What does the relay protection setting unit le mean

In relay protection, 'le' typically represents the rated or reference current for earth fault protection, used as a basis for setting the relay's pick-up current.Definition and ContextThe unit 'le' is...

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What does the relay protection setting unit le mean

In relay protection, 'le' typically represents the rated or reference current for earth fault protection, used as a basis for setting the relay's pick-up current.Definition and ContextThe unit 'le' is commonly used in overcurrent and earth fault relays to indicate the rated secondary current of the current transformer (CT) for earth fault protection. It serves as a reference for calculating the relay's pick-up current, which determines the minimum current at which the relay will operate. For example, if a relay is set to operate at 50% of 'le', it will trip when the earth fault current reaches half of the rated CT secondary current.Relationship to Other Relay SettingsCurrent Setting (CS or Plug Setting): The relay pick-up current is often expressed as a multiple or percentage of 'le'. For instance, a setting of 0.2 le means the relay will pick up at 20% of the rated earth fault current .Plug Setting Multiplier (PSM): PSM is the ratio of the actual fault current in the relay to the pick-up current. It is calculated using 'le' as the reference for the relay's rated current .Time Multiplier Setting (TMS): TMS adjusts the operating time of the relay. While TMS affects the speed of operation, the pick-up threshold is still based on 'le' .Practical ExampleSuppose a CT has a secondary rating of 1 A for earth fault protection. If the relay is set to 0.3 le, the relay will operate when the secondary current reaches 0.3 A. If a fault occurs and the secondary current rises to 0.6 A, the relay will trip according to the time determined by the TMS and the fault current magnitude.Summary'le' = rated secondary current for earth fault protectionUsed as a reference for relay pick-up currentIntegral to calculating PSM and coordinating relay operationEnsures selective and reliable protection of electrical systems Understanding 'le' is essential for correctly setting earth fault relays and ensuring proper coordination with other protective devices in the system.
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