1. VOLTAGE REGULATION
5 June 2014
By : Ernst de Villiers

2. Layout of Presentation
• Problem Statement
• Construction of the Voltage Regulator
• Basic theory of Voltage Regulation
• Implementation of Voltage Regulators
• Voltage Regulators Vs. Load Tap Changers
• Case Study – Commissioning
2

3. 3
Problem Statement
• An ideal electric power system
would supply constant voltage at
rated value for every piece of
equipment.
• Power systems cannot deliver a
constant voltage level due to
line losses caused by the line
impedance and an increase in
load density.
• When voltage profile limits are
exceeded, either performance or
equipment life is sacrificed.

4. How Voltage drops are created
• MV distribution feeders are designed short enough and/or are loaded
so that the voltage profile is kept within specific limits.
4
Medium length line model
Properly-designed distribution feeder

5. Problem Statement
• To minimize the time and expense of serving the new load, the length
of the feeder is usually extended. Hence, in most cases, the feeder
develops an unacceptable voltage drop as shown in the figure below.
5
Increase of load density and feeder length
results in an unacceptable voltage drop.

6. Solution – The Voltage Regulator
6
• A Voltage Regulator can continuously monitor the output voltage
and automatically adjust itself by changing taps until the desired
voltage is obtained .

7. Operational Theory
• A voltage regulator holds line voltage within predetermined limits and
assures the proper operation of connected loads
• To understand how a regulator operates, one must first understand
how a two-winding transformer operates.
7
Transformer Model
Ideal Transformer

8. • These two independent windings can then be connected so that their
voltages may aid or oppose one another.
• Thus, the output terminal voltage can either be measured as the sum
of the two voltages or the difference between them.
• Therefore; transformer becomes a auto transformer with the ability to
raise or lower the primary or system voltage
8
Operation Theory
Step-down Trfr Step-up Trfr

9. 9 9
How does a Voltage Regulator work?
A single-phase regulator is represented by the autotransformer in
the figure below.
•Series Winding – Low voltage Winding
•Shunt Winding – High Voltage Winding
Voltage Regulator Diagram

10. 10
How does a Voltage Regulator work?
By reversing the polarity of the series winding, the autotransformer
can boost (increase) or buck (decrease) the output voltage with
respect to the input voltage
Step-down Trfr
Step-up Trfr
Voltage Regulator Diagram

11. 11
How does a Voltage Regulator work?
Polarity reversing is achieved via a reversing switch. An on-load
tap-changer connects a variable number of turns of the series
winding into the circuit, thereby allowing small increments of
voltage change.

12. 2015-08-11 12
Schematic Diagram – 32 step Voltage
Regulator

13. Non Bridging Equalizing Winding and
Reactor
• The preventive autotransformer is required in order to smoothen the
transient encountered when switching taps.
• Thus, decreasing the interrupted current as the tap changer taps.
• Preventing the regulator from being disconnected from the circuit each
time the tap is changed.
13

14. Voltage Regulator Parts
14

15. Bushing Construction
15

16. Bushings
• The preferred bushing terminals are smooth, hot-dip tinned, copper cylindrical
stems provided with bimetallic clamps that are suitable for accepting
aluminum or copper conductors of 6 mm to 15 mm diameter.
16
BUSHING SPECIFICATION FOR POLEMOUNTED, SINGLE-PHASE, STEP, AUTOMATIC VOLTAGE REGULATORS

17. MOV Surge Arrester
17
At normal voltage the MOV disk is an
insulator and will not conduct current.
But at higher voltages caused by surges
(faults/ lightning) , it becomes a conductor.
Thus, the arrester protects the series
winding from surges.

18. MOV Surge Arrester
11 kV Application 22 kV Application
MCOV: > 2.5 kV >5 kV
Residual voltage: Ures <10.5 kV <20 kV
Rated discharge current 10 kA 10 kA
Creepage 31mm/kV 31mm/kV
18
According to Specification 34-2110:
The surge arrester shall comply with the following parameters:

19. Internal Parts – QD8 Quick Drive tap-
changer
19

20. Reactors
• A bridging reactor is required to maintain continuity during a tap
change and to provide impedance for limiting the amount of current to
be interrupted by the tap changer.
20
Core Type ReactorShell Type Reactor
Core type is designed that the two coils are interlaced resulting in minimal
impedance-to-load current flow and therefore minimal voltage drop.

21. CL6A Control Board
21

22. CL6A Control Board
22

23. Drag-Hand
23
The Yellow tap indicating needle drags minimum and maximum needles.

24. 24
How does a Voltage Regulator work?
Type of Regulators
Two types of regulators:
•Type A
•Type B step-voltage regulators are predominately used for distribution
lines outside of the substation and lateral circuits.

25. 25
Type A Regulator
The tapped series winding is located on the load side of the shunt
winding, and by adjusting those taps the output load voltage
changes.

26. 26
Type B Regulator
The tapped series winding is located on the source side of the
shunt (excitation) winding, and by adjusting those taps the output
load voltage changes.

27. Regulator Ratio
27
Typical maximum boosts and bucks are ±10%.
What will aR and nt=N2/N1 be in the maximum boost and buck positions?
9091.1
1
2

N
N
aR

0909.9091.1
1
2

N
N

28. Voltage Regulation Per Step
• According to AVR Spec 34-2110 – Regulators will provide 10%
regulation with 32 step (16 buck and 16 boost).
• Since 16 steps provides 10% boost (or buck), then a single step will
result in a voltage change of 1/16 of 10%, which is:
• Since “% voltage” is Per Unit voltage x 100, the Per Unit voltage
change per step is
• So we obtain 0.00625 Per Unit voltage change per step.
28

29. • The ratio (N2/N1)effective is then given by the pu voltage change per step
times the number of steps (Tap):
• Note that if Tap is 0, then the effective turns ratio is 0. In this case,
there is no boost, and VL=VS.
29
Voltage Regulation Per Step

30. Line Drop Compensation (LDC)
• Allows a constant voltage to be maintained at a load centre remote
from the regulator.
30

31. 2015-08-11 31
Wiring Diagram – CT Circuit Protection

32. How is it implemented?
• Two or three single-phase regulators banked together make it possible
to regulate the voltage of a three-phase system.
32
Closed-Delta Open-Delta
3 Voltage Regulators 2 Voltage Regulators
15% Regulation of Input
Voltage
10% Regulation of Input
Voltage
Mostly used in ECOU Cost effective

33. Connection Configuration
Two or three single-phase regulators banked together make it possible to
regulate the voltage of a three-phase system.
Closed Delta Implementation Open Delta Implementation
33

34. Configuration
34
Open-Delta connection
Closed-Delta connection

35. How ratings are selected
Two parameters are necessary to elect a voltage regulator:
1) Rated Voltage
2) Rated Current
• Rated Voltage: It must be equal to or higher than the system nominal
voltage.
• Rated Current: It must be equal to or higher than the maximum load
current at the place that regulator is going to be installed.
35

36. Regulator Tests
• The AVR shall have been type tested in accordance with, and found to
comply with, the following requirements of ANSI/IEEE C57.15.
• Impulse test;
• Temperature rise;
• Short-circuit tests – KA rating-3 seconds amps;
• Insulation testing – Megger
36

37. Where to Apply
1) On existing feeders with voltage drop problems
• This is a common application of voltage regulators.
• They are installed before the point that the voltage drop problem starts
under heavy load conditions.
37

38. 38
Where to Apply
2) Important laterals from a main feeder can be effectively
controlled with regulators.

39. 39
3) To serve a remotely located load
These types of loads can be economically and quickly served by extending
the existing feeder and installing voltage regulators to correct for the voltage
drop in the extension.
Where to Apply

40. Operating sequence to put a regulator bank
on bypass – Spec 34-1436
1. Apply all regulators on neutral tap
2. Check regulator incoming and outgoing links to be closed.
3. Close regulator bypass links.
4. Open regulator outgoing links.
5. Open regulator incoming links.
6. Test regulator to be dead.
7. Apply relevant earths
40

41. Operating sequence to put a regulator bank
back in service - Spec 34-1436
1. Remove all earths.
2. Check regulator bypass links to be closed.
3. Close regulator incoming links.
4. Ensure that regulators is on neutral tap.
5. Close regulator bank outgoing links.
6. Open regulator bank bypass links.
7. Put regulator on auto
41

42. 42
Voltage Regulators vs. Load Tap Changers
• The basic function of an electrical utility is to supply power to
customers.
• With system losses and voltage sags that must be corrected by
regulation in order to stay within the voltage limit.
• Even in a real world of ongoing maintenance and occasional
component failure, objectives of minimizing outage time and
limiting failures can be realized.

43. 3 Single phase Regulators Transformer + LTC
One phase offline- replacement of only
one regulator unit.
Failure of one phase of the TC, entire
unit removed – all phase effected.
43
Voltage Regulators vs. Load Tap Changers
One spare regulator unit can be utilized on any of the phases if
maintenance is required.
Full maintenance can be completed without diminishing system
service.
Each Single-phase unit has an independent control to react to
the voltage variances of the phase.

44. 44
Voltage Regulators vs. Load Tap Changers

45. Unbalanced phase voltages – single phase units can respond
individually to these independent feeder models.
By separating each phase into its own unit, every unit is made smaller
and easier to handle.
Bypass switching provides easy installation and the ability to remove a
regulator without dropping the entire bus or feeder.
45
Voltage Regulators vs. Load Tap Changers

46. Cost Comparison
46
• There are some choices to be made in how to regulate voltage; some of
these choices can require significant capital expenditures.
Study done by Cooper Power Systems Ref. Number R225-90-21

47. Prospect - Kaysers Beach Voltage Regulator
• 11kV Pine conductor line that interconnects with Prospect - Gately line
via a normally open point situated at structure PRO-KBH-79.
• Approximately 2078 number of customers – 83km line.
• This feeder is at its voltage limit due to the normal growth from supply
upgrades and new developments in the area.
• The acceptable voltage limit for this feeder is 95% of nominal.
Currently, the minimum voltage is 95%, hence the initiation of this
project.
47

48. Commissioning Test Sheet
• Procedure 34 – 1218 : Presents the Commissioning Check Sheet
48
VOLTAGE REGULATOR
COMMISSIONING CHECK SHEET
WORKS ORDER #
COMMISSIONED
BY:
DATE:
LOCATION:
REGULATOR DETAILS
VR SERIAL #: R =
W=
B=
KV RATING:
CONTROL MODEL: AMP RATING:
Cat Numbre R=
W=
B=
INLAND/COASTAL:
ON-SITE CHECKS
ACTION Yes No COMMENT/VALUE
1. Verify that HV Connections are correct
(2 x VR - Open Delta or 3 x VR - Closed Delta)
2. Verify Regulator & Line voltage is the same
(Name plate & line voltage)
3. Check that Regulator is on By-Pass & Isolated
(By-Pass CLOSED & All Links OPEN)
4. Check that Regulators & Controls are EARTHED
(Individually to same earthing point )
5. Check that all HV connection are TIGHT
6. Check that Regulator is in NEUTRAL position
(Position indicator & FC12)
7. Set Power switch & control switch to OFF position
(All three switches in middle )
8. In Control back panel OPEN knife switch V1, C (and V6 if
present), (pulled out)
(Terminal links)
9. Insulation test must be done
( 5KV Megger )
Ohm
10. Close Source-Load (SL) incoming link
(Operator to close)
CHECK THAT ALL 3 PHASES ARE PRESENT IN AND OUT
11. Measure Voltage terminal V1 to earth and confirm approx
118-122VAC
(If out of range, abort commissioning and investigate)
Volt
R = W= B=
12. In Control back panel CLOSE knife switch V1 (and V6 if
present), (pushed in)
(Terminal links)
13. Check that knife switch “C” is open
(Terminal links)
14. Set Power Switch to INTERNAL
(Power switch up)
Set Clock
( FC 50 )
15. Check NEUTRAL light is on
16. Check settings according to settings sheet (Annexure)
(Note: for testing of up/down tap, set FC56 to Lock Forward)
17. Set control switch to MANUAL
(Control switch down)
18. Manually RAISE tap till Out of Band indication ON
19. Set control switch to AUTO
(Control switch up)
20. Confirm auto-tap LOWER & Out of Band indication OFF
(FC3 Delay plus 2sec per tap)

49. • Evaluation of losses in step-voltage regulators is increasingly a major
consideration when evaluating competitive alternatives.
. Some of the areas that should be evaluated in addition to the cost :
• Maintenance,
• Installation and Operation,
• Technical support,
• Dielectric strength,
• Short circuit strength,
• Losses
49
Regulator Characteristics

50. Thank you
Open for Discussion