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SEL-451 and Frequency Testing Issue

A customer was having problems timing a SEL-451 with a delay setting of 8 cycles. He was measuring a 12 cycle delay when transitioning from 59.5 to 58.5 Hz.

If you look at the spec sheet, the SEL-451 frequency element has a “Maximum Pickup/Dropout Time: 3.0 cycles”. When you add up all of the delays, you are looking at a possible 3.87 cycle delay when testing this relay. Remember to watch the specifications when performing high-speed tests!

The specification also has a “Slew Rate: 15 Hz/s maximum” which means the frequency calculation will only be accurate if the frequency changes less than 15 Hz in a second. An instantaneous transition from 59.5 – 58.5 exceeds that setting which probably caused some problems as well.

SEL-451 Underfrequency and OverFrequency Testing Specifications  SEL-451 Nominal Frequency Rating Specification for Frequency Testing

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About the Author

Chris is an Electrical Engineering Technologist, a Journeyman Power System Electrician, and a Professional Engineer. He is also the Author of The Relay Testing Handbook series and founder of Valence Electrical Training Services. You can find out more about Chris here.

Chris is an Electrical Engineering Technologist, a Journeyman Power System Electrician, and a Professional Engineer. He is also the Author of The Relay Testing Handbook series and founder of Valence Electrical Training Services. You can find out more about Chris here.

Chris is an Electrical Engineering Technologist, a Journeyman Power System Electrician, and a Professional Engineer. He is also the Author of The Relay Testing Handbook series and founder of Valence Electrical Training Services. You can find out more about Chris here.

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