EREC P28 Issue 2 – What has changed from Issue 1 and what are the impacts for those connecting disturbing equipment that causes voltage fluctuation?

1 Jul 2019
TNEI P28 Issue 2

Engineering recommendation (EREC) P28 issue 2 was published by the Energy Networks Association (ENA) in 2018 and it became applicable on the 23rd May 2019. The latest versions of the Distribution Code and the Grid Code have also been updated accordingly, and refer to P28 issue 2.

The previous version of this EREC was published 30 years ago to provide recommended planning limits for voltage fluctuations for connection of equipment to public electricity supply systems in the UK. Since then the factors affecting the distribution and transmission systems as well as the equipment connecting to them have changed. The move towards distributed generation and low carbon technologies using this modern equipment has the potential to cause flicker. The revision of EREC P28 considers these changes and provides updated voltage fluctuation limits.

If you propose to connect equipment which has the potential to cause voltage fluctuation or carry out assessments concerning the stability of connecting such equipment to distribution and transmission networks, you will need to be aware of the new revision.

Previous P28 requirements

According to the UK standards ER P28, the maximum allowable change in voltage at the Point of Common Coupling (PCC) was 3%. The magnitude of this voltage dip was previously measured 30ms after commencement of switching events which occur at least 750 seconds apart. 

New P28 requirements

EREC issue 2 supersedes the ENA Engineering Recommendation P28 Issue 1 1989 and has been extended to cover assessment and limits for rapid voltage changes (RVCs). The new P28 Issue 2 introduces requirements and planning levels for RVCs, imposing envelop based limits on the voltage fluctuation. The planning levels for RVC are specified in the diagrams below, taken from the published document.

Figure 1 – Voltage characteristic for frequent events

Figure 2 – Voltage characteristic for infrequent events

Figure 3 – Voltage characteristic for very infrequent events

P28 Issue 2 includes an improved definition of ‘worst case operating conditions’ to be used in the assessment of voltage fluctuations as well as an intermediate planning level and associated flicker severity limits stated in BS EN 61000-4-15. It also clarifies the information requirements for assessment and responsibilities for provision of information.

To minimise the risk of increased project costs or delays, the new P28 requirements should be considered from the outset. Not understanding the changes to the legislation could result in disconnection of equipment.

From distribution to transmission connections, TNEI can help address any concerns and are well placed to increase your understanding of the changes and how they might affect you.

For more information please contact us.

TNEI are also running P28 Issue 2 training courses throughout 2019. Please get in touch to find out more.

Key contact

Chris Ellis

Chris Ellis

Connections Lead

Chris is the TNEI Connections Team Lead in the Manchester office. Chris brings over 24 years of experience in the energy sector including experience in project management, power system studies, grid code compliance, power system and substation design, protection and control, electrical applications and verification. His experience includes team management and the delivery of complex multi-discipline worldwide technical projects in transmission and distribution planning, design and analysis, HVDC design, AC/DC protection and system studies, substation design, cable assessments, cost benefit analysis and EMC compliance.