SU1460752A2 - Disconnection protection device in a.c. network with solidly grounded neutral - Google Patents

Abstract

The invention relates to electric power engineering, in particular, to a technique for protecting people from electric shock. The purpose of the invention is to increase the noise immunity and enhance the functionality of the device by detecting the phase with inaccurate

Description

one

The invention relates to electric power engineering, in particular, to a technique for protecting people from electric shock and is an improvement of the device according to auth. No. 1061213,

The purpose of the invention is to increase the noise immunity and enhance the functionality of the device by detecting a phase with an unacceptable leakage of current to earth.

In the drawing, a diagram of the device.

The device contains a differential current transformer 1 (DTT) to the output of which are connected a capacitor 2, an amplifier 3 and an amplifier-limiter 4, an analog subtractor 5, whose inputs are connected to the outputs of amplifiers 3 and 4, and the output to the information input of the BANNER circuit 6, the element OR NOT 7, the nepBbtfi input of which is connected to the output of the BAN 6 circuit, and the output to the input of the output relay element 8 controlling the coil of the switching device 9, load current sensor 10, unit 11 for generating a signal according to the speed of load current change which entrance is It is connected to the output of sensor 10, and the output to the prohibiting input of the BAN 6 circuit, three sensors 12-14 of active leakage current to ground, the first inputs of which are interconnected and connected to the output of DTT 1, the second ones are connected respectively

0

0

five

0

directly to the network phases, and the outputs, respectively, to the threshold elements 15-17, three time selectors 18-20 pulses in duration, the inputs of which are connected to the threshold elements 15-17, and the outputs to the inputs of the MEMORY elements 21-23, and 24-26, and the inputs of the element 24 are connected to the outputs of the elements MEMORY 21 and 22, the inputs of the element 25 to the outputs of the elements MEMORY 22 and 23, the inputs of the element 26 to the outputs of the elements MEMORY 21 and 23, the outputs of the elements AND 24-26 are connected to the inputs of the element HJlIi 27, the output of which is connected to the inputs of the element OR 27, the output of which is connected to the second input of the element OR NOT 7, the elements AND 28-30, the first inputs of which are interconnected and connected to the output of the PROHIBITION 6 circuit, and the second inputs - respectively to the outputs of the time selectors 18-20, three elements OR 31-33, and the inputs the element 31 is connected to the outputs of the elements 26 and 29, the inputs of the element 32 to the outputs of the elements 25 and 28, the inputs of the element 33 to the outputs of the elements 24 and 30, and the outputs through one-shot 34-36 are connected to the control inputs of the signaling blocks 37-39 .

The voltage of the sensor signal at the output of the leakage current is determined by the formula

and

Ki COS If

(one)

where UT is the voltage at the DTT output. tf is the shift angle between the voltage UT and the phase voltage of the network.

The choice of the capacitance of the capacitor 2 provides the minimum shift between the voltage U- and the voltage of the phase in which the current leaks to the ground. The capacitance value of the capacitor 2 is in the range of 0.7-1.2 μF.

The selector transmits pulses whose duration exceeds the delay time ti. The value of t is chosen for reasons of detuning from impulse noise and non-hazardous to human leaks current pulses. In practice, t is at least several milliseconds.

The elements of MEMORY 21-23 are made on the basis of the schemes OR NOT.

The device works as follows.

In the initial state, power is supplied only to signaling units 37-39. There are no signals at the control inputs of the blocks — the blocks are in a true state. The output relay element 8 is de-energized.

When the switching device is turned on, the power is supplied to blocks 3-7, 12-33. At the input of each amplifier 3 and 4, due to the natural leakage current, a signal is applied to the ground, which is amplified by each amplifier in the same way.

At the same time, the amplification factor values of amplifiers 3 and 4 and the parameters of limiting amplifier 4 are chosen so that in this mode — the permissible natural leakage current and the absence of human contact — the amplitude at the output of amplifier 4 does not occur. As a result, the inputs of block 5 receive practically equal amplitude signals, and its output voltage is close to zero. The signal at the input of the OR-NOT 7 circuit is zero, and at its output - the logical one .1. The output relay element 8 is triggered, and the electrical installation remains connected to the network.

If we assume that phase A has a weakened insulation compared to other phases and the leakage current to earth exceeds the corresponding currents of other phases, then the voltage

60752,

ten

at the output of blocks 12-14 in accordance with (1) are equal

  Kit., Cos (o) l

and, 0.5 Ki, cos (- | -1:) 0.5

and „0.5Ki, cos (-)

0.3 (2)

The signals to the input of threshold elements 15-17, which are essentially electronic keys,

 are converted into logical signals for, each phase, i.e. the output of element 15 will be logical 1, and

, elements 16 and 17 - logical O. Possible fluctuations of the value of U -U

20 associated with the phase unbalance on the parameters, do not affect the quality of work, since the relations r at iT./U.4 are maintained. Logical information is received through the selectors

- 18-20 pulses to the inputs of the elements of the MEMORY 21-23. The output of the elements 21-23 will be respectively 1, O, O. The output of the elements 24-24 and the element 27 will be logical 0, 30 and, therefore, the state of the relay element 8 will not change.

When a load is switched on, for example, a group of consumers having a relatively large proportion of leakage current in the total natural leakage current to earth, a jump in the leakage current occurs simultaneously with a change in the load current. As a result, the amplitude of the signal at the DTT 1 output can increase to the value at which the output signal in amplifier 4 is limited. In this case, the amplitudes at the inputs of block 5 violate 4b c, and a signal appears at its output that passes the BAN 6 and arrives at the input of the OR-NOT 7 circuit. A logical O appears at the output of the circuit 7, the output relay is de-energized and the electrical installation is disconnected from the network. To prevent such a false disconnect, block 11 receives a signal to prohibit the entry of the BAN item.

5, the signal at the output of the circuit 7 remains zero, and the electrical installation is connected to the network.

Simultaneously from block 11, the signal is fed to the control inputs of the ele144

cops MEMORY. This is necessary in order to record information in the MEMORY element made after the end of the transition process.

When a person touches the .tocurrent parts, for example, phase A, which has an increased value (compared to other phases) of the leakage current

on the ground, the signal at the output of the DTT 1 of the exposure, as compared with the known, closes to the value at which the possibility of detecting a facet occurs; it is restricted in the amplifier 4 and the electrical installation is disconnected from the network. The signals at the output of the sensors 12-14 (before the electrical installation is disconnected) in this case describe the expression in which leakage to the ground is unacceptable.

The positive effect that can be obtained as a result of using the proposed intake is to reduce consumer downtime and increase by electrofusion (2). Consequently, the output of selectors 18-20 will be logical 1, O and O, respectively. is a logical 1, which leads to the appearance of a signal at the control input of the alarm unit 38 and its subsequent operation. This means that the leakage of current to earth in phase A is unacceptable. The residence time of the block 38 in the on state depends on the duration of the –pulse at the output of one or the new 35

In the case of human contact with phase B and commensurability (the worst option) of the natural leakage current to earth in phase A- and leakage current to earth caused by human touch of vase B, the amplitude of the signal at the DTT output 1 changes slightly, t, e, by the output of element 6 will be logical O; the voltages at the output of the sensors 12-14 become equal

and, 0, 5Ki, cos (- - | -) 0,5

and ,, 5ki, cos (- | -) 0.5 and | -Ki, cos (- 1G) -l

(3)

At the inputs of elements 21-23, logical O

 ABOUT

and 1,

TT 4 T1

ABOUT

H

Logic 1 appears at the output of the AND 26 element, which enters the input of the OR 31 element and triggers the alarm block 37 - current leakage to earth in phase B is unacceptable. At the same time, the signal from the element 26 enters the input of the OR element 27, the output signal element OR NOT 7 disappears, which leads to de-energizing the output relay element 8 and disconnecting the electrical installation from the network.

The device automatically records the failures of the elements (breakage, short-circuit) in blocks 3,4,7,8,10 and 11 and some failures in blocks, 12-39,

The advantages of the proposed device in comparison with the known one are the possibility of detecting the

Threat, in which there is an unacceptable leakage. current to earth.

Comparison with the known one is the possibility of detecting the

The positive effect that can be obtained from the use of the proposed power supply is to reduce consumer downtime and increase electrical safety. Reduced customer downtime is achieved by reducing the time to search for damage and, in particular, automatically determining the damaged phase. Electrical safety is enhanced by the fact that the input signal of the damaged phase signaling circuit can be used to start the protective bypass protective device.

phases.

Claims (1)

Invention Formula A device for protective disconnection in an alternating current network with a deaf-earthed neutral on avt., Sv, No. 1061213, characterized in that, in order to increase noise immunity and enhance functionality by detecting a phase with unacceptable leakage of current to ground, three time selectors each of which is connected between the output of the corresponding threshold element and the input of the corresponding element MEMORY, three additional elements AND, the first inputs of which are interconnected and connected to the output of the el PET, and the second inputs are connected respectively to the inputs of the MEMORY elements, three OR elements, while the inputs of the first OR element are connected respectively to the outputs of the first AND element and the third additional AND element, the inputs of the second OR element to the outputs of the second AND element and the first additional element And, the inputs of the third element OR - to the outlets 714607528 the third element And the second additional-. They are connected through the newly introduced legacy elements And, three blocks of signal vibrators, respectively, to the output, controlling the inputs of which of the three elements OR.