Reactive power consumption in modern power system

1. Reactive Power Consumption In Modern POWER System Presented By : Rahul Dey (Electrical 4th Year)

2. INTRODUCTION What is Reactive Power? It describes the background energy movement in an AC system arising from the production of electric and magnetic fields It is the combination of continuous forward-moving or ‘real’ energy flow, combined with the sloshing or ‘imaginary’ energy flow It is used for core magnetization of Alternators It is non-consumable. Only becomes important when ‘electrical load’ contains coils or capacitor

3. AC POWER PHASOR

4. Why Do We Need Reactive Power? Reactive power (VARs) is required to maintain the voltage to deliver active power (watts) through transmission lines “Indexing of Active Power consumption is called Reactive Power !!”Electro-Mechanical devices and other loads require reactive powerReactive power deficiency causes the voltage to sag down

5. Importance Of Reactive Power• Refers to the circulating power in the grid that does no useful work, non consumable• Results from energy storage elements in the power grid (mainly inductors and capacitors)• Has a strong effect on system voltages• It has to be balanced in the grid to prevent voltage problems, has to be maintained for a secure and stable Transmission System• Reactive power levels have an effect on voltage collapse

6. NEED FOR REACTIVE POWER CONTROLDenoting Reactive Power as “Q”: Case 1: Q > Qmax  Excess Q causes excess magnetization in core  Eddy current increases to a high value  Excessive heat generation occurs  Thermal breakdown of the insulation  Unwanted Dead Short Circuit occurs

7. Case 2: Q < Qmin  Insufficient magnetization causes improper work done  Results in large gap between input and output  Localized oscillations occur  System becomes unstable

8. EQUIPMENTSEquipments for Reactive Power Control are:  Synchronous Condenser  Capacitor Bank  Series Compensator  STATCOM  Shunt Reactor  Static VAR Compensator a) Thyristor-Controlled Reactor (TCR) b) Thyristor Switched Capacitor (TSC) c) Saturated Reactors

9. SYNCHRONOUS CONDENSER Synchronous Condensers - Synchronous motor running at no load to provide reactive power support, mainly used to adjust grid’s voltage by either generating or absorbing reactive power, improve power factor Location: At the receiving end of long transmission lines In important substations In conjunction with HVDC converter stations Reactive power output is continuously controllable

10. Working Conditions• Synchronous Motor operating at leading power factor is used for lagging Reactive power control• Under this condition the excitation of motor is greater than its input terminal voltage• Hence the characteristics becomes almost similar to a capacitor• Motor runs with lagging power factor when it is under-excited

11. CAPACITOR BANK• Shunt capacitors - Mechanically switched or fixed shunt capacitor banks installed at substations or near loads• Keeping voltage within required limit Advantage: much lower cost compared to SVCs Switching speeds can be quite fast with current limiting reactors to minimize switching transients.

12. Working Conditions Capacitor bank may be in Star or Delta connection They generate leading VAR, hence compensating the lagging VAR Value of capacitor should suffice the excessive lagging VAR

13. DISADVANTAGES Reactive power output drops with the voltage squared For transient voltage instability the switching may not be fast enough to prevent induction motor stalling Precise and rapid control of voltage is not possible (capacitor banks are discrete devices, but they are often configured with several steps to provide a limited amount of variable control) If voltage collapse results in a system, the stable parts of the system may experience damaging overvoltage, immediately following separation

14. SERIES COMPENSATOR Capacitor connected in series with the load The voltage of the line inductance is compensated by the capacitor voltage Capacitor voltage is inversely proportional to capacitance Hence the value of capacitance is chosen accordingly

15. Advantages: Disadvantages:• Reduces line voltage • Once a capacitor in a drops transmission line gets• Limits load-dependent damaged, then the entire voltage drops power flow scheme is• Influences load flow in interrupted parallel transmission lines • Maintenance is difficult• Increases transfer capability• Reduces transmission angle• Increases system stability

16. FACTS Flexible AC Transmission System : System composed of static equipment, used to enhance controllability and increase power transfer capability of AC transmission Classifications : Series Compensation – FACTS connected in series, acts as a controllable Voltage source Shunt Compensation –FACTS connected in parallel, acts as a controllable Current source1. Shunt Capacitive Compensation – Used to improve power factor2. Shunt Inductive Compensation – Used for charging transmission line

17. Applications Of FACTS Series Compensation:  Shunt Compensation:• Static synchronous series • Static synchronous compensator (SSSC) compensator (STATCOM)• Thyristor-controlled series • Static VAR compensator capacitor (TCSC) (SVC)• Thyristor-controlled series a) Thyristor-controlled reactor reactor (TCR)• Thyristor-switched series b) Thyristor-switched capacitor reactor (TSR)• Thyristor-switched series c) Thyristor-switched reactor capacitor (TSC)

18. Static VAR Compensator (SVC) Static VAR Compensator – Provide fast acting reactive power, regulates voltage and stabilizes system Automated impedance match device, brings the system near unity power factor Principle : Thyristor controlled reactor (TCR) – Consume VARs from capacitive load system Thyristor switched capacitor (TSC) – Add VARs to a inductive load system Harmonic filter – Eliminates harmonic distortions Mechanically switched capacitors or reactors (MSC) Location : Near high and rapidly varying loads, Exmp. Arc Furnaces

19. Static VAR Compensator (SVC)

20. STATCOM Static Synchronous Compensator : Regulating device, acts as either a source or sink of reactive AC power Voltage source converter (VSC)-based device STATCOM generates reactive current if the terminal voltage of the VSC is higher than the AC voltage at the point of connection It absorbs reactive power when amplitude of the voltage source is lower than the AC voltage STATCOM can be designed to be an active filter to absorb system harmonics

21. Advantages Over SVC• Maximum reactive output current will not be affected by the voltage magnitude• Therefore it exhibits constant current characteristics when the voltage is low under the limit• SVCs reactive output is proportional to the square of the voltage magnitude, hence reactive power decreases rapidly when voltage decreases, reducing system stability• Speed of response of STATCOM faster than SVC• Harmonic emission is lower than SVC

22. STATCOM Based On Current STATCOM Based On VoltageSource Converter Source Converter

23. SHUNT REACTORS Shunt reactors – mainly used to keep the voltage down Absorb reactive power in the case of light load and load rejection Compensate the capacitive load of transmission lines

24. HARMONIC FILTER Large quantities of harmonics can lead to malfunctioning of the system that results in downtime and increase in operating costs. A harmonic filter is used to eliminate the harmonic distortion caused by appliances. The harmonic filter is built using an array of capacitors, inductors, and resistors that deflect harmonic currents to the ground. Each harmonic filter could contain many such elements, each of which is used to deflect harmonics of a specific frequency.

25. Harmonic Filter

26. CONCLUSION Voltage control is essential to reduce transmission losses and to maintain the ability of the system to withstand and prevent voltage collapse Decreasing reactive power causing voltage to fall while increasing it causing voltage to rise Raising power factor is a proven way of increasing the efficient use of electricity by utilities & end users Economic benefits for end users may include reduced energy bills, lower cable, transformer losses & improved voltage conditions, while utilities benefit from increased system capacity by improving reactive power management Finally we can say, reactive power is essential in order to supply real power, without it transformers, induction motors will not run in absence of magnetic excitation which is supplied by reactive power

27. ReferencesA Course In Power Systems by J.B.GuptaModern power System Analysis by D.P.Kothari & I.J.Nagrathwww.wikipedia.comwww.google.co.in