The relay shown in Fig. P 7.103 connects the 30 V dc generator to the dc bus as long as the relay current is greater than 0.4 A. If the relay current drops to 0.4 A or less, the spring-loaded relay immediately connects the dc bus to the 30 V standby battery. The resistance of the relay winding is 60 Ω. The inductance of the relay winding is to be determined.
a) Assume the prime motor driving the 30 V dc generator abruptly slows down, causing the generated voltage to drop suddenly to 21 V. Whatvalue of L will assure that the standby battery will be connected to the dc bus in 0.5 seconds?
 b) Using the value of L determined in (a), state how long it will take the relay to operate if the generated voltage suddenly drops to zero.
