SU1425560A1 - Device for measuring insulation resistence in a.c. electric mains - Google Patents

Abstract

The invention can be used in radio-electronic devices intended for digital measurement, as well as tolerance monitoring of the insulation resistance of AC sources and consumers under and without resistance voltage. A device for measuring insulation resistance in AC power grids contains a power supply unit 1, a DC voltage source 4, a voltage divider 2, 3, a choke 5, an analog-time converter 6. The device has a measured accuracy. reni. 1 il.

Description

(L

The invention relates to a measurement technique, in particular, to devices for measuring insulation resistance in electrical networks of alternating current, and can be used in various radio-electric devices intended for digital measurement, as well as tolerance monitoring of the resistance of insulation of alternating current sources and consumers. ,; both under stress and without it.

; The purpose of the invention is to simplify and improve the measurement accuracy of the device.

I The drawing shows a block diagram of the device for measuring 1-sh insulation resistance in AC electrical networks,.

A device for measuring the resistance of insulation in electrical networks: alternating current consists of unit 1: control, voltage dividers 2 and 3, and voltage source 4 of direct current, the positive pole of which is connected to terminal 5 connecting both a monitored network and a voltage divider 2 with the housing; the divider 2 voltage-: ki is connected by one output to the negative pole of the source A of the DC voltage, the other output to the total length of the analog-to-time converter 6 the first measurement; The main input of which is connected to the voltage output of the divider 3 of the second voltage: the measuring input is connected to the output of the voltage divider 2, and the first and second control inputs to the corresponding outputs of the control unit 1.

The device works as follows.

When the device is connected to a controlled network from a source of 4 direct-current DC voltage, a voltage will flow through voltage divider 2 inversely proportional to the insulation resistance of the electrical network, creating a negative voltage across it , and through the voltage divider 3, a current flows, directly proportional to the value of the insulation resistance of the network, creating a drop of positive polarity on it relative to the housing. Control pulses coming from control unit 1 periodically connect the outputs of voltage dividers 2 and 3 to measurement inputs of analog-time converter 6, and the output of voltage divider 3 is connected to the time of the first clock pulse, and the time of the second clock pulse is connected to the output of divider 2 ex. 1ni. Thus, at the output of the analog-time converter 6, a signal is generated, which is proportional to the value of the insulation resistance of the network with a linear dependence over the entire measuring range.

The input signal U, is integrated over a strictly fixed time interval of the first cycle in accordance with the discharge

U, i4 (t),

about

where t is a fixed time interval;

r "(fc) is the function of the input signal from time to time; and, - the result of integration

first measure

and then the result of the integration is written off when integrating in the opposite direction with a fixed signal with the allocation of the time interval required to zero the result of the integration in the first cycle, which can be written as

25 jq

35 (t),

where UgCt) is the function of the copying signal,

t2-t:, t - inherent in time

interval.

When changing the measured and fixed signal with their average values, the last expression can be represented as

Uex tr U3t, 0,

where Ugj is the average input value

voltage Ug - the average value of the reference

tension

Solving this equation for t,,

and

t -; t

 and,

Therefore, the time interval.p, allocated in the second cycle, directly

proportional to the input signal. When connecting to standard fy the voltage of the series-connected reference resistor R, t and a resistor proportional to the insulation resistance of the network R, 3, it follows that the voltage

R

zg

and R

of

related

R.r

Neither

The resistances of the insulation are therefore determined

This dependence is solved by a push-pull integrator, if we choose the value of the reference impedance in accordance with the selected time of the first integration cycle.

Since the voltage drops across the resistances Rar and measured relative to the housing have opposite polarity, the voltage Ug is applied to the first input of the integrator in the first cycle, and the voltage Ugr to the second input of the integrator in the second cycle. In this case, the duration of the second clock in integrator is a time interval

five

0

five

0

shaft proportional to the insulation resistance.

Claims (1)

Invention Formula An apparatus for measuring insulation resistance in ac electrical networks, containing a control unit, a DC voltage source, a first voltage divider connected by one cable to a common bus, and the other to a first output of a DC voltage source, Also, in order to simplify and improve accuracy, a second voltage divider, choke and anapo-temporal converter are introduced in it, the first and second control inputs of which are connected to the corresponding outputs of the control unit The first and second measurement inputs are respectively with the outputs of the first and second voltage dividers, the first terminal of the second voltage divider is connected to the common terminal, and the second output is connected to the second terminal of the DC voltage source and through a choke with a terminal for connected to a monitored network, the output of the analog-to-time converter is the output of the device.