Factors such as limited power supply capacity, impedance mismatch, or inadequate fault simulators can lead to inaccurate results. The new generation of intelligent substations has achieved online monitoring functions for secondary equipment, making some state variables of relay protection equipment become observable indicators. Selectivity is a mandatory requirement for all protection, but the importance of it depends on the application. For example, unselective protection operation during a medium voltage network fault will cause an outage for an unnecessarily large number of consumers. The following Sensing Module mismatch faults on the E300 Overload Relay are displayed in the web page under Diagnostics --> Protection Trip Status tab: The Add-on Profile for the E300 Overload Relay defaults to an XXX-ESM-IG-30A Sensing Module. Retrofitting of relays is the need of the hour because lack of proper testing techniques and misunderstanding of vital procedures may result in under performance of the overall protection system. There are times, however, that the protection system operates incorrectly or "misoperates" due to failure, malfunction, or various other reasons.
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