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Are there usually two trip coils on medium voltage power circuit breakers? 1
- Thread starter bdn2004
- Start date
Basically, yes. For both closing and opening operations, there are specified speeds for the main contacts inside the breakers. Large springs, used to supply the mechanical energy required to open and close the contacts, are charged either by a small motor inside the CB or by the energy released by the other set of springs during contact opening. On closing, the mechanism must close the main contacts at the specified speed, and with additional forces of several hundred to a couple thousand pounds per pole to prevent the contacts from being blown apart. So, in many respects, the two operations do act very much the same, mechanically.
davidbeach
Electrical
If I understand the question correctly, there may or may not be two trip coils depending on specification. But, whether one or two trip coils the trip operation is always in response to the application of the tripping voltage to the trip coil. Two trip coils simply allow redundancy in the trip circuits. Close coils are totally separate, and I've not seen more than one per breaker.
On low voltage ACBs it is possible - although not common - to have a conventional tripping coil and an undervoltage release (UVR) which behaves like a dead man's handle: if power to the UVR coil is interrupted then the ACB will trip.
I have not seen an equivalent to the UVR coil for MV / HV applications - all the tripping coils I am familiar with are energise-to-trip. Dual-redundant coils are certainly available, and triple-redundant coils are sometimes seen on big transmission-class equipment.
I have not seen an equivalent to the UVR coil for MV / HV applications - all the tripping coils I am familiar with are energise-to-trip. Dual-redundant coils are certainly available, and triple-redundant coils are sometimes seen on big transmission-class equipment.
- Thread starter
- #5
We bought a piece of 15kV equipment that had a long lead time on it. It is a large power consumer, and was originally supposed to be fed through it's own main circuit breaker in a separate piece of switchgear. Time went on and they cut out this main bkr to save dollars. The thought is to trip the existing upstream device.
The drawings however for this piece of equipment have not been revised for this change w/o the main. The drawings show two trip circuits in their protection schemes. One is for currents/voltages/etc. The other for immediate conditions such as e-stops/high pressure etc. The latter though is "fail safe" and everything is wired so that its not closing a set of contacts, but opening any set in a long loop of alarms that in turn is connected to a 2nd trip coil.
My question is how to parallel both of these into a single trip signal to trip this upstream device. I suppose it would be easy enough with a relay...
The drawings however for this piece of equipment have not been revised for this change w/o the main. The drawings show two trip circuits in their protection schemes. One is for currents/voltages/etc. The other for immediate conditions such as e-stops/high pressure etc. The latter though is "fail safe" and everything is wired so that its not closing a set of contacts, but opening any set in a long loop of alarms that in turn is connected to a 2nd trip coil.
My question is how to parallel both of these into a single trip signal to trip this upstream device. I suppose it would be easy enough with a relay...
Use a high integrity safety relay from Pilz or one of their competitors for the E-stop circuit. Use it to drop out a conventional trip & lockout (ANSI 86) relay. The process and C&I guys hate the close-to-trip designs we use, but the average trip & lockout relay is only a distant cousin of the average relay used in the C&I world.
It depends on which switchgear you have, some manufacturers do supply UVR coils for MV gear and it is a requirement for some embedded generator schemes as well as the usual shunt trip coil. Be careful using "Safety" relays in DC tripping circuts and carefully check the contact ratings for the unit you intend to use. I have seen systems where the equipment would not trip beacause the safety output contacts had welded in.
- Thread starter
- #9
Is this a fairly new concept - two trip coils in medium voltage breaker manufacture or the IEC standard? We bought a major piece of equipment from an overseas vendor and they claim this is the IEC standard design.
We are connecting our equipment to a system that is ultimately protected by an outdoor oil circuit breaker of 1970's vintage and I only see one trip coil. I just wonder if it is worth investigating adding this fail safe second trip coil...?
We are connecting our equipment to a system that is ultimately protected by an outdoor oil circuit breaker of 1970's vintage and I only see one trip coil. I just wonder if it is worth investigating adding this fail safe second trip coil...?
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- #10
oldfieldguy
Electrical
Working from my own exposure here in the USA, dual trip coils used to be rare outside of HV transmission equipment. In that application, with primary and backup protection, two trip paths and cross-tripping schemes were used.
I am not speaking of the undervoltage trip device employed by some manufacturers, used to open breakers in motor service, etc. I am talking about a separate trip coil that when energized will open the breaker.
In heavy industry, I saw very few companies specify dual trip coils, even in critical equipment installations. If you're going to use a second trip coil, what factors are you employing to make it worthwhile? Separate trip power source? Protective device completely isolated from the primary trip device?
It is interesting to note that in the majority of cases where I have investigated breakers failing to trip, the cause of the failure was mechanical, and a second trip coil usually acts on the same mechanical latch as the first trip coil.
old field guy
I am not speaking of the undervoltage trip device employed by some manufacturers, used to open breakers in motor service, etc. I am talking about a separate trip coil that when energized will open the breaker.
In heavy industry, I saw very few companies specify dual trip coils, even in critical equipment installations. If you're going to use a second trip coil, what factors are you employing to make it worthwhile? Separate trip power source? Protective device completely isolated from the primary trip device?
It is interesting to note that in the majority of cases where I have investigated breakers failing to trip, the cause of the failure was mechanical, and a second trip coil usually acts on the same mechanical latch as the first trip coil.
old field guy
- Thread starter
- #11
Thanks Old Field Guy,
On further examination...there are actually two trip coils on this oil circuit breaker and the other one is connected to the emergency stop circuit. But it's not operated "fail safe" as in if it loses power it activates. It works in parallel with the first trip coil.
If you've followed any of this thread - we bought a piece of equipment that was to be connected to its own switchgear and main breaker. Someone got wise to the fact we could save $$ by eliminating this main breaker and tripping the upstream device, this will of course trip everything else downstream - which we don't think is an issue. The question now is do we put work this fail-safe circuit into the existing emergency trip circuit or just parallel this to the first. Its actually more complicated than what I'm posting....as there are switching schemes that allow this equipment to operate on multiple 15kV circuits....so this 2nd circuit may take some effort to design in.
On further examination...there are actually two trip coils on this oil circuit breaker and the other one is connected to the emergency stop circuit. But it's not operated "fail safe" as in if it loses power it activates. It works in parallel with the first trip coil.
If you've followed any of this thread - we bought a piece of equipment that was to be connected to its own switchgear and main breaker. Someone got wise to the fact we could save $$ by eliminating this main breaker and tripping the upstream device, this will of course trip everything else downstream - which we don't think is an issue. The question now is do we put work this fail-safe circuit into the existing emergency trip circuit or just parallel this to the first. Its actually more complicated than what I'm posting....as there are switching schemes that allow this equipment to operate on multiple 15kV circuits....so this 2nd circuit may take some effort to design in.
bdn2004,
Could you please clarify few things.
You have two trip coils in your oil circuit breaker. One of it is for protection tripping and manual tripping. The 2nd one is for emergency cases.
The new piece of equipment you now have two tripping contacts, one that makes whenever your protection relay operates, the 2nd one is a "fail safe" contact.
If this is the case, you can wire the 1st contact of your new equipment to the 1st trip coil. The 2nd "fail safe" contact can be used to energise the 2nd emergency trip coil in your oil circuit breaker.
We generally have two different power source for the trip coils, energised by two protective relays. Each of the protective relays will have contacts for both the trip coils ensuring redundancy of both relay and power source.
In general, a protection system for a network "n" is designed for "n-1" exigencies.
Could you please clarify few things.
You have two trip coils in your oil circuit breaker. One of it is for protection tripping and manual tripping. The 2nd one is for emergency cases.
The new piece of equipment you now have two tripping contacts, one that makes whenever your protection relay operates, the 2nd one is a "fail safe" contact.
If this is the case, you can wire the 1st contact of your new equipment to the 1st trip coil. The 2nd "fail safe" contact can be used to energise the 2nd emergency trip coil in your oil circuit breaker.
We generally have two different power source for the trip coils, energised by two protective relays. Each of the protective relays will have contacts for both the trip coils ensuring redundancy of both relay and power source.
In general, a protection system for a network "n" is designed for "n-1" exigencies.
- Thread starter
- #13
Inpran,
This load is about 1/4 mile from the oil circuit breakers that protect it. It can be fed from 4 independent sources. There is one remote interposing relay that activates one contact that trips each breaker. There are other interposing relays that segregate the signals between emergency and protection that schemes that operate this one remote interposing relay.
There are other more complicated schemes at the source end (a power plant where the oil breakers are located) that do indeed use this second trip coil and it is connected to emergency stops. This is the case for one of the oil breakers I looked at, but not the case for another, it simply has an open and close coil.
My question is....either a protection trip or an emergency trip will ultimately trip these breakers and as in the existing cases - uses the same trip coil. Our SCADA and annunciation system and the vendor's onboard PLC will make a record of the event and immediately let us know the reason for the trip. And the power source to the interposing relays is DC that is always on - powered through dedicated circuits, alt feeds, generators etc. Why the need to segregate out the emergency trips circuit? Is it just redundancy?
I appreciate the feedback and have involved the vendor in a similar discussion. We are at this time re-evaluating taking out the main breaker. All issues seem to go away if we put that back in.
This load is about 1/4 mile from the oil circuit breakers that protect it. It can be fed from 4 independent sources. There is one remote interposing relay that activates one contact that trips each breaker. There are other interposing relays that segregate the signals between emergency and protection that schemes that operate this one remote interposing relay.
There are other more complicated schemes at the source end (a power plant where the oil breakers are located) that do indeed use this second trip coil and it is connected to emergency stops. This is the case for one of the oil breakers I looked at, but not the case for another, it simply has an open and close coil.
My question is....either a protection trip or an emergency trip will ultimately trip these breakers and as in the existing cases - uses the same trip coil. Our SCADA and annunciation system and the vendor's onboard PLC will make a record of the event and immediately let us know the reason for the trip. And the power source to the interposing relays is DC that is always on - powered through dedicated circuits, alt feeds, generators etc. Why the need to segregate out the emergency trips circuit? Is it just redundancy?
I appreciate the feedback and have involved the vendor in a similar discussion. We are at this time re-evaluating taking out the main breaker. All issues seem to go away if we put that back in.
bdn2004,
The 2nd trip coil is indeed redundant. As has already pointed out in this thread, both the trip coils will activate the same trip latch.
If your system /specifications don't need this redundancy, you can parallel all your trip commands to the same trip coil.
The 2nd trip coil is indeed redundant. As has already pointed out in this thread, both the trip coils will activate the same trip latch.
If your system /specifications don't need this redundancy, you can parallel all your trip commands to the same trip coil.
bdn2004,
You need to look at your trip systems as a whole. For example, in a critical trip system, it doesn't matter how many shunt trip coils you have if you do not have some kind of supervision monitoring the trip supply / field cables / breaker wiring / trip coils and trip contacts etc.
Referring back to your second post, you stated that the original drawings (presumably drawn by the manufacturer of the equipment you are purchasing) called for two trip circuits with one of them in "fail safe" closed loop mode. If you remove the breaker on the manufacturers kit (as you state would like to do) then I would expect that you should at least attempt to copy the same functionality and safety features that they originally designed.
As I stated in my earlier post, some manufacturers can supply DC UVR coils in MV equipment. You can wire a UVR coil in the "fail safe" normally closed loop (supplied from the breaker DC tripping supply) and any contact in that loop will remove the supply from the UVR coil and operate the breaker tripping mech. A further advantage with this type scheme, is that if the breaker tripping supply fails, the breaker will also trip. This may be what the manufacturer of the equipment was trying to achieve, as some of the safety devices they are using may only be available with "open to trip" contacts.
You need to consider all of these points and look further into the safety aspects of the machine, not just your tripping circuit.
You need to look at your trip systems as a whole. For example, in a critical trip system, it doesn't matter how many shunt trip coils you have if you do not have some kind of supervision monitoring the trip supply / field cables / breaker wiring / trip coils and trip contacts etc.
Referring back to your second post, you stated that the original drawings (presumably drawn by the manufacturer of the equipment you are purchasing) called for two trip circuits with one of them in "fail safe" closed loop mode. If you remove the breaker on the manufacturers kit (as you state would like to do) then I would expect that you should at least attempt to copy the same functionality and safety features that they originally designed.
As I stated in my earlier post, some manufacturers can supply DC UVR coils in MV equipment. You can wire a UVR coil in the "fail safe" normally closed loop (supplied from the breaker DC tripping supply) and any contact in that loop will remove the supply from the UVR coil and operate the breaker tripping mech. A further advantage with this type scheme, is that if the breaker tripping supply fails, the breaker will also trip. This may be what the manufacturer of the equipment was trying to achieve, as some of the safety devices they are using may only be available with "open to trip" contacts.
You need to consider all of these points and look further into the safety aspects of the machine, not just your tripping circuit.
I live under a rock.... The Powell 15kV gear we use - we specify dual trip coils on our mains. The emergency trip at the gear is mechanical. We use the 2 trip coils for our relaying, local tripping and remote tripping where required.
So.. in your case your 2nd TC is fail safe, can you used a protection relay with a form c contact? Again, I'm a rookie who live under a rock where we only have Powell 15kV gear... oops and some GE..
So.. in your case your 2nd TC is fail safe, can you used a protection relay with a form c contact? Again, I'm a rookie who live under a rock where we only have Powell 15kV gear... oops and some GE..
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