Faculty of Information Engineering
& Technology
Electrical Machine (ELCT708)
Dr. Adel Ahmed Fouad
Winter 2019
Sheet (8)
Synchronous machine
Solution
Problem (1):
A 3-phase, Y connected, round rotor synchronous generator rated at 10kVA, 230V has a Synchronous reactance of 1.2Ω per phase and an armature resistance of 0.5 Ω per phase. Calculate : a) The percentage voltage regulation at full-load with 0.8 lagging power factor. b) The percentage voltage regulation at full-load with 0.8 leading power factor. c) The power factor such that the regulation is zero on full load.
Solution a)
| |
√
̅ ( )
( ) ( )
√
| | |
| |
|
√
√ b)
̅ ( ) ( )
√
| | | |
| |
Good Luck 

c)
̅ ( )
( ) ( )
√
( ) ( )
√
( ) ( )
√
[
√
( )] [ ( )]
| | | |
[
√
( )] [ ( )]
[ ] (
√
) ( ( ))
√
( )
( )√
( )( )
P.F=cos29.67=0.86 lead
Good Luck 

Problem (2):
A 25kVA, 3phase, Y connected 400V Synchronous generator has a synchronous impedance of 0.05+j1.6 Ω per phase. Determine the full-load voltage regulation and the power angle for these cases: a) 0.8 lagging power factor. b) Unity power factor. c) 0.8 leading power factor.
Solution a) | |
( )
√
̅
√
( )
| | | |
| |
√
√ b) | |
( )
√
̅
√
( )
| | |
| |
| c) | |
( )
√
√
√
̅
√
( )
| | | |
| |
√
√
Good Luck 

Problem (3):
A 30kVA, 3-phase, 230V,Y connected synchronous generator has a synchronous reactance of 0.8Ω. The armature resistance is negligible. Calculate the percentage voltage regulation and the power angle for each of the following cases: a) 50% full-load at unity power factor. b) 25% full-load at 0.8 lagging power factor.
Solution a)
| |
( )
√
̅ ( )
( ) ( )
√
| | | |
| |
√ b)
√
̅ ( )
( ) ( )
√
| | |
| |
|
√
√
Good Luck 

Problem (4):
A 3600 rpm, 60 Hz, 13.8 kV synchronous generator has a synchronous reactance of
20Ω. The generator is operating at rated voltage and speed with the per phase excitation voltage E a
=11.5kV and the torque angle δ=15°
Calculate : a) Stator current. b) Power factor. c) Total output power. d) The maximum power that can be converted from mechanical to electrical form without loss of synchronism. e) The value of armature current for the condition stated in (d).
Solution a)
̅
̅̅̅
̅
√ b)
( ) ( ) c)
| || | (
√
) d)
( )(
√
) e) for max power
√ ̅
̅
Good Luck 