The power loss of the transformer is divided into iron loss and copper loss. Iron loss is also called no-load loss, which is its fixed loss and is the loss generated by the iron core (also called core loss, and copper loss is also called load loss).
Transformer loss calculation formula
(1) Active power loss: ΔP＝Po＋KT β2 Pk
(2) Reactive power loss: ΔQ＝Qo＋KT β2 Qk
(3) Comprehensive power loss: ΔPz＝ΔP＋KQΔQ
Qo≈Io%Sn, Qk≈Uk%Sn
In the formula: Qo - no-load reactive power loss (kvar)
Po--No-load loss (kW)
Pk--rated load loss (kW)
Sn--Transformer rated capacity (kVA)
Uk%--short circuit voltage percentage
β--Load factor, which is the ratio of load current to rated current.
KT--load fluctuation loss coefficient
Qk--Rated load magnetic leakage power (kvar)
KQ--Reactive power economic equivalent (kW/kvar)
The selection conditions for each parameter when calculating the above formula:
(1) Take KT=1.05;
(2) When the minimum load of the system is taken for the 6kV~10kV step-down transformer in the urban power grid and industrial enterprise power grid, its reactive power equivalent KQ = 0.1kW/kvar;
(3) The average load factor of the transformer, for agricultural transformers, β = 20%; for industrial enterprises that implement a three-shift system, β = 75%;
(4) Transformer operating hours T = 8760h, maximum load loss hours: t = 5500h;
(5) The no-load loss Po, rated load loss Pk, Io% and Uk% of the transformer are shown in the product factory information.
Characteristics of transformer losses
Po - no-load loss, mainly iron loss, including hysteresis loss and eddy current loss;
Hysteresis loss is proportional to frequency; proportional to the power of the hysteresis coefficient of the maximum magnetic flux density.
Eddy current loss is proportional to the product of frequency, maximum magnetic flux density, and thickness of the silicon steel sheet.
Pc - load loss, mainly the loss on the resistor when the load current passes through the winding, generally called copper loss. Its size changes with the load current and is proportional to the square of the load current; (and expressed by the standard coil temperature conversion value).
Load loss is also affected by the temperature of the transformer. At the same time, the leakage flux caused by the load current will produce eddy current losses in the winding and stray losses in the metal parts outside the winding.
The total loss of the transformer ΔP=Po+Pc
Transformer loss ratio = Pc /Po
The efficiency of the transformer = Pz/(Pz+ΔP), expressed in percentage; where Pz is the output power of the secondary side of the transformer.
