SKEE 2413 Q1 (a) Define ‘permeability’ [2 marks] (b) A magnetic circuit with a single air gap is shown in the Figure Q(1)a . The core dimensions are: Cross-sectional area A c = 1.8 × 10 -3 m 2 . Mean core length l c = 0.6 m. Gap length g = 2.3 x 10 -3 m. N = 83 turns. Figure Q1(a) Assume that the core is of infinite permeability ( µ r ! ∞ ) and neglect the effects of fringing fields at the air gap and leakage flux. Calculate: (i) The reluctance of the core and that of the gap. [3 marks] (ii) The total flux for a current of i = 1.5 A. [3 marks] (c) The parameters of the equivalent of 110 kVA, 2200 V/110 V transformer, are R 1 =0.22 Ω , R 2 =0.5 m Ω , X 1 =2 Ω , X 2 =5 m Ω , R c =5494.5 Ω , X m =1099 Ω referred to primary. The transformer is operating at full load with unity power factor. (i) Draw the approximate equivalent of the transformer referred to the primary. [4 marks] (ii) Voltage regulation. [8 marks] (iii) Efficiency
SKEE 2413 [5 marks] Q2 (a) Referring to the speed equation of a dc motor, state the possible means by which the motor may be varied.
- Fall '20
- Electric power transmission, Electric power, SKEE 2413