Q4Power System - I
Question
Q.4. What is meant by insulation co-ordination?
Answer
Insulation co-ordination is the process of selecting the dielectric strength (insulation levels) of various equipment in a power system in a graded manner, relative to protective devices, so that insulation failure occurs only in a controlled, least-costly, and safely protected part of the system.
Insulation co-ordination is the systematic correlation of the insulation strengths of all equipment (transformers, circuit breakers, bushings, cables) in a power system with the characteristics of protective devices (surge/lightning arresters), such that under abnormal overvoltage conditions (lightning surges, switching surges), the protective device operates first and limits the voltage stress seen by the costlier equipment to a safe margin below its insulation withstand level (Basic Insulation Level, BIL). This ensures that if insulation failure does occur, it happens at the cheapest, most easily replaceable or safely designed point (e.g., the arrester), minimizing damage and outage cost.