Procedure for potier method
Procedural Steps for Potier Method:
1. Suppose we are given V-the terminal voltage/phase.
2. We will be given or else we can calculate armature leakage reactance XL and hence can calculate IXL.
3. Adding IXL (and IRa if given) vectorially to V, we get voltage E.
4. We will next find from N-L curve, field excitation for voltage E. Let it be if1.
5. Further, field current if2 necessary for balancing armature reaction is found from Potier triangle.
6. Combine if1 and if2 vectorially (as in A.T. method) to get if.
7. Read from N-L curve, the e.m.f. corresponding to if. This gives us E0. Hence, regulation can be found.
An 11-kV, 1000-kVA, 3-phase, Y-connected alternator has a resistance of 2 Ω per phase. The open-circuit and full-load zero power factor characteristics are given below. Find the voltage regulation of the alternator for full load current at 0.8 p.f. lagging by Potier method.
Fig: 1 Fig: 2
The O.C.C. and full-load zero p.f. curve for phase voltage are drawn in Fig 1. The corresponding phase voltages are:
BD = leakage reactance drop IXL = 1000 V − by measurement, AD = 30 A — field current required to overcome demagnetising effect of armature reaction on full-load. From fig 2 we know that,
As seen from O.C.C., field current required for 7,080 V is 108 A. Vector OD (Fig 2) represents 108 A and is drawn ⊥ to OC. DF represents 30 A and is drawn parallel to OI or at (90° 36° 52′) = 126° 52′ with OD. Total field current is OF.