5. A 3-phase, delta-connected load, each phase of which has R= 10 Q and X= 8Q is supplied from a star-connected secondary winding of a 3-phase transformer each phase of which gives 230 V. Calculate (a) the current in each phase of the load and in the secondary windings of the transformer (b) the total power taken by the load (c the power factor of the load Ta 31.1 A: 54 A (b) 29 kW (c) 0.781

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Answer number #5

1. Each phase of a delta-connected load comprises a resistor of 50 a and capacitor of 50 uF in
series. Calculate (a) the line and phase currents (b) the total power and (c) the kilovoltamperes when the
load is connected to a 440-V, 3-phase, 50-Hz supply.
2. Three similar-coils, A, B and C are available. Each coil has 9Q resistance and 12 Q reactance.
They are connected in delta to a 3-phase, 440-V, 50-Hz supply. Calculate for this load:
(a) the line cuIrent
(c) the total kilovolt-amperes
If the coils are reconnected in star, calculate for the new load the quantities named at (a), (b); (c) and
(d) above.
3. Three similar choke coils are connected in star to a 3-phase supply. If the line currents are 15 A,
the total power consumed is 11 kW and the volt-ampere input is 15 kVA, find the line and phase voltages,
the VAR input and the reactance and resistance of each coil.
[(a) 9.46 A; 5.46 A (b) 4480 W () 7.24 kVA]
(b) the power factor
(d) the total kilowatts
[50.7 A; 0.6; 38.6 kVA; 23.16 kWV; 16.9 A; 0.6; 12.867 kVA; 7.72 kW]
[577.3 V; 333.3 V; 10.2 EVAR: 15.1 16.3 O
4. The load in each branch of a delta-connected balanced 3-0 circuit consists of an inductance of
0.0318 H in series with a resistance of 10 2 The line voltage is 400 V at 50 Hz Calculate () the line
current and (if) the total power in the circuit.
5. A 3-phase, delta-connected load, each phase of which has R= 10 2 and X= 82 is supplied from
a star-connected secondary winding of a 3-phase transformer each phase of which gives 230 V. Calculate
(a) the current in each phase of the load and in the secondary windings of the transformer
(b) the total power taken by the load
© the power factor of the load.
6. A 3-phase load consists of three similar inductive coils, each of resistance 50 2 and inductance
0.3 H The supply is 415 V, 50 Hz, Calculate (a) the line current (b) the power factor and (c) the total
power when the load is (1) star-comnected and (i) delta-connected
[O 19 A (m) 24 kW] (London Univ.)
[()31.1 A: 54 A (b) 29 kW (c) 0.78]
[O 2.25 A, 0.47 lag, 762 W () 6.75 A, 0.47 lag, 2280 W] (London Univ.)
Transcribed Image Text:1. Each phase of a delta-connected load comprises a resistor of 50 a and capacitor of 50 uF in series. Calculate (a) the line and phase currents (b) the total power and (c) the kilovoltamperes when the load is connected to a 440-V, 3-phase, 50-Hz supply. 2. Three similar-coils, A, B and C are available. Each coil has 9Q resistance and 12 Q reactance. They are connected in delta to a 3-phase, 440-V, 50-Hz supply. Calculate for this load: (a) the line cuIrent (c) the total kilovolt-amperes If the coils are reconnected in star, calculate for the new load the quantities named at (a), (b); (c) and (d) above. 3. Three similar choke coils are connected in star to a 3-phase supply. If the line currents are 15 A, the total power consumed is 11 kW and the volt-ampere input is 15 kVA, find the line and phase voltages, the VAR input and the reactance and resistance of each coil. [(a) 9.46 A; 5.46 A (b) 4480 W () 7.24 kVA] (b) the power factor (d) the total kilowatts [50.7 A; 0.6; 38.6 kVA; 23.16 kWV; 16.9 A; 0.6; 12.867 kVA; 7.72 kW] [577.3 V; 333.3 V; 10.2 EVAR: 15.1 16.3 O 4. The load in each branch of a delta-connected balanced 3-0 circuit consists of an inductance of 0.0318 H in series with a resistance of 10 2 The line voltage is 400 V at 50 Hz Calculate () the line current and (if) the total power in the circuit. 5. A 3-phase, delta-connected load, each phase of which has R= 10 2 and X= 82 is supplied from a star-connected secondary winding of a 3-phase transformer each phase of which gives 230 V. Calculate (a) the current in each phase of the load and in the secondary windings of the transformer (b) the total power taken by the load © the power factor of the load. 6. A 3-phase load consists of three similar inductive coils, each of resistance 50 2 and inductance 0.3 H The supply is 415 V, 50 Hz, Calculate (a) the line current (b) the power factor and (c) the total power when the load is (1) star-comnected and (i) delta-connected [O 19 A (m) 24 kW] (London Univ.) [()31.1 A: 54 A (b) 29 kW (c) 0.78] [O 2.25 A, 0.47 lag, 762 W () 6.75 A, 0.47 lag, 2280 W] (London Univ.)
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