Main facilities of the substation
The main facilities of the substation include power distribution devices, power transformers, control equipment, automatic protection devices, communication facilities and compensation devices.
Power distribution device
A combined facility of electrical equipment that exchanges power and collects and distributes electrical energy. It includes bus bars, circuit breakers, isolating switches, voltage transformers, current transformers, and lightning arresters. The power distribution device is arranged in accordance with the requirements of the main electrical wiring of the substation. There are two types of layouts: outdoor and indoor. The outdoor layout has different types such as medium-sized, half-height and high-type. 6-10 kV power distribution devices usually adopt indoor type, 35 kV power distribution devices can adopt indoor or outdoor type according to the specific situation, and 110 kV and above power distribution devices usually adopt outdoor type. In polluted areas or narrow places, 110-220 kV power distribution devices are housed. Gas-insulated metal-enclosed switchgear (GIS) has the advantages of small footprint and anti-pollution at the same time. It is also available in indoor and outdoor types.
Power transformer
A device that transforms voltage. It is connected to power distribution devices of different voltages, and is customarily called the main transformer of the substation. Transformers that reduce voltage to supply power to regions or users are called step-down transformers; transformers that increase voltage to transmit power to the power grid are called step-up transformers. When there are two or three voltage distribution devices in the substation, dual-winding or three-winding step-down transformers are used respectively. In power plants, generators are connected to the low-voltage windings of step-up transformers. When the capacity of a single generator is greater than 200 MW, a double-winding step-up transformer is required; when the capacity of a single generator is less than 100 MW, a double-winding transformer or a three-winding transformer can be used. When power needs to be exchanged between different voltage distribution devices, a tie transformer can be used. The tie transformer is generally an autotransformer or a double-winding transformer. If you need to obtain your own power supply from the tie transformer, you need to use a three-winding transformer to connect your own power supply from its low-voltage winding. The power supply for the substation can also be directly connected from the low-voltage winding of the autotransformer.
Control, measurement, signal, protection and automatic device
They are monitoring and protection means to ensure the safe operation of electrical equipment. The control has one-to-one control and line selection control, and its power supply can be divided into strong current (110～220V) and weak current (48 V and below). There are several types of protection: main equipment protection, line protection, and bus protection. There are two types of measurement: conventional measurement and selective measurement, which can display various required electrical measurements. There are two types of signals: audible signal and light signal, as well as strong electricity and weak electricity. When abnormal operation of electrical equipment occurs, the automatic device can automatically complete operations to ensure safe operation in time, such as automatic backup power input device and automatic recloser. The above-mentioned various facilities are generally located in the main control building (room) of the substation. Substations of 330 kV and above generally have a main control building, usually a three-story building; substations of 220 kV and below generally have a single-story main control room; unattended substations generally only build simple controls small room. The control and protection facilities are powered by the secondary circuit power supply of the substation. The secondary circuit power supply includes battery DC power supply, compound rectifier power supply, capacitor energy storage power supply and AC secondary power supply. 220 kV and above substations use battery DC power supplies, and 110 kV and below unimportant substations usually use other types of secondary loop power supplies.
Communication facilities
There are several kinds of microwave communication, carrier communication and optical fiber communication. Microwave communication, carrier communication and optical fiber communication are usually set in substations of 330 kV and above, and only carrier communication and optical fiber communication are set in substations of 220 kV and below. A separate communication building is generally not built in the substation, and the communication facilities are placed in the communication room of the main control building (room).
Compensation device
Reactive power in the power grid requires local balance. In order to balance the reactive power within the power supply range of the substation, install shunt capacitor banks or synchronous regulators in the substation; in order to compensate for the charging power of long-distance transmission lines, it is necessary to install shunt reactors in the substation; System stability, to improve the transmission capacity of the line, sometimes also need to install a series capacitor bank in the substation.
