Zambia substation structure
The substation frame is divided into cement structure and steel structure, including portal type and π type. It also depends on the single or multi-layer arrangement of the device. Let's take a look at the main structure of the substation architecture.
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The substation frame is divided into cement structure and steel structure, including portal type and π type. It also depends on the single or multi-layer arrangement of the device. Let's take a look at the main structure of the substation architecture.
1. Transformer
It is the main equipment of the substation structure, which is divided into two-winding transformer, three-winding transformer and autotransformer (that is, each high and low voltage phase shares a winding transformer group, and a head is drawn from the middle). The high-voltage winding is used as the transformer of the low-voltage winding. The voltage is proportional to the number of turns of the winding, and the current is inversely proportional to the number of turns of the winding.
Transformers can be divided into step-up transformers and step-down transformers according to their functions. The former is used for the sending end substation of the power system, and the latter is used for the receiving end substation structure. The voltage of the transformer needs to be adapted to the voltage of the power system. In order to maintain an acceptable voltage under different load conditions, it is sometimes necessary to switch the taps of the transformer.
According to the tap changer mode, the transformer has on-load tap-changer and no-load no-load tap-changer. The on-load tap transformer is mainly used in the structure of the receiving substation.
2. Transformer
The working principle of voltage transformers and current transformers is similar to that of transformers. They convert the working voltage and large current of high-voltage equipment and busbars, that is, the load or short-circuit current of equipment and busbars, into measuring instruments, relay protection and control equipment in a specified proportion. Low voltage and low current. During rated operation, the secondary voltage of the voltage transformer is 100V, and the secondary current of the current transformer is 5A or 1A. The secondary winding of the current transformer is often connected to the load and is close to a short circuit. Please note: Do not open it, otherwise it will endanger the equipment and people or burn the current transformer due to high voltage.
3. Switchgear
It includes circuit breakers, isolating switches, load switches, high-voltage fuses, etc., all of which are devices for opening and closing circuits in the substation structure. The circuit breaker is used to close and open the circuit under the normal operation of the power system; when a fault occurs, under the control of the relay protection device, the faulty equipment and lines are automatically disconnected, and it has the function of automatic reclosing. In my country, air circuit breakers and sulfur hexafluoride circuit breakers are widely used in substation structures above 220KV.
The main function of the isolation switch is to isolate the voltage during equipment or line maintenance to ensure. It cannot disconnect load current and short-circuit current and should be used in conjunction with circuit breakers. In the event of a power failure, the circuit breaker should be pulled first, and then the isolating switch. When supplying power, the isolating switch should be closed first, and then the circuit breaker should be closed. Misuse can result in equipment damage and personal injury.
The load switch can disconnect the load current during normal operation, but does not have the ability to disconnect the fault current. It is generally used in conjunction with high-voltage fuses of transformers or sockets with voltages of 10KV and above and infrequent operation.
In order to reduce the footprint of the substation structure, fully enclosed combined electrical appliances have been widely used. It installs circuit breakers, isolating switches, bus bars, earthing switches, transformers, outgoing bushings or cable terminations in their respective sealed chambers, and then combines them into an integral shell, which is filled with sulfur hexafluoride gas as an insulating medium. The combined electrical appliance has the advantages of compact structure, small size, light weight, not affected by atmospheric conditions, long maintenance period, no electric shock accident and electrical noise interference. 765KV has been developed before the substation is put into operation. The disadvantage is that the price is relatively expensive, and the manufacturing and maintenance process requirements are high.
4. Lightning protection equipment
The substation structure is also equipped with lightning protection equipment, mainly lightning rods and lightning arresters. The lightning rod is to prevent the substation from being directly struck by lightning, discharge the lightning to itself, and introduce the lightning current into the ground. When lightning strikes the lines near the substation, the lightning wave will enter the substation along the wire and generate overvoltage. In addition, the operation of the circuit breaker can also cause overvoltages. The function of the arrester is to automatically discharge to the ground when the overvoltage exceeds a certain limit, thereby reducing the voltage, protecting the equipment, and automatically extinguishing the arc quickly after discharge to ensure the normal operation of the system.
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