Static var compensator

Jun 17 • Notes • 2549 Views • 1 Comment on Static var compensator

In case if  any system has to operate close to the stability limits in steady state, That is with minimum margins then the fast control of reactive power is essential.since some last years, thyristor controlled static var compensator is used for the fast reactive power control.

Basic static var compensator schemes :-

Static_Var_Compensator

static var compensator

A reactor and a thyristor valve are incorporated in each and every single phase branch.in this system Power is changed by controlling the current through the reactor via thyristor valve. On any state interval is controlled by the  delaying triggering of the thyristor valve relative to the natural zero current crossing through it. Any thyristor controlled reactor TCR  is used in the combination with a fixed capacitor  that is FC when reactive power generation or alternatively, absorption and generation is needed .This is often optimum solution for  sub transmission and distribution.

TCR or FCs are characterized by

Circuit diagram

TCR circuit

  • Continuous control
  • No transients
  • Compact design
  • Thyristor switched capacitor, TSC

Shunt capacitor bank is divided into  appropriate number of branches and Each branch is individually switched on or off via  thyristor valve then The  Switching takes place and voltage across thyristor valve Which is zero, making this virtually transient-free. Disconnection can be effected by the  suppressing  firing pulses to the thyristors that  will be blocked when the current reaches zero.

TSCs are characterized by:-

  • Stepped control
  • No transients
  • No harmonics
  • Low losses
  • Redundancy and flexibility

Thyristor controlled reactor and Thyristor switched capacitor TCR or TSC :

The combined TCR and TSC is  optimum solution in many of the cases. With a TCR / TSC compensator, continuously variable the reactive power is obtained across entire control range and  full control of both an inductive and the capacitive parts of the compensator. the main Principal benefit of this is the optimum performance during major disturbances in  power system like    line faults and load rejections.

TCR / TSC combinations are characterized by these :

  1. Continuous control
  2. No transients
  3. Low losses
  4. Redundancy
  5. Flexible control and operation.
  6. Benefits of static var compensator  to the  power transmission:
  7.  Stabilized voltages in weak systems
  8. Reduced transmission losses
  9. Transmission capacity Increased , to reduce, defer or eliminate  need for new lines
  10. Higher transient stability limit
  11. Damping can be Increased  of the minor disturbances
  12. voltage control  and the stability  Greater
  13. Power oscillation damping  benefits of the static var compensator  to power distribution.
  14. Stabilization of the voltage at receiving end of long lines.
  15. Increased productivity as the stabilized voltage which  means better utilized capacity
  16. Reduced reactive power consumption can give lower losses and improved tariffs
  17. Asymmetrical load Balanced can  reduce system losses and it enables  lower stresses in the rotating machinery
  18. Enables better use of equipment (particularly transformers and cables)
  19. It Reduced voltage fluctuations and the light flicker
  20. Decreased harmonic distortion .

Question answers:

Q1:  Explain the benefits in Railways of static var compensator  ?
Ans: The increase in the traffic on existing tracks combined with the new rail projects of high speed mean rail traction is fast becoming an important load on electrical supply grids .In turn This  is focusing a lots of attention on the efficiency of the centenary as well as the power quality of the surrounding grids. Trains taking power from  centenary need to be sure supply voltages are stable and it do not sag.

Q2: What are the types of static var compensator ?
Ans: Three basic types of static var compensator

1. Variable impedance type
2. Current source type
3. Voltage source type

Q3: What are the static var compensator Control Characteristics?
Ans:-The high voltage is measured at the high voltage side of the transformer  feeding the static var compensator and the current is the reactive current, considered to be positive when static var compensator   is inductive (absorbing reactive power).

• In the control range, the static var compensator  voltage is not maintained constant. The slope of the control characteristics is positive that is from 3 to 5% and helps in

(a) stable parallel operation of more than one static var compensator connected at the same or neighboring buses and

(b) prevent static var compensator  hitting the limits too frequently.

Q4: What are the uses of static var compensator  ?
Ans: static var compensator  are used for

1. Increasing power transfer in long lines
2. Stability improvement (both steady state and transient) with fast acting voltage regulation
3. Damping of low frequency oscillations (corresponding to electromechanical modes)
4. Damping of sub synchronous frequency oscillations (due to torsional modes)
5. Control of dynamic over voltages.

Q5: What is the full form of SR ?
Ans: Saturated Reactor.

GATE Syllabus-

  1. Gate Syllabus for Electronics and Communication 2014
  2. Gate Syllabus for Instrumentation Engineering 2014
  3. Gate Syllabus for Engineering Science 2014

IES Syllabus-

  1. IES Syllabus for Electronics and Telecom
  2. IES Syllabus for General Ability
  3. IES Syllabus for Electrical Engineering

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One Response to Static var compensator

  1. Seetha Manoharan says:

    this is a good article. it clearly explain the concepts.

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