Complete List of Methods for Finding Ground Faults in Single-phase Motors (1)

For small current earthing system, here are some simple and feasible methods to quickly find single-phase grounding fault.
1. Using grounding wire selection devices and fault indicators to locate

Generally, substations are equipped with grounding line selection devices, which may not be accurate at times, but can provide technical reference for manual switching. Then install some ground fault indicators (or short circuit ground two in one fault indicators) on the line to indicate the path of the ground fault. A more reliable method for detecting ground faults is the signal source method, while a more sensitive method for detecting ground faults is the first half wave method or DC transient analysis method. It is recommended to use a combination of two grounding fault indicators to search for grounding faults, with the signal source method as the main method and the first half wave method or DC transient analysis method as the auxiliary method.

2. Using feeder automation methods to locate

If the user has money, it is recommended to use feeder automation methods to find grounding faults. This method utilizes the logic functions of intelligent switches (electric load switches, sectionalizers, circuit breakers, reclosers+FTU) to replace traditional manual search methods, and can automatically achieve fault isolation, recovery, and power transfer.

Assuming a dual power supply handle circuit is divided into 6 sections, which includes 5 intelligent switches (equipped with three-phase five pillar signal PT or capacitive PT on both sides), with the middle one as the contact point, and taking the grounding fault point between the first and second intelligent switches as an example,

(1) The substation will cut off the power supply by grounding the outgoing line, and the intelligent switches in each section of the line will automatically open.

(2) The substation is closed for power transmission, and the zero sequence voltage of the power station does not alarm. The power transmission in this section is successfully restored; If the first intelligent switch FTU detects line voltage but does not detect zero sequence voltage, it will automatically close after a delay of some time. If zero sequence voltage is detected due to grounding fault, it will immediately open and "lock"; The second intelligent switch also detected zero sequence voltage, and the switch did not move and "locked", canceling the "automatic closing after power on delay" function.

(3) The intermediate contact switch detected a unilateral power loss and automatically closed after a delay of some time. As the fault point was not in the section and zero sequence voltage was not detected, the section successfully transferred power supply.

(4) After the contact switch was powered on, the second intelligent switch detected line voltage but did not detect zero sequence voltage. However, there was a "lock" in front, so the "power on delay automatic closing" function was cancelled and the switch remained in the open position.

(5) At this point, the grounding fault point section has been isolated, and other non fault sections have been restored or transferred to power supply.