QUESTION I In a balanced 3-phase 400 V circuit, the line current is 115.5 A. When power is measured by two watt meter method, one meter reads 40 kW and the other zero. (a) What is the power factor of the load? (4) (b) If the power factor were unity and the line current the same, what would be the reading of each watt meter? QUESTION 2 A 3-phase, three wire system, with 400 V between the line wires, supplies a balanced delta connected load taking a total power of 30 kW at 0.8 power factor lagging. (a) (b) Calculate for each branch of the load i. the resistance ii. the reactance (6) If the power factor of the system is to be raised to 0.95 lagging by means of three delta- connected capacitors, calculate the capacitance of each branch assuming the supply frequency to be 50 Hz (10) QUESTION 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, VAR input and the reactance and resistance of each coil. QUESTION 4 (12) 3-phase star connected inductive load when supplied from 400 V. 50 Hz source takes a line current of 10 A at 66.86° with respect to its line voltage. Calculate (a) Phase impedance, phase resistance and phase reactance (b) Power factor and active power consumed (5) (3)
QUESTION I In a balanced 3-phase 400 V circuit, the line current is 115.5 A. When power is measured by two watt meter method, one meter reads 40 kW and the other zero. (a) What is the power factor of the load? (4) (b) If the power factor were unity and the line current the same, what would be the reading of each watt meter? QUESTION 2 A 3-phase, three wire system, with 400 V between the line wires, supplies a balanced delta connected load taking a total power of 30 kW at 0.8 power factor lagging. (a) (b) Calculate for each branch of the load i. the resistance ii. the reactance (6) If the power factor of the system is to be raised to 0.95 lagging by means of three delta- connected capacitors, calculate the capacitance of each branch assuming the supply frequency to be 50 Hz (10) QUESTION 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, VAR input and the reactance and resistance of each coil. QUESTION 4 (12) 3-phase star connected inductive load when supplied from 400 V. 50 Hz source takes a line current of 10 A at 66.86° with respect to its line voltage. Calculate (a) Phase impedance, phase resistance and phase reactance (b) Power factor and active power consumed (5) (3)
Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
Chapter1: Introduction
Section: Chapter Questions
Problem 1P: Visit your local library (at school or home) and describe the extent to which it provides literature...
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Transcribed Image Text:QUESTION I
In a balanced 3-phase 400 V circuit, the line current is 115.5 A. When power is measured by
two watt meter method, one meter reads 40 kW and the other zero.
(a) What is the power factor of the load?
(4)
(b) If the power factor were unity and the line current the same, what would be the reading of
each watt meter?
QUESTION 2
A 3-phase, three wire system, with 400 V between the line wires, supplies a balanced delta
connected load taking a total power of 30 kW at 0.8 power factor lagging.
(a)
(b)
Calculate for each branch of the load
i. the resistance
ii. the reactance
(6)
If the power factor of the system is to be raised to 0.95 lagging by means of three delta-
connected capacitors, calculate the capacitance of each branch assuming the supply
frequency to be 50 Hz
(10)
QUESTION 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, VAR input and the reactance and resistance of each coil.
QUESTION 4
(12)
3-phase star connected inductive load when supplied from 400 V. 50 Hz source takes a line
current of 10 A at 66.86° with respect to its line voltage. Calculate
(a)
Phase impedance, phase resistance and phase reactance
(b)
Power factor and active power consumed
(5)
(3)
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