Document Number: EDS 01-0045 Version: 3.0 Date: 21/06/2016 THIS IS AN UNCONTROLLED DOCUMENT, THE READER MUST CONFIRM ITS VALIDITY BEFORE USE ENGINEERING DESIGN STANDARD EDS 01-0045 OVERHEAD LINE RATINGS Network(s): EPN, LPN, SPN Summary: This standard details the Electricity Networks Association (ENA) Engineering Recommendation P27 Current Rating Guide for UK Power Networks Overhead Lines. Author: Alan Archer Date: 21/06/2016 Approved By: Paul Williams Approved Date: 28/06/2016 This document forms part of the Company’s Integrated Business System and its requirements are mandatory throughout UK Power Networks. Departure from these requirements may only be taken with the written approval of the Director of Asset Management. If you have any queries about this document please contact the author or owner of the current issue. Applicable To UK Power Networks External All UK Power Networks G81 Website Asset Management Contractors Capital Programme ICPs/IDNOs Connections Meter Operators HSS&TT Network Operations UK Power Networks Services Other
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Document Number: EDS 01-0045
Version: 3.0
Date: 21/06/2016
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ENGINEERING DESIGN STANDARD
EDS 01-0045
OVERHEAD LINE RATINGS
Network(s): EPN, LPN, SPN
Summary: This standard details the Electricity Networks Association (ENA) Engineering Recommendation P27 Current Rating Guide for UK Power Networks Overhead Lines.
Author: Alan Archer Date: 21/06/2016
Approved By: Paul Williams Approved Date: 28/06/2016
This document forms part of the Company’s Integrated Business System and its requirements are mandatory throughout UK Power Networks. Departure from these requirements may only be taken with the written approval of the Director of Asset Management. If you have any queries about this document please contact the author or owner of the current issue.
Applicable To
UK Power Networks External
All UK Power Networks G81 Website
Asset Management Contractors
Capital Programme ICPs/IDNOs
Connections Meter Operators
HSS&TT
Network Operations
UK Power Networks Services
Other
Overhead Line Ratings Document Number: EDS 01-0045
Appendix A – Pre-fault and Post-fault Conductor Current Ratings at 500c Operating Temperature ............................................................................................................. 7
Table A1- Aluminium Conductor Steel Reinforced (ACSR), All Aluminium Alloy Conductor (AAAC) and Hard Drawn Aluminium (HDAL) ...................................... 7
Table A2- Hard drawn (HD) Copper and Cadmium (CAD) Copper ................................... 9
Table A3- Covered Core Conductor (CCC) or BLX and Aerial Bundled Conductor (ABC) ...................................................................................................................... 12
Overhead Line Ratings Document Number: EDS 01-0045
This standard details the Electricity Networks Association (ENA) Engineering Recommendation P27 ‘Current Rating Guide for High Voltage Overhead Lines Operating in the UK Distribution System’.
2 Scope
This standard specifies the use of the cable rating tool ‘ORAT 4’ (developed by EA Technology as part of the Overhead Line Strategic Technology Project), which specifies the current ratings that UK Power Networks’ overhead line network should be designed and operated to.
3 Methodology of Conductor Ratings
The ratings contained in ER P27 are based on statistical studies by CERL. These studies provided data on the likelihood of a conductor exceeding its maximum operating temperature for a given continuous current in specified weather conditions. The aggregate period of time during which the conductor exceeds its maximum operating temperature is called the 'exceedance'. It is usually expressed as the percentage of the total time for which the current was maintained. ER P27 makes no distinction between pre-fault and post-fault ratings and allows 0.001% excursion time for single circuits and 3% for double circuits. Under post-fault conditions the duration of the excursion is not set out as in ER P27. Under these conditions and dependant on the network configurations, the percentage exceedance can be altered. Table 1 gives guidance on this. All ratings are appropriate to their maximum operating temperature and the season (winter, spring/autumn, summer), for which an ambient temperature is specified.
4 Circuit Identification
Under ER P27 there is the need to identify the type of circuit you are operating. These types of circuit are identified as:
Single Circuit. Single circuit radial systems. eg. LV and 11kV spur.
Secondary Distribution. These refer to ring-type systems with a number of tapping off points, such as 11kV main lines.
Multi-circuit Primary. These refer to circuits which would be called upon to supply maximum load only in the event of the outage of another circuit, the category therefore includes 132kV and 33kV duplicate transformer feeders, together with some untapped 11kV circuits providing a firm supply to end loads.
Overhead Line Ratings Document Number: EDS 01-0045
Two different ratings criteria will be applied to an overhead line:
Pre-fault Rating. This is the maximum continuous rating appropriate to the season which may be applied without time limitation.
Post-fault Rating. This is the maximum continuous rating appropriate to the season which may be applied in a fault situation until pre-fault requirements can be restored. Normally this would be for a period well within 24 hours.
6 Applying Appropriate Levels of Exceedance
Table 1 gives guidance on the exceedance levels that should be applied to the different types of circuit configurations. It is split into two categories:
Pre-fault. Normal operating conditions that apply to the methodology of ENA P27.
Post-fault. Due to the nature of the circuit configuration and the duration of the running arrangement the exceedance levels have been altered from those set out in ENA P27.
Type of Circuit Load Shape Pre-fault Exceedance Value
Post-fault Exceedance Value
Single Circuit Rating Not Dependant on Load Shape
0.001% 0.001%
Secondary Distribution 0.001% 3%
Multi-circuit Primary
General Distribution 3% 10%
Intensive Industrial or City Centre
3% for loads at
0.96 x Rating 10%
Table 1 – Levels of Exceedance
7 Calculating of Conductor Ratings
The most commonly used conductor ratings have been included in Appendix A of this document.
If additional ratings are required, these will be calculated by the UK Power Networks Technical Sourcing and Standards team within Asset Management, using the EA Technology OHRAT Calculation of Distribution Ratings for Overhead Conductors software.
Overhead Line Ratings Document Number: EDS 01-0045