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Direct Transfer Trip and Direct Under-Reaching Transfer Trip Schemes Video

We’re continuing our end-to-end testing series by looking at the two simplest communication-assisted trip schemes used.  Watch this Direct Transfer Trip and Direct Under-Reaching Transfer Trip Schemes Video to learn more about these two schemes.  You can read the transcript below the video.

If you haven’t watched Understanding Line Distance protection (21), watch it first.

 

Direct Transfer Trip and Direct Under-Reaching Transfer Trip Schemes Video Transcript

Welcome to the third video in our End-to-End Testing series. In this video we’re going to look at Direct Transfer Trip schemes or DTT schemes and then we’re going to look at Direct Under-Reaching Transfer Trip schemes (or DUTTs).

This video is part of a series. If you have not watched Understanding Line Distance Protection, the link is on the screen right now, then go watch that video first, so you get the foundation of what we’re going to talk about in this video so we don’t have to keep repeating ourselves over and over again. Let’s get started.

The first thing that we want to look at is the DTT, or the Direct Transfer Trip scheme and we don’t have a fancy animation built for that one because it’s really simple. What you’re looking at is an excerpt from The Relay Testing Handbook: End-to-End Testing and a DTT scheme is really just sending a signal from one side to the other. That’s what the direct part of Direct Transfer Trip stands for.

There is no reason for you to pull out your fancy GPS test equipment in order to test this scheme. The testing procedure for this scheme is very simple. Put one body at Relay 1, another body at Relay 2, get on your cell phones, and have Person 1 push the Trip button. The Trip button will go to the transmit of Relay 1. It’ll then send a signal to Relay 2. Relay 2 will receive that signal and open the breaker. Body Number 2 pushes their button and then the reverse should happen and Breaker Number 1 should open. Now it doesn’t have to be a trip contact. It could also be a breaker status contact or anything else, but it usually is something very simple. So there’s no reason for fancy test equipment.

The next scheme that we want to look at is the Direct Under-Reaching Transfer Trip and just like the Direct Transfer Trip scheme, Direct means that there’s no communication happening between the two relays. One relay sends the command to the other relay. So once again, there’s no reason for you to get out all your fancy GPS test equipment, because it’s a really simple test.

The top shows the standard distance protection scheme with no communication and the bottom shows the DUTT scheme with communication so that we can see what we’re gaining when we have the communication assisted trip schemes. And the first thing I’m going to do is, I’m going to put the fault  really close to Relay 1. Now if you’ve watched the previous videos, or if you have any understanding of Distance Protection at all, you will know immediately that Relay 1 is going to see Zone 1 and it’s going to see Zone 2. Relay 2, because the fault is still on the line is going to see Zone 2. The difference between the standard distance scheme and the DUTT scheme is that the standard scheme Relay 1 is going to operate instantaneously and Relay 2 is going to operate after a 20 cycle delay, but if you look at the DUTT scheme, Zone 1 still trips the Relay 1 breaker immediately, but it also sends a command to the other side telling it to open as fast as it can, which is typically under 3 cycles, depending on communication delays. The DUTT scheme has saved us 17 cycles.

Now if I move the fault to the other side, you can see that the fault is now close to Relay 2 and the opposite is going to happen. Relay 2 is going to see Zone 1 and Zone 2. Relay 1 is going to see Zone 2 and the breaker connected to Relay 2 is going to open instantaneously and then we’re going to have that 17 cycle delay between the opening of the breaker on Relay 1.

If I go outside of the zone, this relay is going to see Zone 3 and Relay 2 is going to see Zone 2. Zone 2 has a faster time delay than Zone 3, so the Zone 2s are going to operate in the same amount of time. So the DUTT scheme gives us the benefit of saving 17 cycles for faults on the line and then giving us our normal backup protection for faults outside of the line. That 17 cycles might not seem like a big deal, but it is forever in electrical terms and there have been some papers presented that show that the longer a fault stays on the system, the more unstable it gets which is a big deal today.

If you like this animation, and you want to play with it some more, you can click the link below to go to our website and you can play with this animation or all the other ones that we’ve created for the communication trip schemes. I hope you’ve enjoyed this video. If you did, please subscribe to our channel, like, and also look for our next video, which should be about, Permissive Under-Reaching Transfer Trip schemes or PUTT schemes. We look forward to seeing you then, thank you.

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Valence Electrical Training Services is the independent source for protective relay training for relay testers. We offer: • Online Training Courses that can be completed at any location at any time • The Relay Testing Handbook series of books written for relay testers by a relay tester • Hands-On Training Classes where you come to us, or we come to your organization

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