ER P29 Planning Limits for Voltage Unbalance in the United Kingdom
Engineering Recommendation (EREC) P29 provides recommendations and limits for voltage unbalance in public distribution networks operating at 132 kV and below. The scope of EREC P29 applies to the technical evaluation for new loads proposed for connection to the distribution network, which may give rise to voltage unbalance; it does not set generalised network limits. A review carried out on behalf of ENA confirmed that EREC P29 remains technically relevant and has served the industry well but the adequacy of the planning limits and technical requirements needs to be reviewed in light of the following.
- Latest National and International Standards for Electromagnetic Compatibility (EMC) as they relate to voltage unbalance.
- Grid Code modification GC0088, which relaxed the Grid Code limit on voltage unbalance in England and Wales to more closely align with International Standards.
- Modern standards for rotating machines and other equipment and immunity to levels of voltage balance in the Distribution Network - new rotating machines specified to modern Standards (i.e. BS EN 60034-1, BS EN 60034-12 and 60034-26), now give rated power output at only 1% unbalance (as opposed to the 2% mentioned in ER 29 Issue 1).
- Changes in the characteristics of unbalanced demand/generation in single-phase connections that are known to cause voltage unbalance issues.
- Anomalies in measurement time cycles and aggregation intervals for power quality measurements that exist between EREC P29, the Grid Code and standards BS EN 61000-4-30, BS EN 50160 etc.”
A DCRP working group has been established to undertake work to revise EREC P29. This is intended to be a focused review carried out within a 6 month timescale.
The first meeting of the working group is scheduled to take place on the 7 March 2019.
Working Group Membership
 GC0088 Voltage Unbalance Report to the Authority 18 November 2015 Version 1.1