transpower nz
TRANSCRIPT
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 1/21
Main Transmission Planning Criteria
Main Transmission System Planning
Guideline
February, 2005
Page i Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 2/21
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 3/21
Main Transmission Planning Criteria
1. INTRODUCTION................................................................................................. 1
2. RELIABILITY ......................................................................................................1
2.1 DEFINITION........................................................................................................1
2.2 CRITERIA ...........................................................................................................2
2.2.1 Single contingency criterion......................................................................2
2.2.2 Maintenance outage................................... Error! Bookmark not defined.
An underlying assumption of the N-1 criteria is that maintenance is carried out
during times of light load. ....................................... Error! Bookmark not defined.
2.2.3 Multiple contingency.................................................................................. 3
2.2.4 Sub-station arrangement............................................................................3
2.3 RELIABILITY ASSESSMENT ................................................................................3
2.3.1 Load ...........................................................................................................3
2.3.2 Dispatch.....................................................................................................3
3. STEADY STATE PERFORMANCE CRITERIA ............................................. 4
3.1 EQUIPMENT RATINGS ........................................................................................4
3.1.1 Grid owner equipment ...............................................................................4
3.1.2 Generating Unit Rating..............................................................................4
3.2 VOLTAGE QUALITY ...........................................................................................4
3.2.1 Normal Steady State Voltage ..................................................................... 5
3.2.2 Step Change in Voltage - Dynamic............................................................5
3.3 SHORT CIRCUIT LEVELS .....................................................................................6
4. STABILITY CRITERIA ...................................................................................... 6
4.1 TRANSIENT STABILITY.......................................................................................6
4.1.1 Disturbances selected for testing...............................................................7 4.1.2 Auto-reclose of Circuit Breakers ...............................................................7
4.1.3 Fault Clearing Time...................................................................................8
4.1.4 Transient Voltage Performance Criterion.................................................8
4.1.5 Over-voltages due to Load Rejection.........................................................8
4.2 DYNAMIC STABILITY.........................................................................................9
4.3 VOLTAGE STABILITY .........................................................................................9
4.4 FREQUENCY STABILITY .............................ERROR! BOOKMARK NOT DEFINED.
APPENDIX A: SECURITY CRITERIA ................................................................. 12
APPENDIX B: INFREQUENT SWITCHING CRITERIA ..................................15
APPENDIX C: TRANSIENT STABILITY DISTURBANCES ............................ 16
APPENDIX D: DAMPING CRITERIA FOR DYNAMIC STABILITY .............18
Page iii Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 4/21
Main Transmission Planning Criteria
1. Introduction
The purpose of transmission system planning is to develop a reliable and efficient
transmission system for transferring power from areas of generation to areas of
demand (load) under varying system conditions, while operating equipment within
accepted ratings. The system conditions include - changing demand patterns,
generation changes and equipment outages (planned or unplanned).
The planning process involves applying a number of criteria: technical, economic,
environmental and safety to the current or future transmission system. This document
sets out the technical criteria to be applied in planning the main transmission network.
While this document is focused on technical criteria only, readers are reminded that
any proposed transmission development must also consider all other planning aspects
– such as environmental, economic, etc.
The technical criteria used in transmission system planning can be divided into three
main categories, which are covered in this Guideline as per Table 1.1:
Table 1.1: Technical Criteria
Category Defined as Section
System reliability Is the system adequate and secure? 2
Steady state
performance
Is the normal operating state of the system
within prescribed limits?
3
Stability Does the system remain “normal” or return to
normal following a “disturbance”?
4
Additionally, for comparison purposes, the Appendices provide an international
context to the standards and criteria that Transpower applies in meeting each of these
activities.
2. System Reliability
2.1 Definition
The accepted definition of transmission system reliability incorporates assessment of
two basic aspects of the system - adequacy and security. The National Electricity
Reliability Council, USA (NERC)1
has defined these terms to mean:• Adequacy – The ability of the electric systems to supply aggregate electrical
demand and energy requirements of their customers at all times, taking into
account scheduled and reasonably expected unscheduled outages of system
elements; and
• Security – The ability of the electric systems to withstand sudden disturbances such
as electric short circuits or unanticipated loss of system elements.
1 The National Electricity Reliability Council oversees and co-ordinates reliability and security for the
entire United States.
Page 1 Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 5/21
Main Transmission Planning Criteria
2.2 Criteria
Transpower uses a deterministic approach to planning. This approach is consistently
applied in most transmission networks throughout the world.2
The deterministic planning criteria uses N, (N-‘k’) terminologies to describe the
service level for which a system is planned, where ‘k’ is the number of elements outof service at any one time. These terms are defined as follows:
• ( N) criterion denotes that the system is planned such that with all transmission
facilities in service the system is in a satisfactory state and loads may have to be
shed to return to a satisfactory state for a credible contingency event. It could be
said that an N security policy results in a system that is not secure against
contingent events.
• (N-‘k’) criterion denotes that the system is planned such that with all transmission
facilities in service the system is in a secure state and for any ‘k’ credible
contingency event(s) the system moves to a satisfactory state. If any further
contingency events were to occur loads may have to be shed to return to asatisfactory state.
2.2.1 Single contingency criterion
The main interconnected transmission system shall be designed to maintain N-1
security criterion, meaning that the system is in a secure state with all transmission
facilities in service and in a satisfactory state under credible contingent events. N-1 is
a common security standard in many countries including Australia, Ireland, Denmark
and France3. The single contingencies to be considered under an N-1 criterion are:
• loss of a single transmission circuit
• loss of a single generator
• loss of an HVDC pole
• loss of a single bus section
• loss of an interconnecting transformer
• loss of a single shunt connected reactive component, e.g. capacitor bank, SVC
The loss of an element could be either planned (as part of scheduled maintenance) or
unplanned (as an unforeseen event) either by inadvertent disconnection or as a
consequence of a fault occurring in/on the affected element.
2.2.2 Maintenance outagesAn underlying assumption of the N-1 criteria is that maintenance is carried out during
times of light load so that the risk and consequences of an interruption due to
unforseen events is minimised.
2
A 1992 survey by CIGRE confirmed that of 24 countries participating, all used the deterministiccriteria3 Refer to Appendix A for further detail.
Page 2 Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 6/21
Main Transmission Planning Criteria
2.2.3 Multiple contingency
The risk and consequences of less frequent but more extreme credible contingencies
must also be investigated to determine what emergency measures may be required to
minimise the consequences and provide for restoration of supply in the shortest
possible time.
2.2.4 Sub-station arrangement
The sub-station arrangements are chosen to satisfy all the reliability performance
criteria set out in this guideline while allowing for future extensions and maintenance.
2.3 Reliability Assessment
Reliability is assessed by simulating performance of the system with all transmission
facilities in service and then applying credible contingencies to the simulation, while
generation and load patterns are varied to determine whether a satisfactory state for
the system may be maintained for the various generation and load patterns.
2.3.1 Load
All simulation studies shall be performed for system peak load conditions for both
summer and winter periods. Studies may also be performed for light load conditions
where required. These latter studies may be necessary, for example, where
experience has identified that certain system issues arise only under light or trough
load conditions.
If a part of the system is radial, the studies for the radial part of the system must be
carried out for peak load conditions for that area.
2.3.2 Dispatch
Simulation studies shall be carried out for the worst case credible generation dispatch
scenarios. For hydro generation (New Zealand’s main source of electricity), these
include dry, average and wet hydrological scenarios.4
Studies shall also be carried out
for extreme dry scenarios to identify emergency measures that may have to be put in
place.
4 These have been developed within Transpower using information from a number of sources including
NIWA
Page 3 Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 7/21
Main Transmission Planning Criteria
3. Steady State performance
The steady state criteria apply to normal operating conditions and to post-disturbance
conditions once the system settles to new operating conditions. The steady stateperformance criteria for planning are:
Primary transmission equipment must operate within normal ratings when
all transmission facilities are in service.
⎯
⎯
⎯
⎯
⎯
⎯
⎯
⎯
Primary transmission equipment must operate within acceptable short term
ratings during contingencies.
There is no load curtailment required to maintain N-1 security level for
any operating condition.
Voltage quality is maintained as set out in section 3.2
Cascading outages do not occur.
3.1 Equipment Ratings
3.1.1 Grid owner equipment
The grid owner equipment ratings used are drawn from Transpower’s Asset
Capability Information (ACI) database. The ratings for equipment in this database are
in accordance with Transpower policy document TP.GG.01.10 on equipment ratings,
which take into account manufacturer’s recommendations, the age of equipment and
local environmental conditions. The database includes all transmission equipment:
lines, transformers, switchgear, protection and reactive equipment - synchronous
condensers, capacitors, reactors and SVCs.
3.1.2 Generating Unit Rating
The rating of all generating units connected to the grid shall be the ratings provided
by the Generators as part of their Asset Capability Statement provided to Transpower
( as the Grid Owner).
3.2 Voltage Quality
The criteria for voltage in steady state operation are defined by limits set for different
conditions:
Normal steady state voltage
Step change in voltage
Sustained steady state voltage (after tap changing, Reactive Power Controller
and other dynamic sources actions )
These are discussed in the following subsections.
Page 4 Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 8/21
Main Transmission Planning Criteria
3.2.1 Normal Steady State Voltage
The normal steady state voltage at buses shall be as specified in Table 3.1 or as
stipulated in the contract agreement with the customer. Table 3.1 is consistent with
the steady state voltage limits as prescribed in Rule 3.1, Section III, Part C of theElectricity Governance Rules and Regulations (EGRS).
Table: 3.1 Voltage Limits During Normal Conditions
Nominal
Voltage
(kV)
Maximum
Voltage
(kV)
Minimum
Voltage
(kV)
220 242 198
110 121 99
66 69.3 62.7
50 52.5 47.5
3.2.2 Step Change in Voltage - Dynamic
The voltage step change is the dynamic voltage change between the pre-switching
voltage and the prevailing voltage in the period immediately after transient decay and
AVR action but before any manual or slow control action – e.g. manual tap changing,
automatic tap changing, manual switching of capacitor banks under normal operating
conditions. The allowable voltage deviation depends on the frequency of switching –
infrequent or routine.
3.2.2.1 Routine Switching The Australasian standard
5for acceptable voltage deviation during routine switching
is set out in Table 3.2:
Table 3.2 Allowable Dynamic Voltage Deviation
r
no of events per hour
Vdyn/Vn
(%)
MV HV
r ≤ 1 4 3
1 < r ≤ 10 3 2.5
10< r ≤ 100 2 1.5
100 < r ≤ 1000 1.25 1
Note: MV refers to 1 kV < VN ≤ 35 kV
MV refers to 35 kV < VN ≤ 230 kV
Vdyn/Vn – Maximum voltage change for normal operating conditions
The voltage change at buses for routine switching of equipment to control voltage
(e.g. switching of capacitor banks or circuits) must not exceed the value given in
Table 3.2. Currently Transpower plans on the basis of a 2% voltage dip for routine
switching - this is slightly more conservative than set out in the AS/NZS standard.
5 Australian/New Zealand Standard - AS/NZS 61000.3.7:2001,
Page 5 Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 9/21
Main Transmission Planning Criteria
3.2.2.2 Infrequent switching
There are no standards specifying the allowable voltage deviation for infrequent
switching, but it would naturally be greater than for routine switching operations.
Transpower has designed the system based on a 5% variation. Worldwide, the
allowable voltage deviation is 5% to 6% depending on the utility.6
3.3 Short circuit levels
The default planned maximum short circuit levels are shown in Table 3.3. There are a
limited number of locations, such as Otahuhu 110 kV and Islington 66 kV buses,
where the maximum fault levels will exceed the default maximum short circuit levels
shown, and these are documented in other Grid Owner documents.
Table 3.3 - Maximum Short Circuit Power and Current Limits
Nominal
Voltage
Maximum short-circuit
Power and Current Limits
kV MVA kA
220 12,000 31.5
110 6,000 31.5
66 1,800 16
50 1,350 16
33 1,400 25
22 950 25
11 475 25
4. Stability Criteria
The stability of a power system is determined by its ability to remain stable when the
system is subjected to any disturbance. It can be further divided into four categories of
stability:
•
•
•
•
Transient Stability
Dynamic Stability
Voltage Stability
Frequency Stability.
These are discussed in the following subsections.
4.1 Transient Stability
Transient stability refers to the ability of the system to maintain synchronism when it
experiences large disturbances like a line fault or loss of a generator.
6 Refer to Appendix B for further information
Page 6 Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 10/21
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 11/21
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 12/21
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 13/21
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 14/21
Main Transmission Planning Criteria
Appendices
Page 11 Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 15/21
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 16/21
Main Transmission Planning Criteria
also allows for outage of any section of a 132 kV busbar. It does not allow for the
outage of two 330 kV cables, as this is considered too costly.
Supply to the Melbourne and Adelaide CBD’s are designed to meet N-2 criteria.
The 110 kV supply to the Brisbane CBD is being planned so that full supply is
maintained with two 110 kV cables out of service.
United States - Western Electric Co-ordinating Council (WECC),
WECC also uses (N-2) criterion for planning the transmission grid. However, there
are some differences in defining contingencies:
WECC considers bus section outage as a double contingency not a single
contingency.
◊
◊ WECC allows for unplanned outage of two elements with planned load
curtailment or shedding but does not specify the percentage of load that is met
under such conditions.
United Kingdom - National Grid Company (NGC)
The security standard adopted by NGC for the main interconnected transmission
system is (N-2). However, there are significant differences between the NGC system
and the New Zealand system; the NGC system is heavily meshed with generation in
diverse areas, whereas the New Zealand system is comprised of a weak, longitudinal
transmission with significant generation located in a few areas, remote from the
demand. In addition, the NGC demand is around 10 times that of NZ and due to its
density, there are generally alternative supply options to any grid off-take, via the
distribution networks, which means the restoration times can be reduced.
Table A.2 Security Level for Group Demand
Initial System ConditionGroup
Demand Intact System With Single Arranged Outage
Over 1500 MW In accordance with main interconnected transmission system planning criteria
Over 300 MW
To 1500 MW
Immediately
No loss of supply
Note 1
Immediately
Maintenance Period Demand
Within time to restore arranged outage
Group Demand
Over 60 MW
To 300 MW
Immediately
Group Demand minus 20 MW
Note 2
Within 3 hrs
No loss of supply
Within 3 hrs
Smaller of (Group Demand minus
100 MW) and 1/3 Group Demand.
Within time to restore arranged outage
Group Demand
Page 13 Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 17/21
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 18/21
Main Transmission Planning Criteria
Appendix B: Infrequent Switching Criteria
Australia
Western Australia uses +/-6% voltage change for infrequent switching whereas the
regulator overseer - NEC does not make any specific distinction between routine and
infrequent switching. Specifically, the NEC code specifies in Clause S5.3.7 that
voltage should not exceed the following limit:
• Where only one Distribution Network Service Provider or Customer has a
connection point associated with the point of supply, the limit is 80% of the
threshold of perceptibility set out in Figure 1 of AS2279 Part 4; or
• Where two or more Distribution Network Service Providers or Customers causing
voltage fluctuations have a connection point associated with the point of supply,
the threshold of perceptibility limit is to be shared in a manner to be agreed
between the Distribution Network Service Provider and the Code Participant inaccordance with good electricity industry practice.
Ireland
ESB National Grid (Ireland) allows step voltage changes of 3% for capacitor bank
switchings with all transmission facilities in service. It does not specify any step
voltage change for infrequent switchings.
Page 15 Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 19/21
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 20/21
Main Transmission Planning Criteria
CIGRE
CIGRE published a report in 1992 on a survey carried out on standards used in
transmission planning. Of the 24 countries participating, 20 (83%) confirmed use of
3-phase faults to test stability. Other findings included:
• Australia, Brazil and CIS (formerly part of USSR) countries do not plan for 3-phase faults. Australia and CIS use two-phase-to-ground faults and Brazil uses
single phase faults.
• Some countries consider two-phase faults and single phase faults to assess the
effect of torsional interaction and voltage transients to generators and industrial
users.
Page 17 Rev 1.0 15/04/04
7/30/2019 Transpower NZ
http://slidepdf.com/reader/full/transpower-nz 21/21
Main Transmission Planning Criteria
Appendix D: Damping Criteria for Dynamic Stability
The following table compares the criteria across a number of electricity utilities:
Utility Damping Criteria
Transgrid, VENCorp,
Electranet, Western Power
(Australia)
Halving time of the least damped oscillations must
not be more than 5 seconds.
Powerlink Damping ratio of at least 0.05
Elsam (Denmark) Oscillations to be damped within 10-20 seconds
Statnet (Norway) Oscillations to be damped within 10-20 seconds
ESB (Ireland) Damping coefficient of not less than 0.05
UK Power frequency oscillations time constant should
be less than 12 seconds
WECC, (USA) Do not include specific requirement. It is updated
from time to time.
P 18 R 1 0 15/04/04