66 
ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
This method, which enables the designer to test the generator 
in the workshop, gives him a clear idea of the perform- 
ance of the alternator under different working conditions, 
and discloses whether the various items have been properly 
valued. | . 
To understand this important subject it is necessary to study 
the no-load or open cireuit and the short circuit character- 
isti¢s. 
113. Open Circuit Characteristic.—The open cireuit char- 
acteristic, Fig. 34, gives the E. M. F. of the generator in 
terms of, the excitation current or of the equivalent field 
ampere turns, under the condition of a perfectly constant 
speed. 
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TERMINAL PRESSURE IN VOLIB. 
Bae 6 Se ae 
SHORT CIRCUIT CURRENT LV AMPS. 
oO & 0 € 2 M6 8 FS OO 4 
EXCIZATTON CURRENT LV AMEE. 
Fie. 34.—CHARACTERISTICS OF A 235 KVA., 50-CycLE, STAR 
CONNECTED 3-PHASE ALTERNATOR. 
The experimental determination of this curve is a very easy 
one, as it is only necessary to let the alternator run at its 
normal speed excited, and to measure the terminal pres- 
sure of the armature on open circuit, with various values 
of excitation. | 
This test gives the E. M.F. of the armature for the corre- 
