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Power generation Riddle No.12 - Generator Voltage Changing
Grid voltage remains high in 132 Kv Grid, ranging from 138 KV to 145 KV, forcing the generator terminal voltage to its optimum 12 KV, Var loading in the feeders often showing leading, and the var loading of generator is maintained still lagging. why this is happening and what to do to bring the terminal voltage down?
Author : Jayanta - From: India
Sat, May 5th, 2012 - 09:43
whats your AVR type and model? 
Author : f.marandi - From: Iran
Tue, May 22nd, 2012 - 17:59
In connection to infinite grid, we cannot change the amount of voltage which is same generator output voltage. If the generator’s speed does not change and the governor set points have not been changed, the power supplied by the generator must remain constant. Also if the power supplied is constant as the field current is changed, then the distances proportional to the power in below phasor diagram (IA cos θ and EA sin δ) cannot change.  When the field current is increased, the flux φ increases, and therefore EA (=K φ↑ ω) increases. If EA increases, but EA sin δ must remain constant, then the phasor EA must “slide” along the line of constant power, as shown below.
Since Vφis constant, the angle of jXSIA changes as shown, and therefore the angle and magnitude of IA change. Notice that as a result the distance proportional to Q (IAsinθ) increases.
As you can see in below diagram, the angle of generator load current can be changed from leading to lagging situation with reference to generator terminal voltage (Vφ) by field current changing. While the angle of load current always remains lagging referring to generator internal EMF (EA).

Author : Hamid - From: Iran
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