power-factor-correction.pptx
- 1. Active and Reactive Power • When a circuit has resistive and reactive parts, the resultant power has 2 parts: – The first is dissipated in the resistive element. This is the active power, P – The second is stored and returned by the reactive element. This is the reactive power, Q , which has units of volt amperes reactive or var • While reactive power is not dissipated it does have an effect on the system – for example, it increases the current that must be supplied and increases losses with cables 16.6
- 2. Reactive power flow in distribution system result in: • Transformer over loads; • Voltage drops at the end of the lines; • Temperature rise supply cables and thus in active power losses; • Over sizing of harmonic protection devices. Reactive power (KVAR) required by inductive loads increases the amount of apparent power (KVA) in distribution system. This increase in reactive and apparent power results in a larger angle measured between KW and KVA. As θ increases, cosine θ (or power factor) decreases.
- 3. • Consider an RL circuit – the relationship between the various forms of power can be illustrated using a power triangle
- 4. • Therefore Active PowerP = VI cos watts Reactive Power Q = VI sin var Apparent Power S = VI VA S2 = P2 + Q2 definition : p.f. = cos = P/ S P.F. should be close to unity
- 5. Power Factor • Power factor is particularly important in high-power applications It is the measure of how effectively electrical equipment converts electric power (supplied by your power utility) into useful power output. • In technical terms, it is the ratio of Active Power (kW) to the Apparent Power (kVA) of an electrical installation. • The PF play important role in a.c circuits since power consumed depends on this factor. • • 𝑷 = 𝑽𝑰 cos ∅ (for SINGLE PHASE) • 𝑰 = 𝑷/ 𝑽 𝐜𝐨𝐬 ∅ • • 𝑷 = √𝟑𝑽 𝑰 cos ∅ (for THREE PHASE) • 𝑰 = 𝑷/ √𝟑𝑽 𝐜𝐨𝐬 ∅ – power companies therefore penalize industrial users who introduce a poor power factor
- 6. Causes of low power factor : Low power factor results when KW small in relation to KVA. This would occur when KVAR is large. What causes a large KVAR in a system? • …………… Inductive loads • All Ac motors • Transformers • Arc & induction heating furnance • High intensity discharge lighting • All devices using electromagnetic field. Disadvantage of low power factor • large kva rating of equipments. • greater conductor size. • large copper losses. • poor voltage regulation. • reduced handling capacity of system
- 7. Benefits for improving power factor • Lower utility fees by - Reducing peak KW billing demand - Eliminating the power factor penalty • Increased system capacity and reduced system losses in your electrical system • Increased voltage level in your electrical system • Maintain a better voltage regulation on the system
- 8. The problem of poor power factor is tackled by adding additional components to bring the power factor back closer to unity – a capacitor of an appropriate size in parallel with a lagging load can ‘cancel out’ the inductive element – this is power factor correction Consumers of Reactive Power increase power factor: • Capacitors • Synchronous condenser • Phase advancer
- 15. • Reactive power (VAR) compensation is defined as the management of reactive power to improve the performance of ac systems. • Any device which is connected in series or parallel with load and which is capable of supplying reactive power demanded by load is called reactive power compensation device. There are two aspects:- • a) Load Compensation – The main objectives are to :- • i) increase the power factor of the system • ii) to balance the real power drawn from the system • iii) compensate voltage regulation • iv) to eliminate current harmonics. • b) Voltage Support – The main purpose is to decrease the voltage fluctuation at a given terminal of transmission line. • Therefore the VAR compensation improves the stability of ac system by increasing the maximum active power that can be transmitted. Methods of Reactive Power Compensation Shunt compensation Series compensation Synchronous condensers Static VAR compensators
- 16. Shunt Compensation • The device that is connected in parallel with the transmission line is called the shunt compensator. • For high voltage transmission line the line capacitance is high and plays a significant role in voltage conditions of the receiving end. • When the line is loaded then the reactive power demand of the load is partially met by the reactive power generated by the line capacitance and the remaining reactive power demand is met by the reactive power flow through the line from sending end to the receiving end. • When load is high (more than SIL) then a large reactive power flows from sending end to the receiving end resulting in large voltage drop in the line. • To improve the voltage at the receiving end shunt capacitors may be connected at the receiving end to generate and feed the reactive power to the load so that reactive power flow through the line and consequently the voltage drop in the line is reduced.
- 17. • To control the receiving end voltage a bank of capacitors (large number of capacitors connected in parallel) is installed at the receiving end and suitable number of capacitors are switched in during high load condition depending upon the load demand. • Thus the capacitors provide leading VAr to partially meet reactive power demand of the load to control the voltage. • If XC = 1/ωC be the reactance of the shunt capacitor then the reactive power generated of leading VAr supplied by the capacitor: • where, |V2| is the magnitude of receiving end voltage. C V X V Q C C 2 2 2 2
- 18. • When load is small (less than SIL) then the load reactive power demand may even be lesser than the reactive power generated by the line capacitor. Under these conditions the reactive power flow through the line becomes negative, i.e., the reactive power flows from receiving end to sending end, and the receiving end voltage is higher than sending end voltage (Ferranti effect). • To control the voltage at the receiving end it is necessary to absorb or sink reactive power. This is achieved by connecting shunt reactors at the receiving end. • If XL = ωL be the reactance of the shunt reactor (inductor) then the reactive VAr absorbed by the shunt rector: • where, |V2| is the magnitude of receiving end voltage. L V X V Q L L / 2 2 2 2
- 19. • To control the receiving end voltage generally one shunt rector is installed and switched in during the light load condition. • To meet the variable reactive power demands requisite number of shunt capacitors are switched in, in addition to the shunt reactor, which results in adjustable reactive power absorption by the combination. • For high voltage transmission line the line capacitance is high and plays a significant role in voltage conditions of the receiving end. • When the line is loaded then the reactive power demand of the load is partially met by the reactive power generated by the line capacitance and the remaining reactive power demand is met by the reactive power flow through the line from sending end to the receiving end. a) uncompensated transmission line b) compensated transmission line
- 21. Advantages of Series Compensation 1. Increase in transmission capacity – The power transfer capacity of a line is given by sin . X V E P where, E , V are sending and receiving end voltages X is reactance of line & δ is phase angle between E and V • Power transfer without and with compensation: K X X X X X P P X X V E P X V E P L C C L L C L L 1 1 ) / 1 ( 1 ) ( sin ) ( . sin . 1 2 2 1
- 22. 2. Improvement of System Stability • For same amount of power transfer and same value of E and V, the δ in the case of series compensated line is less than that of uncompensated line. L C L C L L X X X X X V E P X V E P ) ( sin sin sin ) ( . sin . 1 2 2 1 • A lower δ means better system stability • Series compensation offers most economic solution for system stability as compared to other methods (reducing generator, x-mer reactance, bundled conductors, increase no. of parallel circuits
- 23. Disadvantages 1. Increase in fault current 2. Mal operation of distance relay- if the degree of compensation and location is not proper. 3. High recovery voltage of lines- across the circuit breaker contacts and is harmful.
- 24. Active Compensation • Synchronous condensers are the active shunt compensators and have been used to improve the voltage profile and system stability. • When machine is overexcited, it acts as shunt capacitor as it supplies lagging VAr to the system and when under excited it acts as a shunt coil as it absorbs reactive power to maintain terminal voltage. • The synchronous condenser provides continuous (step less) adjustment of the reactive power in both under excited and overexcited mode.
- 29. Objective Series Capacitors Shunt Capacitors Improving Power Factor Secondary Primary Improving Voltage level in overhead line system with a normal and low Power Factor Primary Secondary Improving Voltage level in overhead line system with a high Power Factor Not Used Primary Reduce Line Losses Secondary Primary Reduce Voltage Fluctuations Primary Not used