Look before you leap! Practical tips for medium-voltage equipment check out

Over the course of an average day, somewhere in the world, a major medium-voltage electrical failure occurs at a facility. For many outages due to corrosion, heat build-up, insulation failures (some accelerated by contamination or humidity), animals, improperly prepared terminations, or misoperation, the cause is quickly identified and corrected, and the equipment is placed back in service. With property designed, installed, and maintained protection systems, damage is usually limited in scope. However, in cases with extensive, and possibly collateral, damage, the cause may not be found until a thorough analysis and investigation is complete. Unfortunately, the conclusion is never appealing; often, the equipment or system was designed or installed incorrectly or did not perform as designed. Furthermore, the cause of many failures is either inconclusive or misdiagnosed. For those instances when the system did not perform as designed, there are two common causes: lack of maintenance and improper commissioning. This article is not a complete treatise on the subject of testing and inspection required prior to or after energizing medium-voltage switchgear and substation equipment. It does, however, discuss many important aspects of ensuring the protection systems for substation or medium-voltage switchgear are, from an electrical standpoint, ready to be placed in service. The following are discussed: important items to be considered in the commissioning planning stage; practical methods for checking protective device circuits; and common commissioning oversights and how to avoid them.