Transformer selection
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Given the total kilowatt rating of the motors in a workshop, how can one determine the size of the transformer that is needed?
Based on the total power of your motors (the calculated power), taking reactive power into account, it is possible to determine the capacity of the transformer required. By considering the maximum load of each individual motor, you can see whether the selected transformer meets the load requirements. If the capacity of a single motor exceeds 20% of the transformer’s capacity, you need to decide whether to increase the transformer’s capacity or change the way the motors are started. In short, I suggest you take a look at the transformer selection manual.
Calculate the transformer capacity based simply on the total motor capacity! You need to consider the process requirements ； Load properties ； Motor starting method ； Calculations based on whether speed control is required and the motor’s overload factor are needed to determine whether separate rectifier transformers and mixed-power supply transformers are necessary, as well as their connection group numbers, short-circuit impedance, and power supply methods!
Just to add, not all the loads in your workshop will be activated at the same time, right? So, the peak load is not necessarily the sum of the loads of all motors; each motor should have an utilization factor
A simple approach is to use a ratio of 1:1.5 to 2, providing appropriate headroom for easy expansion.
First, calculate the apparent power based on the operating conditions of the load; then, determine the reactive power by taking into account the power factor of the load. The square root of the sum of the squares of these two values gives the apparent power. Finally, select a transformer with a standard capacity that is greater than this value. Refer to the Handbook on Industrial and Civil Power Distribution Design.
I’ve learned from all of you*; you are all experts, while I’m a complete novice when it comes to electricity!
Taking into account the simultaneous rate, the motor starting method, and the compensation level, along with an appropriate margin, generally 20%-45% is reserved.
Distribution transformer; transformer capacity = total motor capacity / 0.70–0.75； For directly-started motors, the capacity of the largest motor shall not exceed 30 percent of the transformer’s capacity; in the case of a main transformer, the load capacity accounts for 70 percent of the transformer’s capacity. The capacity of a three-phase transformer = sqrt(3) × secondary voltage × secondary current