SU543076A1 - Device for protective disconnection in the network with insulated neutral - Google Patents

Description

one

This invention relates to devices that protect a person from electric shock in networks with insulated neutral.

The devices for protective disconnection in the network are known, which ensure electrical safety during operation of electrical installations, in which non-industrial frequency currents (operational currents) are applied, imposed on the currents of the monitored network 1.

Also known are devices for protective disconnection in a network with an insulated neutral, in which a non-industrial frequency generator is connected on one side through filter resistances to the phases of the controlled network, and on the other hand to load resistance ZH. connected to a threshold device, a control device for disconnecting 2. The filtering resistances represent a high resistance to alternating current caused by the mains voltage and a small generator current of the industrial frequency. Provided that the internal resistance Kg of the generator of the non-industrial frequency is close to zero, the voltage (TC at load

Mr.SUfZjf

a-3 (g „+ 22) + 2f

where Ui is the complex voltage of the generator

non-industrial frequency; Zi is the net impedance relative to the ground;

2f - filter resistance.

In addition, it is known that the current through the human body in a network with an isolated neutral for a given phase voltage bf and the resistance of the human body Kh depends entirely on Zv, which consists of reactive and active components. There are such critical values of the insulation resistance and capacitances of the phases of the network relative to the earth, at which the current through the human body does not exceed the safe value. When Z decreases below the critical value, the voltage increases and the protective disconnection of the dollar will operate. However, if the operating current is constant or lower than the power frequency of the network, then the capacitive component of the network phases is either not taken into account, or its effect is so small that it is necessary to reduce the setpoint, i.e., increase the sensitivity of protection. In this case, frequent false

triggered, which is unacceptable. If the frequency of the operating current is higher than the frequency of the industrial network, then the low-conductivity at higher frequencies is greater than at the industrial frequency of the network, and the setpoint value is expected to be more severe. At the same time, when touching the phases, the effectiveness of protection decreases.

To expand the device hold area by automatically adjusting the trigger threshold, a phase detector is additionally introduced into the proposed device, one input of which is connected to the active filter, another input between the non-industrial frequency generator and the resistance, and connecting the output of the phase detector to the input of the threshold block .

The drawing is a diagram of the described device.

The device comprises a non-industrial frequency generator 1, filtering resistance 2, load resistance 3, phase detector 4, block 5 for controlling the response threshold, threshold block 6, and block 7 for turning off. The device is connected to the monitored network 8, I have, the resistance of the insulation 9 against the ground.

The difference in the phase angles of the AFI, defined by I3 |

at

 . Wed „- Wed„ arctg --f- - arctg

n

2- ""

(here, the total reactive and active resistances of the insulation of the network relative to the ground without filtering resistances, Hz and Ru are the reactive and active resistances of the load) is separated by a phase detector 4. The voltage from the output of phase detector 4, proportional to Dfi, goes to the unit 5 control threshold. The response threshold control unit adjusts the threshold unit 6 to the first input depending on the ratio of the active and reactive resistances of the network insulation. By this, the second input of the threshold unit 6 is supplied with a voltage from the load resistance 3, which is determined mainly by the circuit impedance module. The triggering of the threshold unit 6, the output of which is connected to the shutdown unit 7, occurs only when the active and reactive components of the network isolation are less than the critical value. Depending on the frequency of the generator 1 of the non-industrial frequency (i.e., lower or higher than the industrial frequency), the response threshold control unit 5 may adjust the threshold of the threshold unit 6 so that its operation will not depend on the operating voltage (current) frequency.

Such implementation of the proposed device allows to reduce false alarms due to the need to increase sensitivity at frequencies of the generator less than the industrial frequency, and to increase efficiency due to the need to harden the setpoint at frequencies of the generator above the industrial frequency. As a result, the efficiency of the device is increased, regardless of the frequency of the operating voltage, which expands the field of application of the device in the national economy. This device effectively operates on the generator frequencies, both above and the industrial frequency.

Claims (2)

1.N. V. Shipunov “Protective shutdown,“ Energie, M., 1968, pp. 98-99 (analog). 2.E. F. Tsapenko, “Control, insulation in networks up to 1000 V,“ Energie, Moscow, 1972, p. 81-91 (prototype).