SU672692A1 - Device for protecting thyristorized dc drive from short-circuitings in power cable - Google Patents

Description

(54) DEVICE FOR PROTECTING THYRISTOR DRIVE OF DC VOLTAGE FROM SHORT CIRCUITS IN POWER CABLE

The invention relates to a relay protection technique and is intended to be protected against short circuits in a cable of a thyristor direct current drive operating on an active inductive load, which is, for example, a direct current motor for mining coal mines.

A device for protecting objects against short circuits is known, the principle of action of which is based on comparing the current current value with the preceding ones, and the protection setting cpa6aTbiBaHHf automatically changes in accordance with the program for changing the load current 1.

The disadvantage of this device is the low speed and its complexity.

The closest to the invention is a device for protection of direct current grids against short circuits, whose operation is based on measuring a signal proportional to the first derivative of the rate of increase of short circuit current, and which contains a transformer whose primary winding is on

in the power circuit and the executive body associated with the secondary winding 2.

A disadvantage of the device when using it to protect an adjustable direct current thyristor drive from short circuits in the cable are possible failures, since the moment of short circuit can occur during the pause between current pulses in the cable (at small angles of opening the thyristors of the converter) that eliminates the possibility of forming a signal proportional to the first derivative of the rate of increase of the short circuit current.

The aim of the invention is to eliminate false alarms from load currents and increase the sensitivity of protection of thyristor DC drives operating on an active inductive load from short circuit currents in the cable.

Claims (2)

The goal is achieved by the fact that in the device for protecting the thyristor drive of direct current from short circuits in the cable containing the transformer, the primary winding of which is included in the power circuit and the actuator connected to the secondary winding, the wiring element is in junction with the pulse-transmitting element the current of the back of the ferro, with the said element in the form of a valve connected in series with the secondary winding of the transformer. The drawing is a schematic diagram of the device. The proposed device contains a thyristor converter 1, a power cable 2, a load 3 with parameters RH, LH - a current transformer 4. an actuator 5 with element 6 and a converter control unit 7, In normal operation, the thyristor drive when there is no power cable a short circuit, the signal removed from the current transformer 4 is insufficient to trigger the actuator 5 protected. When a short circuit appears in the cable, the amplitude of the current pulses increases, resulting in an increase in the amplitude of the signal removable from the current transformer 4, proportional to the first first derivative of the current pulses, which causes the actuator to operate and the control voltage to turn on. The use of a signal proportional to the first derivative of the leading edge of the current pulses leads to spurious manipulations when attempting to implement protection over the entire control range. This is due to the fact that the pulses of short-circuit currents and loads have a steep anterior f | (jipoHTa, ss) in the short-circuit current when there are large scrubs, 1a thyristor opening. The fan is connected to the carrier of the transformer to prevent signals that are proportional to the leading edge of the current pulses, which eliminates false positives of the device. The first derivatives of the trailing edge of the short-circuit current pulses and loads differ significantly due to the influence of the load inductance. The ratio of the first derivatives of the back edge of the short-circuit current pulses to the load is such that the value of the first derivatives of the back edge of the short-circuit current pulses exceeds the values of the first derivatives of the back edge of the load current pulses over almost the entire range of converter voltage control. This short-circuit protection device is lightweight, occupies a small volume and eliminates the possibility of false positives, which is very important for mining equipment. In addition, the simplicity of the device significantly reduces the cost of its manufacture and maintenance. The device has a short response time, which makes it possible to use it as a protection for the thyristors of the converter against short-circuit currents at maximum voltage at the output of the converter. Accepting current-sensitive protection devices with a constant setpoint of operation significantly limits the allowable voltage control range and, for cable lengths of more than 0.5 km, can protect only at maximum voltage of the converter, which prevents engine control . The described protection device protects the cable against short circuits across the entire voltage control range (practically from 10 to 100 ° / o), under load parameters: inductance L and Lmin, active resistance RmAx 1.5 Ohm. Claim 1. A device for protecting a thyristor DC drive from short circuits in a power cable, containing a transformer, the nervous winding of which is included in the power circuit and the actuator associated with the secondary winding, characterized in that protection sensitivity, by eliminating false positives from load currents, will perform (the body is made with an element that lets them pass from the trailing edge of the current. 2. Device but item I, from which the element is made and the valve included in the pic is consistently with the secondary winding of the transformer. Sources of information taken into account during the examination 1. USSR author's certificate No. 541231, CL And 02 H 3/08, 1976. 2. USSR author's certificate “Cho 162211, cl. H 02 H 3/08, 1964.