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Protection and Safety of People, the LV network, DG systems and Home
Presenter: Associate Professor Nirmal Nair GREEN Grid Conference 2016 Renewable Energy and the Smart grid 10th February, MBIE, Wellington
2
Overview: Contrasting Protection practices of
Generation/Transmission with Distribution/DG
Identifying challenges associated with
protection and safety of Distribution network assets with DG/IES
Steps towards NZ wide guidelines for
Safety and protection for interconnection of
DG/IES to LV Distribution network
Steps towards NZ wide guidelines for Protection and Automation of MV Distribution networks
with DG/IES
Ongoing work: GREEN Grid interconnection
platform, Fault Location Isolation and
Service restoration (FLISR) and Voltage control in LV and MV
with DG/IES
Presentation Flow
3
Ref: NIST (2012)
Asset and network flows that need Safety and Protection
http://www.sgip.org/Smart-Grid-Conceptual-Model-Domains
4
Existing Protection and Automation for Transmission/Generation Infrastructure
• Bidirectional power flows in normal operation and during faults • ICT for operations and protection of transmission/generation assets • Established guidelines for safety of substation assets & operational protection • Fault analysis and service restoration practices mission critical globally
http://www.sgip.org/Smart-Grid-Conceptual-Model-Domains
5
Existing Protection and Automation practices for MV/LV Distribution infrastructure
• Unidirectional flow of power during normal and fault • Predominantly no ICT for protection and very limited ICT for automation • Time-coordination of protection elements through pre-defined settings • Fault analysis methods and service restoration focus is primarily local
http://www.sgip.org/Smart-Grid-Conceptual-Model-Domains
6
Need for revisiting Safety and Protection in Homes & LV/MV distribution
• Safe installation of various Inverter based Energy System (IES) in homes, buildings, industries • Bidirectional flows of power in LV/MV network during normal and fault • Revisiting time-coordination of protection (line crew safety, upstream HV operations security)
http://www.sgip.org/Smart-Grid-Conceptual-Model-Domains
7
Unidirectional power flow in existing Distribution network
Normal operating condition
Reference: Babak E, Impacts of the Distribution System Renewable Energy Resources on the Power System Protection, IEEE PES Transmission & Distribution Conference & Exposition,2014
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Unidirectional fault current flow in existing Distribution network
Fault or short-circuit situation
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Short circuit of appliance
Protection coordination for unidirectional flow of fault current without DG.
• Time-current coordination to ensure operational selectivity • Failure of primary protection results in backup with increased outage footprint
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Impacts of DG on LV/MV distribution network during normal power flows
• Bi-directional power flow in distribution network under normal operation.
• Potential situation of localized voltage rise
causing safety issues.
Over voltage issue with interconnection of distributed generation- Safety!!!
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Effect of sustained overvoltage on home appliances
Short circuit current fed both from upstream and the DG
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Impacts of DG during fault current flow in Distribution network
Fault current changes due to interconnection of DG
Local and global Protection issues with interconnection of DG/IES
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Miscoordination of Protection devices
No communication between devices
Islanding of DG/IES- Safety issue
14
Poses electrical hazard for maintenance crew and public nearby the fault
Protection and safety zones based on Asset location
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Three adjacently overlapping zones of protection & automation: • Home zone, ensuring IES complying with installation and operational standards
• LV zone, evaluating fuse-recloser coordination and transformer protection • MV zone, evaluating consistent DG/IES protection schemes with bidirectional fault flows
This presentations’ focus
GREEN Grid Project Steps undertaken to address safety and protection associated with penetration of DG/IES to NZ homes and distribution networks
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Survey of NZ distribution network ICT infrastructure
Survey protection practices for NZ distribution utilities
Existing DG protection requirements for NZ distribution utilities
Fault behaviour and understanding settings of IES in LV through testing
Pathway chosen for classifying the safety & protection based on voltage and asset class
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Safety and protection guideline
Safety requirements
Installation of DG/IES
Operation of DG/IES
Protection requirements
Protection requirement for LV
Protection requirement for the DG/IES rated up to
10 kVA
Protection of the DG/IES
Protection of the grid
Protection requirement for the
DG/IES above 10 kVA
Protection of the DG/IES
Protection of the grid
Protection requirement for MV
Protection of DG/IES Protection of grid
This presentations’ focus
Safety and protection survey of distribution utilities in NZ
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• A survey of the distribution network protection
technologies and practices by NZ distribution network utilities conducted during 2013-2014.
Section 1- Utility General Information (4)
Section 2- Considerations (3)
Section 3- System Data (14)
Section 4- Phase Protection (4)
Section 5- Ground Protection (8)
Section 6- Reclosing (9)
Section 7- System Faults (7)
Section 8- Cold Load Pickup (6)
Section 9- System Operation (31)
Section 10- Single Wire Earth Return (SWER) (5)
Section 11- Distributed Renewable Generation (4)
Survey of ICT used in NZ distribution networks
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Communication technologies Communication networks Technologies used by NZ utilities Comparison with other countries Applications and requirements NZ future scope
• Joish, H. S. J., Bahadornejad, M., & Nair, N. K. C. (2015). Smart Grid ICT infrastructure: New Zealand perspective. Electricity Engineers Association (EEA) Conference. Wellington, New Zealand.
Fault characterisation of Inverter based DG (IES)
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• Fault characterization is required to quantify
possible impacts of IES on distribution network. • Various control modes of the inverter required for
grid support needs to be tested, with focus on voltage control for safety.
• Anti-Islanding functionality of the inverter for
safety of grid operation. • Robustness/compliance with standards like NZS
4777.2-2015 to ensure coordination amongst all the IES across the network
Fault characterisation of Inverter based DG (IES) : Fault current
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• Characterizing fault current involved voltage dips of up to 10 V to emulate severe faults.
• Test shows fault to be a spike of 4 times rated current. • Spike only for 1/40th of a cycle. • Short circuiting line to neutral also generates similar responses
from inverters.
Mishra, A., Santos-Martin, D., Bahadornejad, M., Nair, N. K. C., & Wood, A. R. (2015). Characterization of inverter fault current and LVRT properties. Paper presented at Electricity Engineering Association (EEA) Conference, Wellington, New Zealand. 24 June - 26 June 2015
Fault characterisation of Inverter based DG (IES) : LVRT properties
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• LVRT required to evaluate system wide impact of grid anomaly and inverter disconnections.
• LVRT of different models were obtained so as to
tailor specific LVRT needs. • Can be modified by change in disconnection time.
• Some inverters found to break compliance with
4777.2 when disconnection times changed.
Fault characterisation of Inverter based DG (IES) : Control modes impacts for voltage safety
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0.00E+00
5.00E+01
1.00E+02
1.50E+02
2.00E+02
2.50E+02
3.00E+02
3.50E+02
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Power and current vs Voltage, Voltage-VAR mode
Volatge Active Power (KW/10) Apparent Power (KVA/10) Current (A*10)
• Capability to maintain voltage is important for IES/home zone safety.
• Most inverters with capacity greater than 3KW have
grid support modes. • The modes include control of reactive and active
power with change in voltage and frequency. • NZS4777.2 (2015) needs inverters to have DRM
modes available for quick access to control modes
Relevant standards identified for safety and protection guidelines in LV and MV
27
AS/NZS 4777 (2015) Grid connection of energy via inverters
IEEE 1547 VDE-AR-N 4105, BDEW 2008
4777.2 (2015) covers the protection and safety requirements set out in:
AS/NZS 3112 Approval and test specification- plug and socket outlets
AS/NZS 3000 Electrical installations (Australian/New Zealand wiring rules)
AS/NZS 5033 Installation and safety requirements for PV arrays
AS/NZS 1768:2007 Lightning Protection
IEC 62109 Safety of power converters for use in photovoltaic power systems
IEC 62109-1 Part 1: General requirements
IEC 62109-2 Part 2: Particular requirements for inverters
AS/NZS 60335 Household and similar electrical appliances-Safety
AS 62040.1.1 Uninterruptible power systems (UPS): Part 1.1: General and safety requirements for UPS used.
IEC 62052.11 Electricity metering equipment (AC): General requirements, tests and test conditions. Part 11: Metering equipment
SR 2010/36 Electricity (Safety) regulation 2010.
IEC 61850 Communication standard for electrical substation automation systems
Evaluation of LV feeder protection schemes with bidirectional fault flows
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Test case for Home zone protection and fuse MCB coordination
Evaluation of MV protection schemes with bidirectional fault flows
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MV case study and faulty relay operations due to DG
Known issues with DG on distribution network are: • Protection device blinding • Erroneous tripping • Sympathetic tripping
Prime cause is uncoordinated bidirectional fault current flows.
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Recommended Safety and Protection guidelines for interconnection of IES to NZ LV network
This presentations’ focus
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Power limitation based on hosting capacity and transformer penetration level
Under Review by GREEN Grid Network Analysis Group
Safety requirement – Lightning & Earthing protection
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• Lightning protection system(LPS) as per AS/NZS 1768 and NZS 5033
• Earthing practices as per section 5.3 of NZS 4777.2(2015) and NZS 3000
Protection of the IES
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Automatic disconnection device
• Automatic disconnection device
shall protect the inverter from the grid related faults/abnormalities as set by the NZS 4777.2(2015)
Under Review by GREEN Grid Network Analysis Group
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Protection of the LV grid
Protection of the grid for the faults contributed from IES
• Various protection schemes based on active as well as passive anti-islanding settings are recommended.
• Power limiting device* settings
are also recommended** based on the transformer penetration limit/hosting capacity *( separate protection relay/four quadrant power meter with programmable
logic controller (PLC)/approved inverter with the ability to adjust net power export to zero) ** Non-Export or Limited Export
Under Review by GREEN Grid Network Analysis Group
36
Safety and protection recommended guideline for interconnection of IES to NZ LV network
This presentations’ focus was Home zone
Guidelines for Above 10 kVA in LV
Operational impacts of bidirectional fault flows for MV protection from both upstream (HV) and downstream (LV)
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• Protection setting impact • False tripping • Sympathetic tripping • Blinding of protection
• Impact on service restoration • Dedicated transformer protection • Coordination with upstream Auto reclosers • Coordination with AUFLS
Auto-recloser coordination
Typical transformer protection
Proposed GREEN Grid Interconnection Platform
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• Disconnect switch • Voltage protection
• Over voltage (59 O) • Under voltage (27 U)
• Frequency protection • Under Frequency (81U) • Over frequency (81O)
• Loss of Main • ROCOF (81R) • Vector shift (78)
• Earth fault and NVD Protection • Earth fault (50N/51N, 50G/51G) • Earth fault Directional (67N/67NC,) • NVD (59N)
• Over Current voltage restraint protection (51V) • Synchronization (25) • Trip supply supervision relay (94) • Power factor or voltage regulation equipment(55) • External system phase unbalance (46) • Directional power for inverter shedding (32) • Fault interrupting devices (AFCI) • Anti _Islanding protection (AS/NZS 4777.2) • SCADA visibility status
Assessing ICT based Transmission protection, multi-functional, multi-vendor schemes for testing of newer ICT
based distribution based schemes grid
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o Intelligent Electronic Device (IEC) based protection
testing involving ICT based schemes
o Implement conventional transmission protection
scheme and enhance utilising IEC 61850
o Test for multi-vendor interoperability and relay
multi-functionality
o Develop strategies for effective tripping times of
relays and incorporate special protection and
automation into known schemes
Some Features
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o Synthetic generation of waveforms for secondary
injection using commercial facilities
o Simulation of real-time fault events by playback
of recorded COMTRADE files
o Testing of multiple relay schemes using time
stamped waveforms (can be adapted to emerging
network clock implementation)
Software platform for integration of IEC61850
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o Requires seamless integration
of IED software from various
devices and vendors
o Knowledge of IEC 61850 global
best practices for substation
automation in HV
o Keep abreast of the
developments for MV and LV
Service Restoration Guidelines with DG/IES: Ongoing work
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FLISR – FAULT LOCATION, ISOLATION AND SERVICE RESTORATION
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Coordinated voltage control methods for NZ distribution following renewable DG at medium, LV and household levels
Ensuring safe operational voltage at all times for distribution network with DG/IES: Ongoing work
Vectors Residential PV-Battery clusters
The GREEN Grid interconnection box, will be helpful to assess coordinated voltage control strategies using existing and newer voltage control devices with the objective being safe and secure operation at all times (normal and faults).
Summary
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Overview: Contrasting Protection practices of
Generation/Transmission with Distribution/DG
Identifying challenges associated with protection and safety of Distribution network assets with DG/IES
Steps towards NZ wide guidelines for Safety and protection for interconnection of DG/IES to LV Distribution network
Steps towards NZ wide guidelines for Protection and Automation of MV Distribution networks with DG/IES
Ongoing work: GREEN Grid interconnection platform, Fault Location Isolation and Service restoration (FLISR) and Voltage control in LV and MV with DG/IES
Protection of High Voltage substation
and network contrasted with
existing MV/LV feeder predominantly radial
without ICT and DG/IES systems
Bidirectional normal & fault flow reviewed,
Different protection and safety issues with
DG/IES identified
Analysis on effect of DG/IES on LV and MV network conducted
Inverter fault response captured
through tests
Guidelines for interconnection of DG/IES in LV
framed
Modelling analysis on understanding effect of DG/IES on LV and MV
network
Survey NZ distribution utilities:
ICT technologies/ practices, MV
protection devices/ schemes, MV
connected rotating DG protection
guidelines
Guidelines for interconnection of DG/IES in MV
framed
GREEN Grid interconnection box under design and IEC 61850 based testing
Coordination existing MV protection devices, and
upstream AUFLS devices identified
Guidelines presented primarily for DG/IES less than 10 kVA
Extra Slides for any Q&A regarding greater than 10 kVA or MV connected IES/DG protection & automation guidelines
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Backup protection requirement for interconnection of IES/DG above 10 kVA to LV network
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Under Review by GREEN Grid Network Analysis Group
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