Low Voltage Disconnector
Isolating switch [1] is a switching device which is mainly used for "isolating power supply, switching operation, connecting and cutting off small current circuit" and has no arc extinguishing function. When the disconnector is in the off position, the contact shall be provided with insulation distance meeting the specified requirements and obvious disconnection marks; When in the closed position, the switchgear can carry the current under normal circuit conditions and abnormal conditions (such as short circuit) within a specified time. Generally, it is used as high-voltage disconnector, that is, the disconnector with rated voltage above 1kV. Its working principle and structure are relatively simple. However, due to its large usage and high requirements for working reliability, it has a great impact on the design, establishment and safe operation of substations and power plants. The main feature of the disconnector is that it has no arc extinguishing capacity and can only open and close the circuit without load current. The entry introduces the functions, characteristics, types, applications, error prevention improvement, maintenance, common problems, etc. of disconnectors.
1. After opening, establish a reliable insulation gap to separate the equipment or lines to be repaired from the power supply with an obvious disconnection point to ensure the safety of maintenance personnel and equipment [2].
2. Change the circuit according to the operation needs.
3. It can be used to open and close the small current in the line, such as the charging current of bushing, bus, connector and short cable, the capacitive current of switch voltage equalizing capacitor, the circulating current during double bus switching and the excitation current of voltage transformer.
4. According to the specific conditions of different structure types, it can be used to divide and close the no-load excitation current of a certain capacity transformer.
Disconnectors are mainly used in low-voltage terminal power distribution systems such as residential buildings and buildings. Main functions: breaking and connecting lines without load.
1. It is used to isolate the power supply and disconnect the high-voltage maintenance equipment from the live equipment so that there is an obvious disconnection point between them.
2. The disconnector shall cooperate with the circuit breaker to conduct switching operation as required by the system operation mode, so as to change the system operation wiring mode.
3. It is used to connect or disconnect small current circuit.
Generally, a group of isolating switches are installed on the front and back of the circuit breaker to isolate the circuit breaker from the power supply and form an obvious disconnection point; Since the original circuit breaker is oil circuit breaker, which needs frequent maintenance, there should be obvious disconnection points on both sides to facilitate maintenance; In general, the outgoing line cabinet supplies power from the upper bus to the lower through the switch cabinet. A group of disconnectors is required in front of the circuit breaker to isolate it from the power supply. However, sometimes there is a possibility of incoming power from the back of the circuit breaker, such as reverse transmission through other loops, capacitors and other devices. Therefore, a group of disconnectors is also required behind the circuit breaker.
The disconnector is mainly used to reliably isolate the power cut part and the live part of the high-voltage power distribution device to ensure the safety of maintenance work. The contacts of the disconnector are all exposed in the air and have obvious breaking points. The disconnector has no arc extinguishing device, so it cannot be used to cut off the load current or short-circuit current. Otherwise, under the action of high voltage, the breaking point will produce a strong arc, which is difficult to extinguish itself, and may even cause flashover (phase to ground or phase to phase short circuit), burn equipment, and endanger personal safety, This is a serious accident called "pulling disconnector on load". Disconnectors can also be used to switch certain circuits to change the operation mode of the system. For example, in a double bus circuit, an isolating switch can be used to switch the circuit in operation from one bus to another. At the same time, it can also be used to operate some small current circuits.
