SU1690061A1 - Device for protection of line feeding valve converter against short-circuit current - Google Patents

Abstract

This invention relates to the field of electrical engineering, in particular, to short-circuit relay protection of a line. The purpose of the invention is to increase the sensitivity when the starting current and short circuit current are commensurable. The goal is achieved by fixing the magnitude of the ratio of the current in the line to the higher harmonics of the current during a short circuit, which increases many times over the normal mode, which makes it possible to clearly distinguish the beginning of the short circuit process from the starting mode of the valve converter, 2 sludge.

Description

WITH

WITH

The invention relates to the field of electrical engineering and can be used to protect both direct current lines and alternating current lines supplying vertical converters with small multiplicities of short-circuit currents relative to the operating current and currents flowing in the line at the time of launch. electric motor powered by the converter.

The purpose of the invention is to increase the sensitivity when the starting current and the short circuit current are commensurable.

Figure 1 shows the structural diagram of the device for protection against short-circuit current of the line supplying the valve converter; Fig. 2 shows graphs of currents in a line, and during normal operation of a single-phase bridge converter even with a short circuit, b - during normal operation of a pulsed converter of direct current and at a short-circuit.

The device contains a current sensor 1, which is connected to a line supplying a valve converter loaded with a DC motor. In DC lines, a calibrated resistor (shunt) connected directly to the line is used as a current sensor 1. In AC lines where galvanic isolation is required, the function of current sensor 1 is the current transformer, the secondary winding of which is loaded with a resistor. A first AC / DC converter 2 and a filter for the 3 highest harmonics of current are connected to the output of current sensor 1. The specified converter performs analog conversion of the input signal. The output of the first converter 2 is connected to the input of the first threshold unit 4 with the element 5 of the operation setting unit and to the input of the dividend of the division unit 6, the input

oh oh oh oh

A divider of which is connected to the filter 3 output of the higher harmonics of the current through the second converter 7 of the alternating current to the constant one. The output of dividing unit 6 is connected to the input of the second threshold unit 8 with the element 9 for setting the response setpoint. The outputs of the threshold elements 4 and 8 are connected respectively to the inputs of the element 10. The output of the element 10 is connected to the input of the output unit 11. The drawing shows a valve converter 12 and a switch 13.

The device works as follows.

The switch on switch 13 and the valve converter 12 in the line current flows, the value of which depends on the load of the engine. Transducers 2 and 7 output signals proportional to the current values of the measured values of the current TOKd value in the line and the effective value of the higher harmonics selected by filter 3. The signal proportional to the actual value of the current in the line is fed to the input of the first threshold unit A, where it is compared with a setpoint from element 5. The signal of the logical unit at the output of the first threshold unit 4 appears when the current exceeds a specified value. At the same time, the inputs from dividing unit 6 receive signals from transducers 2 and 7. Dividing unit 6 determines the ratio of the effective value of the current in the line to the effective value of the current of higher harmonics. The received CHI from the output of the dividing unit 6 is fed to the input of the second threshold unit 8, where it is compared with the setpoint set by element 9. When the signal from the output of the dividing unit 6 is exceeded, the second threshold unit 8 generates a signal of a logical unit, which goes to elements of the input And 10. If there are simultaneous presence at both inputs of the element 11 10 signals of a logical unit, it produces an output signal of a logical unit, which through the output unit 11 enters the input of the switch 13 The latter disconnects the line.

As an example, let us consider the choice of protection settings for a line that supplies a 1-phase bridge rectifier loaded with a direct current motor (see Fig. 2a). The magnitude of the set value of the effective value of the current in the line is assumed to be

3 0.06ln-06 {2 2.511n - (1.2 - 1.5) 1H. where In start gok drpgatel;

1H iomp. Tfk engine. Coefficient - upogvizhality of protection

,, IminK 3 2 - 2.5. “. „

Kr J3 1.2-1.5 3 2- minimum short-circuit current.

5The value of the current value of higher harmonics in the same line.

vg ViT + iT + ... iTT ...

where Ik is the effective value of the k-th harmonic current.

For individual harmonics, the effective values are equal

h ..4 ld 0.9ld. .3ld1 U2l-J

15 0.181.1: ... Ik -Ј7

where Id is the current in the motor core circuit. Effective line current

k-3

 I d VO92 + 0,, 182 + ... -Id Ratio of the magnitude of the current in the line to the magnitude of the higher harmonics of the current

N W rd-VO, 19ShShSh

0

five

0

0

five

Based on the above calculation

a setting of the ratio value equal to - 6 is accepted.

The ratio of the current values during normal operation of the valve converter does not depend on the magnitude of the load current, since the shape of the current curve in the line remains unchanged when the magnitude of the current changes (Fig. 2a).

When internal short circuits occur in the AC converters, including the breakdown of the valve in the rectifier or inverter, as well as when the supply line wires are interconnected, the current in the line becomes sinusoidal, i.e. only the first (fundamental) harmonic remains. With arc short circuits, the current in the supply line has short-term discontinuities when going through a zero value due to the processes of ignition and extinction of the electric arc, and its shape is close to a sinusoid. Therefore, the higher hermonics present in the current have a higher order than the harmonics in the normal mode of operation of the valve converter, respectively, the fractional value of the higher harmonics in the arc current kz is insignificant. In this case, the ratio of the current in the line to the higher harmonics in the case of a short circuit is repeatedly increased.

is compared with the normal mode, which makes it possible to clearly distinguish the beginning of the short circuit process from the starting overload and the normal mode of operation of the valve converter.

Processes similarly occur during the operation of valve converters fed from direct-current lines (contact network of direct-current electric locomotives). In a direct current line supplying a pulse converter that operates on an active-inductive load and counter electromotive force (DC motor, battery charge, etc.), the current flows in the form of unipolar pulses (see Fig. 26 ). The composition of this current includes a constant component (average current) and higher harmonics of the current.

When a short circuit (metallic or arc) occurs, the current in the line becomes constant and does not contain higher harmonics, therefore, here too, the ratio of the current in the line to the higher harmonics increases many times.

Protection against short-circuiting of lines supplying other types of valve converters (1-phase with zero valve, 3-phase with zero valve, 3-phase bridge and others) is similar. At the same time, the number of current sensors and other elements depends on the number of phases and the neutral mode of the transformer feeding the valve converters. Determination of threshold settings

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figure 1

0

five

0

five

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The units are manufactured taking into account the converter circuit and the method of controlling the valves (symmetric or asymmetrical control).

This device allows to obtain the sensitivity of protection of the line supplying the valve converter.

Claims (1)

The invention The device for protection against short-circuit current of the line supplying the valve converter containing a current sensor, the output of which is connected to the input filter of higher current harmonics, two threshold units with elements of the operation setpoint, And element, the first input of which is connected to the output of the first threshold unit and an output with an output of the output unit, characterized in that, in order to increase the sensitivity when the starting current and short-circuit current are commensurate, two transducers are additionally introduced AC-DC to DC current and dividing unit; the input of the first AC-DC converter is connected to the output of the current sensor, and its output is connected to the input of the first threshold unit and to the input of the dividend dividing unit; alternating current into direct current is connected to the output of the filter of higher harmonics of the current, the output of the dividing unit through the second threshold unit is connected to the second input of the element I. ABOUT TonfapamHozi for s / nii Tang arc porotny zam / mm fie. 2