Voltage Regulator Placement &
Settings
Jim Cross, PE
Planning Engineer
Homer Electric Association, Inc.
Kenai, Alaska
Outline
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Why Do We Need Them?
How Do They Work?
How Can WindMil Help Us?
Case Study
References / Questions?
Why Do We Need Them?
•  Utilities are required to maintain acceptable
voltage limits for it customers/members
–  ANSI C84.1
–  RUS 1724D-101A
–  RUS 1724D-113
•  A utility also wants to maintain acceptable
voltages on the equipment it has invested in &
installed on its system.
Why Do We Need Them?
In addition to the actual voltage limits, there are also
guidelines for the voltage drop:
Sec$on of Rural Distribu$on System: Voltage Drop (V) Voltage Drop (%) Substa'on bus to end of primary distribu'on line 8 Volts 6.67 % Distribu'on transformer & service conductors to metering point 4 Volts 3.33 % Customer’s service point to u'liza'on point 4 Volts 3.33 % SOURCE: RUS Guide 169-­‐27, Voltage Regulator Applica'on on Rural Distribu'on Systems Regulators or Capacitors?
•  Capacitors are applicable when the problem
is chronic low voltage, particularly caused
by a low power factor.
•  Regulators are more applicable when the
power factor in generally good, and the
voltage problems are caused by swings in
the system load or supply voltage.
Outline
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Why Do We Need Them?
How Do They Work?
How Can WindMil Help Us?
Case Study
References / Questions
How Do They Work?
•  A voltage regulator is essentially a 1 : 1.1
autotransformer. The top 10% of the winding is
reversible, allowing for raising (boosting) of the
load voltage to 1.1 p.u., or lowering (bucking)
to 0.9 p.u. as necessary.
•  Typically there are sixteen “taps” on the series
winding, so each “step” is worth 10/16 or 5/8%
correction per step.
How Do They Work?
•  While there are 3Ø voltage regulators, it’s more
common to see 1Ø regulators installed on a rural
distribution system. This allows a bank of 1Ø
regulators to independently regulate each phase.
This is often desirable when the feeder loads are
predominantly 1Ø.
•  Load-tap-changers (LTCs) work the same way and
are often found built-in to substation power
transformers.
Regulator Schematics (1 of 2)
R
IL
L
L
I2
IL
+
E2
2
+
+
N
L
Preventive
autoxfm r
+
S
VL
VL
V
S
SL
1
-
I
-
E
1
-
+
VS
IS
IS
N1
+
-
S
SL
This is a Type A voltage regulator: • The series winding is on the load side • The reversing switch allows the series winding to boost or buck as necessary • The preventa've autoxfmr is the mechanism that allows the regulator to switch under load w/o interrup'ng the customer loads Regulator Schematics (2 of 2)
Preventive
autoxfm r
IS
N2
I2
+
S
R
E2
+
I
S
S
+
L
IS
IL
N1
+
VS
+
E
1
+
VL
1
-
-
SL
L
V
S
VL
I
-
L
IL
SL
This is a Type B voltage regulator: • The series winding is on the source side Regulator Sizing
•  The rated range for a typical +/- 10% voltage
regulator is 10%.
•  For a 14.4 kVlg system that needs to supply
400A, the kVA size calculation would be:
kVA = 0.1 x System kVA
= 0.1 x 14.4 x 400
kVA = 576
Regulator Nameplate
In addi'on to the prescribed 576 kVA ra'ng, this regulator has an extra fan ra'ng. If the user constrains the opera'ng range, they can increase the kVA (A) ra'ng. Many regulators do allow for reverse power flow that might be seen during con'ngency opera'on. Regulator Control Settings
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Voltage Setpoint
Bandwidth
Time Delay
Line Compensation (R/X)
Regulator Control Settings
• The set voltage is the desired voltage • The bandwidth se]ng determines the amount of variance allowed before the regulator changes tap • Time delay prevents the regulator from inadvertently tapping for momentary voltage fluctua'ons Regulator Control Settings
•  Utilities typically want to minimize the # of tap-changes
on voltage regulators to minimize maintenance. We
don’t want the regs to tap on every little voltage sag/
swell, so we usually implement a time delay to make
sure we only tap for sustained excursions “outside of
band”.
•  For multiple regulators in series, we typically sequence
the time delays so the regs don’t tap at the same time.
Load Drop Compensation Settings
•  While a regulator will control the voltage at it’s load
terminals, the real goal is to maintain good voltage for
the customers
•  Frequently, we have to locate our regulators away from
the areas where we want to adjust and correct voltages
•  If one can calculate the electrical distance (Z) between
the regulator’s terminals and the load center we wish to
regulate, we can use this to “compensate” the voltage
regulator’s set voltage for the remote load center
Load Drop Compensation Settings
kVA rating
kVhi - kVlow
Vsend
Vload
I line CTp:CTs
Rline + jXline
I comp
R
X
Load
L DC side
1:1
+ V drop kVlow:120v
+
V reg
-
Relay side
+
Vrelay
-
Voltage
Relay
The LDC compensator circuit “fools” the regulator by adding a secondary voltage propor'onal to the voltage drop caused by Rline + jXline. Outline
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Why Do We Need Them?
How Do They Work?
How Can WindMil Help Us?
Case Study
References / Questions
How Can WindMil Help Us?
•  Since WindMil models all of the Z data for
our systems, it can rapidly run voltage
drops for various regulator placement
scenarios.
•  It can also perform the tedious calculations
for the LDC settings if we give it some
guidelines to work within.
WM Regulator Setup
Basic setup for winding config & phase configura'on Set voltage base Equipment defini'on Set voltage Compensa'on se]ngs here, in volts These constrain the VR’s terminal voltage to protect local customer loads WM Regulator Equipment Setup
Equipment name Size, in Amps Defines step size Bandwidth WM Tools – Voltage Profile Plots
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Voltage Profile
Plots after
running Voltage
Drop.
Provides a
great summary
of a feeder
voltage profile
after running an
analysis.
WM Tools – Set Regulation activity
•  Set Regulation calculates line drop
compensation values for each regulator you
select. Set Regulation can calculate these
values based on specified load centers, or it
can calculate them based on a range of
voltages.
WM Tools – Set Regulation analysis
The Regulator Selec'on tab is where the user can see all VRs in the ac've model, pick which ones to evaluate, and show their load center, if applicable. WM Tools – Set Regulation activity
The Regulator Limit Se]ng tab is where one sets limits for voltages & LDC calcula'ons. It also controls some of the ac'vity se]ngs, such as calcula'on tolerances, balanced or unbalanced, etc. WM Tools – Set Regulation activity
The LDC Rules tab is where one sets the rules for op'mizing the desired results. Outline
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Why Do We Need Them?
How Do They Work?
How Can WindMil Help Us?
Case Study
References / Questions
Case Study
•  An industrial customer (in this case an
oilfield owner in a remote location)
approaches the utility and wants to know
how much additional capacity they can
provide w/o a costly line rebuild?
Case Study - Overview
• Approximately nine (9) miles between points of interest • Mostly 1/0 ACSR • From the Tauranien Trail Recloser, the line is essen'ally a dedicated feed • Dedicated sec'on of line runs thru a Na'onal Wildlife Refuge w/ poor soils • Customer owns a significant amount of it’s own 25 kV OH system Case Study - Overview
• Detailed model, no secondaries • Customer’s system is modeled but not used for this demo Case Study - Overview
• End-­‐of-­‐line facili'es between u'lity customer. • This is the study area of interest. • We assume for this presenta'on that customer will make VAR improvements propor'onal to load growth Voltage Profile – Existing
• Nothing remarkable, no issues Case Study - Goals
•  Maximize kVA available to oilfield at end of
line
•  Maintain acceptable voltage for industrial
customer and residential loads on same
feeder near substation
Case Study - Notes
•  Industrial customer actually owns its own 25
kV OH system … responsible for its own
regulation past the metering point.
•  There is already adequate kVAR
compensation and regulation at the end of
the line for existing loads
Case Study Procedure
Utility is experiencing little load growth
in the near-term.
–  Grow residential loads by 5% to provide reserves
going forward.
–  Grow industrial loads until problems are detected.
Solve when possible by addition of regulator.
Case Study – 3000 kW
• Regs are tapped nearly to limits • Upstream customer outside of Range A Voltage Profile – 3000 kW
• Prely big drop in end-­‐of-­‐
line voltage • Since power-­‐factor is good, a new regulator is a logical choice Add a New Line Reg - Floating
• 1st analysis will set reg as floa'ng, regula'ng it’s own terminals • Loca'on driven by desire to keep major equipment on State roads. • Borough (“county”) roads are usually gravel, maintenance snow-­‐plowing efforts onen fall behind Add a New Line Reg - Floating
• 200A regulator is a standard size for the u'lity • Leaving R and X se]ngs at zero (0) means regulate at the load terminals Case Study – 3000 kW + Reg
• Tap posi'ons on exis'ng reg are 9, 8, 8 • No more voltage viola'ons Voltage Profile – 3000 kW + Reg
• New reg • Can we do beler? Set Regulation Set-Up
Case Study – 3000 kW + LDC Reg
• Tap posi'ons on exis'ng reg are 7, 7, 6 • Exis'ng reg source voltage improved from ~ 115 V to over 116 V • S'll no voltage viola'ons Voltage Profile – 3000 kW + LDC Reg
• This por'on of voltage profile gets shined due to LDC Other Considerations
•  Adjust substation regulation set-point
•  Move new regulator around, given
operational, RoW, & construction
constraints
•  Economics
Outline
•
•
•
•
•
Why Do We Need Them?
How Do They Work?
How Can WindMil Help Us?
Case Study
References / Questions
References
•  ANSI C84.1 – 2011, Electric Power Systems and Equipment Voltage
Ratings (60 Hertz), American National Standards Institute. 2011.
•  Distribution System Modeling and Analysis, William H. Kersting. CRC
Press, 2002.
•  REA Guide169-27 - Voltage Regulator Application on Rural
Distribution Systems. US Department of Agriculture – Rural
Electrification Administration, 1973.
•  The Application of Capacitors on Rural Electric Systems. US
Department of Agriculture – Rural Utilities Service, 2001.
•  Power Distribution Engineering: Fundamentals & Applications, by
James J. Burke. Marcel-Dekker, 1994.
•  WindMil 101, by William H. Kersting. Milsoft Users Conference, 2012.
Questions???