In a three-phase balanced circuit with line voltage VL = 440V, what is the phase voltage (Vph) in star connection?

The correct answer is A: 254V. In star connection, Vph = VL/√3 = 440/1.732 ≈ 254V

The resonant frequency of a series RLC circuit is given by:

The correct answer is A: f = 1/(2π√LC). At resonance, XL = XC, leading to the resonant frequency formula f₀ = 1/(2π√LC).

In a circuit, the star-delta transformation is used to:

The correct answer is D: Both A and B. Star-delta transformation converts between two three-terminal network configurations, simplifying circuit analysis by eliminating nodes that cannot be solved directly.

The switching frequency of a PWM inverter is 10 kHz. What is the fundamental frequency of the output if the modulation index is 0.8?

The correct answer is D: 5 kHz. The output fundamental frequency is typically half the switching frequency in standard PWM, or determined by reference signal. With modulation, output frequency follows the reference signal, typically much lower than switching frequency.

The mutual inductance between two coils is independent of:

The correct answer is C: Current flowing through coils. Mutual inductance depends on geometry, coil configuration, and medium properties, but NOT on the current flowing through them.

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Electrical Engg (EEE)

Electrical machines, power systems, circuits

196 Q 7 Topics Take Mock Test

Difficulty: All Easy Medium Hard 131–140 of 196

Topics in Electrical Engg (EEE)

All Circuit Analysis 100 Electrical Machines 100 Power Systems 100 Control Systems 100 Power Electronics 100 Electrical Measurements 40 Digital Electronics 100

Q.131 Easy Electrical Machines

In a transformer, the turns ratio k = N2/N1. If k > 1, the transformer is:

A Step-down transformer

B Step-up transformer

C Isolation transformer

D Auto transformer

Correct Answer: B. Step-up transformer

EXPLANATION

When secondary turns are greater than primary turns (k > 1), voltage is stepped up.

Test

Q.132 Easy Electrical Machines

The slip of an induction motor is defined as:

A (Ns - Nr)/Ns

B (Nr - Ns)/Nr

C Ns/Nr

D (Ns - Nr)/Nr

Correct Answer: A. (Ns - Nr)/Ns

EXPLANATION

Slip s = (Ns - Nr)/Ns, where Ns is synchronous speed and Nr is rotor speed.

Test

Q.133 Easy Electrical Machines

The synchronous speed of a 4-pole, 50 Hz induction motor is:

A 1500 rpm

B 3000 rpm

C 750 rpm

D 1000 rpm

Correct Answer: A. 1500 rpm

EXPLANATION

Synchronous speed Ns = 120f/P = (120 × 50)/4 = 1500 rpm.

Test

Q.134 Easy Electrical Machines

In a three-phase induction motor, the rotating magnetic field is produced by:

A Rotor current alone

B Three-phase stator currents with 120° phase difference

C DC excitation in stator

D Permanent magnets in rotor

Correct Answer: B. Three-phase stator currents with 120° phase difference

EXPLANATION

Three-phase currents 120° apart create a rotating magnetic field that rotates at synchronous speed Ns = 120f/P.

Test

Q.135 Easy Electrical Machines

The back EMF in a DC motor is given by the expression?

A E = PφZN/60

B E = PφZN/120

C E = φZN/60

D E = 2PφZN/60

Correct Answer: B. E = PφZN/120

EXPLANATION

Back EMF in DC motor: Eb = PφZN/120 where P = poles, φ = flux, Z = conductors, N = speed in rpm.

Test

Q.136 Easy Electrical Machines

Which of the following is the primary function of a commutator in a DC machine?

A To convert AC to DC

B To reverse the direction of current in armature conductors

C To reduce iron losses

D To increase flux density

Correct Answer: B. To reverse the direction of current in armature conductors

EXPLANATION

The commutator reverses the direction of current in armature conductors as they move from one pole to another, ensuring unidirectional torque production.

Test

Q.137 Easy Power Systems

Which of the following voltage levels is NOT part of the Indian transmission network classification?

A 400 kV

B 275 kV

C 220 kV

D 150 kV

Correct Answer: D. 150 kV

EXPLANATION

The standard Indian transmission voltage levels are 765 kV, 400 kV, 275 kV, and 220 kV. 150 kV is typically sub-transmission voltage level.

Test

Q.138 Easy Power Systems

In the Indian grid, renewable energy penetration targets for 2024-2025 (non-hydro) approximately target what percentage of total generation capacity?

A 25%

B 35%

C 45%

D 55%

Correct Answer: C. 45%

EXPLANATION

As per India's national renewable energy targets and Ministry of Power guidelines, approximately 45% non-fossil capacity addition is targeted for 2024-2025.

Test

Q.139 Easy Power Systems

Which type of power system stability is primarily concerned with the system's ability to maintain synchronism after a small disturbance?

A Transient stability

B Steady-state stability

C Voltage stability

D Frequency stability

Correct Answer: B. Steady-state stability

EXPLANATION

Steady-state stability examines the system's response to small, gradual disturbances, while transient stability deals with large, sudden disturbances.

Test

Q.140 Easy Power Systems

In load flow analysis, if a bus is specified with PV (constant voltage and active power), what variable is calculated?

A Voltage magnitude

B Reactive power

C Frequency

D Phase angle

Correct Answer: B. Reactive power

EXPLANATION

In PV buses, active power (P) and voltage magnitude (V) are specified, and the load flow solution calculates the reactive power (Q) and voltage angle (δ).

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