SU546829A1 - Device for measuring leakage current of electrically insulating products - Google Patents

Description

The invention relates to the field of measurement technology.

Devices are known for measuring and leakage currents of electrically insulating products (1) containing a source of test voltage and a meter connected in series to the circuit of the product being tested.

It is also known a device comprising a block of sources of test voltages with a switch and a meter connected in series to the circuit of the test item (2).

A disadvantage of the known devices is the low measurement accuracy of the steady-state leakage current, due to the fact that the switching time of the meter and sources of test voltage is carried out in them without taking into account the actual process of establishing the current in a particular monitored sample, either visually according to the meter readings or using additional sensors of time.

In order to improve the measurement accuracy of the steady-state leakage current, the proposed device contains a clock pulse generator with an open contact at .M of the outputs, a release-delay relay, a threshold device with an open contact at the output, a capacitor, and a resistor connected in series to the monitored product. through the capacitor is connected the input of the threshold device, shunted by the contact of the pulse generator connected by its second

output through the contact of the threshold device with the inputs of the switch, made with a delay when triggered, and the relay connected by its output to the control input of the meter.

Improving the accuracy of measuring the steady-state leakage current is achieved due to the fact that the moment of switching of the meter and the sources of test voltage is carried out taking into account the real process

reducing the rate of change of the leakage current and only when it reaches a certain, close to zero, value.

FIG. 1 shows a block diagram of the described device; in fig. 2 - temporary

diagrams that explain his work.

The device contains (Fig. 1) unit 1 of sources of test voltages f / i, Uz. . . Un, the outputs of which are connected to the inputs of the switch 2, made, for example, in the form of a relay switchboard with a delay of control clock pulses, measuring 3, connected between the switch output and one of the input terminals of the device. In addition, the device is equipped with a clock pulse generator 4 with an opening contact 5 and one of the outputs, a normal device 6 with an opening contact at the output, a relay 7 with a delay when released by a resistor 8 connected between the total source of the test threshold and the second input terminal of the threshold devices 6. The input of the threshold device 6 is shunt by the contact 5 of the clock generator and is connected to the resistor 8 via the capacitor 9. The second output of the clock generator through the contact of the threshold terminal Device 6 is connected to the inputs of switch 2 and relay 7. In FIG. 2 marked; a is the process of establishing the dielectric leakage current; b - clock pulses controlling contact o (contact 5 is closed during a pulse); в - clock pulses at the second generator output; r is the input voltage of the threshold device; d is the open-contact time of the normative device; c - clock pulses at the inputs of the switch and the relay; W - N-pulses corresponding to the moment of switching the switch; and - measurement time (delay time of the relay 7 when released). When the device is turned on by the first clock pulse, the switch is started, contacts 5 are opened, relay 7 is turned on. After TU.S:,:., Equal to the delay time when relay 7 is released, it is de-energized and the meter 3 turns off with its output signal The first switch cell, n, will begin the process of establishing (reducing) the leakage current through an insulated product connected to the input of the device (Fig. 2, a). The third (for this example) clock pulse closes the time / 1 contacts 5, and the capacitor 9 is charged to a voltage equal to the voltage drop across the resistor 8. With the contacts 5 open, the voltage at the input of the threshold device At / will change (Fig 2, d) and in each moment of time will be equal to the difference between the current value of the voltage on the resistor 8 and the capacitor 9 at the moment of opening the contact 5. At the moments of time (Fig. 2, d), when the voltage At / exceeds the trigger threshold Un, the output contacts of the threshold device open and the next The driving clock pulse (Fig. 2, b) will not enter the switch control circuit and the relay. Contact 5 is closed again at time i, and the described process will repeat if, for the next clock pulse period, the rate of change of leakage current is sufficient to fulfill the condition AU UnIf the rate of change of leakage current is less than a certain value depending on the sensitivity of the threshold device, over a period clock pulses (between pulses 6 and 7, fig. 2,) the value of At / does not exceed the threshold of operation t / n, and therefore, when the seventh clock pulse arrives, the output: the switches of the threshold device remain closed E, and a clock pulse to be held in the switch control circuit 2 and the relay 7, the output of which include meter. The residual current leakage will be recorded. Thus, in the iredazhedeynom device, the delay of the clock pulses entering the control circuit by the switch and meter, and consequently, the dwell time of the monitored insulating product under test voltage and the moment of fixing the measurement result depend on the actual process of setting the leakage current of a particular monitored product. The switching of the meter and the sources of test na- ture occurs only when the velocity of the leakage current decreases to a certain close to zero and in advance of a predetermined value, i.e. the measurement of the steady-state leakage current is carried out. Due to this, the proposed device, compared to the known ones, has a greater accuracy of measurement of the steady-state leakage current of insulating products and greater reliability and comparability of measurement results. In addition, the proposed device allows one to automate the process of investigating insulated products according to their voltameric characteristics, measured by the values of the leakage current. Forms of the invention The device for measuring the leakage current of electrical insulating products, containing a test voltage block with a switch and a meter connected to the circuit of the product being monitored, is characterized in that, in order to improve the accuracy of the measured leakage current, it contains a generator of clock pulses with an open-circuit contact on one of the outputs, a delayed release relay, a threshold device with an open contact on the output, a capacitor and connected subsequently to a controlled circuit Iseli resistor to which connecting a capacitor across the input of the threshold device, 1punirovanny contact pulse generator, bound in its second output via a threshold device! User inputs commutators adapted during sraatyvanii delay, and the relay is connected to its vyodom to the control input of the meter. Sources of information taken into consideration prp examination. 1.P. T. Oreshkin, “Electrical conductivity of ogéupors, M., Metallurgists, 1965. 2.S. P. Epstein et al. Sat. “Electronic Equipment, Series 8, 1966, vol. 5, p. 106.

r