Three Phase Circuits | Electric Circuits | GATE EE Previous Year Questions

Electric Circuits

Three Phase Circuits Transient Response Graph Theory Two Port Networks Sinusoidal Steady State Analysis Network Elements Network Theorems

Three Phase Circuits

Practice Questions

Marks 1

In the circuit shown below, a three-phase star-connected unbalanced load is connected to a balanced three-phase supply of 100$$\sqrt 3 $$ V with phase sequence ABC. The star connected load has Z_A = 10 $$\Omega$$ and Z_B = 20$$\angle$$60$$^\circ$$ $$\Omega$$. The value of Z_C in $$\Omega$$, for which the voltage difference across the nodes n and n' is zero, is

GATE EE 2022

The line A to neutral voltage is $$10\angle15^\circ\;V$$ for a balanced three phase star-connected load with phase sequence ABC. The voltage of line B with respect to line C is given by

GATE EE 2014 Set 3

Marks 2

The transformer connection given in the figure is part of a balanced 3-phase circuit where the phase sequence is "abc". The primary to secondary turns ratio is $2: 1$. If ( $I_a+I_b+I_c=0$ ), then the relationship between $l_A$ and $l_{\text {ad }}$ will be

GATE EE 2025

In an experiment to measure the active power drawn by a single-phase RL Load connected to an AC source through a $2 \Omega$ resistor, three voltmeters are connected as shown in the figure below. The voltmeter readings are as follows : $\mathrm{V}_{\text {source }}=200 \mathrm{~V}$, $V_R=9 \mathrm{~V}, V_{\text {Load }}=199 \mathrm{~V}$. Assuming perfect resistors and ideal voltmeters, the Load-active power measured in this experiment, in $W$, is ___________ .

GATE EE 2025

Using shunt capacitors, the power factor of a 3-phase, 4 kV induction motor (drawing 390 kVA at 0.77 pf lag) is to be improved to 0.85 pf lag. The line current of the capacitor bank, in $A$, is _________ (Round off to one decimal places)

GATE EE 2025

For a two-phase network, the phase voltages $V_p$ and $V_q$ are to be expressed in terms of sequence voltages $V_\alpha$ and $V_\beta$ as $\begin{bmatrix} V_p \\ V_q \end{bmatrix} = S \begin{bmatrix} V_\alpha \\ V_\beta \end{bmatrix}$. The possible option(s) for matrix $S$ is/are

GATE EE 2024

In the circuit shown, $Z_1 = 50\angle -90^{\circ} \Omega$ and $Z_2 = 200\angle -30^{\circ} \Omega$. It is supplied by a three phase 400 V source with the phase sequence being R-Y-B. Assume the watt meters $W_1$ and $W_2$ to be ideal. The magnitude of the difference between the readings of $W_1$ and $W_2$ in watts is _________________ (rounded off to 2 decimal places).

GATE EE 2024

A 3-phase, star-connected, balanced load is supplied from a 3-phase, 400 V (rms), balanced voltage source with phase sequence R-Y-B, as shown in the figure. If the wattmeter reading is $$-$$400 W and the line current is $$I_R=2$$ A (rms), then the power factor of the load per phase is

GATE EE 2023

A balanced delta connected load consisting of the series connection of one resistor (R = 15 $$\Omega$$) and a capacitor (C = 212.21 $$\mu$$F) in each phase is connected to three-phase, 50 Hz, 415 V supply terminals through a line having an inductance of L = 31.83 mH per phase, as shown in the figure. Considering the change in the supply terminal voltage with loading to be negligible, the magnitude of the voltage across the terminals $$V_{AB}$$ in Volts is ___________ (Round off to the nearest integer).

GATE EE 2023

For the balanced Y-Y connected 3-Phase circuit shown in the figure below, the line-line voltage is 208 V rms and the total power absorbed by the load is 432 W at a power factor of 0.6 leading.

The approximate value of the impedance Z is

GATE EE 2017 Set 2

A three phase balanced star connected voltage source with frequency $$\omega \,\,rad/s$$ is connected to a star connected balanced load which is purely inductive. The instantaneous line currents and phase to neutral voltages are denoted by $$\left( {{i_a},{i_b},{i_c}} \right)$$ and $$\left( {{V_{an}},\,\,{V_{bn}},\,\,{V_{cn}}} \right)$$ respectively and their $$rms$$ values are denoted by $$V$$ and $$1.$$ If $$$R = \left[ {{V_{an}}\,\,{V_{bn}}\,\,{V_{cn}}} \right]\left[ {\matrix{ 0 & {{1 \over {\sqrt 3 }}} & { - {1 \over {\sqrt 3 }}} \cr { - {1 \over {\sqrt 3 }}} & 0 & {{1 \over {\sqrt 3 }}} \cr {{1 \over {\sqrt 3 }}} & { - {1 \over {\sqrt 3 }}} & 0 \cr } } \right]\left[ {\matrix{ {{i_a}} \cr {{i_b}} \cr {{i_c}} \cr } } \right],$$$
then the magnitude of $$R$$ is

GATE EE 2007

A $$400V$$, $$50$$ $$Hz,$$ three phase balanced source supplies power to a star connected load whose rating is $$12\,\,\angle 3\,\,kVA,$$ $$0.8$$ $$pf$$ (lag). The rating $$($$in $$kVAR)$$ of the delta connected (capacitive) reactive power bank necessary to bring the $$pf$$ to unity is

GATE EE 2006

A balanced delta connected load of $$\left( {8 + j6} \right)$$ $$\Omega $$ per phase is connected to a $$400V,$$ $$50Hz,$$ $$3-$$ phase supply lines. If the input power factor is to be improved to $$0.9$$ by connecting a bank of star connected capacitors, the required $$kV$$ $$AR$$ of the bank is

GATE EE 2003

A set of $$3$$ equal resistors, each of value $${R_X},$$ connected in star across $$RYB$$ of given Fig. consumes the same power as the unbalanced delta-connected load shown. The value of $${R_X}$$ is _____________ $$\Omega .$$

GATE EE 1994

Using Thevenin equivalent circuit, determine the $$rms$$ value of the voltage across the $$100$$ $$ohm$$ resistor after the switch is closed in the $$3$$ $$-$$ phase circuit shown in Figure.

GATE EE 1992