System Principle

With the extensive use of ring main units and cable branch boxes in power grids, the problem of quickly locating cable fault sections has become increasingly prominent. The EKL4 short-circuit and earth fault indicator provides an optimal solution to this issue.

The EKL4 short-circuit and earth fault indicator is designed for ring main units and cable branch boxes in 10kV–35kV distribution networks, indicating phase-to-phase short-circuit and single-phase earth faults in corresponding cable sections. As shown in the working principle diagram, when a short-circuit or earth fault occurs in the ring network system, all fault indicators between circuit breaker A and the fault point pass the fault current. After detecting the fault current, the indicators flash and alarm. In contrast, indicators between the fault point and the normally open point do not pass the fault current and remain in normal state (no flashing or alarm). Maintenance personnel can quickly identify the faulty cable section by checking which indicators are flashing.

In the example diagram, the fault occurs between the No. 3 and No. 4 ring main units. Therefore, after opening the load switch of the No. 3 unit and reclosing circuit breaker A, power is restored to the ring main units 1, 2, and 3 and their branch systems. Power to units 4 and 5 is restored by closing the normally open point of unit 6. This isolates only the faulty cable section, ensuring the rest of the network can resume power supply promptly.

Using fault indicators to locate fault sections is far faster and more efficient than traditional methods such as the "two-division method" or trial switching operations, while eliminating associated risks (e.g., accidental injury from insulation tests). It is a proven method to improve power supply reliability.

Overall Working Principle

When a short-circuit or earth fault occurs in the power supply line, the electromagnetic field changes caused by the fault current induce a pulse signal in the measuring coil of the sensor fixed to the cable. When the pulse signal reaches or exceeds the preset fault current threshold, the fault indicator automatically records the fault state, flashes the fault indicator light to give an alarm, and transmits the fault signal to the monitoring center via the remote alarm interface. Maintenance personnel can quickly locate the line fault position through the alarm signal, eliminate the fault in time, and restore power supply.

Main Functions

Short-circuit fault alarm indication: The short-circuit fault sensor is installed on a single-phase cable to continuously monitor current changes in the power supply line. When the current reaches or exceeds the preset short-circuit current alarm threshold (which can be factory-set according to user requirements), the sensor sends an alarm signal, which is transmitted via optical fiber to the indicator host. The corresponding short-circuit fault indicator flashes to give an alarm.

Earth Fault Alarm Indication: The earth fault sensor is installed on the non-shielded part of the three-phase cable branch to detect the zero-sequence current of the three-phase cable. When the value reaches or exceeds the set earth fault current operating alarm threshold (which can be preset at the factory according to user requirements), the earth fault sensor sends an alarm signal, which is transmitted via optical fiber to the indicator host, and the corresponding earth fault indicator flashes to give an alarm indication.

Installation Instructions

1. Installation of the Indicator Host

The indicator host is installed on the front panel of the distribution cabinet.

To remove the host, press the metal spring clips on the host housing.

Cutout dimensions: 91.5mm (tolerance: ±0.3) × 43mm (tolerance: ±0.3)

2. Installation of the Short-Circuit Fault Sensor

Fit the cable clamp around the cable, then insert the two hooks of the sensor along the opening of the clamp. After connecting the sensor and the clamp, tighten the fixing screw on the clamp to secure the sensor to the phase cable. The short-circuit fault sensor must be installed on the branch phase cable of the ring main distribution line and must be firmly sleeved on the tested cable to prevent the optical fiber interface from loosening or breaking due to sensor sliding.

3. Installation of the Earth Fault Sensor

Loosen the screw on the magnetic ring, wrap the non-shielded section of the three-phase cable, then tighten the screw on the magnetic ring. Tighten the strap on the sensor to fix it firmly on the three-phase cable to prevent movement.

4. Connection of the Signal Optical Fiber

Loosen the nut on the fiber optic socket, insert one end of the optical fiber into the socket until the fiber tip is fully seated, then tighten the nut until the fiber is secure. Connect the other end of the fiber to the corresponding socket on the indicator host using the same method and lock it in place. Both sensor connections to the host must be firm to prevent loosening and disconnection, ensuring normal operation of the indicator.

Note: The ends of the optical fiber are specially treated. Do not cut them arbitrarily, as this will affect the normal operation of the indicator!

5. Connection of Remote Signals