Basic Knowledge of Ring Main Unit

Ring Main Unit: indoor ac high voltage gas insulated metal-enclosed switchgear (RMU) is a new generation of switchgear equipment, the main switch can either use permanent magnetic vacuum circuit breaker or spring mechanism vacuum circuit breaker, the cubicle adopts air insulation combined with SF6 gas compartment, which is compact and extensible and suitable for distribution automation.

The ring main unit has the characteristics of compact structure, flexible operation, reliable interlock, etc., and can provide satisfactory technical solutions for various application occasions (especially the places with bad environment) and different user requirements.The use of sensor technology and the latest protection relay, coupled with advanced technical performance and light and flexible assembly solutions, can fully meet the different needs of users.

Ring main unit is suitable for small secondary substation of electric power system, switching station, compact substation, residential district, industrial and mining enterprise, large shopping mall, especially suitable for airport, subway, railway and other occasions with high demand for electricity.

Ring Main Unit Structure

The main component of appearance

1) Current display: pointer ammeter or numerical ammeter;

2) Switch operating position: a. Load break switch operating position  b. Earthing switch operating position

3) Live display: live display of incoming line and outgoing line;

4) Observation window: Observe inside the ring main unit;

5) Cabinet: nameplate, circuit diagram, etc.

Overall Structure

The internal structure is mainly composed of these parts:

1) Interlock mechanism: interlock the load break switch and the earth switch.

2) Load break switch: switch on or off the high voltage power supply.

3) High voltage fuse: overload and short circuit protection for the circuit.

Working Principle of RMU

The ring main unit realizes the connection or disconnection of the circuit through the load break switch inside the cabinet, so as to achieve the purpose of supplying the transformer with high-voltage power supply, and realizes the protection in case of overload and short circuit of the circuit through high-voltage fuse.

How to debug the ring main unit safely

Operation method: After installation of SF6 ring main unit, first confirm that all panels have been installed. First, operate the earth switch, insert the earth switch operating hole with the operator handle provided by the manufacturer, and turn the operating handle counterclockwise to open the earth switch. Then operate the isolating switch, noting that the isolating switch must be operated only when both the earth switch and the circuit breaker switch are in the opening state. Similarly, insert the operating handle into the operating hole of the isolation switch, and turn the operating handle clockwise to make the switch close. The last step is to close the circuit breaker switch. If it is a manual switch, put the operating handle into the operating hole and turn the operating handle clockwise to make the circuit breaker switch close. If it is electrically operated, use the operating handle to enable the mechanism to store energy first and then press the closing button. Now the ring main unit is started working.

Operation Cautions

1. Before operation, it is necessary to wear safe clothes to ensure the safety during operation of the ring main unit.

2. Do not operate with wet hands to avoid electric shock.

3. The operation must be standardized. Do not operate blindly to avoid damage to the equipment.

4. Violent operation is strictly prohibited when using the operating handle of the ring main unit

5. A reliable five-proof interlock is installed between the circuit breaker, grounding switch, isolation switch and the door of the bus room.The circuit breaker switch can only operate the circuit breaker when the isolation switch closes, the isolation switch can only operate the circuit breaker when the circuit breaker and the ground switch are in the opening state, and the grounding switch can only operate the circuit breaker when the isolation switch is in the opening state. Power on operation sequence: grounding switch, isolation switch, circuit breaker switch. Power off operation sequence: circuit breaker switch, isolation switch, ground breaker switch.

Maintenance Contents

1. Check whether the cabinet is out of shape or dirty;Whether cupboard door has the phenomenon that opens, whether to have aperture;Check whether there is foreign body attachment and leakage on the top of the cabinet;Observe whether the window glass is cracked or smudged;

2. Check whether the live display device has cyclic flashing and normal display;Whether the value displayed by the instrument is normal;Whether the contact of static and moving blade becomes hot or discolored;Whether there is discoloration and heating phenomenon in high pressure insurance;

3. Check whether the conductive connection part is loose or falls off;

4. Whether the operation mechanism is flexible;

5. Whether the wire is broken or carbonized.

Maintenance Cautions

1. The parts replaced during maintenance shall be consistent with the specifications, sizes and types of the damaged parts;

2. During installation after disassembly, spare parts shall not be missed or misinstalled;

3. Attention should be paid to corrosion prevention of all metal devices, lubrication of moving parts and loosening of fasteners;

4. Maintenance personnel should understand the basic knowledge of product structure and principle, and clearly understand the content and key points of equipment maintenance.

5. During the maintenance, the maintenance personnel should pay attention to safety, do not enter the electrizing interval or careless operation, which may cause damage to the equipment.

6. Before maintenance, it is necessary to cut off the relevant power supply to ensure the safety of maintenance personnel.

7. In the course of maintenance, if you encounter difficult diseases, you should contact the manufacturer in a timely manner and provide technical support.

8. The inflatable cabinet should be maintained regularly, and relevant records should be made.

9. Keep the installation environment clean, regularly clean the surrounding environment, eliminate the dangerous factors that are not conducive to the normal operation of the inflatable cabinet, so as to ensure the reliability of the inflatable cabinet.

10. The load switch is sealed in a closed device full of insulating gas. It is necessary to check whether the barometer is standard or not.

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