high-voltage ring main switchgear

I. Definition

1. **Basic concept**

- The high-voltage ring main switchgear is a kind of power distribution equipment used in high-voltage power systems. It is mainly applied in ring network power supply systems to distribute, control, and protect high-voltage electric energy from different power sources (such as substations). In ring network power supply, multiple power sources are connected into a ring network through cables or overhead lines. The ring main switchgearis located at the nodes of this ring network to realize flexible distribution and transmission of electric energy.

II. Structural composition

1. **Cabinet body**

- The cabinet body is made of metal materials and has good sealing performance and mechanical strength. The sealing performance can prevent dust, moisture, etc. from entering the interior of the cabinet and avoid affecting the normal operation of internal electrical equipment. The mechanical strength can withstand certain external impacts and ensure the stability of the cabinet during installation and use. The cabinet also has good grounding to ensure the safety of equipment and operators.

2. **Load switch**

- The load switch is an important component in the high-voltage ring main unit. It can connect and disconnect load current under normal conditions and has a certain arc extinguishing ability. Compared with circuit breakers, load switches cannot cut off short-circuit current. However, in ring network power supply systems, by cooperating with fuses, it can effectively control and protect lines.

3. **Fuse**

- Fuses are used in high-voltage ring main switchgear to cut off short-circuit current and overload current. When a short circuit or overload occurs in the circuit, the fuse element will melt and cut off the circuit to protect other equipment from damage due to excessive current. In ring main units, fuses are often used in conjunction with load switches. The load switch is responsible for cutting off load current, and the fuse is responsible for cutting off short-circuit current. This combination method improves the reliability and economy of the equipment.

4. **Earthing switch**

- The earthing switch is used to ground the circuit during equipment maintenance to provide safety protection for maintenance personnel. Before performing maintenance operations, the earthing switch needs to be closed first to ground the equipment and prevent electric shock accidents caused by sudden power supply during the maintenance process. The operation of the earthing switch must be carried out in strict accordance with operating procedures to ensure the safety of the operation.

5. **Current transformer**

- The current transformer is used to measure the current magnitude in the outgoing circuit of the ring main unit. It transforms large currents into small currents in proportion (for example, the standard secondary current is 5A or 1A), so that measuring instruments (such as ammeters) and protection devices (such as relay protection devices) can measure current and judge faults. The secondary side of the current transformer is strictly prohibited from being open-circuited, otherwise high voltage will be generated, endangering the safety of equipment and personnel.

6. **Voltage transformer**

- The voltage transformer is used to measure the voltage in the outgoing circuit of the ring main unit. It transforms high voltage into low voltage in proportion (for example, the standard secondary voltage is 100V), providing voltage signals for measuring instruments such as voltmeters and electric energy meters and voltage protection devices. The secondary side of the voltage transformer is strictly prohibited from being short-circuited, otherwise the transformer will be damaged.

7. **Relay protection device**

- The relay protection device monitors the electrical parameters in the circuit of the ring main unit in real time, such as current, voltage, power, etc. When faults or abnormal conditions (such as overcurrent, overvoltage, undervoltage, etc.) are detected, the relay protection device can quickly send out signals to make relevant equipment (such as load switches, fuses, etc.) act, thereby protecting equipment and lines from further damage. Common types of relay protection include overcurrent protection, instantaneous trip protection, zero sequence protection, etc.

III. Working principle

1. **During normal operation**

- In the normal operating state, the load switch is in the closed state. The current flows from the power source through cables or overhead lines into the ring main unit, and then is distributed to each outgoing circuit through the load switch to transmit electric energy to the user end or the next-level power distribution equipment. The current transformer and voltage transformer monitor the current and voltage parameters in the circuit in real time and transmit signals to measuring instruments and relay protection devices for electric energy metering and operation status monitoring.

2. **In case of fault**

- When a short circuit or overload fault occurs in the outgoing circuit, if it is a short circuit fault, the fuse element will quickly melt and cut off the circuit; if it is an overload fault, depending on the degree and duration of the overload, the fuse or relay protection device may act. For some faults that can be detected by relay protection devices, such as overcurrent faults, the relay protection device will send a signal to trip the load switch (if the load switch has this protection function) or melt the fuse, thereby isolating the faulty part and preventing the expansion of the fault range. The earthing switch plays a role in grounding protection during maintenance to ensure maintenance safety.

IV. Application scenarios

1. **Urban distribution network**

- In urban distribution networks, high-voltage ring main units are widely used. Due to the dense power supply network in cities, the ring network power supply method can improve the reliability and flexibility of power supply. High-voltage ring main units can be installed at various power distribution nodes in cities, such as community power distribution rooms and commercial center power distribution rooms, to realize efficient power supply to different areas of the city.

2. **Industrial park**

- There are a large number of enterprises and electrical equipment in industrial parks, and the reliability requirements for power supply are relatively high. High-voltage ring main units can connect the power sources from different substations in the park into a ring network. When one power source fails, it can quickly switch to other power sources through the ring network to ensure the normal production power consumption of enterprises in the park.

3. **Large buildings**

- The power supply system of large buildings (such as high-rise office buildings, large shopping malls, etc.) is relatively complex and requires reliable power distribution equipment. High-voltage ring main units can be used as part of the building's power supply system to distribute and control high-voltage electric energy from the external power grid, meet the power needs of various electrical equipment inside the building, and at the same time, can quickly isolate faults in case of faults to ensure the safety of electricity use in the building.