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Conversion of line resistance and phase resistance

If the phase resistance of the winding is R phase and the line resistance is R line, the calculation of the line resistance can be calculated according to the series-parallel principle of the resistor.


●Line resistance by phase resistance

When the motor winding is star-connected, the schematic is shown in Figure 1, and the R line = 2R phase.

When the motor winding is at the corner, the schematic is shown in Figure 2, and the R line = 2R phase / 3.


●The phase resistance is converted by line resistance

The formula for calculating the line resistance from the phase resistance can be mathematically converted under different connections.

When the motor winding is star-connected, the schematic is shown in Figure 1, R phase = 0.5R line

When the motor winding is angled, the schematic is shown in Figure 2, and the R phase = 1.5R line.


● Conversion of resistance values at different temperatures

Generally, the DC resistance of a metal conductor has a fixed relationship with its temperature. This relationship is expressed as:

R1=R2×(K+t1)/(K+t2).........(1)

Where: R1 - DC resistance (Ω) at a temperature of t1 ° C;

R2——DC resistance (Ω) at a temperature of t2°C;

K - constant (reciprocal of the temperature coefficient of the conductor resistance at 0 ° C), for copper windings, K = 235, for aluminum windings, K = 225.


● Resistance standard under different test conditions

In the type test report, the specific resistance value is given according to the different insulation grade of the motor, such as the resistance of the B-class insulated motor at 75 °C, while the F-class insulated motor is the resistance at 95 °C, and the H-class insulated motor is Resistance at 105 °C. In the inspection test evaluation standard, it is customary to give the resistance at 20 ° C. When the temperature deviates, it can be converted according to the formula (1).


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