Case Studies of Distribution Asset Failures: Causes and Mitigation

Distribution Assets installed in Customer Substations (CSS) comprise of RMUs, Distribution Transformers and LT Panels with ACBs/MCCBs. For urban installations, the obvious choice is Dry type distribution transformer in view of fire safety and low maintenance cost. These Dry type DTs can be VPI (Vacuum impregnated) or CRT (Cast Resin) type. AEML-D has been using Dry type DTs since early Year 2000 and the performance is satisfactory. Aluminum wound foil type construction has been standardized for CRT DTs which is cost effective and technically superior in view of nearly similar co-efficient of expansion for resin and Aluminum. LT panels with ACBs have been installed as per CEA regulation for Transformer rating 630 kVA & above. These LT ACBs (Air Circuit Breakers) are fixed or draw-out type. During operation, AEML has witnessed some peculiar failure cases which are attributed to gaps in O&M practices and provide an opportunity to re-calibrate the maintenance practices. Four such case studies are presented through this technical paper.