2. CONTENTS
BASICS
TARIFF
POWER FACTOR
CAUSES OF LOW POWER FACTOR
DISADVANTAGES OF LOW POWER FACTOR
POWER FACTOR CORRECTION
METHODS OF POWER FACTOR CORRECTION
ADVANTAGES OF POWER FACTOR CORRECTION
3. BASICS
CURRENT(I): “ The flow of electrons through a conductor”.
In amperes (A)
VOLTAGE(V): “The driving force of electrons through a
conductor”. In volts (V)
POWER(P): “The product of voltage and current”.
In watts (W)
RESISTANCE(R): “To oppose the flow of electrons through it”.
In ohms (Ω)
INDUCTANCE(L): “To oppose the sudden changes in current”.
In henrys (H)
CAPACITANCE(C): “To store electric charge”. In farads (F)
4. OHM’S LAW
Statement:
“At a constant temperature
potential difference (V)
between two end points
of the conductor is directly
proportional to the current
(I) flowing through
that conductor”.
5. REACTANCE: The non-resistive component of impedance in an AC circuit
INDUCIVE REACTANCE:
XL = ωL = 2𝝿fL
where ‘ω’ is angular velocity in rad/sec
‘f ’ is frequency in Hz
‘L’ is inductance in H
CAPACITIVE REACTANCE:
Xc= 1/ωC = 1/2𝝿fC
where ‘C’ is capacitance in F
IMPEDENCE: The total resistance of an AC circuit.
For R-L circuit Z = 𝑅2 + 𝑋 𝐿
2
For R-C circuit Z = 𝑅2 + 𝑋 𝐶
2
For R-L-C circuit Z = 𝑅2 + (𝑋 𝐿~𝑋𝑐)2
6. POWER TRIANGLE
IcosΦ P=V*IcosΦ
Φ V Φ Q=V-IsinΦ
IsinΦ I S=V*I
Where IcosΦ is active component of current
IsinΦ is reactive component of current
V&I are circuit voltage and current respectively.
IMPEDENCE TRIANGLE:
S = 𝑃2 + 𝑄2 𝑍 = 𝑅2 + 𝑋2
S Q Z X
ΦΦ
P R
7. ACTIVE POWER(P):
“The power which is actually consumed or utilized in an AC
Circuit is called active power or true power”. In watts(W). or
It is the active component of current (IcosΦ) and circuit voltage (V).
P = V*IcosΦ
REACTIVE POWER(Q):
“The power which flows back and front or reacts upon itself is called as
reactive power or watt less power”. In (VAR). or
It is the reactive component of current (IsinΦ) and circuit voltage (V).
Q = V*IsinΦ
APPARENT POWER(S):
“The product of circuit voltage (V) and circuit current (I) in an AC
circuit is called apparent power”. In (VA).
S = V*I
8. TARIFF
The rate or charge at which electrical energy is supplied to a consumer is
known as tariff.
Which includes cost for generation, investment cost for transmission,
distribution, operation, maintenance and losses. Along with penalty for
consumers at low power factor.
TYPES OF TARIFF
Simple tariff
Flat rate tariff
Block rate tariff
Two port tariff
Maximum demand tariff
Power factor tariff
9. Power factor tariff
kVA maximum demand tariff
kVA = kW/p.f
kWh and kVARh tariff
kVARh = (kW/p.f)*sinθ
Sliding scale or average power factor tariff
Here the average power factor is taken as 0.8 lagging.
If the power facto is less than 0.8 then the consumer will be
penalized.
If the power factor is grater than 0.8 then the consumer will get
discount.
10. TYPES OF LOADS
RESISTIVE LOAD
If the load consist of resistance then that load is a resistive load. Here voltage and
current are in phase so there is no angle between V&I which results unity power
factor. It consumes active power only.
Examples are incandescent lamp and resistance heater.
INDUCTIVE LOAD
If the load consist of resistance and inductance then that load is a inductive load.
Here voltage and current are not in phase so there is an angle between V&I which
results lagging power factor. It consumes both active & reactive power.
Examples are induction motor and transformer.
CAPACITIVE LOAD
If the load consist of resistance and capacitance then that load is a capacitive load.
Here voltage and current are not in phase so there is an angle between V&I which
results leading power factor. It consumes both active power & compensate reactive.
Examples are capacitors and synchronous condenser for power factor correction.
Φ
Φ
I V
V
I
V
I
11. LEADING AND LAGGING
KVAR (LAG)
KVAR (LAG)
KW
KW
INDUCTION
MOTOR
G
L
OVER-EXCITED
SYN. MOTOR
G
L
KVAR (LEAD)KW
KVAR (LEAD)KW
12. POWER FACTOR
“The cosine angle between voltage and current in an AC circuit”.
or
“The ratio of resistance and impedance of an AC circuit”.
or
“The ratio of true power and apparent power”.
For resistive load power factor is unity.
For inductive load power factor is lagging..
For capacitive load power factor is leading.
Φ V
I V
I
Φ
V
I
13. POWER FACTORS OF SOME COMMON LOADS
S.No. TYPE OF LOAD POWER FACTOR
1. Incandescent lamp 1.0
2. Arc lamp 0.3-0.7
3. Neon lamp 0.4-0.5
4. Fluorescent lamp 0.6-0.8
5. Resistance heater 1.0
6. Induction heater 0.85
7. Arc furnace 0.85
8. Induction furnace 0.6
9. Arc welding 0.3-0.4
10. Resistance welding 0.65
11. Induction motor 0.8
14. CAUSES OF LOW POWER FACTOR
Induction motors
Transformers
Arc or induction heating furnaces
Arc lamps and electric discharge lamps
Variable load
15. DISADVANTAGES OF LOW POWER FACTOR
The rating of alternator, transformer and switchgear increased
(KVA).
The size of the conductor increases.
Power loss in the system increases.
Poor voltage regulation.
System efficiency decreases.
Penalty if power factor tariff.
Overall cost increases.
16. POWER FACTOR CORRECTION
Poor power factor is most commonly corrected
with the insertion of a capacitor or a capacitor bank
(a grouping of capacitors) at the desired location to
perform the correction.
The capacitor provides current that Leads the voltage. This combines
with the current associated with the magnetic fields that Lags the
voltage and cancels it out, if sized correctly.
Synchronous machines (either motors or generators) can also supply
leading current, similar to a capacitor, by over-exciting their rotating
field.
The better power factor improvement is depends on proper selection of
SIZE, LOCAION & METHODS
17. SIZE OF CAPACITOR
System
Voltage
Minimum rating of
capacitor bank
3.3 KV ,
6.6KV
75 Kvar
11 KV 200 Kvar
22 KV 400 Kvar
33 KV 600 Kvar
Ic = I1sinФ1 – I2sinФ2
Where
I1sinФ1 is the reactive component before correction
I2sinФ2 is the reactive component before correction
Ic = V/Xc
Xc = 1/ωc
Ω = 2∏f
18. LOCATON OF CAPACITOR
SERIES CONNECTION:
This method of connection is not much common. Even though the voltage
regulation is much high in this method,
It has many disadvantages. One is that because of the series connection, in a short
circuit condition the capacitor should be able to withstand the high current.
The other is that due to the series connection due to the inductivity of the line there
can be a resonance occurring at a certain capacitive value. This will lead to very
low impedance and may cause very high currents to flow through the lines.
PARALLEL CONNECTION:
This is the most popular method of connection. The capacitor is connected in
parallel to the unit.
The voltage rating of the capacitor is usually the same as or a little higher than the
system voltage.
19. METHODS OF POWER FACTOR CORRECTION
1.STATIC CAPACITOR
2.SYNCHRONOUS CONDENSER
3.PHASE ADVANCERSDENSER
20. 1.STATIC CAPACITOR
Power factor can be improved by connecting static capacitor in
parallel with the equipment operating at low power factor.
The capacitor draws leading current from the supply voltage by
90°.
Then it compensates the lagging reactive components of load
current .
Which results improve the power factor.
For more ratings the capacitor banks are used.
In case of 3-phase system the capacitors can be connected either
in star or delta.
Star for industrial and commercial loads.
Delta for distribution system.
21. ADVANTAGES
They have smaller losses (less than 0.5%).
As it has no rotating parts, require little maintenance.
Higher efficiency (above 99%).
Low initial cost.
It can be easily installed as they are light in weight.
It does not require any foundation.
DISADVANTAGES
They have short service life (8-10 years).
Easily damaged due to over voltage.
If they get damaged, their repair is uneconomical.
22. 2.SYNCHRONOUS CONDENSER
An over-excited synchronous machine running on no-load is
known as synchronous condenser.
The over-excited synchronous motor takes leading current and
behaves like a capacitor.
When it is connected across supply, it draws leading current
and partially or fully compensate the lagging reactive
component of load current
Which results improve the power factor.
In this way power factor can be improved to unity even.
Synchronous condensers are usually used where a large
quantity of corrective KVAR is to be required.
23. ADVANTAGES
By varying the field excitation of synchronous machine, the power factor can
be improved to a finer value.
Synchronous condenser can withstand over loads for short duration.
DISADVANTAGES
The cost is higher than the static capacitor of same size (above 500 kVA) .
The maintenance and operation cost is high.
Considerable losses in rotating parts of synchronous condenser.
Lower efficiency compared to static capacitor (nearly 97%).
Produces noise during operation.
Synchronous condenser is not self starting, hence it require an auxiliary
equipment for starting.
There is a chance to fall synchronous condenser out of synchronism which
leads interruption of supply.
24. 3.PHASE ADVANCERS
The phase advancer is a simple AC exciter
It can be mounted on the same shaft of the main motor
It supplies exciting ampere turns to the rotor circuit at slip frequency.
Then it provides flux which results improve the power factor.
If further increase the excitation the power factor goes to lead like over excited
synchronous motor.
ADVANTAGES
The lagging power factor kVAR drawn by the induction motor can be considerably
reduced by supplying leading ampere-turns at slip frequency.
The phase advancer is conveniently employed where the use of synchronous
condenser is not suitable.
DISADANTAGE
They are not economical for motors below 150 KW.
26. ADVANTAGES OF POWER FACTOR CORRECTION
The rating of alternator, transformer and switchgear
decreased (KVA).
The size of the conductor decreased.
Power loss in the system decreased.
Better voltage regulation.
System efficiency increases.
No penalty if power factor tariff.
Overall cost decreases.
