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Security Management

Outage Planning | Extended Contingent Event (ECE) Categorisation | Security Constraints | Manual Load Shedding

The System Operator implements security policies as defined in Transpower’s connection contract.

The Policy Statement and Procurement Plan provide further information on security policies and the reasons for adopting them.

Specific security studies and co-ordination activities may occur on request to address anticipated security situations, up to about a year in advance. Current forums on short-term security issues can be found in our Consultation section.

The System Operator prepares a System Security Forecast (SSF) to identify potential longer term security and quality requirements.

Outage Planning

Outage Co-ordination is an essential part of managing the operation of the power system in a secure and efficient manner. The Planned Outage Co-ordination Process (POCP) was agreed by the Planned Outage Forum in Oct 2002, and presented to the Grid Security Committee in Nov 2002.

A review of the POCP was completed in 2006 and 2009.

Planned Outage Co-ordination Process Review

A POCP website has been established to host the prototype outage database and a detailed User Guide to the POCP.

http://pocp.redspider.co.nz/

Extended Contingent Event (ECE) Categorisation

In accordance with our obligations under the Security Policy of the Policy Statement, we have assessed the control requirements to categorise the following events as an extended contingent event (ECE):

the loss of an individual 220 kV interconnecting transformer; and
the loss of an individual 220 kV busbar, 110 kV busbar and 66 kV busbar connected to the core grid.

We have concluded that no additional controls are required to treat these potential events as an ECE with all circuits in service i.e., the system is designed to be capable of sustaining such faults without asset or load security concern. The only exceptions to this is the potential loss of the Manapouri busbar which, due to the recent addition of two wind farms in the South Island that do not meet frequency asset owner performance obligations, will require generation at such wind farms to be constrained at times of low load.

For planned outages, we will (in planning time) assess the potential effects of a loss of an individual interconnecting transformer occurring. If such a loss would create the potential for causing cascade failure then we will rely upon any special protection scheme in place to undertake post event load management. If no special protection scheme is in place then the System Operator will take pre-event action. Such pre-event action includes pre event load management, constraint of generation or cancellation of a planned outage. The System Operator is currently working through a process to determine how to make the same assessment for loss of an individual 220 kV busbar, 110 kV busbar and 66 kV busbar connected to the core grid.

The System Operator’s assessment work, from which the above categorisation has been made, is part of its continuing power system security work programme. This programme includes consideration of matters identified during the System Security Review completed in 2009.

Security Constraints

SPD will normally dispatch the lowest-cost generation to meet demand (allowing for co-optimisation of energy and reserves).

When unconstrained dispatch does not allow the System Operator’s security policies to be met - e.g. if transmission assets are expected to be operated beyond rated short-term capability after any defined contingent event - then a security constraint is applied in SPD.

Security constraints may be applied as:

a temporary constraint - to deal with an outage situation when some assets are not available
a permanent constraint - when the normal integrated power system capability and expected generation offers and demand may not result in secure operation.

On the 28th March 2011, we implemented the Simultaneous Feasibility Test (SFT) software which automatically creates security constraints that are applied to SPD.

The information on the constraints generated by SFT and which trading periods the constraint applies is now published through schedules on Comit. The information will be retained for a rolling 12 month period so that a record of constraint history is built up over time. Participants can look up a trading day of interest and see the constraints that were applied for the grid topology and conditions on that day. This will provide an indication of what constraints may be generated by SFT for future trading days that are expected to have a similar grid topology and conditions.

In the interim period, the excel spreadsheet below provides a list of manual constraints that were used prior to implementation of SFT. It is to be noted that this list will not be modified to reflect any constraint changes that occur after the date of SFT implementation. The historical information may be useful to participants as an indication of the branches that may be included in constraints generated by SFT.

The need for this historical list will be superseded over time as information about SFT constraints is made available.

List of Manual Constraints prior to Implementation of SFT (25 Mar 11) [310kB]

In addition to the above historical information, the spreadsheet below has constraints that the System Operator develops using non-automated processes (manual constraints). This list will be updated as and when the constraints in the list are revised.

Where practicable this information will be published two weeks prior to the date the constraints are intended to be first used. Note this may not always be possible where manual constraints have been identified as being required due to the automatic scheduling process not being able to mitigate a security issue which runs one week out.

Manual Constraints Post SFT (updated 2 Feb 12) [18kB]

Procedures for Managing Security Constraints

The System Operator uses a number of procedures to manage the creation and maintenance of security constraints. We have published a combination of procedures and summary flow charts that may be of interest to market participants:

PR-OC-204 Security Constraint Development Overview (Procedure) [388kB]

PR-OC-208 Identify Need for Constraints [647kB]

PR-OC-213 Conduct Peer Review of Constraint [665kB]

PR-OC-229 Update Register, Email Notification, CANs and Updating Website [628kB]

Manual Load Shedding

Manual Load Shedding is the final step in a process that begins, where possible, with the System Operator communicating with the distributors regarding an impending or current Grid Emergency and the likely demand reductions required.

The Electricity Industry Participation Code (the 'Code') requires each distributor to maintain an up to date process for the disconnection of demand for points of connection, which has agreement of both the Grid Owner and System Operator.

A template of the Distributor Manual Demand Disconnection Process is available for use by distributors.

Distributor Manual Demand Disconnection Process [213kB]

If our template is used by the distributor for manual load shedding, the 'Code' requirements are met and the distributor is only required to submit the information as requested in the Distributor Demand Shedding Data Sheet available below.

Distributor Demand Shedding Data Sheet [39kB]

If the distributor chooses to use a different process for manual load shedding then the System Operator will need to:

assess the documents for suitability and accuracy
request Grid Owner Approval for the MLS and process
confirm approval of both Grid Owner and System Operator by letter to the distributor.

If distributors do not have a letter confirming agreement to Manual Load Shedding Schedules at their points of connection, they are requested to submit their MLS details in the format above.

All manual load shedding data is to be sent to system.operator@transpower.co.nz.