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A single data item describing a Modelled Item (e.g. Price at a Node for a single Trading Period)


When a circuit trips it may be to a very short term cause, e.g. it might be struck by lightning. Transpower's control system will try to close the circuit breaker automatically and if the fault has gone the circuit will come back into service.


A link, either a line or a transformer, with electrical characteristics such as Resistance and Reactance and which is capable of carrying a Powerflow on the Transmission System.


A constraint occurs when one or more Circuits reaches its local maximum carrying capacity set by the System Operator to maintain grid security or power quality.

Current Data Set

The set of data currently being displayed in the Presentation Interface. Most of the Presentation Interface functions are concerned with viewing or manipulating the current data set. The current data set may be:

  • A single Trading Period from the Market Data Source
  • A single Period from a Forecast output
  • A summary of all or a range of periods from a Forecast output
  • A single Trading Period from a Scenario

Data Grid

The generic data entry and maintenance component of the Presentation Interface.

All textual data entered through the Presentation Interface is entered through the Data Grid which can appear as:

  • A single data entry field
  • A column of data entry fields
  • A row of data entry fields
  • A table ("grid") of data entry fields

Data Source

A context for interpreting data viewed in EMarketOffer's Presentation Interface (Maps, Reports, Charts and Information Windows). There are three Data Sources: Market, Forecast and Scenario.

Database Connection Configuration

A logical set of standard SQL queries that can be used to access one or more different databases to provide input data for EMarketOffer. Different Configurations allow the same logical data to be accessed from different physical sources. This allows for instance load data to be obtained from tables containing GXP global or SPD Daily Demand data. It also allows the same computer to access local or corporate databases which may be useful for mobile users. Only one configuration can be used for any given operation (e.g. loading data into a Forecast Definition).


The rate of consumption of electrical energy measured in MW/h (1 MW/h = the electrical energy consumed by a 1,000,000 watt appliance in one hour)

Demand Profile

A weekly (Mon - Sun) map of Demand for a given Node expressed as a series of Trading Period quantities used in Forecasting.

Directory Structure

One of two hierarchical folder structures for storing EMarketOffer program files and data files. The program folders must be stored on the local hard drive, while data files may be stored on network drive though this is not recommended. Note that the term Directory and Folder are used interchangeably in Windows systems.


The process of calculating the key Market and Transmission System data for a single historical or forecast Trading Period:

  1. Using historical Demand, Generation and Transmission System configuration to calculate Powerflows for all Circuits
  2. Using a Forecast Definition (Demand, Offers and Transmission System configuration) to calculate Price, Generation and Powerflows

Dispatch Factor

Any individual 'fact' (Attribute) required to calculate a dispatch.

Effective Date Range

The user-defined date range specified in a Forecast Definition expressed as a Start Date and Start Trading Period and an End Date and End Trading Period. Forecast output will contain data for every Trading Period between and including the Effective Date Range start and end Trading Periods. Any date and time (past or future) can be used in the date range, providing the end point follows the start point in time.

Equation Constraint

Specifically within EMarketOffer: any constraint placed by the System Operator on the combined Powerflow of more than one Circuit.

Forecast (n)

The output (data set) from a single execution of the model from a Forecast Definition.

Forecast (v)

The process of using the EMarketOffer model to simulate the behaviour of the NZ electricity Market under a specific set of conditions.

Forecast Data Source

Provides data from Forecast output for viewing in the Presentation Interface and Reports.

Forecast Definition

The set of input data required by EMarketOffer to effectively execute a single Forecast Run of the model.

Forecast Summary

A special variant of the Current Data Set in which the key data across all periods of a Forecast Run are summarised.


The EMarketOffer function that replicates the operation of SPD to produce Forecast output for a specified period of time using a set of user-defined forecast parameters collectively called the Forecast Definition.


The electrical energy produced by one or more generation units measured in MW or MW/h.

Generation Company

A real or supposed Company offering electricity into the NZ Electricity Market.


A situation in which a feasible dispatch solution cannot be calculated from a given set of Dispatch Factors.

Information Grid

Display elements appearing in the Main Window and in Secondary Windows to present text-based information in a Data Grid.

Information Window

An independent Window primarily used for displaying and editing static data related to Modelled Items.

Main Window

The primary control and presentation interface for operating the system and viewing output.


A multi-featured map-based graphical presentation of the Current Data Set.

Marginal Generator

A Generation Unit, the output of which varies in response to changes in load while the output of other Units is held constant.


The New Zealand electricity wholesale market where the spot price for electricity is determined.

Market Analyser

An EMarketOffer feature that derives Powerflows for actual Trading Periods using historical Demand and Generation data.

Market Data Source

The Market Data Source provides historical Market data for viewing in the Presentation Interface and Reports.

Market Operator

A collective term for the providers of a number of operational and administrative services to the market under the wholesale and retail sections of the rules.

Market Participant

Any party involved in the regulation and operation of the NZ electricity Market:

  • retailers
  • distributors
  • generation companies
  • consumers
  • line owners
  • service providers
  • metering equipment owners
  • ancillary service agents
  • data administrators
  • system operator

Modelled Item

Any 'thing' (physical or conceptual) the overall state of which may change through time (typically, but not necessarily every Trading Period). An Item either provides input information for a dispatch simulation (Dispatch Factor) or is used to organise dispatch output.


An offer by a Generation Company to sell a quantity of electricity at a specified price for a specific trading period.

Offer Stack

The stack of individual offers created when all the offers to sell electricity for a given Trading Period are ranked in price order.

Offers Profile

A weekly (Mon - Sun) map of Offers for a given Generation Unit used in Forecasting and expressed as a series of 1 to 5 offered Price and Quantity pairs per Trading Period.

Off-load time

The "15 minute off-load time" is the internationally recognised time required for the SO to perform an optimal redispatch after a contingency. Shorter off-load times may be in place with Special Protection Schemes (SPS) in some cases.

Online Database

A database owned by an organisation using EMarketOffer and containing relevant Market or Transmission System data in relational format.


Planned Outage Co-ordination Platform. The POCP web site contains planned generation and transmission outages updated and maintained by generators and Transpower.


For a given circuit, the average quantity of electricity (in MW) calculated to be flowing in the circuit in any one trading period.

Powerflow Case

The overall context for a single Powerflow analysis. It is the basic element associated with the Powerflow Data Source and is comprised of the Powerflow Case Definition and the Powerflow Case Output.

Presentation Interface

The collection of on-screen information presentation features that allow you to visualise the Current Data Set.


The price of electricity calculated through dispatch for a single Market Node in a single Trading Period.


A user-defined collection of Nodes that may or may not share a common location. Regions are not mutually exclusive and a Node may appear in more than one EMarketOffer Region. A Region becomes a Master Region when it is associated with one or more Sub-Regions.


A single execution of the EMarketOffer model using a specified Forecast Definition to create a single Forecast output data set.


A Scenario is a specialised EMarketOffer Data Source: a snap shot of a single Trading Period created from either a Market or a Forecast Data Source. Unlike other Data Sources the Current Data Set underlying a Scenario can be manually edited.

Scenario Data Source

Provides data from previously saved Scenarios for viewing in the Presentation Interface and Reports.

Secondary Window

A Window containing a view of either the Map or an Information Grid, which can be opened from the Main Window and which contains a sub-set of the information available through the Main Window. Secondary Windows 'follow' the Main Window in that their content changes when the Current Data Set is changed through the Main Window.


Transpower's Simultaneous Feasibility Test software used to calculate equation constraints that protect transmission lines from overloading when another line has an unplanned outage.


The Scheduling, Pricing and Dispatch software used by the System Operator and the Pricing Manager to optimise dispatch and calculate nodal and reserve prices.


Special Protection Schemes, also known as "operational intertripping schemes". These are designed to activate "within the period of voltage recovery following fault clearance".


Transpower's System Security Forecast which is found at


A user defined set of Nodes that is a subset of the Node belonging to the parent Master Region. Any Node belonging to the Master Region set can appear in only one child Sub-Region.


A set of geo-located System Nodes: all Nodes with the first three characters of their name are grouped together under the same substation code which is identified by the same three characters.

Supply Curve

The Supply Stack for a given Trading Period represented as a chart of Offer Price versus Offer Quantity.

Swing Node

A System Node to which energy imbalances are allocated during powerflow analysis. Swing Nodes may be manually allocated by the user during Powerflow Case Definition or automatically selected while running the Powerflow Case.

System Operator

A service provider responsible for day to day scheduling and dispatching of electricity on the Transmission System (currently Transpower).


Transpower Information Exchange: a computer system providing SCADA events and energy, wholesale market prices and schedules, network model and reserve market information to market participants.

Trading Period

The fundamental half-hour interval for which individual Market Prices are calculated.

Transmission System

The national grid: a high-voltage electricity transmission network owned and operated by Transpower, and used to transmit electricity throughout New Zealand.


A pre-defined area of the Main Map which can be recalled to fit into the Main Window or a Secondary Window Map Panel.

Watch Window

A floating, text-based, information grid containing a user-defined sub-list of like items (e.g. Nodes) to be monitored.


Wholesale Information and Trading System: an electronic trading and information system owned by the Electricity Authority and operated by NZX.