VISION INSTITUTE OF TECHNOLOGY
Question Bank
Unit#1
- State the two major advantages and disadvantages of HVDC transmission over HVAC.
- Compare EHVAC and HVDC Transmission system based on their respective technical and economic aspects.
- Explain the surface voltage gradient on conductors and derive the expression for maximum surface voltage gradients for 2-Conductor Bundle.
- Explain the following terms used in EHVAC transmission systems with suitable diagrams (i) sub-transient reactance, (ii) transient reactance, (iii) synchronous reactance of a source, (iv) a.c. and d.c. components and (v) the interrupting current capacity of a circuit breaker.
- Explain clearly how overvoltages are generated when interrupting (i) low
- inductive current and (ii) low capacitive current. Draw a figure showing ferroresonance condition in a network when two poles of a circuit breaker are open, and one pole is closed. Also, explain the methods of reduction of switching surges on EHV systems.
- Explain the functions and role of smoothing rectors in HVDC link operations with mathematical justification.
- Explain the potential applications and types of Multiterminal DC systems.
- Derive the relation for the maximum surface gradient for the bundled conductor having two conductors.
- What are the noncharacteristic harmonics in HVDC systems? How are they generated?
Unit# 2
- List the corona loss formulae based on voltages and voltage gradients.
- Explain the mechanism of formation of a positive corona pulse train.
- Differentiate between a hot lighting stroke and a cold lighting stroke.
- Why the over voltage occurs due to arching ground?
- Explain the operation of various types of HVDC links with suitable diagrams.
- How many types of faults that can occur in HVDC converters?
- Draw the schematic diagram of overcurrent protection in a pole of HVDC link.
- Explain the starting and stopping criterion of HVDC link.
- Explain overvoltage caused by the interruption of low inductive current and capacitive currents.
- Explain methods for the generation of high DC voltage.
- Explain the factors for designing of EHV lines under steady state conditions. Also give its limitations which will govern the design of lines.
- Describe the mechanism of formation of a positive corona pulse train. Why does line generated corona noise does not interfere with TV reception or FM radio reception? What causes interference at these frequencies?
- List down and explain the various design factors under steady state which have to be carried out for the design of EHV lines along with their limiting values.
- What are the standard wave shapes used for the following types of surges?
- Lightning voltage
- Lightning current
- Switching impulse for testing line material
- Switching impulse for transformer tests.
- Give neat sketches and indicate all magnitudes and timings.
- Explain the following:
- Effect of pollution on the performance of EHV lines.
- Measurement of High voltages by Sphere gap