Download Voltage Reduction

Discussion and
Preliminary Findings
Concerning Voltage
Reduction (VR) for
Peak Shaving
December 6, 2012
Presentation to Reliability
Operations Subcommittee
Austin, TX
Mark Carpenter
Sr. VP T&D Operations
December 6, 2012
Voltage Reduction (VR) Overview
 Historically, the effectiveness of VR in ERCOT has been
viewed to provide minimal effectiveness during short supply
conditions;
 Nationwide, the use of VR is on the increase;
 Present residential HVAC loads appear to respond favorably
to VR;
 Nationally, more effectively harvesting the benefits of VR is
improved due to:
 Improvements in load tap-changer (LTC) control systems
 Ability to inexpensively monitor voltage along the distribution
circuit
 Ability to flatten the voltage along the distribution feeder
2
What others in the utility space are seeing:
 Across all circuits, for a 1% drop in voltage, many claim a 0.7 %
drop in sustainable demand reduction is obtained;
 Typical voltage reductions are limited to 5%;
 This results in a demand reduction of 3.5%;
 Generally, the reductions on residential loads is greater than
industrial loads;
 The VAR reduction due to VR is greater than the power
reduction;
 No adverse customer impact has been noted.
3
Residential air-conditioner load appears to respond
well at reduced voltage because:
 AC motors are typically rated 230 volts ( not 240 volts)
 Motors that are not variable speed drive that are not fully
loaded run more efficiently at reduced voltage
Historic view/usage of VR in ERCOT
 Oncor is the only TDSP using VR in ERCOT (EEA2 Reactive
Reserve < 1750 MW)
 Oncor’s use is limited in scope
 Automatic controls only installed on 219 out of 1040 substation transformers that
have LTCs
 Manual controls via patrolmen can be used on other transformers
 Oncor’s use is limited in sophistication
 Automatic controls fool LTC controllers by adding selectable 2.5% or 5% boosting
transformer in control circuit to “fool” normal LTC controller
For EEA Step 2 –
>or= 124V …………5%
123.9V to 121V ….. 2.5%
<121V …………….. 0%
5
While the Oncor LTC control system is simple, it does
not fully harvest the VR potential:
Because the voltage is always lowering at the beginning of the
event, as soon as the voltage gets within the bandwidth of the
controller, the controls stop lowering the voltage. Therefore, the
voltage always ends up being left above the nominal set point,
up to 1.49 V above it (assuming the LTC is set with a 3 V
bandwidth).
Also, because the trigger event usually occurs as load is
increasing, there is a high probability that the voltage will start
off in the lower half of the voltage band prior to the voltage
reduction event being triggered.
6
PUCT Present Voltage Requirements
PUCT Substantive Rule 25.51 references ANSI C84.1 voltage requirements
Range B necessarily results from the practical design and operating conditions on supply and/or user systems, which
are part of practical operations. However, such conditions should be limited in extent, duration and frequency.
Corrective measures shall be undertaken within a reasonable time to bring back voltages within Range A limits, in
cases of Range B values occurrence.
Where Utilities
typically operate
Where utilities
operate during
VR events
110 Volts
Summer 2012 Testing
8
Example Test – Temple North
3:30
3:36
3:42
3:48
3:54
4:00
4:06
4:12
4:18
4:24
4:30
4:36
4:42
4:48
4:54
5:00
5:06
5:12
5:18
5:24
5:30
5:36
5:42
5:48
5:54
6:00
6:06
6:12
6:18
6:24
6:30
6:36
6:42
6:48
6:54
7:00
7:06
7:12
7:18
7:24
7:30
Load (MW)
LOAD COMPARISON VR (9/6) VS NO VR (9/5)
430
425
10
Ended VR
420
415
410
9/5 (101.8F)
9/6 (102.5F)
Difference
405
Started VR
400
395
390
3:30
3:36
3:42
3:48
3:54
4:00
4:06
4:12
4:18
4:24
4:30
4:36
4:42
4:48
4:54
5:00
5:06
5:12
5:18
5:24
5:30
5:36
5:42
5:48
5:54
6:00
6:06
6:12
6:18
6:24
6:30
6:36
6:42
6:48
6:54
7:00
7:06
7:12
7:18
7:24
7:30
Load (MW)
LOAD COMPARISON VR (9/6) VS NO VR (9/5)
430
425
11
Ended VR
Started VR
390
3.0
420
415
-2.0
410
9/5 (101.8F)
9/6 (102.5F)
Difference
-7.0
405
400
-12.0
395
-17.0
Interpolating Oncor’s test results shows significant peak
shaving possibility
Category
Effectiveness (% MW
Reduction)
Current Process (5% &
2.5% Reduction)
Voltage Target Reduction
5% Reduction Process
Scheme
1.67%
2.95%
2.67%
Proven Process
Greatest VR Benefit
Mitigates Low Voltage Risk
While More Logically
Reducing Voltage
Results in Least Load
Shed Mitigation
Greatest Potential for Low
Voltage Issues
New Scheme Required Up-Front Cost and New
Procedures
328.4
580.4
525.3
Benefits
Risks
Interpolated VR
potential (2011 Peak) MW
Current VR XFMRs – 13%
No VR Capability XFMRs – 38%
Transformers w/o
LTCs or voltage
regulators
12
219
641
Transformers with
LTCs or voltage
regulators
821
VR Upgrade Capable XFMRs – 49%
Longer-term varying levels of VR benefit can be
obtained depending on the system investment made:
$$$
Amount of
improvement
not yet
defined
Modify feeder to
flatten voltage
profile
$
$
Improve LTC Control
System
VR Baseline
13
Monitor/control with
end of feeder voltage
Given industry experience and these tests result,
Oncor recommends that ROS:
 Establish a task force to investigate the potential use of voltage
reduction to assist with ERCOT’s resource adequacy challenges
by:
 Reviewing what others are doing in the industry and how they are doing it
 Facilitating testing across ERCOT to validate the VR benefit
 Determining the applicability of VR in ERCOT
QUESTIONS/Discussion?