280 
Transactions of the Royal Society of South Africa. 
We thus see that the speed of the regulator depends upon the size and 
design of the generator. 
With the data before us it is easy to find out whether it is feasible 
to employ a sluggish regulator or not. We register the station load by 
means of a recording ammeter and notice the frequency of the load rushes. 
If they occur more often than expressed by ^, a high speed regulator 
becomes essential for satisfactory working. 
Fast Eegulators. — Fig. 5 represents the no-load characteristic of a 
generator. The normal voltage of the machine is marked by line cel. The 
resistance of a field regulator, when switched in, reduces the excitation 
to ef and the voltage to Oe. When the regulator is short-circuited, the 
excitation is and the voltage Oa. The automatic regulator alternately 
short-circuits and inserts the resistance. 
Suppose the generator is put into operation and that the excitation is e^, 
being about 30 to 50 per cent, of the normal excitation, the resistance being 
inserted in the field winding. The rheostat is next short-circuited and the 
voltage rises rapidly along the no-load curve Ob until it reaches point cV. 
This is the upper limit of the voltage. Assuming that the machine is 
0 
and 
Fig, 5. — Principle of action of a fast reg-ulator. 
