Application of transformer stations in photovoltaic system

Author: Haijun

2023-03-10 10:33

 

In utility-scaled projects, large distributed industrial and commercial projects and energy storage projects, MV station will be used according to the different grid-connected voltage level. MV station as a system of transformer, distribution and ring main unit, the product needs to guarantee the operational safety of the system and the reliability of the power supply.

 

1 MV station

MV station is a kind of power station product that combines the transformer, low-voltage distribution cabinet, high-voltage switchgear and other auxiliary equipment reasonably together, installed in a corresponding protection capacity, can be sealed or semi-enclosed, also can be moved as a whole part. MV station equipment is commonly used in urban power distribution, industrial power distribution and new energy generation systems of 10kV and above voltage levels. The advantages of MV station are compact and simple structure, which can reduce the cost of land and civil construction, and the prefabricated way in the factory can speed up the project installation and commissioning progress. Meanwhile, the system and structure design can be customized according to the project demand, which can meet the use demand under various environmental conditions.

 

2 Types and differences of MV station

A Types of MV station

At present, from the development of the MV station, structure design, primary equipment configuration is mainly divided into American-style MV station, European-style MV station, Chinese-style MV station.

There is a big difference in the appearance in the three types. The European MV station combines MV switchgear, LV switchgear and power transformer in the container, the volume is lager. For American and Chinese MV stations, the power transformers are designed outside the container, so it’s smaller and compact. Circuit breaker in Chinese-style MV stations are installed in the high-voltage cabinet, the load switch is installed inside transformer for America-style MV station, so for American-style MV station, the HV part is compact. For Chinese-style MV station is bigger in volume.

Figure: European-style MV station

B Differences in Equipment Configuration

American-style MV stations combine the transformer body, high-voltage load switch, fuse, and ring main unit inside the oil tank. The high-voltage side uses a fuse for transformer short-circuit and overload protection, while the low-voltage side uses a frame circuit breaker for overload delay protection, short-circuit protection, and ground fault protection. The MV station is equipped with a pressure release valve, oil temperature gauge, and temperature controller to achieve non-electrical protection.

                                                                     

Figure: SLD of American-style MV station

European-style MV stations have two configurations for the high-voltage side: one is to configure a load switch with a current-limiting fuse, and the other is to configure a circuit breaker device. The low-voltage side usually uses a load switch with a fuse. When a European-style MV station uses a load switch and a fuse on the high-voltage side, its high and low voltage protection functions are the same as those of American-style MV stations. When a circuit breaker is configured on the high-voltage side, it adds protection for overcurrent, overload, single-phase grounding, and other faults. The basic protection functions are the same as those of American-style MV stations. Small-capacity European-style MV stations often use dry-type transformers, which only need to be equipped with over-temperature trip protection functions. Large-capacity European-style MV stations use oil-immersed transformers and are often equipped with non-electrical protection functions such as pressure, gas, and oil level.

Figure: SLD of European-style MV station

Chinese-style MV stations mainly use air-insulated ring main unit on the high-voltage side, which are equipped with isolation switches, vacuum circuit breakers, current transformers, zinc oxide surge arresters, cable heads, grounding switches, and live display devices. The low-voltage side is equipped with frame circuit breakers or load switches. The transformers used are mostly oil-immersed. The protection functions of Chinese-style MV stations include overcurrent speed break protection, overcurrent protection, overload protection, and single-phase grounding protection. Non-electrical protection functions include heavy gas, light gas, oil level, and oil temperature protection.

                                                           

Figure: SLD of Chinese-style MV station

 

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