ACE Voltage Regulation

8/10/2019 ACE Voltage Regulation

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Distr ibu t ion Grid Vo ltage

Regu lat ion w ith DERs


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Overview

IntroductionVoltage Regulation Philosophy

Substation Distribution Bus Voltage Regulation

Distribution Feeder Voltage Regulation

Voltage Drop/Rise on Line Transformers, Services andSecondaries

Voltage at the Meter and at the Inverter

Providing Head Room for DERsSeveral Alternatives &

Costs Summary/Proposal

Three Critical Components for Smart Energy


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Subs tat ion Dist r ibut ion Bus Vol tage

Regulat ion Distribution Power Transformers are typically equipped with

Under Load Tap Changers (ULTCs). The ULTC can raise orlower the voltage about 10%, typically with 16 small stepchanges in either direction. When the distribution bus voltagereaches the top or bottom of the set bandwidth for a period oftime, it will operate. If the transformer does not have a ULTC, a

separate voltage regulator may serve the same purpose.

Where a substation bus has load feeders and an expressfeeder to a large (10 MW) PV site, the feeders may havedifferent desired set values for the bus voltage. The expressfeeder tends to have voltage rise from sub to the largegenerator and would be better served by a lower bus voltage,while the other feeders have voltage decrease over distance asthey serve load and can use a higher bus voltage close to thetop of the allowable bandwidth.

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Substat ion Bus Vo ltage Regu lat ion

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Distr ibu t ion Feeder Vo ltage Regulat ion

Utilities regulate the voltage on the distributionfeeders so that the delivery voltage at the customersmeter will stay within +/- 5% of nominal (ie. 120 V +/-5% or 126-114V). The national standard related to

this is ANSI C84.1 In some states, rules are slightlymore stringent and may allow a smaller bandwidth.

Voltage regulators raise or lower the voltage in verysmall steps, typically 5/8% per step for up to 10%

raise or lower. (See previous slide titled Impacts toa Distribution Feeder).


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Distr ibu t ion Feeder Vo ltage Regu lat ion

(cont.)

Utilities also use capacitor banks to support the voltage. Asmore and more reactive load (motors, compressors, etc.) comeon line, capacitors switch on to provide reactive support and inso doing, generally increase the voltage by around 0.52% inthe vicinity of the capacitor bank (see cap banks on previous

slide titled DER Impact to a Distribution Feeder). The next slide depicts a feeder at peak load with 4 voltage

regulation zonesmaintained by the ULTC plus 3 sets ofvoltage regulators. These devices are being simulated in aprogram to provide 124V output, but in reality, the regulators

will typically operate with a 2 volt bandwidth, maintainingvoltage between 123 and 125V. Because of phase loadingimbalance, phases differ in voltage. The voltage regulators arelocated to deliver required voltage for all customers.

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Plot o f Feeder Vo ltage over Distance

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From: Smart Distribution WIKI


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Voltage at the Meter

ANSI C84.1 Guideline: Maintain the Nominal Voltage +/- 5% If the voltage delivered to the meter is 126V, (the maximum

allowable):

As soon as generation output exceeds the load of the

premise, the voltage at the meter will begin to riseand willexceed the ANSI guideline

Export is almost guaranteed for PV systems because solarhas such a low capacity factor, it needs to be sized quite

large to net out the annual energy use

This can be a bigger problem if more than 1 home feeds intothe same transformer or for community energy

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Approxim ate Voltage Drop /Rise (%)

@ Peak, Minimum Load & w ith PV

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Approximate at

PEAK LOAD

without PV

Approximate at

MINIMUM LOAD

without PV

With PV Solar

Causing Export

(at minimal load)

Across Line

Transformer

- 0.5 to2.0% Negligible + 0.3 to +1.3%

On Secondary - 0.5 to -1.5% Negligible + 0.2 to +1.0%

On Service Drop - 1 to -1.5% Negligible + 0.5 to +1%

TOTAL - 2.0 to - 5.0% Negligible + 1.0 to + 3.3%

Note: Negative shows voltage dropping towards the premise and generation system.


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Voltage Rise Examp le at Prem ise

The following Voltage Rise diagram depicts a system that has

significant voltage rise during peak output since there is a fairdistance to the solar system beyond the customer meter.

On a 120V base, the voltage could rise about 4.5 volts betweenthe meter and the PV system. If load is minimal at the premise

and the PV system is at maximum output, there couldpotentially be a 2.1 volt rise from the line transformer to themeter due to the export going from premise to grid.

It is easy to see, that if delivery voltage is at the highest pointon the delivery bandwidth, it will make it very difficult to havevoltage within the ANSI C84.1 bandwidth at the meter.

This facility experienced 127.5V at the meter and 131V at theinverters.

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Vo ltage Rise Diagram

Substation

T1

61.5/71.0 MVA

1200 kVAR

Switched

1200 kVAR

Switched

240 VAC

12/3 and #6 Cu Ground

73 Amp Max

Ground and

Surge Protector

Ground and

Surge Protector

2 2/0 Al

1 1/0 Neutral

1 #2 Al Ground

100 Amp

Breaker

Disconnect

Meter

Junction

Box

House

Breaker

Panel

200 Amp

Outdoor 100 Amp Load

Center

With 6 15 Amp 240 VAC

breakers for solar and

1 20 Amp 120 VAC breaker

for outlet

240 VAC

2 4/0 Al

1 4/0 Neutral/Ground

Line Transformer (Pd. Mt.)

25 kVA

TED

5000

TED

5000

Voltage Rise

Electrical Diagram

Solar System

19.4 kW DC

17.1 kW AC

90 215 Watt Panels

90 190 Watt Microinverters

#8 Ground to each panel and inverter

477 AAC 397 AAC 477 AAC 397 AAC 397 AAC

Enphase Envoy+4.08 Volts

1.7%

+0.96 Volts

0.4%

+3.96 Volts

1.7%

+2.64Volts1.1%

240 V Base

175'

0.6%

1.033pu Typical

(103.3%)

1.05pu Typical

(105%)

25 kV Distribution Feeder

545' 2090' 1000' 600'

240 VAC

2 4/0 Al

1 4/0 Neutral/Ground

200'TED

5000

1.50 Volts


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Overvo ltage at the Inverter

The following scatter plot of voltage measurements at theinverter at an industrial customer shows a variety of voltages atdifferent output levels.

The over voltages most likely occurred at times when the load

at the facility was low and most of the output was beingexportedie Saturday, Sunday or other times the facilityequipment was off.

A red line is drawn at 1.04 pu (per unit) per the state upperlimit, while ANSI C84.1 has an upper limit of 1.05 pu.

Maximum voltage appears to be 1.07 pu, with most pointsbelow that value. This is the equivalent of 2% over 1.05 puwhich is the top of the bandwidth.

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Overvo ltage at the Inverter

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Overvoltage Limit

Source: EPRI Monitoring


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Prov id ing Headroom for DERs

The utility is required to deliver a high enough voltage to insureadequate voltage at the meter during peak load, but yet low

enough to be the proper voltage at low load. Now with DERs,the top voltage needs to give head room to PV and other DERsthat may cause export at low facility load.

Proposal: Deliver a target voltage of 123V (1.025 pu) to the

meter at all times. An alternate would be to deliver 123V duringlow load periods and especially during high solar output. Thiswill give 3 volts or 2.5% headroom for PV or other DERs thatcause voltage rise during low facility load and high output, orperiods of export.

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Typical Voltage Regu lat ion w ith

Violat ions at the Meter

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Voltage Regulation with Headroom toMit igate Violat ions

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A lternat ives fo r Provid ing DER

Headroom

Alternative 1 -- Similar to Conservation Voltage Reduction(CVR), Voltage Regulation Zones can be set to tighterbandwidths with the target voltage reduced to 123V. This typeapproach may require some new voltage regulators, and othervoltage regulators or capacitors to be moved.

Alternative 2With the use of monitoring and active control,such as found in Integrated Volt-VAR Regulation or Control(IVVR or IVVC) the set points for regulation can be changed toinsure adequate voltage at customer premises during peak andlow load in each voltage regulation zone on feeders. This

approach requires communication, monitoring and control butwill probably involve fewer new voltage regulators and lessmoving of existing voltage regulators or capacitors.

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State Vo ltage Requ irements

PHI is considering a target operating feeder voltage of 123V or2-1/2% lower than the maximum (126V) per ANSI C84.1.

PHI proposes that States allow the bandwidth for customers toextend to the full ANSI 84.1 bandwidth. In this way, it will allow

DER systems to have 2-1/2% headroom and operate withoutcausing voltage violations at the meter during export and staywithin ANSI C84.1.

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State Acceptable V Range at Meter In terms of 120V

DE Nominal +/- 5% 114 V126 VMD Nominal +/- 5% 114V126 V

NJ Nominal +/- 4% 115.2 V124.8 V


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Maintaining Vo ltage on High

Penetrat ion Feeders o r Sect ions

Asset Strategy and Planning is deploying the DistributedEngineering Workstation, a time series capable program tostudy DERs and their impact to the T & D system in aggregate.

The goal is to allow higher penetration levels but cut off

installations before steady state high voltage would occur on afeeder.

The program will also study voltage fluctuations and the impactof DERs on automatic line equipment and identify potentialproblems.

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Voltage Regu lat ion - Summary

Although utilities are pursuing various volt-var controlstrategies, what is needed is a strategy and general voltagephilosophy that will maintain proper voltages at peak, at lowload and now during export from DERs.

Establishing these guidelines will provide the base forconsidering what settings smart inverters should use if they willparticipate in voltage regulation.

The above effort needs to consider rural long feeders as well asshort stiff feeders generally found in urban locations. It also

needs to allow for different paths that utilities are taking toupgrade or implement Smart Grid solutions. Ideally, voltagefeedback will be available from AMI systems to insure thatcustomers voltage remains within acceptable limits.

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Voltage Regu lat ion - Summary (con t.)

Germany appears to have a larger allowable bandwidth. TheANSI C84.1 voltage bandwidth of +/- 5% has served customers

well and probably should be maintained. Changing it wouldrequire significant discussion and may lead to problems whenoperating at the extremes.

Going to a flatter feeder voltage can add some cost because it

may add a few more voltage regulation zones to some feeders.

PHI is considering centralized Volt/VAr control as part of aDistribution Automation strategy. If AMI is installed, it willprovide voltage feedback which is important to insure propercustomer voltage. It would also enable flexible load control andinverter control to provide some important parts of an integratedAdvanced Feeder Management System.

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Smart Energy

The following slide outlines three critical components toproviding Smart Energy on the distribution system.

A Smart Grid is essential the ability to operate safely, staywithin capacity ratings, maintain proper voltages at all T & Dlevels during different load and or DER output levels. Itenvisions communications that allow centralized monitoring and

control for utility equipment, signals to premises for flexible loadcontrol, voltage feedback from some premises, and signals sogeneration sources can participate in creating Smart Energy.

A Smart Inverter has communication, monitoring and controlcapabilities to assist in volt-var control autonomously or under

central (Utility) direction. It may also participate in ancillarymarkets and help to provide premium power to the facilityowner. Other non-inverter based distributed generators mayparticipate, but may not have the same functionality.

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Smart Energy (con t.)

The Smart Premise enables the premise owner to control theirenergy use in such a way that saves them money, helps tosupport the grid and maintains their desired lifestyle. It keys offof automated control, based on the premise ownerspreferences that control a variety flexible loads. Appliances

and/or Home Energy Managers will communicate with the utilitythrough the AMI system or by other means and automaticallycontrol equipment at the premise based on the settingsselected or over ridden by the owner.

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S t E


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Smart Energy SMART GRID

ISO(Independent Sys.Operator)

Bulk Generation Bulk Transmission

Synchrophasors

Bulk Load Control

LDC (Local Distribution Co.)

Transmission

Substation

Power Transformers Feeders

DistributedAutomation

Conductors, ALE

Line Transformers

DMS, Advanced FdrMgmt

DSM, DR

AMI Outage Mgmt

Real Time Pricing

Load Profile Info

HAN (Home Area Network) Price and other comm.

SMART PREMISE

HEMS(Home Energy MgmtSystem)

Pricing Signal Response

Peak Load Control

DER (Distributed EnergyResource)

Renewables, CHP, etc.

Smart Thermostat

Smart Appliances

Smart HVAC Thermal Storage

EV Controllable Charging, V2G

Remote Access andControl

Energy Efficiency &Controls

Turn off Phantom Loads

Vacant space mgmt.

Direct Use of DC

SMART INVERTER

Low Voltage Ride Thru

Ramp Rate Control

Autonomous &

Centralized Control

-- VAR/PF Control

Fixed/Dynamic

Algorithim based

Curtailment

Remote Trip

WITH BATTERY

Premium Power

Voltage Control

Frequency Regulation

Spinning Reserve Arbitrage (TOU or Real Time

Pricing)

Demand Side Mgmt

Pk Demand Mgmt.
http://intranet.pepcoholdings.com/ePHI/index


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Steve Steffel, PE

Mgr, Distributed Energy Resources

Planning and Analytics

[email protected]
mailto:[email protected]:[email protected]

ACE Voltage Regulation

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