HV Breaker - Relay

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timm333

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Electrical Design Engineer
High Voltage breakers don't have instantaneous and over current units like low voltage breakers. So when we say a HV breaker is 1200A, does it mean that it can be placed on all circuits which are upto 1200A, and then we can get it tripped separately by using relays like time over current relay and overload relay?
 
timm333 said:
High Voltage breakers don't have instantaneous and over current units like low voltage breakers. So when we say a HV breaker is 1200A, does it mean that it can be placed on all circuits which are upto 1200A, and then we can get it tripped separately by using relays like time over current relay and overload relay?
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Any breaker below 600V (LV class) whether air frame, molded case or insulated case type have a trip unit integral to the breaker. Breakers above 600V (MV class) have external protective relays as you mentioned that perform the same functions as the LV trip units: long time, short time, instantaneous & ground fault tripping functions for circuit coordination.
Your other question about breaker ratings: some draw-out air frame breakers are interchangeable between current ratings but the breaker trip unit or plug must match the bus or cable size to pass code. And the interchangeability due to physical dimensions varies between manufacturers.
 
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1200A rating usually means that the circuit breaker can carry 1200A continuously when oeprating in its ratedambient conditions (40C temperatue, humidty, ventilation etc.)

Protection is provided by protective relays sensing current from the switchgear/breaker CT's and operating the breaker trip coil. Note that LV breakers' trip units are usually self powered. HV breakers require external tripping power source, usually a battery and charger. Modern relays also require power.

A 1200 amp breaker of the same interrupting rating, design, model, manufacturer, control scheme, control voltage etc. can be swapped with another identical breaker.
 
timm333 said:
High Voltage breakers don't have instantaneous and over current units like low voltage breakers. So when we say a HV breaker is 1200A, does it mean that it can be placed on all circuits which are upto 1200A, and then we can get it tripped separately by using relays like time over current relay and overload relay?
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Attached is a line up of a double ended medium voltage switchgear with a differential relay scheme that I sold in the the mid 90's that are installed in the LTV steel plant in East Chicago which may be closed by now. I believe it was 4160V but it may have even been 13.8kv. I can't remember.
For example, on the far left structure you will see (2) breakers using the top one as an example there are (4) NEMA 50/51 (instantaneous - NEMA # 50 and time overcurrent - NEMA # 51 mechanical relays) the top one that is by itself is for the ground, and the (3) in a row are for the 3 phases.
On a schematic the one for the ground would be a device 50/51G and the others just device 50/51. If my memory serves me correctly all 4 are the same devices except the 50/51G is applied differently wired using a zero sequence scheme of CTs from each of the 3 phases.
The breaker itself is stupid and needs to be told what to do, tripped using a shunt trip/spring release mechanism which is commonly powered by a 125v DC source usually a battery bank.
The breaker springs that causes te breaker to close must be mechanically charged by either a hand cranking lever which manually charges the spring or a 125vdc motor which will charge the spring automatically.

All of the relays instantaneous/TC settings must be set as determined by the engineer.
If you look closely there are knob/handles that are uses to operate the breakers manually as well as 2 green and red pilot indication lights powered by 125vdc.

This stuff was fun to sell.
 

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Thanks, this is very good information. But my basic question is still unanswered: If we put the trip unit of 100A on a HV breaker of 1200A, then can we use 1200A HV breaker on a 100A circuit?

Templdl, when you say 50/51G, does it mean relays 50G plus 51G, or does it mean relay 50 plus 51G? When we perform the coordination study, should we coordinate only the phase relays (50/51) with upstream fuse/breaker, or should we also coordinate the ground fault relay with upstream breaker? Also, the zero sequence CT are placed on three phase conductors for ground fault relay; can we also put the CT of ground fault relay directly on the ground conductor?
 
timm333 said:
Thanks, this is very good information. But my basic question is still unanswered: If we put the trip unit of 100A on a HV breaker of 1200A, then can we use 1200A HV breaker on a 100A circuit?

Templdl, when you say 50/51G, does it mean relays 50G plus 51G, or does it mean relay 50 plus 51G? When we perform the coordination study, should we coordinate only the phase relays (50/51) with upstream fuse/breaker, or should we also coordinate the ground fault relay with upstream breaker? Also, the zero sequence CT are placed on three phase conductors for ground fault relay; can we also put the CT of ground fault relay directly on the ground conductor?
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In direct response to your original question, you are correct in that you can put any AVAILABLE trip unit for that breaker in it, up to and including 1200A. BUT, that doesn't mean anything you WANT, only what is offered by the mfr. In many designs the current sensing elements, the CTs, are integral to the frame, not the trip unit, so there becomes a limit to how low of a trip setting can be obtained to work with those CTs. 100AT on a 1200AF seems too low, but I have not bothered to look. On other designs the trip unit is not integral to the breaker itself at all, there is just a shunt trip in the breaker, so you would get any appropriate trip relay system for your system and have it tell the breaker to trip. In that case, it has nothing to do with the rating of the breaker directly, although for sure you will need to coordinate them.

50/51G means 50 + 51G. And no, you would NOT put your ground conductor through the ZSCT.

The nature of your questions has me concerned that you are working outside of your field of experience, training and thereby competency. HV protection systems is not a good place for OTJ training, you should consider getting experienced help here.
 
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timm333 said:
Thanks, this is very good information. But my basic question is still unanswered: If we put the trip unit of 100A on a HV breaker of 1200A, then can we use 1200A HV breaker on a 100A circuit?

Templdl, when you say 50/51G, does it mean relays 50G plus 51G, or does it mean relay 50 plus 51G? When we perform the coordination study, should we coordinate only the phase relays (50/51) with upstream fuse/breaker, or should we also coordinate the ground fault relay with upstream breaker? Also, the zero sequence CT are placed on three phase conductors for ground fault relay; can we also put the CT of ground fault relay directly on the ground conductor?
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I believe that you will see that there are 4 protective relays and not 8.
Are you familiar with a one line that illustrates the switch gear? I agree with Jraef that you may be out of you area of expertise because the terms that we are using are common to those who are have medium voltage experience. Medium voltage is something you don't even want to consider working with if it is outside of your area of expertise in you wildest dreams.
 
timm333 said:
... when you say 50/51G, does it mean relays 50G plus 51G, or does it mean relay 50 plus 51G?
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50/51G is slang, and could be thought of as (50/51)G, the proper ANSI method is to write this as 50G/51G. It is an overcurrent protection function with instantaneous and time delay portions, which is being applied for reacting to Ground faults via a single zero sequence CT. A similar function would be a 50N/51N operation except this is based on the summation of the phase CTs.
 
templdl said:
Looks like it's a modern programable electronic type instead of the old electromechanical type such as the older CO relay as we were previously discussing.
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This relay has been around for several years. If I were designing the protection there would be a bank of CO relays or some other electro-mechanical relays backing up the electronic protection.
 
Jraef said:
The nature of your questions has me concerned that you are working outside of your field of experience, training and thereby competency.
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I really appreciate all the information and comments. HV systems are definitely outside my expertise, and I wouldn't touch one with a 10' (fiberglass) pole and PPE, but I also seldom turn down an opportunity to learn something. To that end, what are a few good sources about protective relays and related gear? I have access to some of the IEEE color books, and there are manufacturer's write-ups, but where should somebody start? Thanks.
 
zbang said:
I have access to some of the IEEE color books, and there are manufacturer's write-ups, but where should somebody start? Thanks.
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I recommend the Red Book and Buff Book for an introduction. Skim through the chapters and get a feel for the equipment, then go back and get into the technical details.

Eaton's Specifying Guide has a good concise section in the front on LV & MV ssytem design.
 
zbang said:
I really appreciate all the information and comments. HV systems are definitely outside my expertise, and I wouldn't touch one with a 10' (fiberglass) pole and PPE, but I also seldom turn down an opportunity to learn something. To that end, what are a few good sources about protective relays and related gear? I have access to some of the IEEE color books, and there are manufacturer's write-ups, but where should somebody start? Thanks.
Click to expand...

Spend some time on the SEL (Schweitzer Relay) website. Their relays are, for the most part, considered some of the best in the industry. Beckwith also makes some good equipment. GE has some decent ones but mostly at the substation level. Multilin used to be top notch but they got bought out by GE a few years back but have gone down ever since. The rest of the manufacturers also have their line as well. But SEL is taking over the market (IMO)

IEEE C37.2 lists the standard device function numbers. Anything by J. Lewis Blackburn is good as gold for learning, he was the god of relaying. The IEEE Buff Book covers protection and coordination. IEEE Blue Book (1015) covers LV breaker application.

There is a lot to know about relay protection, it takes years to become proficient at it. To set relays you first have to be proficient at understanding power system analysis and time current coordination.

A 1200A rated MV breaker is just that. They are designed for 100% operation within rated limits as others have described. The relays are independently installed, and they are set to trip at whatever you want, so, yes, a relay can be set to trip on 100A. As long as you are talking USA rated gear 1200A is the smallest frame your going to get for a breaker. The relays trip the breaker on whatever you set.

BTW: For reference in discussion; low voltage (LV) is voltages up to and including 600V, medium voltage (MV) is over 600V up to, and including 69kV. Over 69kV you get into the HV and EHV systems.
 
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1200A is a standard breaker rating. It doesn't mean the breaker comes with 1200A CT's. You have to specify the CT's you want, based on your what you're protecting with the breaker.

Modern solid state protective relays can do a lot of different things - like monitor your load and report to a building information system or record the waveform at the time of a trip.
 
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