Theory Voltage Regulators

2013 Eaton. All rights reserved.

Theory, Construction and Application

Voltage Regulator Training Schools

2 2013 Eaton. All rights reserved.

Regulator Theory Purpose

What is Voltage Regulation?

Voltage Regulation Providing a consistent

sine way with a nearly constant magnitude to

the load.



Why is voltage regulation needed?

Power quality criteria requires a constant voltage

despite variations in load current

Load current variations are due to:

New loads

Load profiles Daily and Seasonal

CURRENT

TIME OF DAY

12am 6am 12pm 6pm

LOAD CURRENT VS TIME OF DAY



Properly designed distribution feeder

L1

OLTC

L2 L3

+5%

5%

Nominal

Voltage

Minimum Acceptable Voltage Level

Maximum Acceptable Voltage Level

Light Load

Heavy Load

OLTC = On-Load tap changing power transformer



Over Time An increase of load density and feeder

length results in an unacceptable voltage drop.

Also, voltage can drop off due to line losses.

OLTC L1 L4 L2 L5 L3 L6 L7

+5%

5%

Nominal

Voltage

Minimum Acceptable Voltage Level

Maximum Acceptable Voltage Level

Light Load

Heavy Load



Voltage Regulators: Solve voltage drop problem

+5%

--5%

Nominal

Voltage

OLTC R1

L1 L4 L2 L5 L3 L6 L7

Applied at Substation and midpoint of Feeder.



Supplying unregulated voltage effects equipment

Low Voltage

Reduced Heat

output

Over-voltage

burnouts

Brownouts

A 10% voltage

reduction --- light

output reduced

by 30%

Over-voltage

A 10% over-

voltage reduces

bulb by life 70%

Low and high voltage

Increased current

demand

Overheating

Shortened motor life

In addition low voltage

can cause

Reduced starting and

running torques

High voltage

Run hot

Fail prematurely

Low voltage

Electronics become

inoperative

Heating Element Lighting Motors Electronics



To reiterate

Primary purpose of a voltage regulator

Provide regulated voltage to meet power quality criteria

Electronic controls also enable

Peak shaving

Metering

Integrated volt/var control (IVVC)

CBC-8000

Cap Bank Control

CL-7

Voltage Regulator

Control


Regulator Theory

Voltage Regulator

Construction


Regulator Theory Construction

Three basic part of a voltage regulator

Autotransformer - A transformer in which part of

one winding is common to both the primary and

secondary windings

Load Tap Changer - A switch designed to work

under load to change the configuration of a

transformer coil

Voltage Regulator Control - A Control which senses

the system and automatically commands the tap

changer



Vprimary = 1000V Vsecondary = 100V

+

-

-

+

10:1

10:1 Windings Ratio

Output Ratio

Conventional Two-winding Transformer



10:11

10:1 Windings Ratio

Output Ratio

Vprimary = 1000V Vsecondary = 1100V

+

-

-

+

Step-up Autotransformer (+ to ) = Additive Property



10:9

10:1 Windings Ratio

Output Ratio

Vprimary = 1000V

Vsecondary = 900V

+

-

-

+

Step-down Autotransformer (+ to +) = Subtractive Property



Step Voltage Regulator

Stationary Contacts

Movable

Contacts

+

+

_

1

2

3

4

5

6

7

8

N

_



Step Voltage Regulator with Reversing Switch

+

+

_

1

2

3

4

5

6

7

8

N

_

Shown in Step

Down or Bucking

Position



Step Voltage Regulator with Reversing Switch

+

+

_

1

2

3

4

5

6

7

8

N

_

Question:

If there are 8 stationary

contacts, why do we call

it a 32 step regulator?

Add the reversing switch

and you get 32!

Answer:

8 stationary contacts

+ 8 intermediate

positions = 16 steps.



Bridging Reactor

Required to maintain

continuity during a tap change

Provide impedance for limiting

the amount of current to be

interrupted by the tap changer

Moveable

Contacts

Bridging

Reactor

Stationary

Contacts



Non-Bridging Position

Two movable tap changer

contacts on a symmetrical

(even) position

The center tap of the

reactor is at the same

potential.



Asymmetrical Position Occurs when one tap

connection is open before

transferring the load to the

adjacent tap

All load current flows through

one-half of the reactor,

magnetizing the reactor, and

introducing a reactance voltage

drop in the circuit

This transfer takes around 25-

30 milliseconds for completion.

Three current zero

opportunities are required for

arc extinction at a minimum



Bridging Position Movable contacts are in a

bridging (odd) position

Voltage change is one-

half the 1% (5/8%) tap

voltage of the series

winding because of its

center tap and movable

contacts located on

adjacent stationary

contacts.



Two Predominate Types:

ANSI TYPE A (Series After Shunt)

STRAIGHT

Shunt

Winding

Series

Winding

ANSI TYPE B (Series Before Shunt)

INVERTED Series

Winding

Shunt

Winding



Factors to Consider between types: Cost, Losses, Control Accuracy, Short Circuit Withstand

CPS Type A

CPS Type B

1. Series windings are located on the Load side of the Shunt windings

1. Series windings are located on the Source side of

the Shunt windings

2. Has separate control PT to measure the voltage

between the Load and Source-Load bushings and

supply power to the control and motor

2. Does not have a separate PT - Instead has control

windings (tertiary) in main coil to measure the

voltage between the Load and Source-Load

bushings and supply power to the control and motor

3. Typically used for large KVA regulators (500 KVA

and above) since control winding can not

adequately couple with shunt winding and still

achieve ANSI Class 1 control accuracy

3. Typically used for small KVA regulators (416 KVA

and below) since control winding can adequately

couple with shunt winding and still allow for ANSI

Class 1 control accuracy

4. Regulation Range is +10% and -10%

4. Regulation Range is +10% and -8.3%

5. Less economical, taller and heavier

5. More economical, shorter and less weight

6. Low-High-Low Coil Construction allows for

improved short circuit strength (up to 40 times or

20 kA) and lower stray losses

6. High-Low Coil Construction meets ANSI C57.15

short circuit requirement of 25X nominal current

rating



N

1.25%

L

SL

S

SHUNT

WINDING

CONTROL

SERIES WINDING

POTENTIAL

TRANSFORMER

REVERSING

SWITCH

CURRENT

X-FORMER

1 2 3 4 5 6 7 8

Type A


Regulator Theory Construction Type B

N

1.25%

L S

CONTROL

SERIES WINDING

REVERSING SWITCH

CURRENT

X-FORMER

1 2 3 4 5 6 7 8

SL

SHUNT

WINDING

CONTROL

WINDING



Two additional Cooper regulator Types

Used for applications rated 875 A and above

Type TX (Type C on the Cooper nameplate)

Series Transformer Design

Used on 2.5 kV designs

Type AX (Type D on the Cooper nameplate)

Series Autotransformer Design

Used on 5.0 and 7.62 kV designs


Regulator Construction Features



Series arrester



Position Indicators

Current Position Indicator

Corrosion Resistant

20% Larger Viewing Area

Pad-Lockable

Lighter Weight

Slim Profile

Legacy Position Indicator



Control cable

Disconnect plug at both

ends

Easy maintenance

Easy replacement

No conduit

No wiring diagrams

CT Protection Circuit

CT automatically shorted

when control cable is

removed

Quicker and safer removal

of the control box and

cable for field retrofits

Maintenance free



Junction Box & Block

Plug-in junction block wiring harness

New block is completely retrofittable with existing regulators

Prevents possibility of mis-wiring

Inside Tank

(Under cover)

Current Design Legacy Design



Current Transformer

New CT mounting design

Eliminates possibility of cracked CT mounting ear in all-in-one

mold design

Prevents hardware from being over-tightened.

Eliminates stress on CT ears

Current Design

Legacy Design



Inspection Hand Hole Six-inch Diameter cover hole

Vacuum Processing

User access

Inspection

Changing CT connections

Legacy Design

Vacuum Oil Filling

Moisture and air removed

Oil filled and soaked 8-24 hours

2mm Mercury (750 torr)



Core and Coil

Materials similar to those used in Transformers

Epoxy coated paper

Coil sides clamped and hot pressed

Wasted space removed to create lean design using

materials efficiently and keeping losses to a minimum

Coil margins increased for arcing environment

Current carrying leads tied off

with cotton wrap NOT plastic

tie-wraps



Quik Drive Tap Changers Longer Life

20% fewer parts than traditional spring loaded devices less maintenance, longer life, and lower life

cycle costs

The Geneva Gear drive ensures accurate steps without the need for special calibrated springs

resulting in greater tap changing accuracy, extended contact life and less maintenance

Improved Power Quality Taps all 33 positions in less than 10 seconds 5 to 10 times faster than traditional spring drives

The speed result in better power quality and quicker recovery from large voltage excursions, which

protects customer equipment

Lower Operational Costs Installation and maintenance time is reduced, which can save time and money


Regulator Construction Product Scope

Voltage regulator product offering:

Regulation of +/- 10% in 32 - 5/8% steps

55/65 C Average Winding Rise (12% more capacity)

25 to > 2000 Amperes

50 Hz - 6600 V to 33000 V (95-200 BIL)

60 Hz - 2400 V to 34500 V (60-200 BIL)

Mineral Oil or FR3 Immersed

Fan Cooling option (33% more capacity)



Padmount Voltage Regulators Aesthetically pleasing

Reduced costs No Overhead lines or Substation Fences

Less overall land required

Easier to obtain right of way

Innovative

Underground solution

Deadfront connector system Safety

Reliability

Great green solution with FR3



Padmount Voltage Regulators



Three-in-one Padmount Voltage Regulators


Regulator Application


Regulator Application ADD-AMP

Limit range of regulation to

increase current capacity

Soft ADD-AMP

Limits set on control

Can be overridden manually

or through SCADA

Hard ADD-AMP

Set using position indicator

limit switches (yellow tabs)

% Range of

Regulation

% or Rated

Current (A)

at 55 C

+/- 10.0 100

+/- 8.75 110

+/- 7.5 120

+/- 6.25 135

+/- 5.0 160


Regulator Application ADD-AMP

Limited to 668 Amps MAX per ANSI

Useful in an emergency situation when a larger

regulator is not available

Nameplate table lists multiplier to use times the base

(55 C) current

Is limited by the capacity of the tap changer contacts

Uses limit switches in motor circuit to reduce the

number of series winding turns, therefore reducing

heat generated at a given current


Regulator Application Multiple Voltages TAP

IN

USE

LOAD

VOLTS

CONTROL

WDG. TAP

(TANK)

INTERNAL

P.T.

RATIO

R.C.T.

TAP

(CONTROL)

TEST

TERMINAL

VOLTAGE

OVERALL

POT.

RATIO

14400 E1 120:1 120 120 120:1

13800 E1 120:1 115 120 115:1

13200 E1 120:1 110 120 110:1

12000 E1 120:1 104 115.5 104:1

7970 E2 60:1 133 120 66.5:1

7620 E2 60:1 127 120 63.5:1

7200 E2 60:1 120 120 60:1

6930 E2 60:1 115 120.5 57.5:1

Voltage chart

example from a

14400 V nominal

nameplate

Nominal

Voltage

Standard Available voltages (60 Hz)

2500 2500 2400

5000 5000 4800 4160 2400

7620 8000 7970 7620 7200 6930 4800 4160 2400

13800 13800 13200 12470 12000 7970 7620 7200 6930

14400 14400 13800 13200 12000 7970 7620 7200 6930

19920 19920 17200 16000 15242 14400 7970 7620 7200

34500 34500 19920

Standard Voltages


Regulator Application - Connections

4-wire

Grounded Wye

S

L

SL

A

B

C

N

Source

Disconnect

Series

Lightning

Arrester

Bypass Switch

Shunt

Lightning

Arrester

L

S SL S

L

SL

N

VAN

VAN

120 o

VBN

VCN

VCN

VBN

Three single-phase regulators on a 3-phase, 4-wire circuit



3-wire

Open Delta

Disconnect

Switch

Bypass Switch Phase A

Phase B

Phase C

S

L

SL S

L

SL

B

System

Voltage

VAB (1.0 pu)

VCA (1.10 pu)

60 o

VCA

VAB (1.1 pu)

VCB (1.0 pu)

VCB (1.1 pu)

Two single-phase regulators on a 3-phase, 3-wire circuit



3-wire

Closed Delta

Bypass Switch Phase A

Phase B

Phase C

S

L

SL S

L

SL

Disconnect

Switches

S

L

SL

VAC (1.15 pu)

A

B C

A

B C

VBA (1.15 pu)

VCB (1.15 pu)

VBA

(1.00 pu)

3 single-phase regulators on a 3-phase, 3-wire circuit.


Regulator Application LTC Comparison

Why voltage regulators over LTCs?

Regulate individual phases

Separate regulation from voltage transformation

Fast change out

Maintenance will not disrupt service

Versatile & economical

Standardized product

Readily available vs. 1 year lead times



Why voltage regulators over LTCs?

Regulate individual phases

Separate regulation from voltage transformation

Fast change out

Maintenance will not disrupt service

Versatile & economical

Standardized product

Readily available vs. 1 year lead times



Why LTCs over voltage regulators?

LTC ratings go beyond VR ratings

Some prefer 3Ph Ganged Operation for 3PH loads

Reduced contact wear and maintenance

Space

Other reasons?


Regulator Application Cascading Rules

Rule 1: Each succeeding regulator in series down line from the source requires

a longer time delay

Rule 2: The minimum time delay from one regulator to the next in cascade is 15

seconds

3-phase

LTC

transformer

TD = 30 SEC

SVR

TD = 45 SEC

SVR

TD = 45 SEC SVR

TD = 45 SEC

SVR

TD = 75 SEC

SVR

TD = 60 SEC

SVR

TD = 75 SEC



Coordination on a loop system Forward operation

3-phase

LTC

TD = 30 SEC

N.C. N.C.

N.C. N.C.

N.O.

TD 45 SEC TD 60 SEC

TD 60 SEC TD 45 SEC



Coordination on a loop system Reverse operation

N.C. N.C.

N.C. N.C.

N.O.

FTD 45 SEC

RTD 90 SEC

FTD 60 SEC

RTD 75 SEC

FTD 60 SEC

RTD 75 SEC

FTD 45 SEC

RTD 90 SEC

3-phase

LTC

TD = 30 SEC


Regulator Application Leader/Follower

Scheme to keep all regulators on

same tap position replicate 3Ph

Ganged LTC

Communication Loop between

Leader and Followers to insure

locked step

Feedback loop insures

synchronization

Regulates voltage based on Master

device

Requires communication loop

Install dedicated communications

module for each device

CL-7 offers Voltage Averaging and

Max Deviation options


Regulator Application - Paralleling

Why Paralleling?

Handle a larger capacity load or provide continuity and reliability of service for a high priority load.

Concern

In a paralleling application, circulating current flows within the loop when there is a difference of

potential due to the voltage regulators being on different steps. The amount of circulating current is

also dependent on the amount of impedance within the loop.

Voltage regulators have as much as 0.5 % impedance at their maximum tap position and essentially

zero on the neutral position; power transformers typically have impedance around 6%.

Solution Regulators must have a Leader/Follower control setup

VR1

LoadVR2

T1

T2

VR1VR1

LoadVR2VR2

T1

T2

Two Banks of Voltage Regulators Paralleled with a Set of Identical

Power Transformers


Regulator Application Safe Bypassing

Definition: Bypassing is installing or removing a

regulator from service.

Installing or removing an energized voltage

regulator with the tap changer off of neutral will

short circuit part of the series winding!

Before bypassing, the regulator must be in neutral.

Warning!



Prior to Bypassing: Place the regulator in the neutral

position - A minimum of four indicators are recommended to

confirm neutral!

Tap Position 0

At Limit

P.I. ADD-AMP -16, 16

Tap Position 0

At Limit

P.I. ADD-AMP -16, 16

Neutral lamp is ON continuously

Verify the tap position of the control indicates

Neutral by displaying 0

Position indicator is in neutral position

Verify that there is no voltage difference

between the S and L bushings



Prior to Bypassing Take Action to prevent tap-

changer motor operation

Control Function switch is OFF

Important to do this first!

Power switch is OFF

Remove motor fuse

V1 & V6 knife switches are OPEN


Regulator Application Safe Bypassing Regulator Connected Line-to-Ground (GY)

Source Load

Phase A

Neutral

SL

L S

S-DIS L-DIS

B

Start 1 2 3

B C C C O

S-Dis O C C C

L-Dis O O C C

Installation


Regulator Application Safe Bypassing Regulator Connected Line-to-Ground (GY)

Removal Source Load

Phase A

Neutral

SL

L S

S-DIS L-DIS

B

Start 1 2 3

B O C C C

S-Dis C C C O

L-Dis C C O O


Regulator Application Bypass Fault Current

Source current is a function of shunt and load current and is the current to

which the over-current protection responds.

During a bypass fault, the source current only reaches a value of 2 to 3 times

the nominal value not high enough to activate over-current protection.

The circulating current through the series windings when bypassed off neutral

can be 60-100 times nominal.

The magnitude of the circulating current depends upon the regulator type, tap

position and the voltage and current ratings.


Regulator Application Bypassing

Documents

Theory Voltage Regulators