SU1700671A1 - Device for protection of dc network - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to relay protection of a direct current network. The purpose of the invention is to increase the reliability of operation by detuning from load currents. The goal is achieved by taking into account the effect of the initial speed and voltage of the current rise network on the set value for the current increment of 2 s

Description

The invention relates to electrical engineering, and can be used to protect DC networks from short-circuit currents.

The aim of the invention is to increase the reliability of operation by adjusting the load currents.

FIG. 1 shows the structural scheme of the device; Fig 2 - graphs characterizing the operation of the device

The device for protection of the direct-current network contains sensor 1 of the derivative of current, trigger 2, integrator 3, comparator 4, sensor 5 of the line voltage, amplitude detector 6. Output of sensor 1 of the derivative of current is connected to inputs of amplitude detector 6, trigger 2 and integrator 3, the output of the starting organ 2 is connected to the control input of the integrator 3, the output of the latter is connected to the input of the comparator 4, the output of the amplitude detector 6 is connected to the summing input of the comparator 4, the output of the voltage sensor 5 is connected to another input of the comparator Ator 4,

The device works as follows.

FIG. 2 on the left shows the remote short-circuit mode. with a minimum current, on the right - the load mode with a large increment of the current, while the load is near the feeder. Curve 7 is the current change, curve 8 is the time derivative of the current derivative, forward 9 is the trigger level of the triggering organ when it is executed as a comparator, curve 10 is the signal selected by the integrator 3 that corresponds to the current increment, 11 is the threshold the level of operation of the comparator 4, depending on the magnitude of both the initial current flow and the magnitude of the varying voltage from the voltage sensor. Since the current decreases with increasing current, the threshold level decreases

In the short circuit mode. the current rises to its maximum value relatively slowly, since the inductance in the short-circuit circuit is remote to g. due to remoteness, the initial value of the derivative of current 0 is therefore relatively small and the setpoint varies slightly. The voltage from the output of the amplitude detector

WITH

with

VI

About About About vj

6 is fed to the summing input of the comparator 4, which is made subtractive, the setpoint is increased the more, the more io.

In the load mode, the current rises to its maximum value faster, the initial derivative of the current is larger than in the previous case, the setting of comparator 4 rises more, which improves the detuning from the operating modes, and the device in this case does not work.

Accounting for the magnitude of the voltage allows for an additional consideration of the magnitude of the current preceding the short-circuit, and which reduces the magnitude of the current increment, as well as the effect of the voltage fluctuation of the primary network on the magnitude of the current increment.

The protection equation is as follows:

KL D1-К2.и-Кз.1о Uon. where Ki, K2, Kz are the coefficients depending on the features of the execution of the device blocks;

AI - current change;

io is the initial value of the current derivative;

Don. - the reference voltage of the comparator 4.

The amplitude detector 6 may include an adjustable voltage source, a diode, a storage capacitor, a key, resetting the amplitude detector, a buffer amplifier providing matching of the input resistance of the comparator 4 with a permissible storage capacitor, a limiting diode connecting the storage capacitor to the source adjustable voltage. A resistor is typically included in series with the diode, which limits the storage current of the storage capacitor (not shown). After passing the maximum of the signal proportional to the derivative of the current, this maximum is stored on the capacitance, however, being limited from above. The comparator 4 consists of a comparison element and three resistors connected in such a way that they form a summing circuit together with the comparison element.

By changing the values of the resistors, the values of the coefficients Ki can be changed. K2,

Kz and thereby the influence of all three parameters on the operation of the protection device.

The magnitude of the initial derivative of the current depends on the magnitude of the inductance: Io U / L, where L is the inductance of the network. L grows

close to a linear law with increasing distance, and the initial derivative of the current varies in hyperbola. Current increment short-circuit A Ik varies in hyperbola. Detuning only by the magnitude of the current increment is impossible, so in this case an additional parameter is used - the initial derivative of the current. With the approach of the place k.z. to the beginning of the protected area, the increment of the current k.z is increased and,

starting from a certain point, already exceeds the maximum increment of the load current, the effect of the initial derivative of the current is no longer necessary.

The proposed device allows to increase the reliability of the protection device by improving the offset from the load currents.

Claims (1)

Invention Formula A device for protection of the direct current network, containing a sensor of the derivative of the current, to the output of which the inputs of the integrator and the trigger are connected, the output of the latter is connected to the control input an integrator, the output of which is connected to the first input of the comparator, the output of which is the output of the device, characterized in that, in order to increase reliability by detuning from the load currents, a network voltage sensor and an amplitude detector, the main and control inputs of the latter are added to the output of the current derivative sensor and the output of the starting organ, respectively, and the output is connected to the second input of the comparator, to the third input of which the network voltage sensor is connected. figl IftOp.SA.l eleven 70 By & 5l.Z ;; TG j 4zl, Phie.1