ADITYA ENGINEERING COLLEGE (A)

Voltage Control
By

Mr. Ch.B.A.Raju
Dept of Electrical and Electronics Engineering
Aditya Engineering College(A)
Surampalem.
 Aditya Engineering College (A)

Introduction

• The distribution system is said to be well designed if it gives a good quality of

reliable supply.
• Good quality means that the voltage profiles are within the reasonable limits.
In practice, all the equipment on the distribution system are designed to
operate satisfactorily only when the voltage profile on the system corresponds
to their rated voltages or at the most variations are within permissible limits at
the consumers terminals i.e. 5%.
• To keep distribution system voltage that is to increase the circuit voltage when
it is too low and to reduce it when it is to high

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

Importance of voltage control

 When the load on the electrical distribution system changes, voltage at the
customers terminals will also change.
 The variations of voltage at the customers terminals are undesirable and must be
kept within permissible limit for the following reasons

1. In case of lighting loads, the lamp characteristics are very sensitive to change of
voltage.
2. In case of power loads consisting of induction motors, the voltage variations
may cause erratic operation. If the supply voltage is more than normal, the
motor may operate with a saturated magnetic circuit and consequently large
magnetizing current will be drawn. On other hand, if the voltage is too below, it
will reduce the starting torque.
3. Too wide variation of voltage causes excessive heating of distribution
transformers. This reduce the rating of transformers.
Electrical Distribution Systems Ch.B.A.Raju 11/16/2023
 Aditya Engineering College (A)

Method of voltage control

The following methods are used to improve the voltage in the distribution
system

1. Generator voltage regulators

2. Installing voltage regulating equipment and capacitors in the distribution
substations.
3. Load balancing on the primary feeders
4. Adequate size of feeder conductor.
5. Conversion of 1-phase feeder sections to multi phase feeder sections.
6. Shifting the loads to new feeders or new substations.
7. Construct the new substations and primary feeders.
8. Increasing the voltage levels on primary feeders.
9. Location of shunt and series capacitors on primary feeders.
Electrical Distribution Systems Ch.B.A.Raju 11/16/2023
 Aditya Engineering College (A)

Capacitors

• In uncompensated distribution system the reactive power demand is usually

met by the source, thus burden the system and result in poor voltage profile
and increase in losses.

• If the reactive power demand can be met locally then the transmitting of
reactive power from the source to the reactive elements can be reduced.

• Localized meeting of reactive power demand can be achieved by installing

either switchable capacitors or fixed capacitors.

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

Effect of Series Capacitor

• The maintenance of voltage at customer premises within statutory limits a

loads is the responsibility of utility.
• Capacitors can also be installed in series with primary feeders to reduce
voltage drop, but they are rarely employed in this fashion.
• Where shunt capacitors, connected in parallel with the load, correct the
compensation of the current due to the inductive reactance of the circuit,
series capacitor compensate for the reactance voltage drop in the feeder.
• A capacitor in series with a primary feeder serving a lagging p.f. load will
cause a rise in voltage as the load increases.

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

• The p.f. of the load through the series capacitor and feeder must be lagging if
the voltage drop is to decrease appreciably.

• The voltage on the load side of the series capacitor is raised above the
source side, acting to improve the voltage regulation of the feeder.

• Since the voltage rise or drop occurs instantaneously with the variations in
the load, the series capacitor response as a voltage regulator is faster and
smoother than the regulators.

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

• Main draw back of this capacitor is the high voltage produced across the
capacitor terminals under short circuit conditions.
• The drop across the capacitor is IfXc, where is the fault current which is many
times of the full load current under certain circuit conditions.
• It is essential, therefore, that the capacitor is to be taken out of service as quickly
as possible.
• A spark gap with a high-speed contactor can be used to protect the capacitor
under these conditions.
• Because of the potential hazards, series capacitors as voltage regulators are
usually restricted to transmission system rather than in distribution systems.

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

Circuit diagram without and with series compensation

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

Voltage Regulators(or Boosters)

• Voltage regulators are used to hold the voltage of a feeder at a predetermined

value within a limit which the control equipment is capable of maintain and
within acceptable tolerance values for distribution purpose.
• Regulators may be installed at substations or on distribution feeder on poles or
platforms.
• These are essentially autotransformers, with the secondary portion of the coil
arranged so that all or part of its induced voltage can be added to or subtracted
from the line or incoming primary voltage.
• The voltage variations are accomplished by changing the ratio of transformation
automatically without de-energizing the unit.

Voltage regulators are classified in two types and they are

i) Inductive type and
ii) Step type or Tap Changing Under Load(TCUL)type regulators.
Electrical Distribution Systems Ch.B.A.Raju 11/16/2023
 Aditya Engineering College (A)

Induction type regulator

• In this type of voltage regulator, the primary(HV) winding and secondary

winding are so arranged that they rotate with respect to one another as
shown.
• The primary coil is usually the stator and the secondary coil the rotor, the
direction of rotation generally depending on whether the incoming voltage is
to be raised or lowered.
• The voltage induced in the secondary or in series winding will depend on the
position in relation to the primary winding. Depending on the position, the
induced voltage can add to or subtract from the input voltage to obtain the
output voltage.

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

• During the rotation of the primary coil, the moving magnetic field can cause
a large reactance voltage drop in the secondary.

• To cancel this effect, a third coil is mounted at right angle to the primary coil
on the movable core and short circuited on itself.

• The moving primary coil will induce a voltage in the third coil which will, in
turn, set up a moving magnet field of its own, which will tend to oppose that
set up by the motion of the primary coil.

• The reactance of the regulator unit is thus kept essentially constant.

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

Induction type of voltage regulator

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

Step Type Regulators

Step type or TCUL regulators are further classified as either

(i) Station type. Which are 1-ɸ or 3-ɸ and it can be used in substations for bus
voltage regulation or individual feeder voltage regulation.
(ii) Distribution type. Which can be only 1-ɸ and used for pole mounted on
over head primary feeder.
• It is essentially an autotransformer, and is connected in the feeder as same
manner as the induction regulator. This type does not employ rotation of one
of the coil, but changes voltages by means of taps in the primary coils as
shown in fig.
• Most of the regulators are designed to correct the line voltage from 10%
boost to 10% back in 32 steps, with a 5/8 % voltage change per step.

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

• In addition to its autotransformer components, a step type voltage regulator

also has major components namely the tap changing and control
mechanisms.

• Each voltage regulator is consisting of necessary controls and accessories and

so that the taps are changed automatically under loads by a tap changer
which response to a voltage sensing control to maintain a pre determined
output voltage.

• By receiving its inputs from PT’s and CT’s the control mechanism provides
control of voltage level and bandwidth.

• Further, it provides the ability to adjust line drop compensation by selecting

resistance and reactance settings.
Electrical Distribution Systems Ch.B.A.Raju 11/16/2023
 Aditya Engineering College (A)

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

Line Drop Compensation

• Voltage regulators located in a substation or on a feeder are used to keep the
voltage constant at a regulating point with out changing magnitude and p.f.
of load.
• Where it is desired to regulate or maintain the voltage limit at some distance
from the source of the distribution feeders, a lone drop compensator is used
with the contact making voltmeter.
• This is an electrical miniature of the feeder to the point where the regulator
is designed as shown in fig.
• Resistance and reactance values are set on the compensator, the feeder
current, through a current transformer, flows through the compensator,
producing a voltage drop proportional to the current.
• this drop is subtracted from the feeder voltage at the regulator terminals,
thus applying at the contact making voltmeter at a voltage representing the
voltage at the point of compensation.

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

• The point of compensation should be selected so that the customers farthest from
the regulator will have the least lowest permissible voltage under the heaviest load
while the customer nearest the regulator will have the highest permissible voltage
under light load conditions.

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023

 Aditya Engineering College (A)

Thank you

Electrical Distribution Systems Ch.B.A.Raju 11/16/2023