Selection of internal components for box-type substations

Release time:

2021-08-27

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Abstract

Technical key points for component selection in box-type substations: selection of high-voltage side receiving equipment, transformer selection, low-voltage distribution component selection, etc.

　　Box-type substationKey technical points for internal component selection: selection of high-voltage side receiving equipment, transformer selection, low-voltage distribution component selection, etc.

1. Selection of high-voltage side receiving equipment:

For small and medium power users at 10kV, high-voltage load switches are commonly used to interrupt normal load current. The short-circuit current for users is very small. Therefore, in the design of 10kV prefabricated box-type substations, a combination of high-voltage load switches and fuses is usually adopted instead of high-voltage circuit breakers, which can greatly improve the overall investment and economic benefits of the equipment. In a 10kV box-type substation, the high-voltage load switch interrupts the normal load current of the substation system, while the fuse interrupts the fault short-circuit current of the substation system, ensuring the safe and stable operation of the substation system. Compared to the combination of high-voltage load switches and fuses, high-voltage circuit breakers not only have higher costs but also larger dimensions, making them unsuitable for compact box-type substations. Therefore, more than 95% of box-type substations use a combination of high-voltage load switches and fuses.

2. Transformer selection:

Transformers in box-type substations typically use energy-saving dry-type distribution transformers. The capacity of the distribution transformer should be selected based on the characteristics and operating mode of the electrical load. The design capacity of a single distribution transformer should not exceed 1250kVA. If the statistical load capacity is large, it is recommended to choose an automatic switching operation scheme with two transformers. Dry-type transformers do not require checks on oil level, oil temperature, oil quality, oil pressure, and other characteristics; they are also known as maintenance-free distribution transformers. In addition, they have advantages such as flame retardancy and explosion-proof features.

3. Selection of low-voltage distribution components:

Low-voltage distribution cabinets (such as GGD, GCS, MNS, etc.) used in ordinary distribution rooms are arranged separately based on low-voltage distribution functions as basic units and are specifically divided into incoming cabinets, contact cabinets, feeder cabinets, compensation cabinets, etc. The internal integration level of box-type substations is high, and the primary circuit is relatively simple, usually only including incoming and outgoing lines and compensation functions. To reduce the footprint of low-voltage cabinets within the substation, the layout structure of low-voltage electrical appliances should be optimized. The main circuit should use multifunctional universal circuit breakers that can be operated manually and electrically as automatic low-voltage feeder switches and should be equipped with overload long-delay protection, short-circuit short-delay protection, instantaneous short-circuit protection, as well as voltage loss and shunt protection. Various automatic tripping devices and auxiliary structures form a relatively complete integrated protection system. For branch feeders, molded case circuit breakers should be selected with built-in short-circuit protection thermal tripping devices to effectively improve the safety and reliability of feeder circuits.

 

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