How to determine the electrical energy savings when replacing unloaded asynchronous electric motors with lower power electric motors

Replacing unloaded asynchronous electric motors with electric motors of lower power can give up to 10% energy savings. The following considerations should be taken into account: replacing engines with less than 45% utilization is always cost-effective. Replacement motors loaded above 70% are impractical.

The possibility of replacing motors loaded in the range from 45 to 70%, as well as the amount of electricity savings from replacing electric motors of the most common series can be determined by the formula:

where dA — energy saving,%; P — average motor shaft load, kW;

— total losses of active power before and after engine replacement, kW;

Пн — nominal power of motors, kW; Cos fn — nominal cosine «Phi»; tg fn — nominal tangent «Phi»; efficiency — rated engine efficiency;

c = P / Pn = load factor of the motors

K is the economic equivalent of reactive power, which can be equal to:

— when feeding through three transformations — 0.12

— when powered by two transformations — 0.08

— when powered by one transformation — 0.05

— when powered by generator voltage — 0.02.