What is the main electrical equipment of the substation?
A substation is a power plant that converts voltage, accepts and distributes electrical energy in the power system, controls the flow of electricity and adjusts the voltage, which connects the voltage at all levels through the transformer.
In addition, the substation equipment, there are open and close circuit switching equipment, the convergence of the current bus, metering and control with the transformer, instrumentation, relay protection devices and lightning protection devices, in addition to the transformer substation equipment , Scheduling communication devices, and some substation there are reactive power compensation equipment.
Transformer is the main substation equipment, divided into double-winding transformer, three-winding transformer and autotransformer.
Transformer according to its role can be divided into step-up transformer and step-down transformer for the former power system to send the end of the substation, which is used by the terminal substation. The voltage of the transformer should be adapted to the voltage of the power system. In order to maintain a qualified voltage under different load conditions, it is sometimes necessary to switch the tap of the transformer.
According to the tap switch mode, the transformer has load with load voltage transformer and no load without load voltage transformer. The on-load tap-changer is mainly used for receiving substations.
The main function of the transformer is to substation high voltage wire to ground voltage or current flowing through the high voltage wire in accordance with a certain proportion of low voltage and low current, in order to achieve the substation high voltage wire to ground voltage and flow through the high voltage wire Of the effective measurement of the current.
Transformers are divided into current transformers and voltage transformers, respectively, for current and voltage conversion.
Because of their transformation principle and the transformer is similar, so also known as the measurement transformer.
The main role of the transformer:
① transformer can be used to measure or protect the instrument with a circuit circuit isolation, to avoid short-circuit current flow through the instrument, so as to ensure equipment and personal safety;
② because the transformer side and secondary side only magnetic connection, and no electricity directly linked, thus reducing the secondary instrument on the insulation level requirements;
③ the transformer can be a high-pressure circuit into a 100V or 100 / 3V low voltage, the primary circuit in a large current into a small 5A current. In this way, the secondary side of the transformer measurement or protection with the manufacture of instruments can be standardized.
In addition, the secondary winding of the current transformer is often connected to the load close to the short circuit, please note: must not let it open, otherwise it will be due to high voltage and endanger the equipment and personal safety or burn the current transformer.
Switchgear. It includes circuit breakers, disconnectors, load switches, high voltage fuses, and so on.
Circuit breaker in the normal operation of the power system is used to close and disconnect the circuit failure in the relay protection device under the control of the faulty equipment and lines automatically disconnect, you can also have automatic reclosing function. In China, more than 220kV substation use more air circuit breakers and sulfur hexafluoride circuit breakers.
The main function of the disconnector (switch) is to isolate the voltage during equipment or line maintenance to ensure safety. It can not disconnect the load current and short circuit current, should be used in conjunction with the circuit breaker. In the power outage should first pull the circuit breaker after the separation switch power supply should first disconnector after the switch breaker. If the operation will cause damage to equipment and personal injury or death.
The load switch can disconnect the load current during normal operation without breaking the fault current. It is usually used in conjunction with high voltage fuse wire for 10kV and above voltage and not frequently operated transformer or outlet.
In order to reduce the area occupied by the substation, in recent years there has been a sulfur hexafluoride fully enclosed combination of electrical (GIS). It is the circuit breaker, disconnector, bus, grounding switch, transformer, outlet casing or cable terminal, respectively, were installed in their respective sealed room to form a whole shell filled with sulfur hexafluoride gas as an insulating medium. This combination of electrical appliances with compact structure, small weight, light from the impact of atmospheric conditions, maintenance intervals, no electric shock and electrical noise interference and so on. At present, its shortcomings are expensive, manufacturing and maintenance process requirements.
The substation is also equipped with lightning protection equipment, mainly lightning rod and lightning arrester. Lightning rod is to prevent the substation from direct lightning strikes to its own discharge of lightning current into the earth. Lightning waves in the vicinity of the substation on the line when the lightning waves along the wire into the substation, resulting in over-voltage. In addition, the circuit breaker operation also causes an overvoltage. The role of the arrester is when the overvoltage exceeds a certain limit, the automatic discharge to the ground to reduce the voltage protection device discharge and then automatically automatically arc, to ensure the normal operation of the system. At present, the most used is zinc oxide arrester.