RU1802895C - Device for differential current protection with retardation - Google Patents

Abstract

The invention relates to electrical engineering, in particular to relay protection devices, and can be used to protect generators and synchronous compensators. The purpose of the invention is to increase the selectivity of protection. SUMMARY OF THE INVENTION: a device for differential current protection with braking, comprising a circuit for generating differential and brake signals, a circuit for forming a dead zone, an adder, a rectifier and a reacting organ, additionally connected in series with a selective a filter, a second deadband circuit and a rectifier, which increases the selectivity of the protection. 5 ill. ate

Description

The invention relates to the field of electrical engineering, in particular to relay protection devices, and can be used to protect generators and synchronous compensators.

An object of the invention is to increase the sensitivity of protection.

In FIG. 1 is a block diagram of a differential protection device, where: 1 is a diagram for generating differential and brake signals; 2 - low-Q selective filter; 3, 5 is a diagram of the formation of a dead zone; 4, 6 - rectifiers; 7 - adder; 8 - reactive organ,

In the differential current protection device, the brake output of the differential and brake signal generation circuit 1 is connected to the inputs in parallel

connected to the first circuit for forming the dead band, the output of which is connected to the input of rectifier 4 and the low-Q selective filter 2 circuit, the output of which is connected to the circuit for forming the dead band 5 and rectifier 6, the output of which and the output of rectifier 4 are connected to the inputs of the adder 7 the output of which is connected to the brake input of the reacting organ 8, and the working output of the differential and brake signal generating circuit is connected to the working input of the reacting organ 8.

The device operates as follows.

It is known that the transfer function of a selective filter (SF) has the form: P / (P - TiXP -Ta). Low-quality reaction

00

about y

00

Yu

Joint venture

W

SF having material roots on the influence of step function, i.e. The jump of the brake signal at the SF input has the form of a unipolar wave (Fig. 2).

With an external short circuit at the brake output of the circuit for generating the brake and operating signals, a smooth signal jump will occur, which is fed to the SF input. The signal from the output of the SF arrives at the input of the dead band formation circuit 5. Due to the presence of a biasing signal Cdt (Fig. 2) at the other input of the dead band formation circuit 5, a time lag signal appears on its output, the diagram of which is shown in FIG. 3. The presence of rectifiers 4 and 6 avoids the need for protection when the signal disappears from the SF output.

If the value of the constant time Ti SF is of the order of the constant time of the network (0.1 ... 0.3 s), and the value of the constant time Tai is of the order of the equivalent constant time of current transformers (usually 0.02 ... 0.04 s) of protection arms, then at the output of circuit 5 there will be a signal whose maximum is reached after a period of time, depending on the constant times Ti and Ta according to the formula

Ј (+

Ti-T2 h T2 (1

This signal through the adder 7 is fed to the input of the regulatory body 8 as an additional brake signal. Additional braking will be carried out at that time when the unbalance current in the working circuit with the remote external short-circuit is greatest. Thus, the detuning of the protection increases, especially if the main braking has not come into operation.

In FIG. Figure 4 shows diagrams of currents and voltages at the outputs of protection elements with an external remote short circuit.

In this case, the main braking does not work, because the sum of the currents of the arms of the protection is close in magnitude to the current of the beginning of braking 0nto).

The presence in the device of a selective filter with certain values of the constant time Ti and Tg allows for additional braking

5 5

0 5

0

,- -P

- (-

0

differential protection during unbalance current flow and to avoid false triggering.

Consider the short circuit mode in the protection zone. The worst-case conditions for protection sensitivity occur if a nominal load condition has previously occurred that increases braking.

In FIG. Figure 5 shows diagrams of currents and voltages on the elements of the device in this mode. At the same time, additional braking will not affect the sensitivity of the protection, since the signal at the outputs of element 5, element 7 of FIG. 1 in volts in comparison with the working signal with a delay of the order of 0.02 ... 0.04. The indicated time depends on the selected dead threshold and should be longer than the response time of the reactive guard.

At minimum fault currents close to the initial pick-up current, additional braking by itself does not appear due to the dead threshold.

The device is intended to be used in the development of sensitive differential shields of synchronous generators and compensators.

Claims (1)

The claims A device for differential current protection with braking, comprising a circuit for generating differential and brake signals, to the brake output of which are connected in series the first circuit for forming a dead zone, the first rectifier and the first input of the adder, the output of which is connected to the inverse input of the reacting organ, to the direct input which is connected to the differential output of the circuit for generating differential and brake signals, characterized in that, in order to increase the selectivity ty; additionally introduced are a series-connected selective filter, a second deadband formation circuit and a second rectifier, while the selective filter input is connected to the brake output of the differential and brake signals generating circuit, the output of the second rectifier is connected to the second input of the adder. (rig1 Figz FIG. g  Srtu / m  falWH.  & neshn.  Pt / 2.4 and 3 $ Wmp. g Јej int g 1M / J