Standardized test solution for cable cross interconnection system

Cross-connected system

Purpose of measurement

Check the ability of the cable sheath, the insulation joint sheath and the insulation cleat to withstand the specified voltage: check the performance of the nonlinear resistance type sheath overvoltage protector to ensure that the metal sheath of the high-voltage cable can withstand the damage of the external sheath induced by the overvoltage when the cable is subjected to overvoltage: check the size of the contact resistance of the knife (or connecting piece) in the interconnection box.

Scope of application of the project: handover, pre-test

Instruments used (measuring instruments) : DC generator, 1000V digital megohm meter, loop resistance tester.

Test procedure

Dc voltage withstand test of the outer sheath of the cable, the outer sheath of the insulation joint and the insulation splint;

Nonlinear resistance type overvoltage protector;

For carbonized silicon resistor:

After the connecting wire is disassembled, the current value flowing through the resistor is measured after applying the DC voltage specified by the product to the three groups of resistor.

The measured values are compared with the product specifications

For zinc oxide resistor:

Disassemble the connection wire,

Apply DC voltage to the product, when the current in the loop just reaches 1mA, record the voltage at this time, and DC 1mA reference voltage.

The measured U1Ma should conform to the product specification.

Measure the ground insulation resistance of the nonlinear resistor and its leads:

All leads of the nonlinear resistor are connected in parallel and insulated with a grounded housing.

Measure the insulation resistance between the lead and the housing with a 1000V megohm meter.

Interconnection box

Measure the contact resistance of the knife (or connector).

Check whether the knife (or connecting piece) is connected correctly.

Analysis and judgment of measurement results

In the process of DC voltage withstand test of the outer sheath of the cable, the outer sheath of the insulation joint and the insulation splint, it is required to apply a DC voltage of 5kV and the pressure time of 1min, and there should be no breakdown. If there is a breakdown phenomenon, it indicates that there are local defects such as bubbles and mechanical damage in the cable insulation.

In the test of measuring the leakage current of carbonized silicon resistor, if the temperature during the test is not 20°C, the measured current value should be multiplied by the correction factor (120-t) /100 (t is the temperature of the resistor, ℃).

When the ground insulation resistance of the nonlinear resistor and its leads is less than 10 MQ measured with a megohm meter, it indicates that the resistor is damp or aging.

The contact resistance of the knife (or connecting piece) in the measuring interconnection box should not be greater than 20uΩ, otherwise the contact is not good and should be handled.

Test considerations

In the DC voltage test measuring the outer sheath of the cable, the outer sheath of the insulation joint and the insulation splint, the overvoltage protector must be disconnected during the test. The three sections of the cable metal sleeve on the other side of the interconnection box are grounded, so that the insulation splint of the insulation joint can also be combined to test, and then the DC voltage is applied between each section of the cable metal shield or metal sleeve and the ground.