1. A SEMINAR ON Submitted by:- Rakesh Kumar Padhy 0901106221
Electrical engineering
2. CONTENTSPower Factor: An IntroductionTypes of circuit Linear
Circuit Non-linear CircuitImportance of power factor in
distribution systemsDisadvantages of low power factorPFC in linear
loadsThe APFC (Automatic Power Factor Correction) unitParts of the
APFC unitMaintenance of the APFC unitConclusion
3. Power factor: An introductionIt is the ratio of real power
flowing through the load to the apparent power in the circuitIt is
also defined as the cosine of the angle between the voltage and
current phasesIt is a dimensionless no between 0 and 1Whether the
current is leading or lagging the power factor is termed as leading
or lagging PF correspondingly
4. Types of CircuitThere are two types of circuits based on the
type of current waveform Linear loads Non-linear loadsThe type of
loads which doesnt change the current waveform shape are known as
linear loadsThe loads on the others case which change the shape
(distort) the current waveform are termed as non-linear
loadsDistortion decreases average power transmitted to the
load
5. Variation of PF in transmission systemsGenerally due to
inductive loads the power factor never remains unity in realityA
capacitive network gives reactive power and an inductive network
takes the sameIn both the cases the power factor becomes less than
1 causing more current to be transferred for the same amount of
real power
6. Disadvantages of low PFVoltage regulation becomes
poorGreater amount of apparent power needed to get the same amount
of real powerThe increase in reactive power increases the current
flowing through the networkSize of the transformer, switch gears
etc. increase thereby increasing the transmission cost
7. Power Factor Correction for linear loadsVarious methods of
power factor correction (PFC)are adopted to minimize the apparent
power as: Using capacitor banks in Automatic Power Factor
Correction (APFC) units For high voltage rating the power
electronic devices such as Static VAR compensator or STATCOM are
used Its also a good practice to use an unloaded synchronous
motor
8. APFC unitIts an automatic system adjusting itself to control
the power factor above a desired value by a bank of capacitors
switched by means of contractorsContractors are controlled by a
regulator that measures PF in the networkDepending upon the load PF
the controller will adjust the PF by switching the necessary no of
capacitors from the bank
9. Parts of the APFC unit1.Reactive power control relay Capable
of measuring the reactive and active power of the network Works in
conjunction with a capacitor bank Controls the programmed target PF
by activating/deactivating the capacitors
10. The main functions of the reactive power control relay
Automatic connection detection (Star or Delta) Automatic detection
of capacitor stages Patented characteristics avoiding compensation
of very low active power Reactive power requirement-switching delay
time Alarm signals for Failure to reach the target PF Overcurrent
in the capacitor Defects at capacitor stages
11. 2.Network connection pointsSince the power factor of the
loads is to becompensated hence the connection of the APFC unit
isalways done in parallel with the supply connection.Generally Y-
connection of the capacitor bank ispreferred because the
transmission distribution ofthree phase distribution system above
132 kv is Yconnected always
12. 3.Slow-blow switches Slow blow switches are always used
because of the following requirements To sustain the inrush and
starting current surges due to vehicular loads It offers a time
delay between overloading and fusing They can withstand heavy
currents (about ten times the rated)
13. 4.Inrush current contactors Used for damping the inrush
current arising due to Remaining capacitor voltage due to fast
switching Short circuit power of supply Fault level of supply
networks The contractors also protect the welding of the main
contacts of the contactors Prevent the capacitors from high
stress
14. 5.Capacitor BankThe capacitor bank is themain part of the
APFCunits. Large capacitor banksare installed in the APFCswhich
switch in order tomeet the desired powerfactor requirement.
Eachcapacitor is individuallyfused with appropriatelysized current
limit fuse.
15. 6.Control Transformer Monitors the switchboard load (or
load to be corrected) Placed physically above (towards the supply)
the connections for the PFC system In case more than one
transformers are fitted they are always connected in series as they
work as CT
16. Maintenance of the APFC unitThe major maintenance checks
involved for the APFCunit are In out of maximum demand hours (eg.
Late nights or weekends) switch off the system after internal and
external checks Remove contactor tops and inspect for contact wear,
check capacitance of each capacitor Check (and adjust if necessary)
all connections to contactors, capacitors, fuses etc. Re-energize
system and check current (true RMS) and harmonics drawn by each
capacitor step. Check voltage level and fuses
17. Conclusion Hence the APFC units correct the power factor
above a decided value by switching the appropriate no of capacitors
from the capacitor bank In non-linear loads we use inductors,
filters, valley-fill circuit etc. to suppress harmonics as they
cause the current wave form to be distorted