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TechAdvantage 2015
SMART VOLTAGE REDUCTION
David Aldrich, P.E.
Beckwith Electric
BECKWITH
ELECTRIC
CO.INC.
727.544.2326
[email protected]
Discussion
 LTC Control Basics
 Smart Voltage Reduction
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What, Why?
How- Historical and “Smart” Methods
Interaction with Capacitors
Improving CVR Factor (CVRf)
LTC Control Basics
 To accomplish voltage regulation,
these minimum parameters must be defined
 Bandcenter (V)
 Bandwith
 Time Delay
LTC Control Basics
 Additional Functions of Modern LTC Controls
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Line Drop Compensation
Blocking
Reverse Power
Voltage Reduction
Tap Position Monitoring
Transformer Paralleling
Advanced Smart Grid Communications
Data Logging, SOE, Power Quality
Condition Based and Automated Maintenance
Conservation Voltage Reduction
 Conservation Voltage Reduction (CVR)
 Part of Voltage/VAr Optimization (VVO)
 Intentional lowering of distribution circuit voltage
within lower band of allowed ANSI C84.1 (2006)
 Standard for Electric Power Systems and Equipment – Voltage Ratings
•
•
Range A is the optimal voltage range
Range B is acceptable, but not optimal
VVO and CVR - Why

Lowering distribution voltage levels during peak periods to
achieve peak demand reductions

Reducing voltage levels for longer periods to achieve
electricity conservation

Reducing energy losses in the electric distribution system
Expected benefits include deferral of capital expenditures, energy
savings, and greater operational flexibility and efficiency
Voltage and Reactive Power Management – Initial Results: US DOE, 12/12
Conservation Voltage Reduction - What
 Goal of voltage reduction is to reduce load
V= I * R for resistive load
The lower the V the lower the I
The lower the I, the lower the I2R = W (constant Z load)
 Ex., incandescent lights, strip heaters
Not true if load is not constant power type (constant PQ load):
 Ex., motors, power supplies
Can be deployed at:
 All times
 For load reduction periods
 During system emergencies when the voltage is collapsing
due to more load than available generation or supply
% VR
pf 1.0
Load Reduction
pf 0.9
Load Reduction
2%
1.5 %
0.5%
4%
3.0 %
2.0%
EPRI “Distribution Green Circuits” Report - 2010
Load Models and CVR Factor

Load models
 Constant Power (PQ)
 Constant Impedance (Z)
 Constant Current (I)
 CVRf = ∆P/∆V
 0.8 to 1 is typical
 Greater than 1 is really good
Load current changes inversely
to the change in voltage
Load current changes
linearly with the change in delivered
voltage, and the demand varies as a
squared function of
the voltage change
Power delivered to the load
varies linearly with the change in
voltage delivered to the load
Evaluating Conservation Voltage Reduction with WindMil® - Milsoft
Substation
Traditional VVO & CVR
Cap #2
Cap #1
With both caps on
VVO
With cap #1 on only
CVR – Conservation Voltage Reduction
Voltage Profile
Capacitors affect voltage level, losses, capacity, etc.
Loads only
General Rules for Coordination

Series Regulators
 Regulator closest to source taps first (shortest time delay)

Multiple Cap Banks (Voltage Controlled)
 Cap banks furthest from source close first, open last

Caps switch before regulators
 Decreases LTC/regulator operations
 Save asset
 Saves maintenance $$$
Historical Voltage Reduction
 Load Reduction called with Load
Management Software
 Load Reduction Software » SCADA »
Output Relay » LTC/Regulator Input
 Output relays connected to auxiliary
summing transformer with multiple taps
 Auxiliary summing transformer has taps
connected/disconnected by control relays
to create a higher sensing voltage the LTC
or Regulator Control
 This higher voltage, sensed by the
LTC/Regulator Control, would now cause
the control to issue tap-down commands
to lower voltage
 The control would not know that it is in
voltage reduction mode, and would simply
react to the sensed voltage change
LINE
VT
SUMMING
TRANSFORMER
SCADA
CONTACTS
FOR VOLTAGE
REDUCTION
LTC
CONTROL
Historical Voltage Reduction - Disadvantages
 The time delay to tap is still in play
 The percentage of reduction is fixed due to the taps
on the summing transformer
 Each percentage reduction point required an auxiliary
relay
 If the communications failed while in reduction, the
LTC or Regulator would remain in voltage reduction
Voltage Reduction in Modern Controls
Controls typically support three reduction levels
Reduction level range set from 1 -10 %
Typical for static or digital controls:
Contact sensing inputs
 The contacts would be from a SCADA RTU and/or
local switches
For digital controls, additionally:
Using the integrated HMI on the control (buttons)
Using PC software locally
Using SCADA interface (ex., DNP from RTU)
Using Ethernet by radio (ex., DNP TCP/IP)
Using Cellular or other medium
Example for Local Interface on Control
Typical Digital Voltage Regulator Control
HMI and Buttons
Voltage Reduction LED
Contacts Used for Voltage Reduction
Typical Digital Voltage Regulator Control
Voltage Reduction in Modern Controls
 Voltage Reduction changes the bandcenter to induce
controls to lower voltage instead of increasing sensed voltage
Signal to control can be:
o SCADA to contacts, contacts to control
o Direct SCADA DNP write to control
Time delay skipped on initial voltage reduction command
Because bandcenter is being altered, entering reduction does
not always reduce voltage, or reduce near amount of
requested reduction
Voltage Reduction
Bandcenter set to 122V, Bandwidth of 3V
Apply a 2% reduction
122 – 122* 0.98 = 119.56 or 119.6
Upper rail = 119.6 + (3/2) = 121.1
Lower rail = 119.6 – (3/2) = 118.1
123.5
3
120.7
122.0
121.1
120.5
120.7
Before Reduction
119.6
3
118.1
After Reduction
 Assume 0.75V/tap (10V/16 taps = 0.75V/tap)
 120.7V before reduction, after reduction that value is still in-band
 Results in no voltage reduction, 0%
Voltage Reduction
Bandcenter set to 122V, Bandwidth of 3V
Apply a 3% reduction of
122 – 122* 0.97 = 118.34 or 118.3
 Upper rail = 118.34 + (3/2) = 119.8
 Lower rail = 118.34 – (3/2) = 116.8
123.5
3
119.95
122.0
120.5
119.8
120.7
Before Reduction
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
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
119.2
118.3
3
116.8
After Reduction
Assume 0.75V/tap (120*10%=12V; 12V/16 taps = 0.75V/tap)
120.7V before reduction, 2 Taps Down Taken
Tap 1 = 119.95, Tap 2 = 119.2
% = ( | V1 - V2 | / ((V1 + V2)/2) ) * 100
= ( | 120.7 - 119.2 | / ((120.7 + 119.2)/2) ) * 100 = 1.25% reduction
Voltage Reduction
Bandcenter set to 122V, Bandwidth of 3V
Apply a 4% reduction of
122 – 122* 0.96 = 117.12 or 117.1
 Upper rail = 117.1 + (3/2) = 118.6
 Lower rail = 117.1 – (3/2) = 115.6
123.5
3
119.95 119.2
122.0
118.45
120.5
120.7
118.6
117.1
Before Reduction
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After Reduction
3
115.6
Assume 0.75V/tap (120*10%=12V; 12V/16 taps = 0.75V/tap)
120.7V before reduction, 3 Taps Down Taken
Tap 1 = 119.95, Tap 2 = 119.2, tap 3 = 118.45
% = ( | V1 - V2 | / ((V1 + V2)/2) ) * 100
= ( | 120.7 - 118.45 | / ((120.7 + 118.45)/2) ) * 100 = 1.88% reduction
Voltage Reduction
 A “Block Lower” setting of 118 will stop control
from performing voltage reduction if low limit
setpoint is violated
 Be sure “Block Lower” setting does not interfere
with voltage reduction
123.5
3
119.95 119.2
122.0
Block Lower
118.45
120.5
120.7
118.6
117.1
115.6
Before Reduction
After Reduction
3
Voltage Reduction Turnoff Timer
 Used to turn off Voltage Reduction (VR) if entered via SCADA or
pulsed contacts
 Intent is to remove voltage reduction mode if SCADA is lost and
communications goes down
 Control will automatically remove VR once the timer expires, even if
SCADA is still communicating
o New signal during timing interval would keep VR going
Voltage Reduction - Summary
o The control will never reduce the actual voltage by the
percentage requested
o The larger the bandwidth, the less actual reduction
o The “Block Lower” setting:

Blocks tap lowers if
measure voltage is
less than setpoint
o No time delay when
entering or exiting
voltage reduction
Voltage Reduction – Present Method
 If the goal of voltage reduction is to reduce voltage, we want
to finish reduction on lower end of band, not higher end
 Previous example: 3% request, 1.25% delivered
123.5
3
119.95
122.0
120.5
119.2
119.8
120.7
Before Reduction
118.3
116.8
After Reduction
3
Smart Voltage Reduction
Apply a 3% reduction of
122 – 122* 0.97 = 118.34 or 118.3
Upper rail = 118.34 + (3/2) = 119.8
Lower rail = 118.34 – (3/2) = 116.8
Temporarily:
• Disable Upper Band Limit
• Use Bandcenter as Upper Band Limit
123.5
3
119.95
119.2 118.4
122.0
120.5
120.7
Before Reduction
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
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
117.7
119.8
118.3
3
116.8
After Reduction
Assume 0.75V/tap (120*10%=12V; 12V/16 taps = 0.75V/tap)
120.7V before reduction, 4 Taps Down Taken
Tap 1 = 119.95, Tap 2 = 119.2, Tap 3 = 118.4, Tap 4 = 117.7
% = ( | V1 - V2 | / ((V1 + V2)/2) ) * 100
= ( | 120.7 - 117.7 | / ((120.7 + 117.7)/2) ) * 100 = 2.52% reduction
Leaving Voltage Reduction – Present Method
Unintended Results: Cap Banks May Stay On Too Long
REDUCTION kV
NORMAL kV
TEST MVAr
NORMAL MVAr
 Typically when entering reduction, all switched capacitors will
close as the voltage is reduced (assumed voltage control)
 This may cause circuits to be leading when in reduction
 When leaving reduction, some of the capacitors need to be
switched off to get back to unity power factor
Leaving Voltage Reduction - Present Method
119.2
123.5
119.95
122.0
120.5
119.8
3
3
120.7
118.3
116.8
During Reduction
Normal Operation
This may not be a high enough voltage to cause
voltage controlled capacitors to switch off
Leaving Voltage Reduction:
Smart Voltage Reduction Method
119.2
119.95
122.2
121.5
123.5
122.0
3
120.5
119.8
3
The extra voltage will
now allow the
capacitors to start
timing to an open
120.7
118.3
116.8
During Reduction
Normal Operation
 Lower band is temporarily disabled to force voltage to
finish between bandcenter and high band edge
 Once voltage crosses bandcenter, lower band edge
becomes active again
Cap Banks Opening After Leaving Reduction
Smart Method Employed
REDUCTION kV
NORMAL kV
TEST MVAr
NORMAL MVAr
Smart Voltage Reduction
About Those Capacitors...
 Proper coordination with switched capacitor banks will maximize the
amount of reduction possible
 The majority of the load on any feeder is at the feeder. The load drops
more the further we get from the substation
o (EPRI: 50% Load, 1st 25% of Feeder)
 To get maximum benefit out of reduction, the lowest voltage needs to be
were the highest current is (Zone 1)
115 KV
12 KV
12 KV
XFMR
12 KV
Substation
400
amps
600
kVar
1.1 V
300
amps
115 KV
115 KV
600
kVar
0.8 V
Zone 1
600
kVar
1.9 V
600
kVar
2.1 V
100
amps
50
amps
Zone 2
Positive Reactive Compensation

Using a positive X to bias bandcenter during reduction would allow
control to further lower voltage close to regulator as VArs go leading
 Push voltage lower as control detects leading VArs

Lowest voltage will be at regulator – voltage will be higher down
feeder as VArs go leading
Positive Reactive Compensation
 Setting added so control treats VArs
differently in voltage reduction
 Allows control to reduce voltage further as
down line as capacitors close
 If capacitors are out-of-service, control
will dynamically know not to lower voltage
as much while in reduction
 No communications required
Smart Voltage Reduction
About Those Capacitors...
Secondary Voltage
 Down stream capacitors, when closed will provide voltage
support at end of circuit
 Regulator detecting a leading power is an indication that
downstream voltage is higher than source voltage due to
voltage rise of cap banks
 This allows regulator to reduce voltage even lower
126 Vac
126
“Flipped Circuit”
120
Traditional
VVO
114 Vac
114
0
1
2
3
4
Distance
5
6
7
8
Present Method: V1 Pre
Smart Method: V1 Post
Applied on LTC
CVRf of 1.2 to
1.4 obtained
"Can a Grid be Smart without Communications? A look at an Integrated Volt VAR Control (IVVC)
Implementation," Barry Stephens, Georgia Power; Bob McFetridge, Beckwith Electric, April 25, 2012
Summary
 A new method exists for voltage reduction that
delivers closer to called percentage
 Coordination of capacitors with LTCs and
regulators provides VVO
 Using positive reactance compensation when in
voltage reduction, along with proper amount of
capacitance, allows “circuit flipping” of voltage
profile for even greater CVR factor
TechAdvantage 2015
QUESTIONS?
SMART VOLTAGE REDUCTION
David Aldrich, P.E.
Beckwith Electric
BECKWITH
ELECTRIC
CO.INC.
727.544.2326
[email protected]
References

ANSI C84.1, “Standard for Electric Power Systems and Equipment
– Voltage Ratings”

“Distribution Green Circuits Interim Report – 2010,” EPRI

“Evaluating Conservation Voltage Reduction with WindMil®,” Milsoft

“Voltage and Reactive Power Management – Initial Result,” US
DOE, 12/12

"Can a Grid be Smart without Communications? A look at an
Integrated Volt VAR Control (IVVC) Implementation," Barry
Stephens, Georgia Power; Bob McFetridge, Beckwith Electric, April
25, 2012
Annex: Percent Calculations