SU1367087A1 - Device for protective switching off in mains with insulated neutral - Google Patents

Abstract

This invention relates to electrical engineering and is intended to protect thyristor electric drives of mechanisms powered from a network of limited power with insulated neutral from unacceptable reduction in insulation resistance. The purpose of the invention is to improve the measurement accuracy of the insulation resistance and increase the speed of the device. When closed in the positive wire of the thyristor electric drive 16, the current flows through the cathode group of thyristors, leakage resistance, earth, rectifier 8, control key 7, integrator 6, relay element 5 volts. the corresponding phase of the switch 9 through a group of 11 valves. When a 4-negative wire of the electric drive 16 is closed (A closed circuit is formed to flow the leakage through the valve group 10, the switch 9, the rectifier 8, the ground, the controlled contact 7, the integrator 6, the relay element 5, the leakage resistance and the anode group of the thyristors of the electric drive 16. In case of leakage in the phase conductors of the supply network, the current is closed through both valve groups 10 and 11. The generator 13 controls the operation of the switch 9 and the driver 14, which controls the operation of the switch 7 and the integrator 6, ensuring the accumulated signal is reset. NCU each period rabo- you switch 9. 2 yl. slab with a CD cx

Description

one

The invention relates to electrical engineering and can be used to protect drag motors, dredgers, excavators, and other mechanisms that receive electrical energy from a network of limited power with an insulated neutral, from unacceptable reduction in insulation resistance.

The purpose of the invention is to improve the measurement accuracy of the insulation resistance and increase the speed of the device.

Figure 1 shows the block diagram of the proposed device} in figure 2 is a timing diagram of the operation of the device.

The proposed device contains a source 1 of a network with an isolated neutral, connected to the network by a protective-switching device with power contacts 2, kinematically connected with an electromagnetic coil 3.

In the power supply circuit of the coil 3 there is a closing contact 4 of the relay element 5, the first main input of which is connected to the output of the controlled integrator 6. One input of the integrator 6 is connected via a sequentially connected control key 7 and the rectifier 8 to the output of the switch 9 whose inputs are connected to common points of valve groups 10

and 11. At the same time, each pas is connected to a star.

the valve groove is a star and has opposite polarity with respect to one another. The rectifier 8 is equipped with an earthing switch 12. The control input of the switch 9 is connected to the generator 13 and to the control signal generator 14, the outputs of which are connected to the control inputs of the switch 7 and the integrator 6.

The second compensating input of the relay element 5 is connected to the matching device 15 connected to the mains. A transformer with a rectifier at the output can be used as a matching device. The electricity consumer from the network is a thyristor drive 16.

The diagram (Fig. 1) shows the leakage resistance: R, .- in the positive wire of the electric drive 16 j Ru, - in the negative wire of the electric drive 16; RMJ in the phase conductors of the mains.

five

0

15

0

25

thirty

35

40

The device works as follows.

When the thyristor electric drive 16 closes in the positive wire, the leakage current flows through the cathode group of the thyristors of the electric drive 16, leakage Ry, ground, rectifier 8, control key 7, integrator 6, relay element 5 and into the corresponding phase of the switch 9 through valve group 11 .

When closed in the negative wire of the electric drive 16, a closed loop is formed to flow the leakage current through the valve group 10, switch 9, expander 8, ground, controlled contact 7, integrator 6, relay element 5, leakage resistance R | j and electric drive thyristor anodic group sixteen.

In case of leakage in the phase conductors of the supply network, the current is closed through both groups of 10 and 11 valves.

Considering the time diagram of the device (Fig. 2), it can be seen that for the period T of the switch 9, the integrator 6 accumulates a signal proportional to the total leakage current signal in various parts of the power supply network, with the exception of harmful (noise) transient information in the measuring circuit of the device .

Exclusion of harmful information occurs due to spreading of the key 7 for a time t, which is controlled by the output signal of the driver 14.

The duration of the signal for unlocking the key 7 (time t, in Fig. 2) is determined from the relation

 vk q

Where

ow

Eq

input impedance of a safety device;

Ls; - equivalent to the capacity of the mains supply relative to the earth, equal to the sum of the capacities of individual (C;) sections of the power circuit.

The period of operation T of switch 9 is determined from the following conditions:

55

T g 6/1, T ,,

 0.12 s 5

where is the mains frequency.

The introduction of distinctive features in the protective shutdown device allows, with a 50 Hz power supply frequency and a 1 µF power supply capacity, to increase the switching frequency of the switch 4-5 times compared with the prototype, providing a speed of 0.2 s.

You switch the measurement circuits in the measuring circuit of the device and eliminate the influence of harmful (noise) interference from switching transients. So, the switch operation frequency in comparison with the prototype can be increased by 4-5 times, which significantly increases the speed

The signal-on input A of the relay is Q disconnect. In addition, the rate monotonously increases to a value proportional to the total value of the leakage current in the network (figure 2) -. The signal at the input A of the relay element monotonously increases to a value that is proportional to the total value of the leakage current in the network (figure 2).

The generator 13 controls the operation of the switch 9 and the driver 14, which in turn controls the operation of the switch 7 and the integrator 6, ensuring that the accumulated signal is reset at the end of each operation period of the switch 9.

If in the process of increasing the input signal at the input A of the relay element 5. its value exceeds the setting value of the relay element 5, the latter is triggered and by its closure contact 4 turns on the coil 3 of the protective-switching device that disconnects the thyristor drive 16 from the mains. The signal at input B of relay element 5 compensates for the effect of changes in the supply voltage on the setpoint value.

Compared with the α-prototype, the proposed technical solution allows to increase the accuracy of leakage resistance measurement and shutdown speed by increasing the electrical safety of the operating personnel and increasing the overall reliability of the protected actuators.

Claims (1)

Invention Formula about five A device for protective disconnection in a network with an insulated neutral, containing two groups of valves connected to the phases of the network, connected in a star of opposite polarity, the common points of which are connected to the switch and rectifier. the grounding generator, the output of which is connected to the control input of the switch, the relay element, the compensating input of which is connected to the network through the matching 0 block, characterized in that, in order to improve the measurement accuracy of the insulation resistance and increase the speed of the device signals, serially connected key and integrator, the control inputs of which are connected respectively to the first and second outputs of the driver, the input of which is connected to the output of the generator, with the key input is connected to the output of the rectifier, and the integrator output is connected to the main input of the relay element. five 0 T WVVYI BUT en nfYYWn IWVrn 2 MT / VWI V p t 2