1) a) A 350KW, 220V, 4 pole, lap wound dc generator has the 600 armature conductors. If brushes are given a lead of 8 electrical degrees, find the number of demagnetizing and cross magnetizing ampere turns per pole. Shunt field current may be neglected.
b) Explain what is commutation? Describe the various methods for improving the commutation.
2) A short shunt compound generator supplies the current of 150A at the voltage of 230V.The resistance of shunt field is 30?, and the series field is 0.01 ?, armature is 0.02 ?, the total brush drop is 2V and the iron and friction loss is amount to 1.3KW. Determine
a) Generated E.M.F
b) Copper loss
c) Output power of the prime mover driving the generator
d) Generator efficiency.
3) The Hopkinson’s test on two shunt machines gave the following results.
Line voltage = 230V, line current excluding the field current = 25A; motor armature current = 250A; field current = 2A, Determine the efficiency of each machine under this load condition. Provided the armature resistance of each machine is 0.2 Ω.
4) a) Describe the Ward Leonard type of speed control with the help of suitable diagram.
b) A dc shunt generator delivers a 25KW at 220V while running at 1200 rpm. Rf = 120 Ω, Ra = 0.2 Ω. Find the speed of the machine running as a dc shunt motor taking 25KW at 220V. Enable 1V per brush contact drop.
5) a) Describe the approximate equivalent circuit of the transformer
b) Draw the phasor diagram for the transformer loaded with:
i) Inductive load
ii) Resistive load.
6) Determine the all day efficiency of the 1000KVA transformer whose copper loss and iron losses at full load are 3.5KW and 5.2KW respectively. During the day of 24hrs it is loaded as follows.
Number of hrs Load in KW Power factor
4 1000 0.9
8 700 0.7
8 400 0.5
4 --- ---
7) Deduce the equation for saving of the Cu for an autotransformer. Specify its different limitations and applications.
8) a) Describe the 3 phase to 2 phase and the 3 phase to 6 phase transformer conversion.
b) Describe the Scott connection in a transformer in detail.
9) Explain what is a synchro? Describe the operation of a synchro as an error detector in detail.
10) Deduce the torque equation of the PMBL DC motor describing all the parameters included in it.