Extended Reserve

On 29 April 2021 the Authority held an engagement session for the extended reserve Code amendment consultation.

The following presentation was discussed. Participant question and answers are also included below.

The Electricity Authority (Authority) published the system operator’s proposed Automatic Underfrequency Load Shedding (AUFLS) data specification in January 2020. Feedback on the specification was received from PowerCo Limited, Vector Limited and Energy Market Services.

The following response answers the queries raised by both Vector and PowerCo regarding the proposed direction of the Extended Reserve project and how the system operator will use the data requested.

Response to Distributor feedback on the system operator AUFLS data requirements

The Electricity Authority (Authority) published the system operator’s proposed Automatic Underfrequency Load Shedding (AUFLS) data specification in January 2020. Feedback on the specification was received from PowerCo Limited, Vector Limited and Energy Market Services.

The following response answers the queries raised by both Vector and PowerCo regarding the proposed direction of the Extended Reserve project and how the system operator will use the data requested.

Extended reserve project direction

In October 2019 the Authority decided to refocus the Extended Reserve project. This meant the sole focus and objective of the project is now to transition to a 4-block AUFLS scheme in the North Island. The role of the Extended Reserve Manager was disestablished and the concept of centralised selection and procurement of AUFLS is no longer being developed. It is now expected that distributors will manage their AUFLS feeders under a regime that does not require dynamic setting or regular reconfigurations.

As a first step, the system operator will be analysing the provision of the current North Island 2-block AUFLS scheme. This will establish a detailed understanding of the risk of over and under arming on an island-wide basis. This will be followed by confirmation of the 4-block scheme design and the start of the transition planning with distributors.

In parallel, the Authority will develop and consult on a Code amendment to support the implementation and ongoing operation of the 4-block AUFLS scheme.

Data collection will be resource intensive

We acknowledge that some distributors may need to allocate significant resource to retrieve and format the data requested. The formal data request is not expected to be made until after July 2020, which gives distributors the time to ensure the appropriate resource is in place to retrieve the data. We expect distributors to use the following months to prepare for the system operator data request and allow the data collection to progress as efficiently as possible.

We also expect the data format used for the initial analysis work will form the basis of an ongoing monitoring regime once the 4-block AUFLS scheme is in place. Investment made by distributors in data retrieval and reporting systems would be part of an investment in satisfying future monitoring obligations. 

Why we need data collection

The system operator will use the AUFLS data to analyse the current levels of 2-block AUFLS provision. This will allow their engineers to baseline the 2-block AUFLS provision and identify any immediate issues that may need to be resolved. The information gathered will also be used to improve the system operator’s modelling of AUFLS in their system security tools.

Once completed, the results of the baselining exercise will inform the system operator’s planning for the 2 to 4-block transition.

The data specification will form the basis of the ongoing monitoring of the 4-block AUFLS scheme. This monitoring is expected to take the form of periodic data review to confirm that changes in network use have not significantly impacted AUFLS provision.

Consideration for interruptible load 

In the context of AUFLS data provision, interruptible load refers to controllable load that is procured by the system operator for the purposes of instantaneous reserve. The interruptible load can be offered into the market by the distributor or by an agent.

The data specification is structured to provide the gross load on a feeder as a data point and provide the ancillary information as may be required, such as potential interruptible load connected to the feeder. This structure will allow the system operator to use the gross load data where their analysis requires it but still be able to subtract the interruptible load data if necessary.

Provision of network single line diagrams

The system operator has requested network single line diagrams as a part of the data specification to help understand the AUFLS relay implementation within the distribution network. No information beyond the AUFLS relay installation, or any information for those feeders with no AUFLS relays installed, will be required.

Historically, assumptions around AUFLS provision levels have been conservative as the system operator had limited understanding of the individual AUFLS configurations across the distribution networks. By collecting the single line diagrams, the system operator engineers aim to:

• understand the connection of distributed generation behind the AUFLS relays and its impact on AUFLS provision;
• understand the configuration and management of the AUFLS scheme, particularly in validating assumptions around over provision of AUFLS;
• use the single line diagrams to provide context when assessing block size and likely behaviour during an AUFLS tripping event;
• improve the accuracy of the AUFLS modelling in the system operator security tools;
• better co-ordinate the secure transition from 2 to 4-block AUFLS across the North Island.  

The Authority and system operator staff are intending to engage more closely with industry as soon as we are able. We will discuss any issues distributors may have providing the diagrams and the formats through which they would prefer to provide the information. 

The system operator has been developing a data specification for historical AUFLS demand data. This data will be used to baseline the current level of North Island AUFLS provision and inform the transition planning for the 4-block AUFLS scheme.

The data specification is also intended to apply to future operational monitoring of the 4-block AUFLS scheme. The data format and submission tools will be refined during the first half of 2020. The request for data is expected to be sent to current AUFLS providers mid 2020.

Please email extended.reserve@ea.govt.nz with any feedback and questions on the draft data specifications. The data specification will be finalised after 7 February 2020.

Investigation

There will be an initial investigation phase where the current 2-block automatic under-frequency load shedding (AUFLS) arrangements will be reviewed in detail.

Engagement

The Authority and the system operator (Transpower) will be meeting with distributors and direct connect consumers in the North Island to discuss the project, consult on their views and answer any questions.