Master student Tsyplakova D.D., Ph.D.Dyakov I.A.

Tambov State Technical University, Russia

Calculation of power losses in transformers

Power losses in transformers are composed of the losses of active and reactive power. Active power losses are, in turn, from loss on heating of the windings of the transformer depending on the load current, and losses of heat in the steel, independent of the load current. Active power losses is expressed by the following formula:

,                          (1)

where- power loss short-circuit of the transformer (losses in the windings) at rated load, kW; - power losses transformer no-load (iron loss), kW; – the load factor of the transformer, n-is the number of transformers.

Loss of reactive power is also composed of two components: losses induced by the scattering of the magnetic flux in the transformer and depending on the square of the load current, and the magnetization losses of the transformer, independent of the load current and the load currentIõõ.Loss of reactive power is determined from the following expression:

,                                   (2)

where- loss of reactive power in the transformer, kVAr;- loss of reactive power in the transformer at idle (losses on remagnetization), kVAr; - loss reactive power dissipation in the transformer at full load, kVAr.

In turn:

,                                               (3)

whereSòð.í– nominal transformer capacity, kVA; Iõõ– no-load current of the transformer, in %.

,                                             (4)

whereUê–the thermal short-circuit voltage of the transformer, in %.

Power taking into account power losses in the transformers required for further calculations (for example, if you select cable lines) is determined as follows:

,                                           (5)

whereÐï – the active power taking into account power losses in transformers, transmitted by cable lines, kW; P – active power, kW.

Similarly, find the reactive power transmitted on the cable line (CL):

,                                       (6)

The total power is calculated by the formula:

.                                             (7)

Example of calculation of power losses in TP

For Example: Sòð.í=400 (kVA), ÊÇ = 0,93 ; , , , , P = 232,78 (kW), Q = 282,15 (kVAr).

Then by (1) to(7) we get:

Compensation of reactive power in transformers

Most of the receivers in the process consumesfrom the network in addition to active power reactive. The transfer of a significant amount of reactive power on the lines through the transformers of the power supply system is disadvantageous because of occurrence of additional losses of active power and energy in all its elements, and also due to additional voltage losses.

The optimal value of the power factor in the enterprise is produced by reactive power compensation as the natural action (by improving modes of operation of the receivers), and by installing compensating devices in the respective points of the power supply system.

The capacity of the compensating device Qê is defined as the difference between the reactive load of the enterprise QS and maximum reactive power provided to the grid company by the condition of its mode Qý:

,              (8)

where- the tangent of an angle conforming to the enterprise the conditions for obtaining power.

Compensating devices installed on the 10 kV side of the enterprise.

Reactive power after compensation is defined as:

                                                  (9)

wheren-is the number of capacitor units.