SCR j is fired and forces self-commutation with- 

 in the correct time limit. 



The various safety checks and circuits 

 designed into the FFEM system which will 

 automatically shut the system down are: 1) 

 high or low current overload, 2) reverse 

 discharge of capacitor banks, and 3) loss of high 

 or low voltage. In addition, all systems are 

 electrically isolated from the primary electrical 

 source. 



Power Supply 



The FFEM power supply consists of the 

 following: 1) a vjiriable high voltage supply 

 capable of through 300 v DC at 25 amp DC 

 and 2) a fixed low voltage power supply 

 producing 28 v DC at 7 amp DC (Figure 8). 

 These power supplies share a common ground; 

 thus a three-conductor number 10-wire power 

 cable is required to interconnect the FFEM 

 power supply with the FFEM pulser. 



High voltage.— The high voltage supply is 

 basically a slave full-wave rectified L-C 

 (L-inductor, C-capacitor) filter power supply. 

 The input is 230 v AC single phase power 

 applied at the main input. This output is 

 connected to a 0-300 v AC variac. The high 

 voltage power supply output is floating relative 

 to shipboard ground. 



Low voltage.— The low voltage power 

 supply consists of a 28 v DC 7 amp, regulated 

 power supply and a step-down transformer. An 

 interlock exists between the high voltage and 

 low voltage supplies. This interlock prevents the 

 low voltage from being applied to the pulser 

 SCR before the high voltage is properly adjusted 

 to approximately 25 v. Also, the interlock 

 removes the low voltage if there is a failure in 

 the high voltage supply. 



The FFEM power supply uses a 0-300 v panel 

 volt meter and a double set point 0-30 amp 

 meter for monitoring output parameters. The 



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Switching C ircuit 



Commufotion 

 Circuit 



Figure 7. — High power switching and commutation circuit. 



