Selection of prefabricated substation

1. Selection of the power receiving equipment on the high voltage side of the prefabricated substation

For 10kV small and medium-sized power users, high-voltage load switches of box-type transformers are often used to interrupt normal load currents, and American transformer users rarely interrupt short-circuit currents. Therefore, in the design of dry-type transformer 10kV prefabricated box-type substations, high-voltage load switches and fuse combinations are usually used to replace high-voltage circuit breakers, which can greatly improve the comprehensive investment and economic benefits of equipment. In the 10kV box-type substation, the high-voltage load switch realizes the interruption of the normal load current of the substation system, and the fuse realizes the interruption of the fault short-circuit current of the substation system to ensure the safe and stable operation of the substation.

Compared with the high-voltage load switch plus fuse combination electric appliance, the high-voltage circuit breaker not only has a higher cost, but also has a larger overall size. High-voltage power distribution cabinets and low-voltage power distribution cabinets are not suitable for box-type substations with narrow and compact internal spaces. Therefore, more than 95% of box-type substations adopt high-voltage load switches and fuse combination appliances for their high-voltage power receiving equipment.

2. Selection of low-voltage power distribution part of prefabricated substation

The low-voltage power distribution cabinets (such as: GGD, GCS, MNS, etc.) used in ordinary power distribution rooms are individually combined and arranged in accordance with low-voltage power distribution functional units. Specifically divided into incoming cabinets, contact cabinets, feeder cabinets, compensation cabinets, etc., and box-type substations

Its internal integration is relatively high, and the primary circuit is relatively simple, usually only including incoming, outgoing, and compensation functions, because in order to reduce the floor space of the low-voltage cabinet in the box transformer, the layout of low-voltage electrical appliances should be optimized. Multifunctional universal circuit breakers should be used in the main circuit, that is, an automatic low-voltage feed switch that can be manually and electrically operated, and is equipped with overload long delay, short circuit short delay, and short circuit instant protection, as well as loss of voltage and shunting. A variety of automatic releases and auxiliary structures constitute a comprehensive protection system with a relatively complete system. For branch feeder circuits, plastic case circuit breakers should be selected, and their own short-circuit protection thermal trip devices should be used to effectively improve the safety and reliability of the feeder circuit.

3. Selection of pre-installed substation transformers

Box-type substation transformers usually use energy-saving dry-type distribution transformers. The capacity of the distribution transformer should be selected according to the characteristics of the electric load and the operation mode. The design capacity of a single distribution transformer should not exceed 1250kVA. If the statistical load capacity is large, it is recommended to choose the automatic switching operation scheme of two transformers. Dry-type transformers do not need to check the oil level, oil temperature, oil quality, and oil pressure and other characteristic parameters. They are also called maintenance-free distribution transformers. In addition, they have the advantages of flame retardancy and explosion protection. They are designed in pre-installed box substations. Become the preferred transformer type.

4. Design of additional functions of prefabricated substation

According to the pre-installed box-type substation use environmental conditions and other conditions, it should be considered to install anti-condensation, street lamp lighting time control and other automatic control system devices. The box-type substation shell structure should have very good durability, corrosion resistance, and resistance to internal arc faults. For a 10kV terminal box-type substation, if its capacity is below 500kVA, it is recommended to use a non-metallic shell from economic considerations.