One of the main element or function in the GE L90 relay is current differential. Testing of this element might be tricky. This require formula to calculate the pickup current depend on what terminal is used whether terminal 2 or 3. In this page, will be discuss what formula to use in different situation. But first, check the basic requirements of relay testing. Basic Requirement For Relay Testing Requirements: See the requirements page Isolation of the equipment or circuits: Complete the hazard sheet Phone control room and pick up the necessary switching steps. Complete all the issued switching steps as per approve operating order. Do prove-test-prove and apply earths or lock and tag that issued by the controller as per approved operating order. Define permit area that issued by the controller as per approve operating order. Pick up the permit (Work Authority) Complete the sign on/off sheet. Do the isolation for relay testing as per approved ITP (Instruction Test Procedure) Test the re...