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Examoogle • User • info@examoogle.com • EE-2024-8821
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In inverse characteristic of relay as current increase operation time will be
Increase
Decrease
Remain same
None of above
Decrease
Quick Summary: An inverse time relay is a protective device where the operating time is inversely proportional to the magnitude of the fault current. As the fault current increases, the relay operates faster to isolate the faulted section of the power system.
An inverse time relay is a protective device where the operating time is inversely proportional to the magnitude of the fault current. As the fault current increases, the relay operates faster to isolate the faulted section of the power system.
t=InK — where t is operating time, I is fault current, and K, n are constants depending on relay type
The relay design utilizes a torque-producing mechanism (often electromagnetic induction) where the operating torque is proportional to the square of the current. Since the time of operation is inversely proportional to this torque, a higher fault current results in a significantly reduced operating time, preventing damage to electrical equipment.
Inverse Time Overcurrent Relays (IDMT) are widely used for feeder protection.
The 'inverse' characteristic ensures selectivity; distant faults (lower current) take longer to clear, while nearby faults (higher current) clear instantaneously.
Standard curves include 'Standard Inverse', 'Very Inverse', and 'Extremely Inverse'.
Provides coordinated protection across various sections of the grid.
Ensures faster operation for more severe fault conditions.
Requires careful setting of Time Multiplier Setting (TMS) and Plug Setting Multiplier (PSM).
Coordination can be complex in meshed power systems.
Radial distribution feeder protection.
Transformer backup protection.
Transmission line protection.
In a Definite Time Relay, operation time remains constant regardless of current magnitude above the pickup value.
The characteristic curve for an inverse relay is typically plotted with current on the x-axis and time on the y-axis, showing a hyperbolic decay.
B is correct — In an inverse characteristic relay, the operation time decreases as the fault current magnitude increases to ensure fast fault clearing for severe conditions.
Always remember that in power system protection, 'Inverse' always implies an inverse relationship between the magnitude of the stimulus (current) and the response time of the relay.