Most of the 3kV-66kV distribution networks in China adopt low current grounding methods, namely non effective grounding of neutral points, including ungrounded neutral point systems and neutral point grounding systems through arc suppression coils or high resistance. The advantage of a neutral point non effective grounding system is that in most cases, it can automatically extinguish the arc and restore insulation when single-phase grounding occurs. However, in the event of a grounding fault, in order to expand the fault due to the increase in non fault phase voltage, the faulty line must be identified and cut off as soon as possible, which raises the issue of single-phase grounding fault line selection. This problem has not been well solved for a long time, which hinders the development of distribution network automation.

Our company's small current system grounding line selection device is a product developed by upgrading and transforming the current "small current grounding line selection device" in the domestic market. When a single-phase grounding fault occurs in a low current grounding system, this device has the function of automatically alarming and accurately finding the faulty line. Prominent solved the problem of long-term reliable operation of the device in harsh environments. Its structure is more reasonable and lightweight, which can be used for the renovation of old power plants and substations, as well as for the construction of new power plants and substations, directly forming a comprehensive automation system.

1. Applicable fields

This device is suitable for small current system grounding selection and timely alarm under the following conditions, or for single-phase grounding protection tripping.

A small grounding current system with a neutral point not grounded; Voltage level: 0.38-66KV; small grounding current system with neutral point grounded through arc suppression coil or high resistance; The number of bus segments shall not exceed four, and the total number of outgoing circuits shall not exceed 56 for the system.  

It can be widely used for power supply systems in substations, power plants, hydropower stations, as well as large factories and mining enterprises such as petroleum, chemical, metallurgical, coal, railway, and construction.

2. Device features

1) High reliability: Adopting foreign high-speed DSP chips and CMOS industrial grade chips, the design is unique, with electromagnetic shielding, software and hardware redundancy, fast operating speed, strong anti-interference ability, and low power consumption.

2) The screen adopts a wide temperature LCD display, which can facilitate human-machine dialogue and easy operation.

3) High quality analog-to-digital converters have good temperature resistance, fast conversion speed, and high measurement accuracy.

4) High density, high-speed sampling, complete data acquisition for all channels within one cycle.

5) Zero sequence voltage startup, equipped with multiple line selection algorithms to adapt to different operating conditions.

6) It has alarm functions for system grounding faults, device faults, and device power outages.

7) Automatically identify changes in the parallel operation of the parent system and quickly and accurately monitor the system according to the changed operating mode.

8) Communication interfaces: RS-232, RS-485, RS-422, Ethernet port (optional function). Suitable for unmanned substations or comprehensive automation equipment.

9) The fault record information can be recalled 20 times through the LCD screen, and the information will not be lost after the device loses power.

10) The device adopts a plug-in structure and a new modular circuit design. After the device is put into operation, there is basically no need for on-site maintenance.

11) Timing function: B-code timing, pulse timing. (Optional feature)

12) Phase detection function: Determine which phase in the grounding line is grounded. (Optional feature)

13) Printing function: Print grounding records. (Optional feature)

14) One on one alarm for branch (optional function)

15) One on one tripping of branch (optional function)

1. Environmental temperature: -10 ° C to+50 ° C

2. Atmospheric pressure: 80-110kPa

3. Relative humidity of air: 90% (25 ° C), 50% (40 ° C)

4. The usage location shall not contain explosive media, and the surrounding media shall not contain conductive media or gases that corrode or damage insulation. The environment shall not be filled with steam or contain severe mold.

5. The installation site should have wind, rain, sand, and dust prevention facilities.