06-03-2013, 11:06 AM
Regulation Methods of Alternators
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INTRODUCTION
When an alternator is subjected to a varying load, the voltage at the armature terminals varies to certain extent, the amount of this variation determines the regulation of the machine.Phasor diagram of an alternator at lagging power factor is as follows.
STEPS:
1. By suitable tests plot OCC and SCC
2. From the OCC find the field current If1 to produce rated voltage, V.
3. From SCC find the magnitude of field current If2 to produce the required
armature current.
4. Draw If2 at angle (90+Φ) from If1, where Φ is the phase angle of current from
voltage. If current is leading, take the angle of If2 as (90-Φ).
5. Find the resultant field current, If and mark its magnitude on the field current
axis.
6. From OCC. find the voltage corresponding to If, which will be E0.
3) ZPF method (Potier method)
Conduct tests to find I) OCC (upto 125% of rated voltage) II) SCC (for rated current) III) ZPF (for rated current and rated voltage) IV) Armature Resistance (if required)
ASA method
Conduct tests to find I) OCC (upto 125% of rated voltage) II) SCC (for rated current) III)ZPF (for rated current and rated voltage) IV) Armature Resistance (if required)
Steps:
1. Follow steps 1 to 7 as in ZPF method.
2. Find If1 corresponding to terminal voltage V using air gap line (OF1 in figure).
3. Draw If2 with length equal to field current required to circulate rated current
during short circuit condition at an angle (90+Φ) from If1. The resultant of If1 and
If2 gives If (OF2 in figure).
4. Extend OF2 upto F so that F2F accounts for the additional field current accounting for the effect of saturation. F2F is found for voltage E as shown.
5. Project total field current OF to the field current axis and find corresponding
voltage E0 using OCC.