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2016 Smart Grid R&D Program
Peer Review Meeting
Adaptive Protective Relaying for Microgrids
Mohamed El Khatib
Sandia National Laboratories
August 16, 2016
December 2008
Adaptive Protective Relaying for Microgrids
Objectives & Outcomes
Life-cycle Funding
Summary ($K)
Prior to
FY 16
FY16,
authorized
FY17,
requested
Out-year(s)
- $100K $200K
Technical Scope
To investigate the challenges facing the
development of efficient protection schemes for
microgrids. Special emphasis is on microgrids
with high penetration of inverter-interfaced
renewable energy where fault current could be
too limited for traditional overcurrent protection to
work efficiently.
• Survey current and proposed practices in
microgrid protection.
• Investigate the challenges facing the
development of advanced non-overcurrent
microgrid protection schemes ,including;
• impedance-based protection
• transient-based protection.
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December 2008
Microgrid Protection Challenges
• Microgrids comes in different sizes, configurations and generation mix.
• No standard protection scheme is available for all microgrids.
• Renewable-rich microgrids could have too limited fault currents for efficient overcurrent protection operation.
• Protection of microgrids with dynamic boundaries has not been addressed.
• It is important, from a protection perspective, to address protection concerns for two types of microgrids:
• Advanced Microgrids: protection design is easier as higher investment in protection system could be justified because of size and criticality of load.
• Networked Microgrids: protection design will have to work efficiently across multiple microgrids with dynamic boundaries on the DS.
3
December 2008
Microgrid Protection Needs
4
• Development of efficient protection schemes for microgrids is crucially needed to:
• Enable integration of higher penetration of renewables
• Enable the safe deployment and support of “networked microgrids” for resilience improvement
• Advanced protection schemes are needed to protect against high-impedance faults, which is very hard today
• Current protection schemes are problematic with microgrids
• Overcurrent protection can’t detect faults with high use of inverters
• Differential protection is expensive to use in many microgrid applications
Efficient microgrid protection schemes will also be beneficial for protecting distribution systems with very high penetration of
renewable generators.
December 2008
Microgrid Protection Technical Approach
December 2008
Current Progress
• Studied microgrid protection challenges
• Detailed literature survey and evaluation of both current microgrid protection practices and newly proposed protection schemes
• Based on this review we have developed two non-overcurrent protection schemes applicable to inverter-dominated low-fault (renewable-rich) microgrids :
• Impedance-based protection scheme
• Transient-based protection scheme
• We have performed simulation studies to test these protection schemes
December 2008
Utilize Protection Zones for Microgrids
• A protection zone is defined as: “a part of the microgrid bordered by a set of fault interrupting devices”
• Allows efficient protection for advanced and dynamic boundary microgrids
7
December 2008
Impedance-based Protection
8
• Impedance is a better fault indication than current magnitude especially in low-fault, renewable-rich microgrids.
• More robust than overcurrent protection and less expensive than differential protection
• However, traditional distance-based impedance protection will be complicated to use for a microgrid due to feeder tapping, small feeders lengths, etc.
• We have formulated and tested different impedance-based protection designs.
• Impedance-based pilot scheme: impedance elements detect the fault and direction elements locate the fault.
December 2008
Impedance Relay Test Cases
Case 1: Synchronous generator test case
Case 2: PV test case
December 2008
Impedance Relay Test Cases (Cont.)
Voltage and current waveforms at the impedance relay for Case 1
December 2008
Voltage and current waveforms at the impedance relay for Case 2
Impedance Relay Test Cases (Cont.)
December 2008
Impedance trajectories during fault for Case 1 and 2
Impedance Relay Test Cases (Cont.)
December 2008
Impedance-based Pilot Protection Scheme
December 2008
Impedance-based Protection Summary
14
• This approach has been able to detect all faults during current testing – More testing is underway.
– Works well with Protection Zone concept and approach
• Currently conducting additional fault testing and analysis
• Plan to evaluate implementation issues related to communication requirements, cyber security issues, directional relays design issues, and implementation costs
December 2008
Transient-based Protection
15
• Based on detecting faults by analyzing fault-generated transients
• Several case studies have been conducted to investigate the sensitivity of transient-based protection to grid configuration, inverter controls, and fault inception angle.
• Implementation in the field faces several current challenges.
– However, this approach is potentially less expensive than differential protection and more robust than overcurrent protection
• This approach is promising for both low-fault microgrids and can be extended to protect against high-impedance faults in both Microgrids and distribution systems.
December 2008
Transient-based Test Cases
• A IEEE 13 bus system was modelled in PSCAD.
• A detailed inverter model with current limiters was connected at node 675 through a delta/YG interface transformer.
• Out of the total 67 faults simulated, 56 faults could be detected based on transient analysis.
• Transient based technique were able to detect all line-to-line and three phase faults.
• Several line-to-ground faults could not be detected because transients were too low, but could be detected based on zero sequence
December 2008
Transient-based Protection Case Study (Cont.)
Current waveform at inverter side for a BC fault at node
646
Current waveform at grid side for a BC fault at node
646
December 2008
Transient-based Protection Case Study (Cont.)
Envelope of transient signature for BC fault at node 646
December 2008
Transient-based Protection Summary
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• Discrimination between fault transients and other non-fault transients could be challenging.
• Combination of transient-based protection with voltage-based and zero-sequence protection could potentially provide a robust protection solution.
• Communication-assisted transient-based protection could be achieved by comparing transient signatures from different locations to locate the fault, potentially, using PMUs.
• Processing time must be kept low to ensure fast fault clearance.
December 2008
Future Research Directions
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• These first-year efforts have provided the foundational work for the development of advanced protection schemes for microgrids and distribution systems
• Developed two promising protection schemes for advanced and networked microgrids
• Hardware-in-the-loop demonstration of the developed schemes is planned for next year.
• Study implementation issues associated with:
• Impedance relay design
• Identify fault location based on transient signatures
• Communication issues for both approaches
• Estimate capital and operational costs
December 2008
Include any back-up slides you would like to provide to the
peer reviewers and DOE program managers for additional
information. The back-up slides will not be shared with
others, unless specifically stated by the presenter.
Back-up Slides
21
December 2008
Microgrid Protection Survey
• Beside overcurrent and differential, other protection schemes were proposed in the literature.
• Undervoltage based protection:
• Not efficient in determining fault location. Also, discrimination between faults and normal operation is very hard. It could be used in conjunction with overcurrent for enhanced reliability.
• Transient-based methods:
• Reported methods lack rigorous study of the impact of microgrid configuration or generation dispatch on protection efficiency.
• Other schemes use transient-based differential protection which is more expensive and less robust than conventional differential protection.
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December 2008
Microgrid Protection Challenges (Cont.)
Entities Microgrids Microgrids created by
islanding parts of the DS
Protection system could be tailored to the specific application
Protection system will be inherited from the DS
Load criticality could justify higher investment in protection
Cost is a major concern since upgrading the host DS protection could be
prohibitively expensive
Typically small in size Could be large in size
Less likely to have dynamic boundaries More likely to have dynamic boundaries
– challenging!
Less impact on DS resilience improvement
Could greatly enhance DS resilience
December 2008
Microgrid Protection Current Practices
• Overcurrent and differential protection are the main schemes in use today.
• Other protection schemes proposed in the literature lacks rigorous validation and demonstration.
• Undervoltage based protection:
• Not efficient in determining fault location. Also, discrimination between faults and normal operation is very hard. It could be used in conjunction with overcurrent for enhanced reliability.
• Transient-based methods:
• Reported methods lack rigorous study of the impact of microgrid configuration or generation dispatch on protection efficiency.
• Other schemes use transient-based differential protection which is more expensive and less robust than conventional differential protection.
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December 2008
Overcurrent vs. Differential Protection
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December 2008
Impedance-based Pilot Protection Scheme
December 2008
Impedance-based Pilot Protection Scheme
December 2008
Transient-based Protection Case Study
Current waveform at inverter side for a AG fault at node 633 Insufficient transient signature for detection!
December 2008
Transient-based Protection Case Study (Cont.)
Seq. components of voltages at grid side for AG fault at node 633 Fault could be easily detected based on zero-sequence!
December 2008
Impedance-based Dynamic Boundary Centralized Protection Scheme
December 2008
Practical Implementation Issues
31
• Backup for loss of communication:
– assume breaker fail and open a larger zone.
• Fault interruption speed:
– always a concern for communication-assisted protection schemes.
– Even an inverse-time overcurrent relay, if it detects the fault, would take few cycles to pick up given the fault magnitude.
– Consider the scheme as a backup protection for traditional overcurrent protection.
• Weak Infeed Issues:
– Could be an issue for grid-connected mode for a fault on the grid side of the microgrid. • Undervoltage element at the microgrid PCC could resolve this case.
December 2008
FY17 Proposed Plan
32
• FY17 plan consists of two main topics related to microgrid protection:
- Develop guidelines for designing microgrid protection.
- Develop and demonstrate advanced microgrid protection schemes.
December 2008
FY17 Plan – Microgrid Protection Guideline
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• Motivation:
– Microgrid protection design is not standardized.
– Interactions between microgrid and hosting DS protection.
– Protection design should be tailored to specific microgrid and should consider, among others, factors like: • Cost: how much could be spent on the protection system including
fault interrupting devices number and types?
• Reliability: in case of a fault, should the faulted section only be tripped or is it allowed to trip the whole microgrid?
• Expected fault levels: what are the fault levels in the microgrid? What is the minimum fault level ? What is the difference between the minimum and maximum fault levels (islanded vs. grid-connected) ?
• Topology: What are the operating topologies of the microgrid (radial, mesh or both)? Is there a chance of the microgrid operating with dynamic boundaries?
December 2008
FY17 Plan – Demonstrate Advanced Protection Schemes
34
• Thorough study if the issues facing the implementation of impedance-based protection scheme will be conducted.
• Further development of the communication-assisted protection schemes including: – Investigate the use of communication-assisted schemes and micro-PMUs to
improve the robustness of transient-based protection schemes.
– Perform Hardware-in-the-loop testing for validation.
• We are and will continue to collaborate with New Mexico State University.
• Industry participation is being sought. (currently we are in talks with SEL and Eaton).
• We will collaborate with Los Alamos county DPU, as a utility partner, in the development and validation of the proposed protection schemes.
December 2008
FY17 Timeline
Due Date Milestone Description
Q1 1- Gather stakeholders input on microgrid protection design guideline. 2- Investigate implementation issues for impedance-based protection for microgrids.
Q2
1- Publish draft microgrid protection design guideline for review by stakeholders. 2- Investigate communication-assisted protection schemes for microgrids and investigate the use of micro-PMUs.
Q3 1- Finalize microgrid protection design guideline. 2- Develop communication-assisted protection schemes for microgrids and investigate the use of micro-PMUs.
Q4 1- Perform HIL testing for the transient-based protection schemes. 2- Publish technical report detailing the design, testing and guidelines for the developed advanced protection schemes.
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December 2008
Collaborators
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• We are collaborating with New Mexico State University in investigating transient-based protection methods for microgrids.
• Collaboration with industrial partner is being sought and would be in place for the development of advanced protection schemes in the next year (we are currently in talks with SEL and Eaton).
• Collaboration with Los Alamos DPU is planned for the development of advanced protection schemes in the next year. – Los Alamos county DUP operates a microgrid test bed in Los Alamos with
real customers testing high penetration of renewable energy onto a residential distribution feeder. Included are a 1 MW solar array, an 8.2 MWh utility scale battery storage system, and a micro energy management system tied to a microgrid with 1600 residential customers with smart meters.
December 2008
Publications
• Elkhatib, M.E.; Brahma, S.; Ellis, A, "Advanced Protection Schemes for Renewable-Rich Microgrids", accepted - Niagara 2016 Symposium on Microgrids, Niagara-on-the-lake, ON, 20-21 Oct, 2016.
• Elkhatib, M.E., "Impedance-based Protection Scheme for Inverter-dominated Dynamic Topology Microgrids", submitted - IEEE Smart Grid Transaction - Manuscript ID: TSG-00750-2016.
• Elkhatib, M.E.; Brahma, S.; Ellis, A, “Protection of Renewable-rich Microgrids", submitted - IRED 7th conference.
