SU983579A1 - Device for checking cable article insulation resistance - Google Patents

Description

The invention relates to electrical engineering, in particular to measurement instrumentation technology, and can be used to measure the insulation resistance of cables, wires and cords in the process of testing them with high alternating voltage.

A device for monitoring the resistance of an electrical circuit of a direct current is known, comprising a source of alternating test voltage, a phase-sensitive circuit, a voltage transformer, a rectifier, a zero-indicator, a relay. In case of a poor ISOLATION condition, the relay triggers to the output of the null indicator tl.

The disadvantages of this device is the lack of complexity and impossibility of quantitative control of insulation resistance, i.e. his measurements.

The closest to the technical essence of the invention is a device for determining the insulation resistance of cable products from a self-discharge curve, containing a high-voltage source of constant voltage, and a voltmeter that measures the voltage on the test object, when it is self-discharged

from the source. The self-discharge curve calculates a constant discharge time, which, with the known electrical capacity of the product, allows us to determine the insulation resistance 2j. The disadvantages of this device are the need for a long time to remove the self-discharge curve and the impossibility of combining it with the process of testing the insulation by alternating voltage.

The aim of the invention is to extend the functionality

15 devices.

g

This goal is achieved by the fact that in the device for monitoring the insulation resistance of cable products,

20 containing the source of the test voltage, the output of which is connected to the first terminal of the monitored cable product, and a voltmeter, an ammeter of alternating current,

25 a capacitor, a diode to a resistor, while the second terminal of the monitored cable product is connected to the common bus of the source of the test voltage through two parallel

30 connected circuits, the first of which is formed by a series-connected ammeter of alternating current and a capacitor; the second is connected by series-connected diode and a resistor, in parallel with which a voltmeter is connected. A peak voltmeter is used, and a high alternating voltage source is used as the source of the test voltage. The drawing shows an electrical diagram of a device for measuring the insulation resistance of cable products. The circuit includes a high voltage test source 1, a cable product 2., ammeter 3, a capacitor 4, a diode 5, a resistor 6, and a peak voltmeter 7. The device operates as follows. The part of the test voltage designed to form a constant voltage is formed by a capacitive divider composed of a cable capacitance and a capacitor 4. A few periods after the high voltage source 1 is turned on, a fixed mode is established in the circuit, when superconductor occurs on capacitor 4 voltage pockets of variable and constant components. In this case, diode 5 is almost in the closed state for the entire period, and the distribution of the alternating voltage on the capacitive divider is completely determined. the capacitance ratio of the product: And the capacitor 4, and the constant component of the circuit is approximately equal to the amplitude of the variable component released on the capacitor 4. because under the action of the constant component the leakage current flows through the insulation of the cable due to the self-discharge of the capacitors of the capacitor 4 and the product 2. The reduction in the constant component leads to the fact that a positive voltage appears on the anode of the diode 5, relative to the cathode, the diode 5 opens, through it pulse passes current which restores the constant voltage component on the capacitor 4 and product 2. The measured value of the voltage pulse on resistor 6 calculates the amplitude of the recovery current pulse 1 |, then the known values of the restoration current pulse and the capacitive current of the product - I, measured by an ammeter 3, the insulation resistance of the cable is calculated using the formula -YW en-bL 1o A o o the capacitive current of the product; the amplitude of the impulse voltage recovery of the DC voltage P - (1 "- -, and - voltage drop on the calibrated resistance xga - auxiliary capacitor capacitance; . e i, and are the current values of the current in the diode and the voltage across it; U is the angular frequency of the test voltage source. The capacitance of the auxiliary capacitor 4 is chosen 20–100 times the maximum capacity of the cable products, which ensures that the test voltage is kept within the required limits. Compared with known devices, the proposed has the following advantages: a) combining insulation resistance measurement operations and insulation testing with high alternating voltage, which reduces the monitoring time; b) improving the measurement accuracy of the insulation resistance; Since the self-discharge energy of the capacitances and the energy of the DC component recovery are equal to each other, the amplitude of the current pulse greatly exceeds the leakage current, which allows measuring the larger resistances (hundreds of megaohms) when using an AC voltage amplifier in the voltmeter circuit which is unlike. dc amplifiers used to measure small leakage currents are drift-free and provide more reliable resistance measurements.

Claims (2)

1. Author's certificate CGCt 189484, cl. G 01 R 27/08, 1963. 2. Gorodetsky S.S., P.M. Test of cables and wires, M., Energy ,, 197l p. 66