AC MACHINE FUNDAMENTALS:AC MACHINE POWER FLOW AND LOSSES

AC MACHINE POWER FLOW AND LOSSES

A power flow diagram is a convenient tool to analyze ac machines. Figure 5.9 illustrates the power flow diagram of an ac generator and an ac motor.

The losses in ac machines are

1. Rotor and stator copper (I2R) losses

2. Core losses

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3. Mechanical losses

4. Stray losses

The stator copper losses in ac machines are the heat losses from the conductors of the sta- tor. They are given by

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The mechanical losses are caused by bearing friction and windage effects while the core losses are caused by hysteresis and eddy currents. These losses are called the no-load rota- tional losses of the machine.

All the input power at no load is used to overcome these losses. Therefore, these losses can be obtained by measuring the power to the stator at no load.

electrical equipment troubleshooting and maintenance-0031Stray load losses are all miscellaneous losses that do not fall into one of these categories. They are taken by convention as 1 percent of the output power of the machine. The overall efficiency of an ac machine is defined as the useful power output to the total input power:

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