NPP – Grid Interface Key Areas - iaea.org · PDF fileNPP – Grid Interface Key...
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NPP – Grid Interface Key Areas David Ward UK IAEA Technical Meeting on Flexible (Non-Baseload) Operation for Load Follow and Frequency Control in New Nuclear Power Plants Erlangen, Germany, 6 - 8 October 2014
NPP – Grid Interface Key Areas - iaea.org · PDF fileNPP – Grid Interface Key Areas . ... power programme and the electrical grid is one of those ... electricity regulator . 10
IAEA Technical Meeting on Flexible (Non-Baseload) Operation for Load Follow and Frequency Control in New Nuclear Power Plants
Erlangen, Germany, 6 - 8 October 2014
Presenter
Presentation Notes
“NPP-Grid Interface” Summary Starting from the Milestones document, summarises a number of key issues concerning the relationship between the NPP operator and the grid system operator, including some relevant to flexible operation This presentation has been included mainly for the benefit of new-comer countries – those planning to build their first NPP 29 slides including this 2555 words in the Notes. OK for 20-25 minutes. [The pictures show Calloway NPP in the USA and Sizewell B in the UK]
Operating a grid system?
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IAEA “Milestones” Guide
NG-G-3.1(2007)
“Milestones in the Development of a National Infrastructure for Nuclear Power
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Presenter
Presentation Notes
This is the IAEA’s main Guide for countries starting a nuclear power. It summarises the nineteen infrastructure issues that have to be considered in the development of a nuclear power programme and the electrical grid is one of those infrastructure issues.. But it is a very important one. This Guide does not specifically mention flexible operation.
Phases and Milestones
4 Source: Figure from IAEA NG-G-3.1(2007)
Presenter
Presentation Notes
This diagram is taken from that guide and illustrates the three main phases The first phase is before the government has made a firm decision to proceed with a nuclear power programme. This phase is mostly information gathering. In the second phase, a decision has been made to proceed with a nuclear programme, and preparations are made to be able to issue a bid invitation specification to possible nuclear plant vendors. In the third phase the vendor is selected, contracts are exchanged, and the nuclear plant is built. After the end of Phase 3 the nuclear plant starts commercial operation. The guide summarises the matters to be considered against each of the 19 infrastructure issues during these phases, but only very briefly
IAEA Technical Report
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NG-T-3.8 (2012)
“Electric Grid Reliability and Interface with Nuclear Power Plants”
Presenter
Presentation Notes
This Technical Report published by the IAEA in 2012 provides much more detail of the issues related to the grid infrastructure. It emphasises the importance of establishing a good co-operative relationship between a NPP developer or operator and the grid system operator. This should start very early in the planning stage. Like most IAEA publications, it can be downloaded free of charge from the IAEA website. Paper copies are available for purchase. Much of what is in this presentation is in that Technical Report.
Mutual Dependence
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NPP Export power
Import power for start-up and
shutdown
The Grid System
Presenter
Presentation Notes
We have to remember that there is a strong mutual dependence between NPPs and the electrical grid system The nuclear plants require the grid to export their power, but they also require the grid to supply power reliably for reactor start-up, for shut down, and during plant outages. Our nuclear plants are designed to degraded grid supplies or loss of off-site power without undue risk, but it is always preferred to maintain supplies from the grid to the NPP.
Mutual Dependence
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NPP
Reactor trips Voltage control
Frequency control
Transients Abnormal Voltage
Abnormal Frequency Loss of supply
The Grid System
Presenter
Presentation Notes
The behaviour of the grid system can affect the nuclear power plant. Voltage transients or abnormal voltage or frequency may cause plant systems to trip or function incorrectly. Loss of the connections to the NPP will cause a reactor trip, and not provide post-trip power Similarly unplanned reactor trips can cause problems for the grid system operator. If the NPP does not operate correctly to control system voltage or frequency, the stability or security of the network could be affected. It the NPP is able to operate flexibly, it can help to maintain the stable and secure electricity system it needs.
NPPs Prefer a Reliable Grid
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• Frequency well controlled (+/- 1%) • Voltage well controlled (+/- 5%) • Reactor trip does not cause abnormal
voltage or frequency • Abnormal voltage or frequency is rare • Loss of grid supply to NPP is rare • System collapse/blackout very rare
Presenter
Presentation Notes
Almost all existing NPPs operate in a stable and reliable grid. New NPP designs expect the grid to be reasonably stable and reliable. The slide summarises some typical parameters of such a grid. Note that the parameters include a well-controlled system frequency, and the expectation that abnormal frequency is a rare occurrence. If NPPs are able to operate flexibly, they can help to ensure that this is the case.
Organisations Involved
• Grid System Operator • Transmission System Owner • NPP owner/operator • Owners/operators of other generation • Electricity or Energy Regulator • Nuclear Regulator
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Often same organisation
Presenter
Presentation Notes
This slide summarises the various organisations that have an interest in control of the grid system, and a stable system frequency. The grid system operator is that organisation that is responsible for the national or regional control centre. The transmission system owner is that organisation that owns and maintains the transmission system. In many countries these are the same company or organisation. But in some countries (e.g. in parts of the USA) they are separate organisations. The responsibility of the other organisations is perhaps more obvious. In some countries where the electricity system is still state-owned or state-controlled, the Grid System Operator may be part of the same organisation as the owner/operator of the power stations. Where there has been market deregulation, this is never the case. The NPP owner/operator will need to establish good working relationships with all these other bodies.
Grid System Operator
Responsible for real time secure operation of the transmission system: • Forecasts demand • Instructs power plants to change output to
match demand • Monitors and controls power flows • Monitors and controls frequency & voltage • Must satisfy the energy/electricity regulator
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Presenter
Presentation Notes
This slide summarises the basic responsibilities of the grid system operator. This organisation is responsible for the secure operation of the system in real time. It has to forecast demand, and ensure that power stations are operated to match that demand and to control frequency. It has to monitor and control power flows on the transmission system and to control frequency and voltages. The Grid System Operator is primarily responsible for the safety and security of the electricity system as a whole and may have to satisfy the requirements of the country’s energy regulator or electricity regulator. The grid system operator does not have any direct responsibility for nuclear safety and had no connection with the nuclear regulator..
NPP Operator
Responsible for operation of the nuclear plant • Has the primary responsibility for nuclear
safety • Must satisfy the requirements of the nuclear
regulator • Has commercial incentive to maximise
output and income • Has incentive to maximise life of the plant
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Presenter
Presentation Notes
It is the operator of the nuclear plant that has the responsibility for nuclear safety, and needs to satisfy the requirements of the nuclear regulator. The operator of the NPP will also have a strong commercial incentive to maximise generation, and hence maximise income. It also has the incentive to maximise the life of the plant. The responsibilities of the NPP owner/operator and the grid operator are rather different, and may come into conflict. Hence in the IAEA technical reportt concerning the grid, we emphasise that it is necessary for the company that will be the NPP operator to establish a good working relationship with the Grid Operator. This needs to start in Phase 1 of the Milestones document.
Grid System Operator
• Carries out long term studies of the system • Designs modifications to the transmission
system • Plans maintenance outages on the
transmission system • Establishes the technical requirements for
the grid and for generators
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Presenter
Presentation Notes
In addition to controlling the real time operation of the electricity system as a whole, the grid system operator is also responsible for carrying out long term studies of electricity system, and for designing upgrades to the transmission system. For this reason the future NPP owner/operator will need to liaise with the grid system operator from a very early stage in planning a new NPP. But in addition the Grid system operator is usually responsible for establishing the technical rules for the grid system and for generators, and for ensuring that those rules are obeyed.
Grid Code (Technical Rules)
A document that defines the technical requirements for equipment and its operation
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Presenter
Presentation Notes
There needs to be a document that defines these technical requirements for the equipment and for the operation of the grid system. This is particularly important in countries where the grid system and the power plants are owned or operated by different companies. In Great Britain we have such a document and we call it the “Grid Code”. Other countries have similar documents, which they may call a “Grid Code” or it may have a different name. The illustration shows the Nordic Grid Code which applies in Norway, Sweden, Denmark, and Iceland. There may be other documents too – In GB we also have a “security standards” document that specifically deals with the design of the transmission system
Manuals/ • Jordan http://www.ideco.com.jo/portal/OtherFiles/Library/GCMCJune2009.pdf
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Presenter
Presentation Notes
This lists some example grid codes or similar documents and their web addresses where you can download them. All of these shown are in English. I have checked hat all these links are current. [When I did a mission to Nigeria in 2009, they had what I believed at the time was a significant error in the code, which I mentioned in my final report. I haven’t checked to see if it has been modified since]
Usually specifies • Normal performance of the grid
• Frequency, voltage, harmonics, phase imbalance, fault clearance times
• Required performance of generating units • Planning information to be exchanged • Operational information to be exchanged • Operational procedures
Presenter
Presentation Notes
This slide summarises the usual contents of a Grid Code or similar document. It should describe the normal performance of the grid such as Frequency range for normal operation Voltage range for normal operation Likely magnitude of harmonics Likely magnitude of phase imbalance (negative phase sequence The fault clearance times of circuit breakers ….and so on It should also state the performance that is required from generating units - which I will describe later. It should describe the information that has to be exchanged for planning purposes, such as generator parameters, planned outage dates etc. Finally it should describe the procedures to be used in actual operation, such as what information has to be exchanged between NPP control rooms and the grid control centre, and how the grid system operator should instruct Generating plants to change load. In some cases (but not GB) it may also specify the design requirements of the transmission system.
What Types of Flexible Operation?
• Planned load changes to match forecast demand
• Load changes to balance renewables • Load changes on instruction or automatically
• Within hours • Within minutes • Within 10-30 seconds (AFC)
• Emergency load drops or trips
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Presenter
Presentation Notes
The Grid Code may specify the flexibility requirements for generating units. These could include any or all of the of different forms of load variation listed here
Baseload and Flexible Operation
17 Source: Drawn by author for draft IAEA publication
Presenter
Presentation Notes
This diagram is one I showed earlier for the different kinds of load changes. Ideally the Grid Code should specify the requirements for each of these
Planned or instructed load changes
It is important to specify the load changes that will be required: • How large? • How quickly? • How often?
How much notice? Will requirements for NPPs be the same as other generators?
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Presenter
Presentation Notes
If the Grid operator wants the nuclear plant so be able to operate flexibly, it is important to specify how flexible. For planned or instructed load changes, it is important to know how large they will be,, how quickly load will need to be changed and how often.
Frequency Response (AFC)
19 Source: GB Grid Code
Presenter
Presentation Notes
Similarly for provision of automatic frequency control, it is necessary to specify how much the output should change, and how quickly. The illustration shown is from the GB Grid Code – this specifies the requirement to be able to increase output by 10% of rated output within 10 seconds of a large frequency drop. There are separate requirements for immediate response, and longer term response. Note that different grid operators specify this requirement in different ways and with significantly different numbers for magnitude and speed of response.
Emergency Actions
• Transmission fault near a NPP may cause: • Stability problems • Need for reactor trip within
seconds • Or:
• Overloading of transmission circuits
• Need for rapid load reduction within minutes
20 Source: Internet photo
Presenter
Presentation Notes
This slide was also in my previous presentation. If it is helpful to the grid operator to be able to request rapid deloads or reactor trips, but the circumstances need to be specified and agreed. If this is not in the grid code or similar document, then it should be in some separate agreement.
Grid Code Requirements
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• It needs to be clear and unambiguous
• It must be capable of change • It must be compatible with
capability of nuclear plant • If it applies to nuclear, it must
also apply to other generators
Presenter
Presentation Notes
Experience in countries that have a Grid Code or similar document is that it needs to be clear and unambiguous. It is not easy to write such a technical document. [it is in the interest of the NPP operator to ensure that the interpretation of the Grid Code rules is agreed before they are applied to the NPP]. It is also the experience that the Grid Code may need to be modified or updated as circumstances change. The NPP owner/operator will need to monitor any proposed changes to ensure they are compatible with the available NPP designs. If the rules in the Grid Code are to be applied to NPPs, it is important that they are applied fairly to other generators too. [ In one potential newcomer country I learned that an IPP (Independent power producer) had negotiated not to provide frequency control on its plant. This would then increase the likelihood that a future nuclear plant would have to provide such capability!]
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“MILESTONES” - GRID ISSUES IN
THE THREE PHASES
Presenter
Presentation Notes
I now return briefly to the milestones document, and suggest a few things to consider related to the grid, in each of the three phases.
Grid - Phase 1
Consider • Expected growth of grid capacity • Historical grid performance • Potential to improve grid characteristics • Capacity of grid compared with unit size of
available NPPs • Grid connections to suitable sites • Need for nuclear to be flexible
23 Adapted from IAEA NG-T-3.8 (2012)
Presenter
Presentation Notes
Phase one is before a firm decision is made to develop a nuclear programme. The main requirements are to establish the current performance of the grid, and the likely way that demand will grow, generation will be added and the transmission network will be developed in the coming years. This includes the extent to which new renewables such as wind and solar power will be added to the network. A key point is to consider the likely capacity of the grid in future, in comparison with the unit size of available NPP designs. Also included is a consideration of the likely need for nuclear plants to operate flexibly, and the nature of the flexible operation required.
Grid – Phase 2
• Carry out detailed studies • Decide suitable site for NPP • Plan grid connections to the NPP site • For Bid Invitation Specification:
• Define grid characteristics • Define performance requirements for NPP
24 Adapted from IAEA NG-T-3.8 (2012)
Presenter
Presentation Notes
In Phase 2, after a decision has been made to definitely proceed with the construction of a nuclear plant, it is necessary to carry out detailed studies, to confirm the suitable site for the NPP, and to plan the grid connections to it. But it is also necessary to determine details that will go into the Bid Invitation Specification which is to be submitted to the vendors. For the grid this includes: The expected characteristics of the grid (range of frequency and voltage, likelihood of loss of grid connection etc.) The performance requirements of the NPP as defined by or agreed with the grid operator (e.g. the extent of flexible operation that is required.)
Grid - Phase 3
• Complete grid connections to NPP site and grid upgrades and enhancements
• Monitor growth and performance of the grid • Establish formal agreements between grid
company and NPP • Establish good communications • Train grid operators in NPP characteristics
25 Adapted from IAEA NG-T-3.8 (2012)
Presenter
Presentation Notes
Phase three is the period when construction of the plant takes place. This can take a number of years, and the grid can change during this time, so it is important to monitor such changes, particularly if they are different from what was expected. Before the NPP starts operation, is is sensible to have formal agreements in place between the NPP and the grid system operator, and to establish good communications between the two organizations, for both operational an strategic matters. It is important to provide training to the staff in the grid company control centre so that they fully understand the capabilities and needs of the nuclear plant, and the extent to which it can provide flexibility services.
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A POTENTIAL PROBLEM - LOW INERTIA
Presenter
Presentation Notes
To finish this presentation, I would like to briefly mention a new problem related to the grid. This is currently perceived as a big issue in Great Britain – our National Grid Company have a whole chapter about it in their annual “Ten Year Statement”! The problem is to do with system inertia.
Inertia Problem
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48.6
48.8
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Minimum 48.8 Hz
Rate of Fall Depends on System Inertia
Source: National Grid publication
Presenter
Presentation Notes
This is a chart you have seen before – a big frequency dip in GB in 2008. The key point is that the initial rate of fall of frequency, after the trip of a large generating unit, depends on two things: The size of the generation loss The total system inertia
Inertia Problem
Turbine generators contribute inertia to the grid (stored energy about 5MWs/MVA)
But •Variable-speed wind turbines •Solar panels •HVDC inverters Contribute no inertia to the grid
28 Source: Microsoft graphics
Presenter
Presentation Notes
The system inertia is provided by the rotors of the large turbine generators on the system. Typically they have a stored energy, due to this inertia, of about 5 MW-seconds per MVA of capacity. Part of this energy is released as extra power output as they start to slow down after the trip of a large generating unit. However, modern large variable-speed wind turbines do not contribute any inertia to the system (they do not change speed as system frequency falls). Similarly, solar panels provide no inertia. Nor does the inverter of a HVDC link when it is acting like a generator and providing energy to the system.
Inertia Problem - conclusion
If you replace turbine generators with: •Large wind turbines •Solar panels •HVDC inverters Frequency control becomes harder: •Frequency changes faster •Generators need to respond faster
29 Source: Microsoft graphics
Presenter
Presentation Notes
So the result is that if you replace large turbine generators with wind turbines, solar panels and HVDC connections importing power from elsewhere, the system inertia will be reduced. This means that frequency control will become more difficult. Frequency will change faster after any change in generation or demand. As a consequence frequency is likely to be more variable, and the grid operator may request that generating units providing frequency control should provide more response and to provide it more quickly. There are some other measures that could be taken, such aa Require wind turbines to provide simulated inertia Similarly for HVDC converter stations. Require wind turbines to operate in AFC mode Similarly for HVDC connections (these measures probably not applicable to solar panels) But it is an issue that requires serious consideration if there is to be a large percentage of renewable generation on the system.
