Electrical Engineering Mock Interview Questions & Practice

What is ripple factor, and what does it indicate about a rectifier's output?

Key points to cover:

• Ratio of the AC (ripple) component to the DC component in the output
• A lower ripple factor indicates a smoother output
• Closer to purely DC

What is the role of the inductor in a DC-DC converter?

Key points to cover:

• Stores and releases energy during the switching cycle
• Smooths current flow
• Enables voltage step-up or step-down through controlled energy transfer

What is Pulse Width Modulation (PWM), and how is it used in inverter control?

Key points to cover:

• Varies the width (duty cycle) of switching pulses
• To control the effective output voltage/waveform shape
• Used in inverters to approximate a sinusoidal output

What is electric field intensity, and why is it particularly important in high voltage equipment design?

Key points to cover:

• The force per unit charge at a point in an electric field
• Insulation failure is driven by exceeding dielectric strength
• At points of high field concentration, not just voltage magnitude

What is a high voltage impulse test, and what real-world phenomenon does it simulate?

Key points to cover:

• Applies a very short-duration, high-magnitude voltage impulse
• To equipment
• Simulates transient overvoltages like lightning strikes or switching surges

What is a switching overvoltage, and what typically causes it in a power system?

Key points to cover:

• A transient overvoltage arising from switching operations
• E.g. circuit breaker opening/closing, capacitor bank switching
• Caused by sudden circuit changes interacting with system L and C

Explain Thevenin's theorem and its practical use.

Key points to cover:

• Any linear two-terminal network can be replaced by an equivalent voltage source
• In series with a resistance, as seen from those terminals
• Useful for simplifying analysis, especially with a variable load

What is the power factor in an AC circuit, and why does it matter?

Key points to cover:

• The cosine of the phase angle between voltage and current
• Represents the fraction of apparent power doing useful work
• Low power factor means more current needed for the same real power

What are Z-parameters (impedance parameters) used for in two-port network analysis?

Key points to cover:

• Characterize a two-port network
• By expressing port voltages as linear combinations of port currents
• Useful for representing networks in series connection

What is the difference between a series-wound and a shunt-wound DC motor?

Key points to cover:

• Series-wound: field winding in series with armature, high starting torque
• Series speed varies significantly with load
• Shunt-wound: field winding in parallel with armature, relatively constant speed

What is the purpose of laminating the core of a transformer?

Key points to cover:

• Reduces eddy current losses in the core
• By breaking up the conductive path for induced eddy currents
• Into thin, electrically-insulated laminations

What is synchronous speed, and what factors determine it?

Key points to cover:

• The speed of the rotating magnetic field produced by the stator
• Determined by supply frequency
• And the number of poles of the machine

What is the role of a substation in a power system?

Key points to cover:

• Performs voltage transformation (step-up or step-down)
• Includes switching/protection equipment
• Controls and safely routes power flow between transmission and distribution

What is the difference between overcurrent protection and differential protection?

Key points to cover:

• Overcurrent protection trips when current exceeds a threshold, regardless of location
• Differential protection compares current entering and leaving a protected zone
• Trips only on an internal fault, offering more precise/selective protection

What is a short-circuit fault, and why is fault analysis important in power system design?

Key points to cover:

• An abnormal, typically low-impedance connection between points
• Not meant to be connected
• Fault analysis is important to correctly size protective equipment

What is a transfer function, and how is it defined for a linear time-invariant system?

Key points to cover:

• The ratio of the Laplace transform of a system's output
• To the Laplace transform of its input, assuming zero initial conditions
• Fully characterizes the input-output behavior of an LTI system

What is steady-state error in a control system, and what factors influence it?

Key points to cover:

• The difference between desired input and actual output as time approaches infinity
• Influenced by system type (number of integrators in the open-loop transfer function)
• Influenced by the type of input applied (step, ramp, parabolic)

What is a root locus plot, and what does it show?

Key points to cover:

• A graphical plot showing how the roots of a system's characteristic equation move
• In the s-plane as a system parameter (typically gain) varies
• Shows how gain affects stability and transient response