The average value of the sine wave over one complete cycle is actually zero. Hence, for a sine wave, the average value is defined over half the period. The average value expressed in terms of peak value is given by Average value = 0.637 × peak value
Given Data Voltage Va = 200 v Armature Resistance Ra = 0.5Ω Armature Current Ia = 20 A Induced EMF = Ea = ? The Induced EMF of a DC machine working as a Motor is Ea = Va − IaRa Ea = 200 − 20 × 0.5 Ea = 190 V
Isolator or disconnecting Switch: An isolator is a switch that is designed to open a circuit under no-load condition. Its main purpose is to isolate one portion of the circuit from the other and is not allowed to be opened while current is flowing in the line. Such switches are used on both sides of a circuit breaker so that its repair works or replacement could be done. Note that an isolator is never opened until the circuit breaker in the circuit is opened and it is closed before the circuit breaker is closed. If an isolator is switched OFF when a high current is flowing through the circuit, a heavy spark will be produced. This heavy spark may break the supporting insulator of the isolator which may cause a fatal accident to the operator.
EXAMIANS