This video will show you how to look at the manufacturer’s instruction manual to understand how that element is supposed to operate. We also added some tips that show you how you can convert logic diagrams into schematics that any relay tester should understand.
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SEL-351 50-Instantaneous/Definite Time Overcurrent Element
You can download the SEL-351 Relay Instruction Manual Here
SEL-351 51-Time Inverse Overcurrent Element
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Chris,
Beginning at 6.50 minutes of the SEL-351 50-Instantaneous/Definite Time Overcurrent Element video, how did we go from discussing a 50G element to referencing the 51G element? This part kind of lost me. Could you explain this in a little more detail?
Thanks for the comment.
The official designation for 50 is instantaneous, but all modern 50 elements can have a time delay. They should really be renamed definite time overcurrent. We didn’t jump from 50 to 51, we jumped from 50P (phase overcurrent) to 50G (ground overcurrent). The instantaneous/definite time element has three functions in an SEL.
* 50 is non-directional and always on,
* 67 will only work if the AND gate inputs are on
* 67T will only work if the 67G1 is ON for longer than the timer setting
The 50P has similar logic, but it is on different drawings; so we shifted to the 50G1/67G1/67G1T logic to show everything on one drawing.
A lot of relay testers get stuck on these points and start reprogramming the relay to the simplest version of it, which can often disable the relay if the Torque Control or directional settings are incomplete or wrong.
Ok. Thanks Chris that makes sense to me. I think I got stuck on when you worded (if that’s a word lol) the 50G element that we were discussing as a 51 element. That’s what through me off que! Your classes and seminars have been a tremendous help for my and my career! I am waiting on your next book and hopefully it’s own Protection Schemes Vol. 1,2, & 3!!!! Yes, everyone I am a Chris Werstiuk FAN!!!!
Correction 5:50 minutes is where I think it started.
For the GE relay, why do we need a timer for phase instantaneous over current ? Isn’t it suppose to operate as soon as it picks up ?
It can. But all digital relays allow for a time delay. Definite time overcurrent is a better description of the element in the modern era. We show an example of how that time delay can come in handy in the overcurrent chapters of The Relay Testing Handbook: Principles and Practice.
Hi,
On the SEL 51 element at time 3:30 when the switch has closed. Is the path downstream of the switch to the timer sending the fault current to the timer to “fill-in” the settings for the timer? (magnitude of the current determines where the timer starts off at?)
-thanks
Yes. The timing element uses all of the settings in the box to calculate the time delay. I wouldn’t say starts off at though. It would probably be better to say they are inputs to a dynamically changing formula. For example, the current could rise after the timer starts that would speed it up.
I hope that answered your question.
Hi Chris,
Appreciate if you can go through Siemens logic elements in detail as you did for SEL and GE from lecture on GE & Siemens.
Thanks
Joshua
I will try. If anyone knows how I can get in touch with a North American Siemens rep, please let me know.
Thanks for the suggestion,
Chris