Ⅰ. Protection equipment for oil-immersed power transformers
The protective equipment of 10 kV oil-immersed power transformers mainly include circuit breakers, load switches and fuses.
A circuit breaker, also known as a switch, plays the role of turning on and off the circuit in the circuit, but it has a strong "arc extinguishing" ability, so it can not only control the on-off of electrical appliances, but also automatically trip in the event of a short circuit. Cut off the circuit; the circuit breaker, also known as the switch, plays the role of turning on and off the circuit in the circuit, but it has a strong "arc extinguishing" ability, so it can not only control the on-off of electrical appliances, but also in the event of a short circuit. Automatic trip, cut off the circuit.
The load switch is developed on the basis of the isolation switch, that is, the knife switch. This china transformer has good operation ability and can also cut off the load current. It has a certain "arc extinguishing" ability, but its "arc extinguishing" ability is not large. The "obvious disconnection point" is formed, which is conducive to maintenance, etc., but cannot cut off the short-circuit current, so it is often used in combination with the fuse, which solves the problem of operation and obvious disconnection point, and has the ability to cut off the short-circuit current.
Fuse, also known as insurance, also plays the role of turning on and off the circuit in the circuit. Within the scope of its ability, it has a strong "arc extinguishing" ability and can be used for the protection of electrical equipment; but it cannot be operated with electricity. Or replace it, it is not very convenient to use.
The load switch has low investment, but cannot break short-circuit current, and is rarely used; the circuit breaker has good technical performance, but the equipment investment is high, the use is complicated, and it is unrealistic to widely apply; the protection configuration of the load switch and fuse combination can be avoided. The circuit breaker with complex operation and high price is used to make up for the short-circuit current of the load switch, and it can also meet the needs of actual operation. Therefore, this configuration is often used as a protection method for oil-immersed transformers.
Ⅱ. The combination of load switch and fuse to protect oil-immersed power transformer has the following advantages:
1. The performance of opening and closing the no-load oil-immersed transformer is good. For oil-immersed transformers such as the 110kv oil immersed power transformer, the general capacity is not more than 1 250 kVA, and rarely reaches 1600 kVA. The no-load current of the transformer is generally about 2% of the rated current, and the no-load current of the larger transformer is smaller. When the ring main unit opens and closes the no-load oil-immersed transformer with low current, the performance is good, and high overvoltage will not be generated.
2. Good performance in protecting oil-immersed transformers. Using a load switch to increase the breaking capacity of a backup current-limiting fuse is more effective than using a circuit breaker, and sometimes the latter cannot even play an effective protective role. Relevant information shows that when a short-circuit fault occurs in an oil-immersed transformer, the pressure generated by the arc and the air bubbles formed by oil and gas will occupy the space originally belonging to the oil, and the oil will transmit the pressure to the transformer oil tank. As the short-circuit state continues, the pressure will increase. It rises further, causing the tank body to deform and crack. In order not to destroy the tank body, the fault must be removed within 20 ms. If a circuit breaker is used, due to the relay protection plus its own action time and arc extinguishing time, its full breaking time is generally not less than 60 ms, which cannot effectively protect the transformer. The high breaking capacity backup current-limiting fuse has a quick-break function, and it has a current-limiting function, which can remove the fault and limit the short-circuit current within 10 ms, which can effectively protect the transformer. Therefore, high breaking capacity backup current-limiting fuses should be used instead of circuit breakers to protect oil-immersed transformers.
3. The china oil type transformer has a certain price advantage. Although with the development of vacuum combination switches, some types of vacuum combination switches are cheaper than load switches, but they need to be equipped with corresponding protection devices, so there is no price advantage. Therefore, the combination of load switch and high voltage fuse has been widely used in the protection of small and medium capacity oil-immersed transformers.
