From the perspective of economic operation, parallel operation of distribution transformers must consider the active power loss and reactive power loss of the distribution transformer.

Because when the grid provides reactive power, it will also cause active power loss in the grid and distribution transformers.

Therefore, the reactive power loss is often converted into active power loss, and the economic equivalent coefficient C of reactive power is generally used for conversion (calculated at 0.1 when the system is at the maximum load and 0.06 at the minimum load).

When there are several distribution transformers operating in parallel, the calculation of the number of parallel transformers for different loads can be done as follows.

Considering the same capacity and form of distribution transformers operating in parallel, the number of distribution transformers that need to be put into operation under different load conditions can be determined according to the following formula.

When the load increases

S>Se√n(n+1)▲Po+C▲Qo/▲Pd+C▲Qd

It is more economical to invest one more of the n distribution transformers operating in parallel.

When the load decreases

S< Se√n（n-1)▲Po+C▲Qo/▲Pd+C▲Qd

It is more economical to remove one of the n distribution transformers operating in parallel.

Where S ……total load, kVA;

Se……The capacity of each press, kVA;

n……The number of distribution transformers in operation sets;

▲Po……The total active power loss at no load, KVA;

▲Qo……The total reactive power loss at no load, Kvar;

▲Pd……Total short-circuit active power loss, KVA;

▲Qd……Total short-circuit reactive power loss, Kvar;

C… The economic equivalent coefficient of reactive power.