functional diagram

devices.

In each phase, there are blocks 1-3 of forming signals proportional to the modules of the phase currents (max detector). The outputs of the blocks 1-3 are connected to the inputs of the block 4 for the allocation of the sum of the phase currents and the block 5 for the selection of the maximum of the phase currents. The output of block 5 is connected (via a resistor 6) to the working input of the additionally introduced comparison block 7, and the output of block 4 is connected to the brake input of the same comparison block 7. The input of the first main actuator (comparator) 8 is connected via resistor 9 to the output block 5 for the selection of the maximum of the phase currents, and through a resistor 10 and a mode switch 11 is connected to the output of the block 7 of the comparison. The comparator 8 can be connected to the block 7 additionally via the inverting block 12 and the resistor 13. The input of the second additional actuator (comparator) 14 is connected to the output of the block 5 via the resistor 15, and to the output of the block 7 through the resistor 16. Comparators 8 and 14 may have different voltages Ucpi and Ucp2 trigger thresholds.

The device works as follows.

At the outputs of blocks 1-3, straightened and smoothed voltages appear, the magnitudes of which are proportional to the moduli of the phase currents. In the general case, the phase current module can be either the largest 1µm, or the smallest 1 mn or intermediate 1 c out of three modules. In the three-phase symmetric short-circuit (short-circuit) mode, the modules of the three currents are the same 1 µm I With a two-phase short circuit on the protected line without load currents (limit asymmetry (L

with

ate

00

ate

CX)

ate

s

the second type of mode: the current moduli have the following relations;

0: 1p. (2) | .Л2)

micron

 0.871

(3)

GZ)

where G is the three-phase short-circuit current in the same place. With a two-phase short-circuit for a 35/6 kV pull-down transformer I / A-1 without load currents (maximum unbalanced mode of the first type), the current modules are determined by the relations

1mk (2D) | (g); 1pr (A) in (D) 0.5 | (

The load currents (electric motors, etc.) on the protected line with an external (on the other line) two-phase short-circuit near the substation buses have ratios

u (2B), (3n)., p (2B)) (3n)

where g is the load current when the electric motors are started up, for example, after an unsuccessful automatic restarting (AR) with the remaining external two-phase short circuit,

Under the Current mode, only in one phase mainly refers to a double short circuit to earth on different 35 kV overhead lines, when the current moduli are determined by the ratios

1mk (-) 0.87 | P) / 1,, 48 | (3); ,

With the mentioned double earth fault, the current in each of the two lines forms a loop with a large area (the current goes through one wire, and back through the earth under the wire), as a result of which, on an overhead line without a cable, the resistance to current increases 1.8 times compared with a two-phase short circuit on one line.

At the output of block 4, the voltage is proportional to the sum of the modules of three currents

21f 1mk + 1pr + 1

mn

and enters the brake input of unit 7 of the comparison.

At the output of block 5, the voltage is proportional to the modulus of the highest current KilMK, where KI is a coefficient, and is fed to the working input of block 7 comparison. At the output of the comparison unit 7, the signals fed to the working and brake inputs are subtracted, as a result of which the output voltage is proportional to the function

choo

five

0

five

0

five

0

Р7 К11мк-21ф.

. The parameters of blocks 4 and 5 and resistor b are made so that, and then the zero output signal in block 7 occurs when the input signals of the formation blocks 1-3 are proportional to the currents at different types of two-phase short circuits without load currents (the mentioned asymmetric modes of the second or of the first type) or proportional to the load currents of the intact line at the mentioned external two-phase short-circuit. With a three-phase symmetric short circuit, the output of block 7 has a negative signal proportional to the current module 1 micron 1 and only one input current on a 35 kV overhead line appears at the output of block 7, a positive voltage proportional to the current module,.

The input of the first comparator 8 (at the position of the mode switch 11 shown in the drawing) is the sum of the signals from the maximum modulus extraction unit 5 from the phase currents 1 μk and from the comparison unit 7, the second signal being relatively small, correcting (the resistor 10 is approximately 10 times larger than resistor 9). With this design, the comparator 8, together with the entire device, performs the function of a three-phase current relay, which has the same sensitivity to the short-circuit location in the region between the three-phase short circuit and the second limiting asymmetrical mode of the second type (the boundaries enter the region), and the device has 13% more sensitive to the mentioned limit asymmetrical mode of the first type, and also has a 100- (87-48) less sensitivity to the pulsed mode of only one input current on a 35 kV overhead line.

The input of the second comparator 14 receives, for example, with the same coefficients the output signals of blocks 5 and 7. (resistances of resistors 15 and 16 are the same). If there are still different voltages Ucpi and Ucp2 of the thresholds for comparators 8 and 14, then the comparator 14 together with the whole device performs the function of a second three-phase current relay, which is insensitive to a three-phase short circuit (and even more so to other three-phase symmetric modes), has the same sensitivity as the comparator 8, when the mentioned limiting asymmetrical modes of the second and first types occur, and also in the mode of only one input current on a 35 kV overhead line has a sensitivity of 100- (2-0.48-0.87) 70, more than Mode three-phase short-circuit. In order both in the mode of only one input current and in the mode of three-phase short circuit, the sensitivity to the short circuit location is the same, it is necessary for the comparator 14 to have the voltage Ucp2 of the response threshold 10% higher than the analogous voltage Ucpi for the comparator 8.

So that with the help of comparator 14, to improve the sensitivity of the double circuit to earth on different lines of 35 kV. It is necessary with the help of an additional filter-relay of current 1o of a zero sequence when current appears temporarily to withdraw from the sensor a phase current phase B or received from its current transformer, or created by the equation

| in (d + 1s).

In addition to the need to have the same sensitivity to the short circuit location, also in the mode with a current in only one phase, sometimes there is a need to reduce the sensitivity to the total, two-phase short-circuit current and load. This may be necessary when the relay protection is redundant with respect to protections that are located closer to the energy consumers. This additional expansion of functionality is achieved if the mode switch 11 is moved to another position in order to connect the inverting unit 12, which will change the sign of the signal coming from the comparison unit 7 to the comparator 8. With this design, the device parameters are chosen so that the input of the comparator 8 signals from the outputs of block 5 and block 7 were received with the same coefficients. In this case, the characteristic carried out by the comparator 14 together with the elements of the entire device can remain unchanged.

In the first version, when the mode switch 11 is in the position shown in the drawing, this device can also be used to protect the 6 kV line supplying the powerful asynchronous electric motor. In such conditions, together with the common elements of the device, the comparator 8 will provide general relay protection for the line and the electric motor, and the comparator 14 will provide a special sensitive protection against winding short circuits in one of the phases of the electric motor. In this case, the comparator 14 will respond to a voltage proportional to the function

Fl4 - 3 IMK 2. 1ph - (IMK IMH) + (IMK - Inp).

Such protection against winding faults in one phase of an electric motor will be more

sensitive than protection, made using a filter relay of currents 12 of the reverse sequence (filter relay FTOP), and will also be more sensitive than protection with an actuator that reacts to a voltage proportional to the difference between the maximum and minimum phase currents Fb (1 micron 1 mn).

Coil closures in the same phase of an electric motor cause phase currents that form an isosceles triangle of vectors with an angle a between currents of equal modulus. In this case, the range of variation of this angle a is 60 ° 120 °.

In the three protections mentioned, which act upon coil closures in a single motor phase, the indicated functions, to which the actuators react, can be taken with different general coefficients, therefore, in order to compare

The sensitivity of the aforementioned three defenses, the table gives the dependencies on the angle "of the following relations of each of the indicated functions to the corresponding extremely large value of its function

Ai4 Fi4 / Fi4 PB; I Ftop 12 / 12PB;

 / FbPB,

where PB - indexes that denote the maximum

large amount.

From the table it can be seen that the comparator 14 in this device is the most sensitive to the windings in one phase of the electric motor; the FTOP filter relay is average in sensitivity.

Thus, this device provides increased sensitivity to windings in one phase of an electric motor; expanding the functionality by extending the same sensitivity to the short-circuit location to the mode with current in one phase of the 35 kV line; additional

enhanced functionality by reducing sensitivity to the Total Current of a two-phase short circuit and load.

Claims (1)

Formula invented and A three-phase current relay containing three phase generator modules of phase currents, the outputs of which are connected to the inputs of the maximum phase current isolation unit (max-selector) and the sum selection unit phase currents associated with the actuator, characterized in that, in order to increase the sensitivity to the mode with increased one of the phase currents, a comparator unit, five resistors and a second actuator are additionally introduced, and the output of the maximal phase currents output unit is connected through the first resistor with the operating input of the comparison unit, the output of the allocation unit of the sum of phase currents is connected to the brake input of the same comparison unit, and to the outputs of the maximum current phase separation unit and the comparison unit at oedinen respectively through the second and third resistors input of the first main actuator body (comparator), and by the fourth and five resistors are connected to the input of the second additional actuator (comparator), while the transmission coefficient of the signal from the output of the maximal phase current extraction unit to the output of the comparison unit is two times greater than that of the output unit of the sum of the phase currents; the signal through the third resistor to the input of the first main actuator is 0.07-0.13 of the transfer coefficient through the second resistor; the signal transfer ratio through the fifth resistor from the output of the comparison unit to the input the second additional actuator is equal to 0.8-1.0 signal transfer coefficient through the fourth resistor. IA