Compute the operating time of an inverse-time overcurrent relay per IEC 60255-151: t = TMS·(k/((I/I_s)^α − 1)). Supports Standard Inverse (SI), Very Inverse (VI), Extremely Inverse (EI) and Long-Time Inverse (LTI) curves, and samples a T-I characteristic.
Execution
Run this tool
Fill in the form, run the tool, and review the result in one place.
Samples
Examples that match this tool
Related
Continue with connected tools and hubs
Result
Ready for a run
Run the tool to preview files, text, structured data, or streamed output here.
Learn when to use this tool, what it supports, and how real users apply it.
Key facts
Category
Math & Numbers
Input types
select, number
Output type
json
Sample coverage
4
API ready
Yes
Overview
Calculate the operating time of inverse-time overcurrent protection relays according to the IEC 60255-151 standard. This calculator supports Standard Inverse (SI), Very Inverse (VI), Extremely Inverse (EI), and Long-Time Inverse (LTI) curves, allowing electrical engineers to determine trip times and generate T-I characteristic data points using pickup current, fault current, and time multiplier settings.
When to use
Designing electrical protection coordination schemes for power distribution networks.
Verifying relay trip times during commissioning or periodic maintenance testing.
Generating T-I (Time-Current) curve data points to plot protection characteristics in engineering reports.
How it works
1Select the IEC 60255-151 curve type (Standard, Very, Extremely, or Long-Time Inverse) to define the curve constants k and alpha.
2Input the primary pickup current (I_s), the applied fault current (I), and the time multiplier setting (TMS).
3Specify the number of curve sample points and decimal precision to generate the detailed T-I characteristic dataset.
4Run the calculation to obtain the exact relay operating time and the sampled curve points in JSON format.
Use cases
Calculating the trip time of a feeder relay under a specific short-circuit fault current.
Determining the grading margin between upstream and downstream relays to prevent nuisance tripping.
Generating data points to model relay characteristics in power system simulation software.
Examples
1. Standard Inverse Relay Trip Time Calculation
Protection Engineer
Background
An engineer needs to verify the trip time of a feeder protection relay configured with a Standard Inverse (SI) curve during a 500 A fault.
Problem
Determine the exact operating time when the pickup current is set to 100 A and the TMS is 0.2.
How to use
Select 'Standard Inverse (SI)' as the curve type, set the pickup current to 100 A, the time multiplier to 0.2, and the fault current to 500 A.