BEE Power System 3 — Questions and Answers
Question 1: Which method is commonly used to solve the power flow (load flow) problem in large power systems?
- Gauss-Seidel method only
- Newton-Raphson method (Correct answer)
- Runge-Kutta method
- Euler's forward method
Correct answer: Newton-Raphson method
The Newton-Raphson method converges quadratically and handles large, ill-conditioned systems better than Gauss-Seidel, making it the industry standard for load flow.
Question 2: What is the function of a static VAR compensator (SVC) in a transmission system?
- To generate active power during peak demand
- To provide dynamic reactive power support and voltage regulation (Correct answer)
- To reduce harmonic distortion in the line current
- To increase the thermal rating of conductors
Correct answer: To provide dynamic reactive power support and voltage regulation
An SVC uses thyristor-controlled reactors and capacitor banks to rapidly inject or absorb reactive power, maintaining bus voltage within limits.
Question 3: The equal-area criterion in power system stability analysis is used to assess:
- Steady-state voltage stability
- Transient (first-swing) stability (Correct answer)
- Small-signal stability
- Frequency regulation performance
Correct answer: Transient (first-swing) stability
The equal-area criterion determines whether a synchronous generator will remain stable after a sudden disturbance by comparing accelerating and decelerating energy areas on a P-δ curve.
Question 4: Which parameter of a transmission line is primarily responsible for the charging current?
- Series resistance
- Series inductance
- Shunt capacitance (Correct answer)
- Shunt conductance
Correct answer: Shunt capacitance
The shunt (line-to-ground) capacitance of a transmission line causes capacitive charging current to flow even when no load is connected.
Question 5: A generator's synchronizing coefficient Ps is positive. What does this indicate?
- The generator is operating in the unstable region
- The generator tends to return to synchronism after a small disturbance (Correct answer)
- The rotor angle exceeds 90 degrees
- Active power output is zero
Correct answer: The generator tends to return to synchronism after a small disturbance
A positive synchronizing coefficient (dP/dδ > 0) means the machine develops a restoring torque when displaced from equilibrium, ensuring steady-state stability.
Question 6: In a distribution system, what is the advantage of a ring (loop) network over a radial network?
- Lower installation cost
- Higher supply continuity and improved reliability (Correct answer)
- Simpler protection coordination
- Lower conductor cross-section requirement
Correct answer: Higher supply continuity and improved reliability
A ring network supplies each load from two directions, so a single fault or maintenance outage does not interrupt supply, improving reliability.
Question 7: What is the primary purpose of the excitation system of a synchronous generator?
- To control active power output
- To regulate the DC field current and thereby control terminal voltage and reactive power (Correct answer)
- To provide mechanical torque for starting
- To limit short-circuit current during faults
Correct answer: To regulate the DC field current and thereby control terminal voltage and reactive power
The excitation system adjusts the rotor field current, controlling the generator's terminal voltage and its contribution to reactive power in the system.
BEE Power System 3
Which method is commonly used to solve the power flow (load flow) problem in large power systems?