Download File - ELECTRICAL ENGINEERING DEPT, DCE

DHANALAKSHMI COLLEGE OF ENGINEERING, CHENNAI
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
EE 2036 FLEXIBLE AC TRANSMISSION SYSTEM
QUESTION BANK
UNIT - I
PART – A
1. Write the method to control the reactive power in an electrical network.
The reactive power can be controlled by series and parallel connected reactive power
generators.
2. List out the objectives of FACTS.
The objectives of FACTS controllers are
 To increase the operational reliability of transmission system
 To obtain economical operation of power system
3. Define – FACTS
FACTS is defined as power electronics based equipment to control the flow of AC power
in the transmission system.
4. Distinguish between Thyristor Switched Series Capacitor and TCSC.
Thyristor Switched Series Capacitor (TSSC)
 This permits a discrete control of the capacitive reactance.
 This consists of a series connection of multiple TCSC modules together.
Thyristor Controlled Series Capacitor
 This offers a continuous control of capacitive or inductive reactance.
 A smooth transition from the capacitive or inductive mode is not permitted.
5. List out the types of compensators used for passive compensation.
The types of passive compensators are
 Shunt capacitors
 Shunt reactors
 Series capacitors
 Synchronous condenser
6. List out the functions of dynamic series compensation.
The functions of dynamic series compensation are
 It increases the system stability
 It reduces the load dependent voltage drops
 It reduces the system transfer impedance
 It increases the load flow control for specified transmission system
 It increases the damping of active power oscillations
7. Write the sources of reactive power.
The sources of reactive power are
 Over excited synchronous machines
 Capacitor banks
 The capacitance of overhead lines and cables
8. List out the types of series connected FACTS controllers.
The types of series connected FACTS controllers are
 Thyristor Controlled Series Capacitor
 Thyristor Controlled Series Reactor
 Thyristor Switched Series Capacitor
 Thyristor switched Series Reactor.
9. List out the types of shunt connected FACTS controllers.
The types of shunt connected FACTS controllers are
 Static Var Compensator
 Thyristor Switched Reactor
 Thyristor Switched Capacitor
 Static Synchronous Compensator.
10. List out the advantages of FACTS controllers.
The advantages of FACTS controllers are
 It improves the transmission system operation
 It reduces the infrastructure investment
 It has less environmental impact
 It consumes less implementation time.
UNIT - II
PART – A
1. Why is the shunt compensation made always at midpoint of the transmission system?
The shunt compensation is made always at midpoint of the short transmission line to
improve the voltage to the required value of capacitance.
2. List out the applications of SVC.
The applications of SVC are
 Stability enhancement
 Damping of sub synchronous oscillations
 Improvement of HVDC link performance
3. Write the advantages of slope in the SVC dynamic characteristics.
The advantages of slope in the SVC dynamic characteristics are
 Significance reduction of the reactive power rating
 Prevention of reaching reactive power too frequently
 Sharing of reactive power during operation of multiple compensators in parallel.
4. What is the contribution of two torque components of generator in improving the system
damping?
Synchronizing torque ensures that the rotor angles of different generators do not drift
away when subjected to a large disturbance.
Damping torque determines the frequency of oscillations.
5. Define – Static Var Compensator
Static Var Compensator is defined as a shunt connected static var generator or absorber
whose output is adjusted to exchange capacitive or inductive current so as to maintain or control
specific parameters of the electrical power system.
6. List out the different types of SVC.
The different types of SVC are
 Thyristor Controlled Reactor
 Fixed Capacitor- Thyristor Controlled Reactor
 Thyristor Switched Capacitor
 Thyristor Controlled Reactor- Thyristor Switched Capacitor
7. What is the effect of synchronizing torque in power system?
The effect of synchronizing torque is to maintain the rotor angles of different generators
and do not drift away, when subjected to a large disturbance.
8. List out the main components of SVC.
The main components of SVC are
 Coupling transformer
 Thyristor valves
 Reactors
 capacitors
9. List out the advantages of SVC.
The advantages of the SVC are
 Improves the transient stability of system
 Changes the susceptance of passive devices to control reactive power.
 Improves power transfer capacity of a transmission line.
10. Define – Thyristor Controlled Reactor
Thyristor Controlled Reactor is defined as a shunt connected, thyristor controlled inductor
whose effective reactance is varied in continuous manner by partial conduction control of the
thyristor valve.
UNIT - III
PART – A
1. Define – Bypassed Thyristor mode
Bypassed thyristor mode is defined as the thyristor triggered continuously and therefore
the valve stays conducting all the time. In this mode, Thyristors are made to conduct with a
conduction angle of 180 ̊. Gate pulses are applied as soon as the voltage across the thyristor reaches
zero and becomes positive, resulting in a continuous flow of current through the thyristor valves.
2. What is the indication of voltage collapse points?
Voltage collapse is mathematically indicated when the system Jacobian matrix becomes
singular. The collapse points are indication of the maximum loadability of the transmission lines
or the available transfer capability.
3. List out the two basic approaches for controllable series compensation.
The two basic approaches for controllable series compensation are
 Fixed series compensation
 Variable series compensation
4. Write the different modes of operation of TCSC.
The different modes of operation of TCSC are
 Bypassed thyristor mode
 Blocked thyristor mode
 Partially conducting thyristor or capacitive verniar mode
 Partially conducting thyristor or inductive verniar mode
5. List out the advantages of TCSC.
The advantages of TCSC are
 Rapid, continuous control of the transmission line series compensation
 Damping of the power swings from local and inter area oscillations
 Suppression of sub synchronous oscillations
 Decreasing DC offset voltages
 Reduction of short circuit current
6. List out the operating limits of TCSC.
The operating limits of TCSC are
 Voltage limits
 Current limits
 Firing angle limits
7. How is TCSC modeled for long term stability studies?
For long term stability studies, the TCSC is modeled for the time limited overload
capability must be considered for both capacitive and inductive verniar operation.
8. List out the requirements of good damping control.
The requirements of good damping control are
 System should be robust in the desired damping over a wide range of system
operating conditions.
 It should be reliable.
9. Write the need for firing angle limit of the TCSC.
The need for firing angle limit of the TCSC is
 The TCSC does not experience the resonant region
10. List out the main roles of TCSC for damping control.
The main roles of TCSC for damping control are
 During normal operating condition stabilize both post disturbance network
interaction
 Prevent local instabilities within the controller bandwidth.
UNIT - IV
PART – A
1. Write the salient features of UPFC.
The salient features of UPFC are
 Voltage regulation
 Series compensation
 Phase shifting
 Real and reactive power flow control
2. Differentiate STATCOM from SVC.
S. No.
1
2
3
4
STATCOM
It acts as voltage source behind a reactance
It is not sensitive to transmission system
harmonics
It has a longer dynamic range
It generates less harmonics
SVC
It acts as a variable susceptance
It is sensitive to transmission system
harmonics
It has smaller dynamic range
It generates more harmonics
3. Distinguish between UPFC and IPFC.
S. No.
1
2
3
4
UPFC
Voltage regulation is possible
Series compensation can achieved
Phase shifting is possible
It controls real and reactive power flow
IPFC
Voltage regulation is not possible
Series compensation cannot be done
Phase shifting is not possible
It controls the real and reactive power flow
4. What is the role of a DC link in UPFC?
The role of DC link in UPFC is
 To connect the Static synchronous Compensator(STATCOM) and a static series
compensator(SSSC).
 The combination is used to allow the bidirectional flow of real power between
series output terminals.
5. List out the applications of STATCOM.
The applications of STATCOM are
 It can perform effective voltage regulation and control.
 It improves steady state power transfer capacity.
 It improves transient stability margin
 It damps the sub synchronous power system oscillations.
6. Define – Unified Power Flow Controller (UPFC)
The Unified Power Flow Controller is defined as the last generation of FACTS devices
which can control all the three parameters of line power flow simultaneously. (Impedance, voltage
and phase angle)
7. List out the control parameters of UPFC.
The control parameters of UPFC are
 Line Impedance
 Voltage
 Phase angle
8. List out the different types of shunt converter modeling.
The different types of shunt converter modeling are
 Current model
 Real and reactive power injections
 Current source in parallel with shunt susceptance
 Voltage source model
9. Write the various operating modes of UPFC.
The various operating modes of UPFC
 Reactive power control mode
 Automatic voltage control mode
10. List out the applications of UPFC.
The applications of UPFC are
 It improves damping of power system.
 It enhances the power system stability.
UNIT - V
PART – A
1. Define – Co-ordination of FACTS
The co-ordination of FACTS is defined as the FACTS controllers are tuned simultaneously
to create overall positive improvement of the control scheme.
2. Classify FACTS controller interaction.
The FACTS controllers are classified as
 SVC-SVC interaction
 SVC-TCSC interaction
 TCSC-TCSC interaction
 SVC-HVDC interaction
3. How is co-ordination of FACTS controllers carried out?
The co-ordination of FACTS controllers carried out in the following combinations
 Multiple FACTS controllers of a similar kind
 Multiple FACTS controller of a dissimilar kind
 Multiple FACTS controllers and HVDC converter controllers
4. List out the frequency ranges for different control interactions.
The frequency ranges for different control interactions are
 Steady state interactions (Frequency range: 0 Hz)
 Electromechanical oscillation (Frequency range: 0 – 3/5 Hz)
 Small signal or control oscillations (Frequency range: 2 - 5 Hz)
 Sub synchronous resonance interactions (Frequency range: 10 – 50/60 Hz)
 Electromechanical transients, high frequency resonance or harmonic resonance
interactions and network resonance interactions (Frequency range: ˃15 kHz)
5. Define – Small Signal Oscillations
The small signal oscillation is defined as the oscillations in the range of 2 to 15 Hz
occurring between individual FACTS controllers and the network controller and the network or
between FACTS controller and HVDC links are called small signal oscillations. The emergence
of these oscillations significantly influences the tuning of controller gains.
6. Write the factors dependent on small signal oscillations.
The factors dependent on small signal oscillations are as follows
 The network strength
 FACTS controllers parameters
 Interaction between voltage controllers of multiple SVC’s
 The resonance between series capacitor and shunt reactor
7. List out the main control schemes for FACTS controllers.
The main control schemes for FACTS controllers are
 Steady state power flow control
 Transient control for improving first swing stability
 Power oscillation damping control to damp the power system oscillations
8. Write the different groups of dynamic interactions.
The different groups of dynamic interactions are
 Multiple SVC interactions phenomenon which is primarily due to the coupling
between voltage control loops of SVC’s
 Torsional interaction phenomenon of SVC’s and multi mass turbine generator
(T-G) sets
 Dynamic interaction phenomenon between SVC’s and series capacitor
compensated lines with or without considering Torsional oscillations of T-G sets
9. List out the design steps followed in the controller design.
The design steps followed in the controller design are
 System model derivation
 System performance specification
 Selection of the measurement and control signals
 Co-ordination of the controller design and
 Justification of the design and performance evaluation
10. Write the two types of power oscillation damping controllers in power systems.
The two types of power oscillation damping controllers in power system are
 Power System Stabilizer (PSS)
 FACTS Power Oscillation Damping controllers