This document discusses various methods of voltage control in power systems, including static shunt capacitors, static series capacitors, static shunt reactors, synchronous condensers, tap changing transformers, booster transformers, and SVC-Static VAR Compensators. Static shunt capacitors and static series capacitors inject reactive power to increase voltage, while static shunt reactors absorb reactive power to reduce voltage. Synchronous condensers can operate as either capacitors or reactors depending on their excitation to regulate voltage. Tap changing transformers and booster transformers also control voltage through adjusting transformer ratios.

1. METHODS OF VOLTAGE CONTROL
 Excitation control
 Static Shunt capacitors
 Static series capacitors
 Static shunt reactors
 Synchrous condensers.
 Tap changing transformer.
 Booster transformer
 Regulating transformer
 SVC-Static VAR Compensators.
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2. SHUNT CAPACITORS:
 It supplies reactive power for both Transmission and distribution side.
 Connected to bus bar or tertiary winding of main TF.
 It can controlled by switching.
 Supplies reactive power to lead the current from voltage.
 Power factor improved.
 VAR α V2
Voltage rise by Shunt C:
Volt drop without Shunt C:
⌂V = (P2R +Q2X) / V
Volt drop with Shunt C:
⌂V’ = [P2R + (Q2-Qc)X ]/ V
Capacitor voltage rise : ⌂Vc = QcX / V
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3.  It is connected series in the line to compensate the inductive reactance
of line.
 Increases maximum power transfer, reduces reactive power loss.
 Under fault condition voltage across the C rises. So fault current also
increases 4 times of rated current.
 Zinc oxide varistor is used to bypass the current and give to the load.( it
is for particular level of currents)
 Drainage reactance used to prevent the current flow through the breaker
and bypass to the varistors for particular limits.
 Exceeds the current limit means, reactor allows the current, the given to
breaker. It disconnect the C from fault current.
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SERIES CAPACITORS

4.  V= IR cosØr + IXLsinØr –Ixc sinØr
= IR cosØr + I(XL-Xc)sinØr
The voltage boost producesd by series capacitor
is
⌂V= I Xc sinØr
Improve the volt regulations in distribution feeders.
Improve system stability.
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5. SHUNT REACTORS
 Used to reduce the voltage rise in open circuit with light loads.
 It absorbs the reactive power. Used in longer EHV lines.
 It is connected by switching operation to the lines.
 But in heavy loads some reactors are disconnected by switching and
breakers.
 Used to maintain nominal voltage under light load conditions.
 Some reactors are permanently connected to the lines.
 It can connected to lines or tertiary winding of TF.
 Tap changing Reactors also used to connect the reactor w.r.t loads.

6. SYNCHRONOUS CONDENSERS
 Synchronous motor running over excited means supply reactive power.
 Synchronous motor running under excited means absorb reactive
power.
 The running of synchronous motor is controlled by AVR in field of Syn
motor.
 It is also called as active compensators.
 Used in HVDC lines and voltage controls with upset conditions with Volt
regulators.
 It is connected to the tertiary wing of TF.
 It can operate as shunt C for over excited condition (Eg cosα > V)
 It can operate as shunt inductor for under excited condition (Eg
cosα < V)
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7. Finding ghe value of syn compensation:
V1=V2+ I (R + jX)
I=Ic+I2
I2 is the lagging current.
V1=V2+IR cosϴ + IX sinϴ
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8. REFERENCES:
 Jeraldin Ahila M., “Power system operation and control”, Lakshmi
Publications, 2015.
 Kundur P., ‘Power System Stability and Control, Tata McGraw Hill Education
Pvt. Ltd., New Delhi,10th reprint, 2010.
 R3. Hadi Saadat, ‘Power System Analysis’, Tata McGraw Hill Education Pvt.
Ltd., New Delhi, 21st reprint, 2010.
 R4. Ramanathan V., “Power System Operation and Control,” Charulatha
Publications, 2015.
 R5. Gross C.A., “Power System Analysis,” Wiley India, 2011.
 Google and Wikipedia.
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