According to P = E*V*sin(delta)/X formula active power output is proportional to the sine of the load angle delta. then why normally the load angle of the alternator is kept low (20-40 degree) in generating station when we could have got more power from the same alternator?

 

If the angle goes over 90 degrees you have a problem - and pole slipping will result. Since there is always a chance of a system disturbance that could temporarily increase the load on the machine, and hence the load angle, there must be some safety margin. At 30 degrees, the supplied load is half the maximum before slippage occurs, and at 45 degrees you have about 70 % of maximum.

 

Rock… The formula refers to Steady-State operating conditions, i.e., no changes. At 90º the system will not survive System Transients such as electrical-faults or even operational changes.

For example, if there is a load change, the prime-mover will respond but because of system-inertia the change is delayed, resulting in a deficit of the area under the Load-Angle vs Power diagram because of the shape of the Sine-curve! At 90º it “flattens” somewhat thereby precluding recovery.

A detailed discussion would probably irk too many posters! However, I believe that anyone who has conducted a Transient-Stability-Study understands the reason for the 20-40º range!

I suggest you search the Control.Com Archives for similar topics!

Regards, Phil Corso ([email protected])

 

Because, the load depends on a output current (stator current). this output current depends on a angle between generator voltage and grid voltage. When you increase this load angle, power will gradually increase. when you have more load angle, there is a probability of losing the phase sequence between grid and generator voltage. If we lost the phase sequence, machine will be disconnected from the grid i.e.de-synchronised. are you satisfied with this?