Logical Data Structure

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EMarketOffer uses two broad types of data:

Static Data: Static data describes the Items Modelled in EMarketOffer (e.g. Generator maximum capacity).

Dynamic Data: Dynamic data describing the state of the Modelled Items defined by the static data and changes rapidly over time, typically by Trading Period (e.g. Nodal Price)

Contents

Terminology

EMarketOffer's data design consists of 'things' (or items) included in the model, and the characteristics of those 'things'. In this manual the 'things' are called Entities and their characteristics are called Traits. Traits may be static or dynamic.

For example the Circuit Entity can have the static Traits of Start Node and End Node, and the dynamic Traits of Powerflow and Loss by Trading Period.


NOTE: : Static data is not permanently fixed and may, at times, be quite changeable, but within the context of EMarketOffer it is not necessary to be able to track such changes down to the Trading Period level.


Modelled Entities

Four broad categories of entity are modelled in EMarketOffer:

Entity Type Relate To
System
The physical Transmission System
Market
The routine operation of the wholesale Market (Offers, Load, Price)
Commercial
Generation Companies and their retail and hedging operations
Geographical
Physical points and regional positioning

System Entities

The following table lists and describes the System entities modelled in EMarketOffer.

Entity Description Attribute (Trait)

System Node

Any point in the NZ Transmission System to which a Circuit can be connected
  • Name

Substation

One or more System and/or Market Nodes located at a single geographical location
  • Name
  • Component Node

Circuit

A branch (Circuit) conducting power on the NZ Transmission System
  • Name
  • From Node
  • To Node
  • Contributes to HVDC (Yes/No)
  • Resistance
  • Reactance
  • Capacity (Summer/Winter)

Branch Constraint

A Transpower defined Constraint affecting a single Circuit (by imposing a limit on power transfer on the circuit)
  • Name
  • Circuit
  • Start Date and Period
  • End Date and Period
  • Value

Equation Constraint

A Transpower defined Constraint involving more than one circuit
  • Name
  • Start Date and Period
  • End Date and Period
  • Affected circuits
  • Constraint Equation
  • Limit (RHS)

Reserve Region

A Transpower defined Region used for calculating
  • Reserve Region Name

Market Entities

The following table lists and describes the Market entities modelled in EMarketOffer

Entity Description Attribute (Trait)

Market Node

A system Node at which electricity can be injected or withdrawn and for which a Nodal Price is published in the NZEM
  • Name (System Node)

Unit

A single physical electricity generation Unit for which Offers can be made
  • Name
  • Connection (Market Node)

Generator

A logical collection of (typically geographically co-located) Units
  • Name
  • Component Units

Commercial Entities

The following table lists and describes the Commercial entities modeled in EMarketOffer

Entity Description Attribute (trait)

Company

An owner of Generation capacity
  • Name
  • Unit(s)
    • Unit Name
    • Cost in dollars per MWh
  • Retail Node(s)
    • Node Name
    • Percentage load owned
    • Retail price in dollars per MWh
  • Hedge Contract(s)
    • Reference Node name
    • Hedge start date
    • Hedge start period
    • Hedge end date
    • Hedge end period
    • Strike price in dollars per MWh
    • Quantity (MW)

Geographical Items

The following table lists and describes the Geographical items modelled in EMarketOffer

Item (entity) Description Attribute (trait)

Region

A logical collection of Substations (typically but not necessarily geographically co-located)
  • Name
  • Component System nodes

Note: The Items listed above are not all modelled at the same level in EMarketOffer. For example no distinction is made in the program between System and Market Nodes with Prices being calculated for all System Nodes in Forecasts. Also Branch Constraints are treated as complex attributes of individual circuits rather than Items in their own right.


Dynamic Data

Dynamic data Traits that changes value frequently, typically by Trading Period. The following table lists the dynamic data items modelled in the EMarketOffer:

Modelled Item Attribute Units Comment
Circuit
Capacity
MW
Can be re-rated by the Trading Period
Powerflow
MW
Price Separation
dollars per MWh
Price difference on a constrained Circuit
Losses
MW
Loading
ratio
Ratio of flow to capacity
Company
Generation
MWh
Across all Generators owned by the Company
Generation Revenue
dollars
Generation Cost
dollars
Based on Generation marginal cost
Retail Load
MWh
Across all Nodes supplied by the Generator
Retail Revenue
dollars
Retail Cost
dollars
Nodal Price - Retail Price
Hedge Cash Flow
dollars
(Nodal Price - Strike Price) * Quantity
Total Cash Flow
dollars
The sum of all revenues and costs
Equation Constraint
Limit
MWh
Can be re-rated by the Trading Period
Value
MWh
Freedom
MWh
Limit - Value
Company
Generation
MWh
Node
Load
MWh
Generation
MWh
Price
dollars per MWh
Losses
MWh
Region
Load
MWh
Across all Region Nodes
Generation
MWh
Across all Region Nodes
Price
dollars per MWh
Across all Region Nodes
Losses
MWh
Across all Region Nodes
Reserve Region
Offered Fast Reserve
MWh
North and South Island
Offered Sustained Reserve
MWh
North and South Island
Cleared Fast Reserve
MWh
North and South Island
Cleared Sustained Reserve
MWh
North and South Island
Price Fast Reserve
dollars per MWh
North and South Island
Price Sustained Reserve
dollars per MWh
North and South Island
DC Offset Fast Reserve
dollars per MWh
North and South Island
DC Offset Sustained Reserve
dollars per MWh
North and South Island
AC Offset Fast Reserve
dollars per MWh
North and South Island
AC Offset Sustained Reserve
dollars per MWh
North and South Island
Base Risk Fast Reserve
MW
North and South Island
Base Risk Sustained Reserve
MW
North and South Island
Risk Adjustment Factor Fast Reserve
North and South Island
Risk Adjustment Factor Sustained Reserve
North and South Island
Substation
Load
MWh
Averaged across all Nodes
Generation
MWh
Averaged across all Units
Price
dollars per MWh
Averaged across all Nodes
Losses
MW
Averaged across all Nodes
Unit
Generation
MW
Fast Reserve dispatched
MW
Sustained Reserve dispatched
MW
Marginal Indicator
Indicates if Unit was marginal for the Trading Period in question
Risk Setter
Indicates if Unit was setting the risk for the Trading Period in question
Maximum Generation
MW
Maximum generation a unit is capable of producing in the Trading Period (used in Reserves calculation)
Fast Reserve Offer Quatity (PLSR) bands 1-3
MW
Fast Reserve Offer Price (PLSR) bands 1-3
dollars per MWh
Fast Reserve RSlope (PLSR) bands 1-3
Sustained Reserve Offer Quantity (PLSR) bands 1-3
MW
Sustained Reserve Offer Price (PLSR) bands 1-3
dollars per MWh
Sustained Reserve RSlope (PLSR) bands 1-3
Fast Reserve Offer Quantity (TWD/ILR) bands 1-3
MW
Fast Reserve Offer Price (TWD/ILR) bands 1-3
dollars per MWh
Sustained Reserve Offer Quantity (TWD/ILR) bands 1-3
MW
Sustained Reserve Offer Price (TWD/ILR) bands 1-3
dollars per MWh
Frequency keeping band
MW


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