P0 – no-load loss, mainly iron loss, including hysteresis loss and eddy current loss;

The hysteresis loss is proportional to the frequency; it is proportional to the power of the hysteresis coefficient of the maximum flux density.

The eddy current loss is proportional to the product of frequency, maximum flux density, and thickness of the silicon steel sheet.

PC – load loss, mainly the loss of resistance when the load current passes through the winding, generally called copper loss. The size varies with the load current and is proportional to the square of the load current; (indicated by the standard coil temperature conversion value).

The load loss is also affected by the temperature of the transformer. At the same time, the leakage flux caused by the load current will cause eddy current loss in the winding and generate stray loss in the metal part outside the winding.

Total loss of dry transformer ΔP=P0+PC

Loss ratio of oil-immersed transformer = PC / P0

The efficiency of the rectification to the transformer = PZ / (PZ + ΔP), expressed as a percentage; where PZ is the secondary side output power of the transformer. First, the calculation of the variable power loss: the loss of power of the transformer is composed of two parts: iron loss and copper loss. The iron loss is related to the running time, and the copper loss is related to the load. Therefore, the lost power should be calculated separately.

1. Calculation of iron loss: The iron loss of different models and capacities, the calculation formula is:

Iron loss (kWh) = no-load loss (kW) × power supply time (hours)

The no-load loss (iron loss) of the distribution transformer is checked by the attached table. The power supply time is the actual running time of the transformer, which is determined according to the following principles:

(1) For users who are continuously powered, calculate by 720 hours for the whole month.

(2) Due to the power grid, intermittent power supply or power-limiting pull, according to the actual power supply hours of the substation to the user, can not be based on difficult calculations, still calculated according to the whole month, after the transformer power failure, self-falling fuse tube power supply station The time should be deducted when calculating the iron loss.

(3) The user with the integrated clock on the low-voltage side of the transformer is calculated according to the accumulated power supply time of the accumulated clock.

2. Calculation of copper loss: When the load rate is 40% or less, it is calculated according to 2% of the total electricity consumption (measured by the electric energy meter). The calculation formula: copper loss (kWh) = monthly electricity Quantity (kWh) × 2%

Because the copper loss is related to the load current (electricity), when the monthly average load ratio of the distribution is more than 40%, the copper loss should be calculated at 3% of the monthly electricity consumption. The monthly electricity consumption at a load rate of 40% is checked by the attached table. The calculation formula of the load rate is: load rate = copying power / S. T. Cos¢

Where: S – rated capacity of the transformer (kVA); T – calendar time of the whole month, take 720 hours;

COS¢——power factor, take 0.80.

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