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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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Substation Design | Power System Analysis

Direct Transfer Trip Scheme

Direct Transfer Trips (DTT) are initiated from station relays when a severe event occurs in the substation. Some of these events are breaker failure, bus faults, transformer failure, etc. A lockout relay (86 device) is assigned to each event.

The lockout relay in the station is pretty essential. When operated due to any of the events indicated above, it trips all the breakers connected to it. So for example, for a bus fault, the bus differential relay will operate the bus lockout relay which will trip and blocks re-closing of all the breakers connected to the bus. If the breaker is at a remote location and can’t be physically wired, a DTT signal is sent to it via the protective relays using the pilot channel.

The figure below shows which all lockout relays are typically used to initiate the DTT. The substation design affects this. For example, a ring bus substation or a breaker-and-a-half substation has a breaker failure lockout assigned to each breaker. For other designs, a breaker failure event trips the bus lockout relay. Whichever case you are presented with, a contact from the lockout is assigned to the relay that can key the DTT signal to the remote end breaker.

Note that lockout relays are typically used to initiate DTT. In which case, the intent is to trip all breakers without any delay. There is no logic or reasoning – just trip. Remaining events like faults on lines are taken care of by the pilot schemes which have intentional delay for coordinating the breaker trips.

Direct Transfer Trip Quiz

Get ready to learn this topic like never before.

For a transformer fault at substation 2, would you transmit DTT to substation 1?

Fault current contribution from substation 1 can be stopped by tripping 2CB1. DTT transmission to Substation 1 not required.

Fault current contribution from substation 1 can be stopped by tripping 2CB1. DTT transmission to Substation 1 not required.

For a temporary fault on the transmission line, would you transmit DTT from either one substation?

Faults on the transmission line are usually temporary. Line protection relays require time to implement its reclosing logic. DTT is not initiated.

Note that designing the protection system is an art and not an exact science. How the relay engineer "paints" differs from utility to utility. For instance, certain t-lines pass through a dense forest while others through an arid desert. The utility engineer dealing with the trees (causing higher temporary faults) may choose to go with reclosing logic - no DTT. In the case of the desert, the faults could be interpreted as permanent and whichever relay detects the fault using its Zone 1 elements, transmits DTT to the remote-end substation relay.

Note that designing the protection system is an art and not an exact science. How the relay engineer "paints" differs from utility to utility. For instance, certain t-lines pass through dense forest while others through an arid desert. The utility engineer dealing with the trees (causing higher temporary faults) may choose to go with reclosing logic - no DTT. In the case of the desert, the faults could be interpreted as permanent and whichever relay detects the fault using its Zone 1 elements, transmits DTT to the remote-end substation relay.

For what kind of fault at Substation 1 would you transmit a DTT to Substation 2 (to trip breaker 2CB1)?

For the fault scenarios listed, there is no way to stop the fault contribution from Substation 2. There is no breaker on the line-exit at Substation 1 (You cannot use a switch to interrupt load or fault current. Learn more ). If one existed, tripping it would suffice, and a DTT wouldn't be necessary.

For a fault on Bus 1, would you implement a direct transfer trip (pilot) scheme to trip breakers tied to the same bus?

All breakers shown are within the substation. You can wire the trip 'a' contact from a lockout relay to breaker's trip coil physically. Therefore DTT scheme is not required.

Assume circuit breaker 3CB2 fails at substation 3. DTT is transmitted to Substation 2 to trip 2CB1 and 2CB3. Which auxiliary relay would you install at Substation 2 to trip breakers 2CB1 and 2CB3?

A quick word on 94 and 86.

94 relay - when its operating coil is energized - it trips. When de-energized, it resets automatically.

86 relay - when its operating coil is energized - it trips. When de-energized, it does not reset. Someone needs to be at the substation to reset it.

Considering the severe event did not occur at Substation 2, it makes no sense in installing a lockout at this station and needlessly sending someone to reset it. A  94 relay is used in this scenario. Some utilities may also use microprocessor relays to trip the breaker (instead of a 94 aux relay).

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This article, part of a series, covers the essentials on pilot relaying and pilot protection schemes. If not done already, start at the beginning.

• Basics of Pilot Relaying & Application Considerations For Transmission Line Protection
• Directional Comparison Blocking Scheme (DCB)
• Permissive Overreaching Transfer Trip Scheme (POTT)
• Directional Comparison Un-Blocking Scheme (DCUB)
• Direct Transfer Trip Scheme (DTT)  (This is technically not a pilot scheme but requires a pilot channel)

5 thoughts on “Direct Transfer Trip Scheme”

What is the difference between DTT and Carreir aided protection

Awesome! simply explained, thank you!

Thanks a lot, for my reverensi supervisor E.M .PT.reCOnsult , in G.I.S 150kV. Jati Waringin .Jaka Mulya . Bekasi Barat.

Dear sir, Please leave me a test mail to [email protected]

hi . sir i want to ask you, about DTT , in my plant we used Relay UR GE L90 for line Upstream – Downstream arround 4 Kilometer. which event trip by DTT and force to 87 L trip and then Lockout relay 86 , but in may event record relay we not having any problem about diffrensial current it so normal , but DTT was aktif and trigger for DTT from Asym DET and LOSTPKT. can you explain to me why DTT its aktif ? and how about trigger DTT like ASYM DET & LOSTPKT because in my logic diagram i cant find them,

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MICROGRID DIRECT TRANSFER TRIP DESIGN AND SIMULATION

Powertech labs is offering a new service to design, simulate, and test direct transfer trip for microgrid implementation..

Protection Co-ordination of Microgrids

The rapid development of distributed energy resources (DER)—such as solar photovoltaics, wind energy, battery storage, and hydrogen and electric vehicles—is revolutionizing the energy industry. For utilities, one common challenge in the proliferation of DER is to ensure the proper management of the microgrid in protection co-ordination with the utility grid.

For example, microgrids are usually located in remote or rural areas and connected to the utility’s long radial distribution feeders. In these configurations, when a fault is detected by the utility recloser, the recloser should send a protection trip signal to the microgrid controller to disconnect the microgrid from the system. This direct transfer trip (DTT) prevents the microgrid from islanding with the utility’s downstream feeders.

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Substation Protection

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• First Online: 21 July 2018
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• Richard Adams 4  

Part of the book series: CIGRE Green Books ((CIGREGB))

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The role of protection is not to prevent a fault from occurring but deal with it if one occurs and protect the power network as well as the primary equipment. Protection should detect and isolate the faulty equipment as quickly as possible in order to:

Minimize the risk of instability in the system including generators

Minimize damage to the faulty item of equipment

Minimize risk of damage to adjacent healthy equipment

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The following are not specifically referred in the previous section, nor meant to be an exhaustive list, but rather a possible source of further, more detailed information should the reader be interested. The E-CIGRE website is a very useful source of information published by the Study Committees of CIGRE

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Baxter, H.W.: Electric Fuses. Edward Arnold, London (1950)

Electricity Training Association: Power System Protection 4 Volume Set. The Institution of Engineering and Technology, London (1995). ISBN: 978-0-85296-847-5

Wright, A., Newberry, P.G.: Electric Fuses, 3rd Edition. The Institution of Engineering and Technology, London (2004). ISBN: 978-0-86341-399-5

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CIGRE Publications

TB 359 – Modern Distance Protection Functions and Applications, 2008

TB 431 – Modern Techniques for Protecting Busbars in HV Networks, 2010

TB 432 – Protection Relay Coordination, 2010

TB 463 – Modern Techniques for Protecting, controlling and monitoring power transformers, 2011

TB 465 – Modern Techniques for Protecting and Monitoring of Transmission Lines, 2011

TB 546 – Protection, Monitoring and Control of Shunt Reactors, 2013

TB 587 – Short Circuit Protection of Circuits with Mixed Conductor Technologies in Transmission Networks, 2014

TB 629 – Coordination of Protection and Automation for Future Networks, 2015

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Power Systems, Ramboll, Newcastle upon Tyne, UK

Richard Adams

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Correspondence to Richard Adams .

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CIGRE Study Committee B3, Power Network Consulting Pty Ltd, Adelaide, Australia

Terry Krieg

Siemens Transmission and Distribution, Manchester, UK

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Adams, R. (2019). Substation Protection. In: Krieg, T., Finn, J. (eds) Substations. CIGRE Green Books. Springer, Cham. https://doi.org/10.1007/978-3-319-49574-3_32

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DOI : https://doi.org/10.1007/978-3-319-49574-3_32

Published : 21 July 2018

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