Exercise 01
A single-phase four-pole alternator has 100 conductors. The flux per pole is 25 mWb and the frequency is 50 Hz. A voltage with an R.M.S value of 267 V is measured across the armature.
1. Find the number of pole pairs.
2. Calculate the rotor speed of the alternator.
3. Calculate the Kapp coefficient of the alternator winding.
Exercise 02
The rotor of a three-phase alternator operates at 50 Hz and rotates at a speed of 750 rpm. Its stator has 120 equidistant distributed slots, each slot contains 4 conductors. All slots are used.
The three windings are star-connected and their resistance is neglected. The Kapp coefficient is 2.14. We give the flux per pole as a function of the excitation:
The alternator provides a purely inductive current of 150 A under a line voltage of 962 V (between lines) with an excitation of 15.4 A.
1. Calculate the number of pole pairs of the alternator.
2. Calculate the no-load voltage for Ie = 15.4 A.
3. Calculate the synchronous reactance per phase for this excitation.
Exercise 03
A three-phase alternator has a star-connected stator. Its rotor rotates at a speed of 1500 rpm. The resistance of one phase is 0.8 Ω. The following no-load characteristic was noted:
A short circuit test revealed Isc = 48 A for an excitation current Ie = 0.5 A.
1. Calculate the synchronous reactance X or Lω.
2. The alternator delivers a line current of 30 A online to an inductive receiver with a power factor of 0.8 at a line voltage of 400 V. Calculate the intensity of the excitation current.
3. Find graphically the value of the phase voltage at the alternator output in the following operating mode: I = 18A, a 0.6 capacitive power factor, Ie = 1 A.