SWITCHING EQUIPMENT 591 



voltage of 1.5 per cell above mentioned. Oil switch batteries are 

 frequently, therefore, designed to work at five times the one-hour 

 rate when the maximum possible load is to be carried with the 

 motor generator set shut down. In order to determine the 

 maximum possible load, it is usual to figure that not more than 

 two remote-control switches will be closed at one time, and not 

 more than one-half of the total number of automatic switches 

 will be tripped simultaneously. When more than twenty oil 

 switches are installed, it is considered safe to figure on not more 

 than one-third of the total number of automatic switches being 

 tripped at the same time. The duration of any single switching 

 operation is but a fraction of a minute, and a battery subjected 

 to intermittent discharges at high rates recuperates rapidly during 

 the intervals of rest, so that a battery figured, as above, will easily 

 handle as many successive operations as are liable to be required. 

 The current required for the operation of oil circuit breakers, etc., 

 varies with the size and make, and should be obtained from the 

 respective manufacturers. 



In some cases an emergency station lighting circuit may be 

 arranged for connection to the oil switch battery in case of com- 

 plete interruption of other sources of light. To provide for this, 

 a battery of greater ampere-hour capacity may be required than 

 that determined by the oil switch service alone. 



In order to permit giving the battery a charge to maximum 

 voltage by raising the voltage of the generator without subjecting 

 the signal lamps and remote-control apparatus to this high voltage 

 a tap is taken from the battery to the switchboard by means of 

 which a group of 10 cells may be cut out. At the beginning of 

 charge the entire 60 cells are connected to the dynamo, whose 

 voltage is raised sufficiently to deliver the charging current, 

 while 50 cells are connected across the control circuit. The cur- 

 rent required for the signal lamps under these conditions passes 

 through the end cell group in addition to the charging current of 

 the main battery, and the charging of the end cells is, therefore, 

 completed before that of the main battery. The end cell group 

 is then cut out and the charging of the remaining 50 cells is com- 

 pleted. The maximum voltage of these 50 cells at the end of 

 charge will be nearly 140 volts. The signal lamps are designed 

 to stand this voltage for a short time, and the standard remote 

 control apparatus will operate satisfactorily at this voltage. 



