facing the challenges of der operations · jeffrey m. triplett, p.e. power system engineering, inc....

Jeffrey M. Triplett, P.E.

Power System Engineering, Inc. www.powersystem.org

February 26, 2015

TechAdvantage 2015

Facing the Challenges of DER Operations

© 2015 Power System Engineering, Inc.

Participation is Encouraged

ASK QUESTIONS!


Typical Interconnection Process • Application

• Preliminary Review

• Screening Process

• Engineering Studies

• Study Results and Construction Estimates

• Contracts

• Design

• Order Equipment and Construction

• Inspection, Testing & Commissioning

3

Not the topic of our discussion today, but NRECA has developed a DG Toolkit that can be used to assist in the process


NRECA Distributed Generation Toolkit • Available on Cooperative.com and NRECA.coop -

https://www.cooperative.com/InterestAreas/Generation/DistributedGeneration/Pages/default.aspx

• Recently updated with new documents added with consideration of FERC SGIP amendment in 2013 – Business and Contract Guide for Interconnection (Updated) – Consumer Guidelines for Interconnection (Updated) – Model Long Form Interconnection Contract (Updated) – Model Short Form Interconnection Contract (Updated) – <10 kW Inverter Based Process (New) – Pre Application Report (New) – Pre Application Report Response Template (New) – Sample PV Testing and Commissioning Checklist (New)

• The model forms within the DG Toolkit are provided as guides and should not be used verbatim. Local factors need to be taken into account.

4




Open Modeling Framework

• NRECA/Co-op led effort to create a system modeling tool

• Can incorporate co-op distribution systems with a common user and data interface

• Models many things from new distribution equipment/controls to impact of PV solar and new energy efficient appliances on the distribution system

• Will be available to co-ops 1st/2nd Qtr 2015 • Some of you may have attended the TechAdvantage

session yesterday that provided an introduction. For additional information please contact David Pinney at [email protected]

mailto:[email protected]


Today’s Focus Today we are going to discuss the operational aspects to be considered after the DER is connected and commercial.

6

Source: Southwest Windpower

Source: marathonroof.com


Ongoing DER Consideration • After DER is connected to the system…..then what?

– Do standard operating procedures need to change? – Do work rules need to change? – Should the DER be monitored? – What about power quality and reliability? – Is there anything we can learn to improve the process? – What about future changes in technology and how the

equipment is operated? – What if more DER is connected or the load changes? – What changes to existing equipment and systems may be

needed?

7


• Backup generation used by members during outages is not new and has been a concern that has been handled with

– Strict work rules

– High emphasis on safety

– Member education

• Properly interconnected DER systems can be safely managed as well by adhering to these same principles

Operational Concerns


• During outages, co-op personnel have existing work rules when working on the system to restore power

• Adding DER to the system can create the potential for portions of the system to become energized if proper protection is not in place at the DER interconnection

– IEEE 1547 specifically requires that DER separate and not re-energize a de-energized system

– Your interconnections standards should address specific requirements

• Even with proper protection in place at the interconnection, do existing work rules and practices need to change to maintain safety and reliability?

Abnormal System Conditions


• Set reclosers to one-shot-to-lockout (if available) and tag

– Hot Line Tag or non-reclose settings on electronic reclosers

– One-shot handles on hydraulic reclosers

• Bypass reclosers that do not have one-shot-to-lockout capability with fuses to eliminate potential for reclose operations

• Goal is to clear a fault as quickly as possible, limit arc flash energy and to make sure that the system does not close back in to the fault

Common Practices – Energized Work


• The addition of DER has the potential to increase available fault currents and incident energy levels during arc flash events

• When working in areas with DER present, we need to make sure that during a fault condition the DER separates quickly and does not close back in to the system until the system is restored to normal for at least 5 minutes – IEEE 1547 requirement – An inverter meeting UL 1741 disconnects in 2 seconds or less and

only reconnects after 5 minutes of normal utility conditions • Best practice is to disconnect DER during energized work

Impact of Adding DER to Energized Work


• The addition of DER has the potential to complicate maintenance procedures due to protection schemes that are added to accommodate the DER

– Direct Transfer Trip (DTT) schemes

– Reclose/Close blocking

– Reverse power

– Directionalized overcurrent elements

Impact of Adding DER During Maintenance


Example DTT Scheme

13

Two co-op reclosers (F4 and 4E) to send DTT to co-op owned interconnection recloser (RI) to disconnect the DER any time they are opened. This ensures a possible island condition does not occur.

DTT


Example DTT Scheme – Form 6 Controls

14


• Example:

– A recloser is to be bypassed and removed for service

– This recloser is integrated with a DTT scheme such that any trip condition or manual open sends a trip signal to a remote breaker at a DER installation

– Maintenance procedure now needs to be modified to include either

• Disabling the DTT feature while this recloser is bypassed

• Taking the DER offline during this procedure

Impact of Adding DER During Maintenance


Modifications to Account for DER

16

“Disable DTT” disables sending of DTT to interconnection protective device


Modifications to Account for DER

17

“Block Close” does not allow recloser to be closed as long as voltage present on DER side

Voltage/Frequency trips backup DER protection (under co-op control)

Recloser set to trip or switch to an alternative protection profile when DTT comms lost for a set time period

Targets programmed to display additional protective functions

Recloser integrated into SCADA for monitoring and control.


• An area of the system has been backfed from an adjacent substation area

while a substation is taken offline for maintenance

• A recloser at the temporary open point is planned to be closed and briefly parallel the two substations together for a short time while the normal open point is re-established

– Both substations are in phase – Eliminates the need for a brief outage during switching

• However, this recloser is programmed to block closing if voltage is present on the load side due to a downline DER installation

• Switching procedure now needs to be modified to include disabling the voltage block feature while this switching is being done

Substation Substation

N.O.

18

Another Example


• Section 444 of the NESC details requirements

• “Records shall be kept on all contractual utility interactive systems on any electric supply lines. When these lines are de-energized according to Rule 444C, the utility interactive system shall be visibly disconnected from the lines.”

NESC Requirements for De-energized Work


• The National Electric Code (NEC) requires a disconnecting means in a “readily accessible location” be installed – Readily accessible to whom? – Should you also require a disconnect be

installed? – If so, who pays for this?

• Your Interconnection Standards and Technical Requirements should address these questions – Be sure to review any state requirements – Ultimately, need to have capability to

obtain a visible open that can be locked open and tagged.

Disconnect Switch

© 2015 Power System Engineering, Inc. Source: SMA Solar Technology

Typical Inverter Means of Disconnection The AC Disconnect is what needs to be readily accessible to cooperative personnel


• Addition of DER to distribution system may increase time to troubleshoot an outage

– Time to open, lockout and tag all locations

– What happens if there are a significant number of locations?

– What impact might this have on reliability indices?

• What do you do if co-op personnel do not use DER disconnects during emergencies and large outages?

• SCADA can be used to open a recloser or even a motor-operated switch with tags put on in SCADA, but most of the time this will not be sufficient.

De-Energized Work Practices Concerns


• Location of DER systems need to be marked on truck maps and/or in co-op GIS system

– Some co-ops have developed a decal to put on any transformer that has DER attached to the secondary as a reminder to field personnel that DER is present

• Specific switching orders may need to be created for those areas with DER installed

• Specific policies dealing with DER interconnections and related work rules may need to be created and then enforced

Documentation


• How comfortable are you with protection devices being under the control and care of the DER customer?

• Can you always trust that the DER customer will not inadvertently disable or alter the protection on their side of the PCC?

• Can you always trust that their devices will be properly maintained, tested and kept in good working condition?

• Is additional “backup” equipment required on the cooperative system to ensure protection needs are met regardless of how DER equipment reacts, or does not react, to a condition on the system?

Additional Concerns to Consider


Power Quality

25

Source: Electric Light & Power


Power Quality • Possible power quality concerns

– Harmonics – DC current injection – Flicker – Voltage transients – Voltage sags/swells

• Is power quality metering/monitoring necessary? – Metering before to determine baseline – Metering after to determine impact from DER – Can existing devices be used? – What additional skill sets are required to adequately address this?

26

Source: SEL


Higher Penetration Levels

27

Source: Solar City

Source: marathonroof.com

What happens when penetration levels go from one or two connections on a circuit to many connections?


Solar/Wind Farms

28

Source: ECN Magazine Source: National Wind Farm Developers

Not really talking about solar/wind farms when we discuss “high Penetrations” because these farms are typically interconnected at one point and appropriate protection and monitoring can be added for the entire farm.


• As the number of residential-sized DER installations increase, the aggregate impact will need to be considered

• Aggregate amount of DER required to cause any concern is dependent on the feeder serving these areas and the loads present

• Biggest concern –reverse power flow on the distribution system during periods of high generation and low load – Distribution system and protection schemes in localized areas may need

to be designed or modified to handle this

– Voltage rise and/or voltage unbalance may be a concern

– Voltage sags/swells/flicker may be a concern with large numbers of small units operating together due to a common event, such as cloud cover and rapid changes in wind

High Penetration Considerations


When generation exceeds load in an area, reverse power flows can occur

Normal Open Point

Some equipment can be programmed to handle this. Devices like fuses and simple OCRs cannot and may need upgraded.

Peak and minimum load/generation data can be collected from line sensors and controls

During backfeed conditions, the system is changed entirely and DG may not be able to be accomodated


• Reverse power flows through equipment can have unintended consequences: – Protective devices may not provide proper protection – Alternate protection schemes may be required – DA and FLISR schemes are impacted – Voltage regulators may not operate correctly unless they are

operated in a “co-generation” mode

• Most modern microprocessor-based controls have the capability to sense reverse power and operate accordingly

• Load data can be collected from line sensors or controls to determine peak and minimum load/generation data for a zone

31

High Penetration Concerns – Reverse Power Flow


• Once generation output exceeds load, steady-state voltage rise can become a concern

• Residential feeders are vulnerable as loads are lightest during the day when PV output is the highest

• High penetrations of DER located close to the end of the line are of particular concern

• Longer lines with smaller wire have more prevalent steady-state and transient voltage issues

33

High Penetration Concerns – Steady-State Voltage Rise


Substation DER Facility

If the generation output is significant during times of light loading, voltage rise can be a concern.

Voltages outside of ANSI Standard ranges can be detected through a deployed AMI system, voltage monitors, SCADA, field measurements, or through consumer complaints. There are several options available to limit voltage rise caused by DER installations. These include allowing the proposed generation to absorb reactive VARs (if possible), the installation of voltage regulators, limiting the amount of real power output from the DER unit, adding load, or a combination of these.

Voltage ProfilePhase A Phase B Phase C

Circuit Element Name

SOU

RC

E

Bus Regs

0 1 2 3 4 5 6 7 8 9

Vol

tage

(V)

133132131130129128127126125

DER Impact: Voltage Rise Example


Steady-state voltage & power quality data can be collected across the system from a deployed AMI system or from line sensors / SCADA

Normal Open Point

May need to upgrade certain equipment (or even add) and integrate with SCADA to collect needed data


• The closer that the generation capacity is to the load, the greater the risk for an island to form

• Passive anti-islanding schemes (over/under voltage and frequency) may not be adequate

• Active anti-islanding detection schemes are better but may interact or interfere with each other as penetration increases

• A large number of inverters actively trying to detect an island may have an impact on power quality

37

High Penetration Concerns - Islanding


• Small DER units are typically programmed with similar protective settings to meet IEEE 1547 requirements

• Large numbers of small DER units suddenly coming online or dropping offline due to a common event have the potential to create voltage sags and swells – PV and cloud cover – Rapid changes in wind

38

High Penetration Concerns – Voltage Transients


• Small DER units are typically single-phase installations

• Voltage imbalance stemming from unequal amounts of generation output on each phase is a concern with high enough penetrations

• Voltage imbalance leads to – Unacceptable levels of neutral-

earth voltages

– Increased losses

– Increased voltage drop/rise

– Increased contribution to negative sequence voltage levels

Voltage ProfilePhase A Phase B Phase C

Vo

ltag

e (

V)

126

124

122

120

118

39

High Penetration Concerns – Voltage Imbalance

© 2015 Power System Engineering, Inc. 40 Source: www.esmap.org

“Smart” Inverter Capabilities Many new inverters have the capability to produce or consume reactive power with a fast response to changing requirements

http://www.seabay.org/


• Inverter rated 1 kVA capable of producing

• During high wind or solar availability, inverter may (or may not) be producing maximum real power output, and therefore have capacity for producing reactive power

• During low wind or solar availability, inverter may have plenty of excess capacity for producing reactive power

Volt-Amps Power Factor Watts VARs1000 1.0 1000 01000 0.95 950 3121000 0.9 900 4361000 0.85 850 5271000 0.8 800 600

41

Inverter Capabilities


• Recently, IEEE 1547 was amended to allow DER to actively regulate voltage

• Most DER systems today are operated with a – Constant real power setting – Constant power factor setting – typically unity

• DER attempts to maintain constant power output at the desired power factor – Exerts no direct influence on the system voltage – An indirect influence may be seen as discussed previously with

voltage rise stemming from reduced load flows • Most DER have the capability to actively regulate voltage, though,

including inverters

42

Active Voltage Regulation


• Utilities are required to maintain adequate voltage and frequency levels across their systems during steady-state and transient conditions

– Utility plans the system and upgrades as needed

– Specific protection schemes are implemented

– Reactive power requirements not being met by customers are responsibility of the utility

43

Active Voltage Regulation – Utility Perspective


• DER has the capability to be integrated into utility operations to provide active voltage regulation and voltage/frequency support during system events

– DER may have no financial incentive to do this though

– DER actively regulates voltage by dynamically changing reactive power output

– Key is to put this capability under utility control

– Centralized vs. Decentralized control architecture

44

Active Voltage Regulation – DER Perspective


• Centralized controller operated by the utility makes decisions and sends commands to individual DER installations – Substation level – System level

• Primary Advantage: Knowledge of a larger area is available when making decisions

• Primary Disadvantages: Requires a centralized controller (DMS or SCADA) and a communication network between the centralized controller and each DER installation

45

Centralized Utility Control


• Easiest way for DER to provide active voltage regulation is to operate the unit in a “constant voltage” mode – DER continues to export real power – DER varies reactive power output within its ability in an attempt to

maintain a constant set voltage level

• Limitation of this scheme is that only the voltage at the DER point of interconnection is being considered in the decision to export/consumer reactive power

• Schemes also being considered where DER installations exchange information with neighboring installations to collectively make local control decisions

46

Decentralized Control


• During system events (faults), the voltage and/or frequency on the utility system may begin collapsing

• DER has the potential to support the utility system during these events – Not talking about instances where DER is contributing to a local fault,

but broader system events, such as on transmission – This is why one of the IEEE 1547 underfrequency element requirements

includes an adjustable setpoint for frequency and clearing time – With high penetrations of DER, do not want to trip significant DER

resources offline suddenly with voltage and frequency elements during a system event because the problem may become worse

47

Voltage and Frequency Ride-Through


• Presently, most DER installations are not controlled or dispatched by the utility – DER customer determines when they will operate and to what extent,

taking into consideration any specific constraints defined by utility during study process

– Obvious exception is DER installations owned and operated by utility

• Consideration being given to utility integrating system control with DER installations to dispatch DER as needed

48

Dispatchable DER


• IEEE 1547 requires DER to disconnect during times when utility power is lost at the PCC – Prevents an unintentional island – Safeguards workers and customer equipment

• Microgrid concept involves separating from the utility system in order to serve local loads with local generation resources, and possibly energy storage, during utility outages – Forms an intentional island – Autonomous and automatic detection of outage and separation from

utility – Autonomous and automatic detection of restored utility power and

synchronization/reconnection to utility

49

Microgrids – Autonomous Operation


Comments? Questions?


Power System Engineering, Inc. Name: Jeffrey M. Triplett Title: Utility System Consultant Office: 740-568-9220 Mobile: 740-525-0070 Email: [email protected] www.powersystem.org

Thank You!

mailto:[email protected]

facing the challenges of der operations · jeffrey m. triplett, p.e. power system engineering, inc....

Documents