Economic considerations for new energy switchgear

As the capacity of new energy sources such as wind power and photovoltaic power grid-connected continues to increase, the demand for high voltage, high current, and high short-circuit current increases. For switchgear, the higher the voltage, the greater the current, and the greater the short-circuit capacity, the higher the price.

72.5kV equipment is much higher than 40.5kV. For large currents such as 4000A and 5000A, the heat generation of switchgear is proportional to the square of the current. Increasing the number of copper bars, increasing the cross-sectional area of the copper bars, and reducing the resistance, if the heat generation balance of current and resistance is to be achieved, the resistance must be reduced by the square level, that is, the cross-sectional area of the copper bars must be increased by the square level, which is extremely uneconomical.

Similarly, for short-circuit current, basically multiple sections of incoming lines are connected in parallel, and the superimposed short-circuit current is too large. If all equipment uses high short-time withstand current switchgear, the cost increase is also huge.

Therefore, it is necessary to comprehensively consider economic solutions. Renewable energy generation has its periodicity and uncertainty. For example, photovoltaics have high efficiency and high output at noon and afternoon, and electricity is continuously connected to the power grid, resulting in a rise in system current. At night and in the morning, the current is relatively small, and the current is also relatively small. It is necessary to balance the power generation of one day, one month, and one year, as well as the changes in ambient temperature.

A major factor affecting the current carrying capacity of switchgear equipment is the ambient temperature. Taking the maximum temperature of 110℃ and the allowable temperature rise of 70K as an example, the standard ambient temperature is 40℃. If the ambient temperature is only 0℃, the current carrying capacity can be increased by 25%, and the current carrying capacity of 3150A switchgear can be close to 4000A.

High-current switchgear generally adopts fan forced cooling. Air cooling can quickly reduce the temperature rise of the switchgear. The natural cooling current is 2500A. By adding a fan, the current carrying capacity is increased to 5000A, and the temperature rise can not exceed the standard. The fundamental reason lies in how big a fan you use, or how much capacity reduction you allow if the fan is broken.

Therefore, it is necessary to balance the average current of one day, the ambient temperature value of one year, and the value of electric energy generation, etc. For example, the maximum output current is 3150A in general, and the limit output current is 4000A when the ambient temperature is 40℃ in summer. There are only 480 hours in a year, and the rest of the current is less than 2500A. Then we can use 2500A without adding fans, and achieve 4000A switch cabinet design through fan cooling.

They are all 4000A switch cabinets, so what is the significance? As mentioned above, the switch cabinet uses 3 100*10mm copper bars for natural ventilation to achieve 3150A. By adding four 50W fans on the top of the cabinet, turning on the fans can meet the 4000A temperature rise requirements.

The switch cabinet uses 2 100*10mm copper bars for natural ventilation to achieve 2500A current carrying capacity. By adding four 80W fans on the top of the cabinet, turning on the fans can also meet the 4000A temperature rise.

The price of wind turbines is almost the same, while the price of copper bars is 1/3 different. A cabinet costs a few thousand yuan, and the copper bars saved by the full arrangement of main busbars, incoming lines, busbars, etc. are considerable.

Similarly, the wind power switch adopts an open circuit breaker combination, which does not need to consider the installation space and has low cost, matching the life of the wind turbine.

The use of a small-level short-circuit capacity switch cabinet can save a lot of equipment investment, and the economical fast current limiter can realize the rapid removal of short-circuit current, quickly reduce the risk of system damage, ensure safe operation, and save power loss.

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