Page 235 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Predetermination of efficiency
• Swinburne’s Test

• No-load Test
• Losses Method
• Only for machine with constant flux
• shunt and compound
No load test
Run machine as a motor on no-load at

rated voltage and rated speed
Note down I and I sh
0
I = I - I sh
a0
0

Measurement of armature resistance
VI method
Calculate the ‘hot’ resistance, 1.2 R

Supply voltage = V
No load current = I o
No load input = VI watt
0
Power input to armature = V (I −I ) ;
sh
0
Power input to shunt = V I sh
No-load power input to armature supplies the following:
(i) Iron losses in core (ii) friction loss (iii) Windage loss and
(iv) armature Cu loss, (I - I ) Ra or Ia0 Ra
2
2
0
sh
FINDING CONSTANT LOSSES(WC)
222

CITS : Power - Electrician & Wireman - Lesson 30-37