SU748633A1 - Device for directional protection of ac mains from short-circuiting - Google Patents

Description

:. I. ; This invention relates to electrical engineering and is intended to protect an alternating current network element from short-circuiting. The protection monitors both the magnitude of the current of the protected element and the phase relation between current and voltage. A device for protection containing phase comparisons made on a transistor U is known. The device closest to the invention according to its technical nature is a protection device containing measures 1 (current and voltage transformers, limiting resistors, a diode, phase comparison blocks and executive relays In this case, the phase comparison units may be implemented, for example, in a transistor. The protection responds to the active component of the current of the SCHEDLEED network element {2. However, in a multiphase network, installation is essentially necessary. sets in terms of the number of phases, which complicates the device. The purpose of the invention is to simplify with a large number of phases of the protected network. The goal is achieved in that the device for directional protection of AC mains from short circuits, containing the measuring transformer respectively the voltage, the secondary winding of which through a resistor is connected to the base-emitter junction of the transistor, the measuring current transformer, the secondary winding of which is first-terminated resistor Through the second resistor, it is connected by one output to the first input pole of a semiconductor rectifying bridge, to the output poles of which there is a wire; the emitter and collector of the specified transistor, as well as the actuator, are inserted; between the connecting pins and the second input poles of the tynovMHyToro semiconductor rectifying bridge and the common point of the secondary windings of the measuring current transformers, and the executive body through phase diodes introduced by the number of phases, 37

The stars are linear according to the circuit, parallel to J n6 is connected to the secondary windings of measuring current transformers, and its controlled input is connected to the midpoint of the specified resistor voltage divider.

FIG. 1 is a schematic diagram of the device; in fig. 2 shows time diagrams of voltages and currents passing through a resistor voltage divider in a symmetrical mode. .

The device contains in each phase current measuring transformers 1, shunted by resistors 2 connected to a star 3. Current measuring transformers 1 current through resistors 4 and the input poles of semiconductor rectifying bridges 5 include a resistor voltage divider 6, an unregulated resistor 7 of which is bridged by a capacitor 8, and an adjustable resistor 9 serves to adjust the protection. On the output policies of bridges 5, emitters and collectors are connected by transistors 10 whose basic transitions are connected through rheistors 11 to the corresponding secondary windings 12 of measuring voltage transformers 13, the primary windings 14 of which are connected to the phases of network 15. The actuator 16 is connected to measuring transformers I of current through three diodes 17, connected to the star, and includes a thyristor

18, the cathode of which is connected to a common point 3 of measuring current transformers 1,

a series-connected Zener diode 19 and a diode 20, connected to the midpoint of the resistor divider voltage 6, and the threshold organ 21.

The device works as follows. The currents of each phase of the current measuring transformers 1 are passed through resistors 4, bridges 5, transistors 10 and a resistor divider voltage 6, when transistors 10 of the corresponding phase are open. The transistors 10 are open for a half period from the corresponding point in time for each phase, when the basic-smitter transitions of these

opening transistors are supplied to the transistors.,

The average current value is determined through a resistor de-energizer 6 voltage for an active-inductive circuit, which is mostly industrial loads. A reference point is selected that coincides with the moment when the voltage of phase A (Fig. 2) passes through zero. In the time interval from O to H, the current of phase A does not coincide in sign with the voltage of phase A; therefore, in this time interval, the current of phase X is taken to be negative. During this period of time, the transistor 10 of the phase C is open and the current of the phase C coincides

on the sign with the voltage of phase A and therefore the current of phase C through the resistor divider 6 is positive. In the time interval from O to 1, the current through the resistor divider 6 is equal to the difference in the currents of the transformers 1 of the current of phase C and phase A. From the time point H, the current of phase A passes through zero and, until the moment of burden 3t / j, coincides in sign with the current of the phase Syv resistor divider The 6 voltages are summed. From the instant / 3 the transistor 10 of the phase C is closed, the current from the transformer 1 of the current of the phase C stops and until time D only the current of the phase A passes through the resistor divider. From the moment of time, the transistor 10 of phase B opens, but until the time in the resistor divider voltage, it met the current of phase A, and from time 4 V to time jt they add up. This is repeated in subsequent periods of the period. The current from the measuring transformers 1 of the current ui / okol through the resistor divider 6 during the half-period (in the time interval from zero to M - a negative sign, in the time interval from H to 3t - a positive sign). If the currents are equal in three phases, the average current through the resistor voltage divider is determined:

S g l; J, i, H ...

i. g

-s naji-dlu / t4 gus g v

wed

s, n

. g

.n., 4..ri ... n.3V2.3H-Kc4 to

l-3t-n | cos О coslf - «- cos if- coa3t

 cos

- factor zaschity with a three-phase short circuit.

Thus, the average current through a resistor is divided into voltage 6 at a three-phase short circuit and motor overload is proportional to the active component of the current.

By varying the resistance of the adjustable resistor 9 of the resistor divider voltage 6, the pickup current setting is selected. The voltage on the unregulated resistor 7 reaches the value of the breakdown of the zener diode 19, which is located in the control circuit of the thyristor 18. The thyristor 18 opens and the currents or measurement current transformers 1 through the diodes 17 pass through the threshold element 21, which operates and turns off the damaged network element.

Thus, by appropriately connecting a resistor voltage divider

succeeds -. use one executive body in the protection of multi-phase net, without compromising the protection characteristics. Protection is simple and less expensive.

Claims (2)

1. Doroguntsev b. G.Ovcharenko N.I. Ele. Automatic devices of power systems. M., Energie, 1970, fig. 6-1. 2. USSR author's certificate number 555487, cl. H 02 H 3/16, 1975.