2 The electric power company is concerned with the loading of its transformers. Since it is responsible for a large number of customers, it must be certain that it can supply the demands of all customers. The power company's transformers will deliver rated kVA to the secondary load. However, if the demand increased to a point where greater than rated current were required, the secondary voltage would have to drop below rated value. Also, the current would increase, and with it the PR losses (due to winding resistance), possibly causing the transformer to overheat. Unreasonable current demand could be caused, for example, by excessively low power factors at the load. The customer, on the other hand, is not greatly concerned with an inefficient power factor, provided that sufficient power reaches the load. To make the customer more aware of power factor considerations, the power company may install a penalty on the customer's bill. A typical penalty-power factor chart is shown in Table 7.3. Power factors below 0.7 are not permitted. A 25 percent penalty will be applied to any billing after two consecutive months in which the customer's power factor has remained below 0.7. Table 7.3 Power factor Penalty 0.850 and higher None 0.8 to 0.849 1% 0.75 to 0.799 2% 0.7 to 0.749 3% Courtesy of Detroit Edison. The wye-wye circult shown in Figure P7.72 is representative of a three-phase motor load. Assume rms values. a. Find the total power supplied to the motor. b. Find the power converted to mechanical energy if the motor is 80 percent efficient. c. Find the power factor. d. Does the company risk facing a power factor penalty on its next bill if all the motors in the factory are similar to this one? 52 j62 preee RO 1202 2n/3 12020 50 120Z-2n/3 j6!