Download Victoria Transfer Limit Advice

VICTORIAN TRANSFER LIMIT
ADVICE – VOLTAGE
UNBALANCE
FOR THE NATIONAL ELECTRICITY MARKET
Published: April 2017
VICTORIAN TRANSFER LIMIT ADVICE – VOLTAGE UNBALANCE
IMPORTANT NOTICE
Purpose
AEMO has prepared this document in accordance with the Power System Stability Guidelines to advice Registered
Participants of the voltage and transient stability limits for flows to and from Victoria, as at the date of publication.
Disclaimer
The limits set out in this document are current as at the date of publication, and may be recalculated at any time in
accordance with the requirements of the National Electricity Rules (NER) and relevant procedures and guidelines
made by AEMO under the NER, including the Power System Stability Guidelines.
© 2017. The material in this publication may be used in accordance with the copyright permissions on AEMO’s website.
Australian Energy Market Operator Ltd
ABN 94 072 010 327
www.aemo.com.au
[email protected]
NEW SOUTH WALES QUEENSLAND SOUTH AUSTRALIA VICTORIA AUSTRALIAN CAPITAL TERRITORY TASMANIA WESTERN AUSTRALIA
VICTORIAN TRANSFER LIMIT ADVICE – VOLTAGE UNBALANCE
VERSION RELEASE HISTORY
Version
number
Release date
5
07 April 2017
Clare Paynter,
Ben Blake
Completed doc review, updated to new AEMO template. Updated limit
equations for Heywood third transformer.
4
4 April 2013
Ben Blake
Updated equation 6 for outage of Heywood – APD with both Heywood
transformers in service
3
9 November
2012
Ben Blake
Removed equation 16 based on new studies
2
16 October
2012
Ben Blake
Correction to note on calculation of APD load in equations 5, 9, 11, 12 and
13; fixed URLs for new AEMO website
1
31 August
2012
Ben Blake
Initial version
4
4 April 2013
Ben Blake
Updated equation 6 for outage of Heywood – APD with both Heywood
transformers in service
© AEMO 2017
Author
Comments
1
VICTORIAN TRANSFER LIMIT ADVICE – VOLTAGE UNBALANCE
CONTENTS
VERSION RELEASE HISTORY
1
1.
INTRODUCTION
3
1.1
1.2
1.3
1.4
Other AEMO publications
Calculating transient and voltage stability limits
Methodology
Conversion to Constraint Equations
3
3
3
3
2.
VOLTAGE UNBALANCE
4
2.1
2.2
2.3
General Principles of Voltage Unbalance Constraints
Process
Outages
4
4
4
MEASURES AND ABBREVIATIONS
6
Units of measure
Abbreviations
6
6
© AEMO 2016
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VICTORIAN TRANSFER LIMIT ADVICE – VOLTAGE UNBALANCE
1.
INTRODUCTION
AEMO is responsible for calculating the maximum transient and voltage stability limits into and out of Victoria
(National Electricity Rules (NER) S5.1.2.3) in accordance with Power System Stability Guidelines1. This document
describes the values for these transfer limits for a number of outage conditions (where one or more transmission
elements are out of service) in Victoria.
This limits advice document also describes the methodology used by AEMO to determine the transient and voltage
stability limits.
The limit equations for system normal cases are described in a separate document, Victoria Transient and Voltage
Stability – System Normal2.
1.1
Other AEMO publications
Other limit advice documents are located at: http://www.aemo.com.au/Electricity/National-Electricity-MarketNEM/Security-and-reliability/Congestion-information/Limits-advice
1.2
Calculating transient and voltage stability limits
Transfer limit equations are developed for power transfers into and out of Victoria (known as import and export
limits respectively). Maximum export is limited by transient stability whereas maximum import is determined by
voltage stability.
Transient stability limit equations are derived from a large number of transient stability studies. Studies are based
on the application of a 2-phase to ground fault at the most critical fault location.
Voltage stability limit equations are derived from a large number of load flow studies. Studies consider the trip of a
large generator, the loss of Basslink when exporting from Tasmania (Tas) to Victoria (Vic), and where appropriate
the fault and trip of a critical transmission line or transformer.
1.3
Methodology
The methodology for calculating voltage and transient stability limits is given below:
1.
Generate a set of Power System Simulator for Engineering (PSS/E) cases to represent a wide range of
operating conditions.
2.
Execute a binary search algorithm to search for limiting interconnector power transfer.
3.
Linear regression and statistical limit determination.
1.4
Conversion to Constraint Equations
This document does not describe how AEMO implements these limit equations as constraint equations in the
National Electricity Market (NEM) market systems. That is covered in the Constraint Formulation Guidelines,
Constraint Naming Guidelines and Constraint Implementation Guidelines. These documents are located in the
Congestion Information Resource (CIR) on the AEMO website:
http://www.aemo.com.au/Electricity/National-Electricity-Market-NEM/Security-and-reliability/Congestion-information
1
AEMO, Power System Stability Guidelines, Available at: http://www.aemo.com.au/Electricity/National-Electricity-Market-NEM/Security-andreliability/Congestion-information,Viewed on 31 August 2016.
2
Available at: http://www.aemo.com.au/Electricity/National-Electricity-Market-NEM/Security-and-reliability/Congestion-information/Limits-advice
© AEMO 2017
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VICTORIAN TRANSFER LIMIT ADVICE – VOLTAGE UNBALANCE
2.
VOLTAGE UNBALANCE
2.1
General Principles of Voltage Unbalance Constraints
Voltage unbalance is based on the levels of negative sequence voltage. As specified in S5.1a.1 of the NER, the
negative sequence voltage needs to be limited to 0.5% of nominal voltage for busbars greater than 100 kV. With
the introduction of generation in the southwest of Victoria, AEMO has determined that under specific outage
conditions, the voltage unbalance at the Portland smelter (APD) 500 kV busbar can exceed these levels.
The limit equations are defined such that the simulated negative sequence voltage on the APD 500 kV bus does
not exceed 0.4 % of nominal voltage3 for system normal and prior circuit outage conditions. This allows for a
margin of 0.1%, which is considered a minimum requirement to account for the following:

Other sources of unbalance, including effect of loads and generation that were not represented. The
simulation results only represent unbalance associated with the transmission network.

Sufficient measurements of voltage unbalance in the APD area that are not presently available to enable
verification or calibration of the simulation model4.
As well, the maximum simulated voltage unbalance at APD without the additional generation in the south west of
Victoria is 0.4%.
The voltage unbalance levels at APD are influenced by a combination of:

Voltage balancing effect (or reduction of negative sequence voltage) at Mortlake caused by the Mortlake
generators.

Power flow and associated negative sequence voltage across the Mortlake (MOPS) to Moorabool (MLTS),
and Mortlake (MOPS) to Heywood (HYTS) to APD No. 2 500 kV lines (which are not fully transposed).

Power flow on the Moorabool (MLTS) to Tarrone (TRTS) to Heywood (HYTS) to APD No. 1 500 kV line
and mutual coupling with the MOPS-MLTS and MOPS-HYTS-APD No. 2 500 kV lines.
These factors can produce additive or counteractive effects on negative sequence voltage at APD, depending on
the direction of power flow in the MOPS-MLTS and MOPS-HYTS-APD No. 2 500 kV lines and adjacent MLTSTRTS-HYTS-APD No. 1 500 kV line.
2.2
Process
A number of voltage unbalance simulations were performed using a Power Systems Computer Aided Design
(PSCAD) model of the 500 kV network. From these results, limit equations were produced to keep the level of
voltage unbalance at APD at or below 0.4% during specific outages on the 500 kV network. These equations
quantify the relationship between generation, Vic to SA transfer (via Heywood), and where relevant, APD load,
such that the simulated voltage unbalance at APD will not exceed 0.4%.
It is assumed that the net APD load can vary between 405 MW to 615 MW, and Portland wind farm is capable of
generating up to 100 MW.
2.3
Outages
2.3.1
TRTS-HYTS-APD No.1 500 kV line
Note: for this outage, all three Heywood transformers remain on load.
For one Mortlake generator in service only:
Equation 1:
Mortlake generation ≤ 75 - 0.75 x (APD load – Portland WF – 485)
Equation 2:
Mortlake generation + 0.589 x VicToSA ≤ - 0.75 x (APD load – Portland WF – 485)
3
4
Line to Line = 2 kV and Line to Neutral = 1.15 kV
Heywood voltage imbalance measurements are expected to be available late 2013
© AEMO 2017
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VICTORIAN TRANSFER LIMIT ADVICE – VOLTAGE UNBALANCE
Equation 3:
Mortlake generation ≤ 75 + 0.75 x (APD load – Portland WF – 485)
Equation 4:
Mortlake generation + 0.589 x VicToSA ≤ 0.75 x (APD load – Portland WF – 485)
Conditions:


The lower value of equations 1, 2, 3 or 4 should apply
If either equations 1, 2, 3 or 4 give a negative value, their value should be clamped to zero
For two Mortlake generators in service:
Mortlake generation + 0.353 x VicToSA ≤ 60 - 1.28 x (APD load – Portland WF – 485)
Equation 5:
However, once implemented, it was revealed that the National Electricity Network Dispatch Engine (NEMDE)
produced unfeasible market results with these limit equations (such as exporting more generation from SA than
was available with contingency frequency control ancillary services). As a result, limit equations 1, 2, 3 and 4 have
been replaced by constraining Mortlake generation to zero MW.
Mortlake generation = 0
2.3.2
HYTS-APD No. 1 500 kV line
Note: for this outage, all three Heywood transformers remain on load.
Mortlake generation - 1 x VicToSA ≤ 810
2.3.3
HYTS-APD No. 2 500 kV line
No limitations.
2.3.4
MOPS-HYTS-APD No. 2 500 kV line
Note: for this outage, all three Heywood transformers remain on load.
For one Mortlake generator in service only:
Mortlake generation + 3.2 x VicToSA ≤ -380 + 5 x (APD load – Portland WF – 485)
Conditions:

Where (APD load – Portland WF) is less than 485 MW, the value of (APD load – Portland WF) should
be 485 MW

If this equation gives a negative value, then its value should be clamped to zero
For two Mortlake generators in service:
Mortlake generation + 0.55 x VicToSA ≤ 220
Conditions:

If this equation gives a negative value, its value should be clamped to zero
Like the TRTS-HYTS-APD outage, these limit equations resulted in unfeasible market results. As a result, limit
equations 1 and 2 have been replaced by constraining Mortlake generation to zero MW.
Mortlake generation = 0
2.3.5
MLTS-TRTS No. 1 500 kV line
No limitations.
Note: Macarthur Wind Farm generation is limited to 0 MW, however this is due to fault current limitations, rather
than unbalance.
© AEMO 2017
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VICTORIAN TRANSFER LIMIT ADVICE – VOLTAGE UNBALANCE
MEASURES AND ABBREVIATIONS
Units of measure
Abbreviation
Unit of measure
MW
A Megawatt (MW) is one million watts. A watt (W) is a measure of power and is defined as one
joule per second and it measures the rate of energy conversion or transfer.
Abbreviations
Abbreviation
Expanded name
AEMO
Australian Energy Market Operator
APD
Alcoa Portland Smelter
APD
Alcoa Portland Smelter
CIR
Congestion Information Resource
HYTS
Heywood Terminal Station
kV
Kilo-volt
MLTS
Moorabool Terminal Station
MOPS
Mortlake Power Station
NEMDE
National Electricity Market Dispatch Engine
NER
National Electricity Rules
Portland WF
Portland wind farm generation, MW
PSCAD
Power Systems Computer Aided Design
PSS/E
Power System Simulator for Engineering
VicToSA
Flow from Victoria to South Australia, measured at Heywood 500kV terminal station, MW
© AEMO 2017
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