Exercise 01
We consider a three-phase alternator of 79 kVA, 400 V, 50 Hz, 12 poles. At the speed 500 rpm, the “no load” and “short circuit” characteristics are given by the relations:
E = 18.3 . Ie and Icc = 11 . Ie
The resistance measured between two phase terminals (phase-to-phase resistance) is 0.5 Ω with star coupling.
1. From the characteristics obtained from previous tests, deduce the values of the elements of the synchronous reactance model.Exercise 02
A three-phase alternator whose armature windings are star-coupled, produces an RMS voltage of 2.8 kV and a frequency of 50 Hz at no load operating mode.
The stator winding has 3 slots per pole and per phase and 12 conductors per slot.
The useful flux under a pole is 54 mWb. The rotation speed of the rotor is 500 rpm.
1. Calculate the number of pole pairs of the alternator.
2. Calculate the number of active conductors per phase.
3. Determine the Kapp coefficient of the machine.
4. At rated power, the alternator supplies a current of 700 A to a load which absorbs power P = 2.4 MW with a power factor cosφ = 0.9.
The efficiency of the alternator is 88%.
4.1 Calculate the line voltage U between two terminals of the armature under load.
4.2 Calculate all the alternator losses.