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Q1— Section header —
1.1Explain why a DC shunt wound motor needs a starter on constant voltage mains. (3\
1.2A series wound DC motor runs at 900 r/min when taking 30 A at 230 V. The total resistance of the armature and field circuit is 0,8 Calculate the value of the additional resistance required in series with the
1.3Draw the magnetic characteristic curves of the following compound wound generators: Over compounded Under
1.4A DC shunt generator delivers 5 kW at 250 V when driven at 1 500 r/min. The shunt circuit resistance is 250 and the armature c ircuit resistance is 0,4 The iron, friction and windage loss is 250 W. Determine the torque required to drive the generator.
Q2— Section header —
2.1A coil of 30 resistance and 0,07 is connected in parallel with a circuit consisting of a 135 microfarad capacitor in series with
2.1.1The total current (6\
2.1.2The current in each branch (4\
2.2Circuit A consists of a 6,8 ohm resistor and a 170 microfarad capacitor connected in series. Circuit B consists of a resistor and an inductive reactance connected in series. Both circuits A and B are then connected in parallel across
2.2.1The current (4\
2.2.2The impedance (2\
2.2.3The power factor (1\
2.3State any THREE characteristics of a resonant series circuit (3\ [20] 808008520
Q3— Section header —
3.1List THREE types of transformer losses (3\
3.2A single phase transformer has a supply voltage of 230 V. It has an equivalent resistance of 0,3 and an equivalent leakage reactance of 0,75 referred to the primary side. The secondary side is connected to a coil with a resistance of
3.3single phase transformer of 15 kVA, 1 800/180 V has a percentage impedance of 4 + j6 percent.
3.3.1The equivalent resistance and leakage reactance (6\
3.3.2The per unit voltage regulation at a power factor of 0,8 lagging (2\ [20]20
Q4— Section header —
4.1Draw a circuit diagram to show how a single wattmeter can be used to measure the total power drawn by a balanced star connected load. (3\
4.2A three phase induction motor develops 28 kW when running at 86 efficiency and a power factor of 0,86 lagging. Calculate the readings on each wattmeter connected to read the input power. (7\
4.3A load of 2,8 MVA at 33 kV and power factor of 0,86 lagging is supplied by a single phase transmission line that has a resistance of 3,6 and a reactance of 7,5 per conductor.
4.4Calculate the capacitance per phase of a 100 km , three phase line if the conductors have a flat regular spacing of 1 between adjacent conductors with transpositions.
Q5— Section header —
5.1Briefly explain the distribution factor (2\
5.2Explain why slip is necessary for an induction motor to develop torque. (2\
5.3A three phase, four pole star connected alternator delivers line voltage of 380
5.3.1The frequency (2\
5.3.2The number of turns per phase (3\
5.3.3The useful flux per pole (3\
5.4three phase, 50 Hz induction motor has six poles and runs at a speed of 900 r/min when the total to
5.4.1The total power input to the rotor (4\
5.4.2The rotor copper loss in watts (4\ [20] TOTAL: 100 808008520