Grid Code – Subgroup of OTEG
Offshore Grid Code Subgroup rd3 Meeting 26/03/2007
Notes of Meeting
thNational Grid office, Northampton 26 March 2007
John Greasley (JG) National Grid (Chair)
Nasser Tleis (NT) National Grid
Joe Duddy (JD) Renewable Energy Systems (on behalf of Centrica)
Bridget Morgan (BM) Ofgem
Hamish Dallachy (HD) SPT
Paul Newton (PN) E.ON
Robert Longden (RL) Airtricity
Peter Jones (PJ) ABB
Goran Strbac (GS) DTI Centre for Distributed Generation and Sustainable
Biljana Stojkovska (BS) DTI Centre for Distributed Generation and Sustainable
Ham Hamzah (HH) RWE
Philip Baker (PB) DTI
Andrew Mann (AM1) Ofgem
Anthony Mungall (AM2) Ofgem
Stephen Curtis (SC) National Grid
Brian Taylor (BT) National Grid
Mark Perry (MP) National Grid
Duncan Hughes (DH) National Grid (Technical Secretary)
JG acknowledges receipt of an e-mail from HH, PN JM and RL detailing concerns about the progress of the Grid Code subgroup. JG explains that the information to be presented to the group over the course of the meeting should resolve these issues. The group agree to discuss the points raised in the email in detail after National Grid has presented their work and conclusions.
AM1 (Ofgem programme manager) updates the group on overall progress of the Offshore Electricity Transmission project.
HH raises point about technical standards for Offshore Electricity Transmission. NT explains that this is out with the current scope of the group but that consideration will need to be given to the issue, by the appropriate group, in the future.
JG goes through actions from previous meeting. Group agree these have been completed.
Grid Code – Subgroup of OTEG
3.2 Connection Conditions
3.2.1 Applicability of Grid Code Requirements
NT begins presentation detailing National Grids final proposals on Grid Code changes and amendments to accommodate Offshore Electricity Transmission.
PN and JD raise issue with the definition of an Offshore Generator and how Grid Code requirements will apply with respect to generator size. JD explains that using a blanket definition to apply full Grid Code requirements to all Generators situated offshore could result in prohibitive costs to small experimental generation connections such as tidal or wave projects. NT agrees that this is not the intention of the proposal and that this scenario should be avoided.
NT outlines National Grid’s views on the definition of an Offshore Generator and the potential for aggregation of individual windfarm ‘strings’ into a single Balancing Mechanism Unit (BMU)
or Power Park Module (PPM).
JD proposes that the existing size criteria used to determine the application of Grid Code requirements is applied to offshore generation or that a new term of Offshore Power Park Module is created to capture larger applications whilst allowing smaller projects to connect without being subject to full Grid Code requirements.
The group agree that the inclusion of a new term ‘Offshore Power Park Module’ or significant revision of the existing Power Park Module definition represents the best solution to this issue.
Action 1 – All parties to provide feedback regarding classification of Offshore Generators.
3.2.2 Reactive Capability Requirement / Voltage Control
NT explains objectives, methodology and results behind the 1500MW and 500MW studies carried out by National Grid.
NT states that National Grid’s final proposal is that a reactive capability requirement of unity power factor be placed on the Generator at the Offshore Grid Entry Point and that the existing -/+ 0.95 power factor requirement be placed on the Offshore Transmission Owner at the Onshore Grid Entry Point. This would apply to projects using both AC and DC link technology.
JD queries if this requirement would represent a fixed capability or a minimum requirement e.g. could an Offshore Generator and Offshore TO enter into a commercial agreement for the generator to provide a MVAr capability above unity? RL highlights the potential impact this may have on areas such as connection offers and TNUoS charges. NT states that the aim of this proposal is to provide a generic minimum requirement in order to give clarity to all parties. HH states that the Grid Code should not specifically prohibit an Offshore Generator from providing a capability above unity. NT states that Grid Code connection condition principals, which are minimum requirements, cover this.
NT asks for formal feedback of any comments and alternatives for consideration.
Action 2 – All parties to provide feedback regarding reactive capability and voltage control proposals.
3.2.3 Voltage Limits
NT describes National Grid’s final proposal for voltage limits within Offshore Transmission
Networks. This takes the form of a -/+ 10% limit at all voltage levels. No voltage step change limits are proposed offshore.
Grid Code – Subgroup of OTEG
JD explains that the Electricity Safety Quality and Continuity Regulations (ESQCR) may state required limits at different voltage (possibly -/+ 6% below 132kV). If this is the case the Grid Code policy recommendations will need to be in line with this.
Action 3 – All parties to provide feedback regarding voltage limits proposal.
GS gives a brief presentation detailing work carried out by DTI Centre for Distributed Generation and Sustainable Electrical Energy. GS states that their conclusions support National grid’s proposals on reactive capability and voltage limits.
3.2.4 Fault Ride Through (AC)
MP explains National Grid’s proposal for Mode A Fault Ride Through requirements for AC
connected Offshore Generators. The intention is to provide a generator requirement at the Offshore Grid Entry Point which avoids the need for the generator to use data on the offshore transmission network. The proposal includes a requirement to ride through a voltage depression to 15% for 140ms and, subject to further work, requirements matching those for onshore generators for longer duration events.
PN and JD query that it may be unlikely that a fault on the main onshore system will result in voltage at the Offshore Grid Entry Point falling as low as 15%, therefore the proposed requirement is too onerous.
NT explains that this proposal is based on work carried out when defining generic requirements for onshore wind farms (H0/4) where wind turbine manufacturers stated that turbines could ride through this level of voltage dip. Recent information from manufacturers suggest ability to ride through lower volts at the turbine terminals.
JD proposes that the a generator should be allowed to comply either with a generic requirement at the Offshore Grid Entry Point or, in the event that the Generator has visibility of the Offshore TO’s network, be able to ride through a fault causing 0 volts at the Onshore Grid Entry Point.
NT outlines benefits of a single generic provision at the Offshore Grid Entry Point including increased clarity for developers and the ability to confirm compliance via factory testing.
HH asks about power recovery requirements. NT states that this will apply as stated for onshore Generators.
NT states that some further work is required before proposal for the Part B Fault Ride Through requirement can be finalised.
Action 4 – National Grid to circulate to group proposal for Part B Fault Ride Through requirements when available.
Action 5 – All parties to provide feedback regarding Fault Ride Through for AC connected Offshore Generators.
3.2.5 Fault Ride Through (DC)
MP details National Grids proposal for Fault Ride Through requirements for DC connected Offshore Generators. This proposal takes the form of specifying an ability to ride through a load rejection that would be equivalent to that caused by applying the fault ride through voltage profile for AC connected Offshore Generators at the Offshore Grid Entry Point.
PJ offers to pass any technical questions members of the group may have onto ABB’s
Grid Code – Subgroup of OTEG
The group agree that further investigation is required into DC fault ride through requirements.
Action 6 – All parties to provide feedback regarding Fault Ride Through for DC connected Offshore Generators.
3.2.6 Power Output with Falling Frequency
MP states that current Grid Code requirements for power output with falling frequency will be applied to Offshore Generators. There are no objections to this proposal.
3.2.7 Frequency Response
MP states that current frequency Response requirements will apply to Offshore Generators whether connected via an AC link or a DC link.
For DC connected Offshore Generators MP explains that a policy recommendation will be required that obligates the Offshore TO to facilitate the provision of frequency response from the Offshore Generator.
The group agree with these proposals.
3.2.8 Other Connection Conditions
NT explains that all outstanding Connection Conditions are detailed in the supporting documentation circulated to the group.
HH asks about the -/+ 5MVAr dead band specified for the unity power factor requirement. NT clarifies that this relaxation is to accommodate the use of discrete reactive devices (e.g. an MSC).
3.3 Planning Code / Data Registration Code
NT outlines the proposed changes required to the Planning Code and Data Registration Code in order to facilitate the proposed Grid Code policy recommendations.
No comments are recorded by the group.
3.4 Operating Code / Balancing Code
BT details the proposed changes to the Operating Code and Balancing Code in order to accommodate Offshore Electricity Transmission Networks.
BT states that embedded transmission (an Offshore TO connecting to an Onshore DNO) is out of the scope of this group and will be dealt with by a separate Embedded Transmission work stream.
BT informs the group of the Offshore Grid Code Safety Co-ordination group and invites anyone wishing to be represented on the group to contact him.
There are no further comments from the group regarding the Operating and Balancing Codes.
3.5 Further Work to Deliver Terms of Reference
Grid Code – Subgroup of OTEG
NT proposes that National Grid will circulate a first draft of the Grid Code policy report ahead of the next (and final) meeting. NT also asks all parties to supply all comments on any issues rdto National Grid by Tuesday 3 April for inclusion in the draft report and to clarify areas where further investigation is required.
rdAction 7 – All parties to submit any comments or suggestions to National Grid by Tuesday 3
3.6 Any Other Business
HH proposes that an Offshore Generator should have a choice in what voltage level it wishes to connect at. The group agree that the GB SQSS subgroup recommendations must be checked to assess whether this is possible.
The proposals to date are based on an Offshore Grid Entry Point at 33kV, as was agreed in the first meeting. To reconsider the proposals in the existing timescales will be challenging. The group agree that further consideration is required but that full proposals within the group’s timescales may not be possible.
PN states that the group has so far been focused on the Grid Code but must make sure that proper consideration is given to the consequential changes to STC as required by the Terms of Reference.
4. Date of Next Meeting
thThe next meeting was previously scheduled for Wednesday 18 April. However the group
agree to try to re-schedule this at Ofgem’s request. JG proposes that the meeting take place as near as possible to the previous date.
Action 8 – DH to reschedule next meeting and inform group.