Cross-connection of power cables involves connecting the end of phase A to the beginning of phase B, the end of phase B to the beginning of phase C, and the end of phase C to the beginning of phase A, dividing the entire cable into 3n segments. This allows the induction current in the cable core conductors into the shield to cancel each other out. Cross-connection is used for shield grounding in high-voltage single-core cables over long distances.
When conducting a DC withstand voltage test on cross-connection insulation to ground, the sheath overvoltage protector (SPD) must be disconnected. The three cable segments on the other side of the interconnection box must be grounded. The insulation rings of the insulation joints must be tested. A DC voltage of 10kV must be applied between the metal shield or metal sheath of each cable segment and ground for one minute.
For the SPD mentioned above, the zinc oxide resistor and nonlinear resistor, as well as their insulation resistance to ground, must be carefully considered.
During the test, a DC reference current is applied to the zinc oxide resistor, and the voltage drop can be measured to obtain the DC reference voltage. At the same time, after all the leads of the nonlinear resistor are connected in parallel and insulated from the grounded casing, the insulation resistance between the leads and the casing can be measured with a 1000V megohmmeter (not less than 10MΩ).
The performance test for power cable cross-connections begins by placing all interconnection box connectors in their normal operating positions. A three-phase balanced test current of approximately 100A is applied to each phase of the cable conductors. Maintaining the test current constant, the metal sheath current and voltage to ground at the cross-connection box are measured. After measurement, the test current is reduced to zero and the power is disconnected. The connectors near the cross-connection box are then reconnected to simulate a faulty connection. The test current is then increased to 100A again. The metal sheath current and voltage to ground at the cross-connection box are measured. After measurement, the test voltage is reduced to zero, the power is disconnected, and the correct connection position is restored.
Contact resistance in the interconnection box: After completing the aforementioned tests on the sheath overvoltage protector, the switch (or connector) is restored to its normal operating position. The contact resistance of the switch (or connector) is measured using a double-arm bridge (the value must not exceed 20μΩ).
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