SYNCHRONOUS GENERATORS 323 



A successful parallel operation of several stations on a system 

 is, as a rule, not difficult, inasmuch as the line characteristics, i.e., 

 resistance and reactance, are generally such that they little inter- 

 fere with the synchronizing force of the generators. This force is, 

 as stated, greatest when the machines are over-excited, and the 

 only case where a machine would drop out of step would be on 

 extensive systems where large lagging currents are required for 

 voltage regulation. These currents naturally greatly reduce the 

 synchronizing force in that they weaken the field, but there is 

 generally no danger of a shut-down unless a very heavy load should 

 suddenly come on. 



Many different methods are used for dividing and regulating 

 the load on a large system. In some cases one or more generators 

 in a large station or one or more stations in a large system will do 

 the governing, taking care of the load, the other generators or 

 stations being then operated with constant gate opening and con- 

 stant load. Plants having large pondage are usually selected to 

 take care of the load fluctuations while those with little or no 

 storage should preferably be operated so as to take the full flow of 

 the stream. In many systems such stations are equipped with 

 induction generators which require very little attention, possibly 

 only once a day. They may be started up in the morning or kept 

 running all the time, and as they are dependent on the other 

 synchronous apparatus on the system for their excitation, their 

 speed and frequency is determined by them. As there are no 

 governing devices, means must be provided for disconnecting the 

 units from the system as well as shutting the gates, should the load 

 be dropped for some reason or other, thus preventing overspeed. 



When steam-turbine stations are used as auxiliaries these carry, 

 as a rule, little load ordinarily, but on the contrary, often a full 

 load of wattless current, and besides they are always ready in 

 case of emergency to pick up the load. 



In this connection it may be well to point out a fallacy that 

 often exists with large customers, in that they specify that their 

 lines shall be independent of the rest of the system and that their 

 load be supplied by separate generators. Such requirements are, 

 of course, based on an assumption that a better service can be 

 obtained in this way, as his lines or generators are not affected by 

 the fluctuation on the rest of the system. This is, however, in 

 most instances not the case, as changes in his load will affect the 



