Curious on what everyone?s opinions are on zsi and where can I find more information on it. I have done a google search but can only find the same paper from squared d or some manufacturers brochures. I was looking more for construction specifications how the equipment is mounted and internally wired (fiber or copper), limitations, do?s and don?ts, cost / life cycle analysis, and if there are any UL or industry standards that indicate how ZSI works or is every manufacture?s work a little bit differently. I am interested in this topic but there seems to be very little information available. (for equipment rated 600V and below). Thanks.
Zone Selective Interlocking
- Thread starter Mike01
- Start date
- Status
zog
Senior Member
- Location
- Charlotte, NC
A more specific question would help, not sure if you are looking for basics or a more in depth question about a specific ZSI system. Here is the basic version.
The breakers talk to each other, if the main breaker gets a trip signal it "asks" all of the feeders if they have one, if not, the main trips. Allows for tighter coordination and good method for arc flash reduction. Most modern trip units have the feature built in, standard on a few, optional on most, so there is nothing else to mount but the trip units need to be connected to communicate. IF you are using the communications cababilities on your trip units already there is nothing to enabling ZSI, however, I dont think setting up all the communications just for ZSI is very cost effective.
I know this is all very basic, feel free to ask more detailed questions if you have them.
brian john
Senior Member
- Location
- Kilmarnock, Va
- Occupation
- Retired after 52 years in the trade.
The maunfactueres data is all I have ever seen. The systems we have worked on were hard wired controls.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
As Zog said, ZSI is built into the trip unit.
Every one I have ever seen is hardwired with a simple 2-conductor cable (about 22AWG). Due to the speed they operate at there is no time available for communication latency. Some of them look for the presence of a restraint signal while others look for the absence of one. I know that Schneider Electric (Square D) has interface modules that allow some of their different breaker models to interface, but other than that you normally cannot interface different brands/manufacturers of ZSI equipment.
Every one I have ever seen is hardwired with a simple 2-conductor cable (about 22AWG). Due to the speed they operate at there is no time available for communication latency. Some of them look for the presence of a restraint signal while others look for the absence of one. I know that Schneider Electric (Square D) has interface modules that allow some of their different breaker models to interface, but other than that you normally cannot interface different brands/manufacturers of ZSI equipment.
Zsi?
Zsi?
From what I Understand the ZSI does not coordinate a system, zone selective helps with an already coordinated system it interlocks the short time and ground faults not the instantaneous region of the breaker if the instantaneous is not disabled it is still active. If it is setup correctly the instantaneous is disabled and ZSI sends a restraint signal to allow the branch breaker to trip prior to the main, if no restraint signal is sent than the overcurrent device will trip without delay (faster than instantaneous) this allows for better coordination and a far reduced arc flash category. With the introduction of electronic trip breakers for molded case and insulated case this has become more acceptable in the MCCB range and is a way to help coordinate a system and reduce arc flash while utilizing potentially smaller gear in leau of switchgear construction, this would facilitate switchboard construction with group mounted branches and still allow for coordination and arc flash reduction. My question is. Is there a standard for ZSI or a performance standard for all manufacturers to follow? Or can each manufacturer operate their system a little differently? Also how is this internally wired I have heard that it takes a higher skill set to set up terminate and commission this type of gear not to mention the additional testing cost required at startup. What type of wire is required I also herd that the conductors have to be the same length to insure correct operation and larger cables to insure low impedance to insure correct operation? I was looking for something to help write a performance specification for a ZSI system in leau of just stating provide a ZSI system. Also is the coordination / arch flash software recognizing this technology?
Zsi?
From what I Understand the ZSI does not coordinate a system, zone selective helps with an already coordinated system it interlocks the short time and ground faults not the instantaneous region of the breaker if the instantaneous is not disabled it is still active. If it is setup correctly the instantaneous is disabled and ZSI sends a restraint signal to allow the branch breaker to trip prior to the main, if no restraint signal is sent than the overcurrent device will trip without delay (faster than instantaneous) this allows for better coordination and a far reduced arc flash category. With the introduction of electronic trip breakers for molded case and insulated case this has become more acceptable in the MCCB range and is a way to help coordinate a system and reduce arc flash while utilizing potentially smaller gear in leau of switchgear construction, this would facilitate switchboard construction with group mounted branches and still allow for coordination and arc flash reduction. My question is. Is there a standard for ZSI or a performance standard for all manufacturers to follow? Or can each manufacturer operate their system a little differently? Also how is this internally wired I have heard that it takes a higher skill set to set up terminate and commission this type of gear not to mention the additional testing cost required at startup. What type of wire is required I also herd that the conductors have to be the same length to insure correct operation and larger cables to insure low impedance to insure correct operation? I was looking for something to help write a performance specification for a ZSI system in leau of just stating provide a ZSI system. Also is the coordination / arch flash software recognizing this technology?
brian john
Senior Member
- Location
- Kilmarnock, Va
- Occupation
- Retired after 52 years in the trade.
ZSI is also available as a feature on some stand alone GFP relays for bolted pressure switches.
http://ecatalog.squared.com/catalog/174/html/sections/07/17407045.html
http://standards.ieee.org/reading/ieee/std_public/new_desc/colorbooks/242-2001.html
http://ecatalog.squared.com/catalog/174/html/sections/07/17407045.html
http://standards.ieee.org/reading/ieee/std_public/new_desc/colorbooks/242-2001.html
Last edited:
mdshunk
Senior Member
- Location
- Right here.
That feature has got to be a real problem solver, eh? Nothing to figure out for coordination, so it would seem. Just hook them up to each other.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Coordination is still required. If trip units are restrained they will follow their set points: bad setpoints=bad coordination. The furthest down stream feeder device in the chain may never get a trip/restrain signal (which one depends on the manufacturer), because it is the final OCPD or the device below it does not have ZSI, so it normally is set to trip after a delay. This means that any restrained upstream device needs to have a coordinated delay. ZSI is not for coordination - ZSI is to speed up tripping when things go wrong. Why wait seconds to trip if you are the backup protective device?
No standard, each manufacturer is on their own.mike01 said:
Generally, there is very little skill required. The Square D units, everyone has been mentioning, require a simple 2 conductor "Belden style" cable. Testing is also very simple: 1) connect the test set with the device restrained (the last device in the chain is always self-restrained) and see if it follows its trip curve just like any standard test, 2) perform the same test without the restraint signal and and see if the device trips "immediately".
Some manufacturers have introduced very complicated "computer controlled" interlocked systems (GE comes to mind) for automatically modifying the trip curves of breakers to reduce arc flash incident energy. These systems are vastly different than what I think of when I hear the term ZSI.
zog
Senior Member
- Location
- Charlotte, NC
I think you can get just about anyones comms to interface with anyone elses system, just a few different systems out there, might not be easy, but can be done.
zog
Senior Member
- Location
- Charlotte, NC
Good stuff Jim, I agree with all you said. Wish Jaref was here, bet he has some good knowledge to share on the subject, where are you Dr Evil??
??
??
It sounds like it just a twisted pair between trip units to send a restraint signal to hold off or trip instantenously The important thing to remember is that it interlocks short time and ground fault not the instantaneous portion of the trip curve, or at least that is what square d promotes do all manufacturers work the same way? It sounds like to each their own. This comes up because in systems where you have a COPS system or a system that is required to be selective coordinated with a breaker to breaker main to distribution in a switchboard construction this would be a viable alternative. Typically you would see a switchgear construction and a main with no instantaneous to aide with coordination of downstream breakers, if you attempt to coordinate breakers of the ICCB or MCCB type it becomes more difficult not quite impossible in the instantenous rage without significantly increasing your frame sizes. manufacturers recommend placing higher frame breakers with lower frame trip settings basically purchasing and installing a 1200AF with a 600AT and a 400AS you are spending the cost for a 1200AF breaker for 400A worth of capacity. Why not install breakers main and distribution in switchgear construction with electronic trip charactstics coordinate your system in your long time and short time disabled the instantaneous (on the main) and ZSI enabled with the branches as long as you utilize ZSi this would allow you to use switchboard construction maintain a 3 cycle trip characteristic and coordinate your system at a lower cost than switchgear. However I had a testing firm indicate approx 10K to commission and test a ZSI system. But how often does this need to be calibrated and how reliable is it? With no performance standard it sounds like everyone?s could work with slight differences.
So is one way better than the other?
Is it really that easy?
So there is no set standard on this how do you specify a ZSI system?
As a testing firm if it trips faster that "instantous" as indicated how do you incorporate an arc flash study are there ZSI curves or is this a hand drawn curve to find the "band" min. and max. unlatching time?
??
It sounds like it just a twisted pair between trip units to send a restraint signal to hold off or trip instantenously The important thing to remember is that it interlocks short time and ground fault not the instantaneous portion of the trip curve, or at least that is what square d promotes do all manufacturers work the same way? It sounds like to each their own. This comes up because in systems where you have a COPS system or a system that is required to be selective coordinated with a breaker to breaker main to distribution in a switchboard construction this would be a viable alternative. Typically you would see a switchgear construction and a main with no instantaneous to aide with coordination of downstream breakers, if you attempt to coordinate breakers of the ICCB or MCCB type it becomes more difficult not quite impossible in the instantenous rage without significantly increasing your frame sizes. manufacturers recommend placing higher frame breakers with lower frame trip settings basically purchasing and installing a 1200AF with a 600AT and a 400AS you are spending the cost for a 1200AF breaker for 400A worth of capacity. Why not install breakers main and distribution in switchgear construction with electronic trip charactstics coordinate your system in your long time and short time disabled the instantaneous (on the main) and ZSI enabled with the branches as long as you utilize ZSi this would allow you to use switchboard construction maintain a 3 cycle trip characteristic and coordinate your system at a lower cost than switchgear. However I had a testing firm indicate approx 10K to commission and test a ZSI system. But how often does this need to be calibrated and how reliable is it? With no performance standard it sounds like everyone?s could work with slight differences.
So is one way better than the other?
Is it really that easy?
So there is no set standard on this how do you specify a ZSI system?
As a testing firm if it trips faster that "instantous" as indicated how do you incorporate an arc flash study are there ZSI curves or is this a hand drawn curve to find the "band" min. and max. unlatching time?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I know of nothing, other than marketing fluff, that says a "signal" or "no signal" system has any advantage. If the interconnect cable is broken what happens to your ZSI? If there is no restraint signal does the device trip fast or does it follow a curve? Does it make a difference?
I have seen different manufacturers' systems combined by using interposing relays, but from what I was told, there were some major timing issues that had to be considered.
I have seen different manufacturers' systems combined by using interposing relays, but from what I was told, there were some major timing issues that had to be considered.
Marketing Fluff
Marketing Fluff
some marketing "fluff" indicates this as a coordination advantage. If the cable is broken or damaged I would hope you would get an alarm, and if something were to happen it could possibly take in excess of 3cycles to clear the fault therefore if a switchboard were utilized with ZSI the board would could possibly be destroyed beyond repair? This would have to be a risk analysis that would have to take place that is why I ask if anyone has a life cycle or clairbration requirements is it a "set it and forget it" of does it need to be reviewed anually?
Marketing Fluff
some marketing "fluff" indicates this as a coordination advantage. If the cable is broken or damaged I would hope you would get an alarm, and if something were to happen it could possibly take in excess of 3cycles to clear the fault therefore if a switchboard were utilized with ZSI the board would could possibly be destroyed beyond repair? This would have to be a risk analysis that would have to take place that is why I ask if anyone has a life cycle or clairbration requirements is it a "set it and forget it" of does it need to be reviewed anually?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
ZSI is not a calibrated function, it should be reviewed as often as you do the trip unit itself.
If you are talking about clearing in less than 3 cycles as the reason for ZSI, then I agree you would want it to default to an unrestrained trip. However, ZSI does not make the device clear a fault any faster. Effectively all it does is turn the ST function down causing the device to begin to open sooner.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Watching the elections...
I think most of the meat of it has been covered well. I'll just reiterate that it does not replace coordination, it enhances it. Coordination in and of itself is necessary to ensure that a fault is cleared at the closest possible point so that equipment is not stressed any more than necessary. The problem is, if you get a ground fault in between two coordinated breakers, the fault is cleared only after the higher level device's setting is exceeded because it has no idea that the fault is not trying to be cleared at a lower level device. So the stress is applied at the upstream device's level, something that may subject the equipment to unnecessarily high levels of mechanical force.
ZSI is a way of changing the trip settings depending on where the fault occurs. Say for instance that you have two Switchboards, one feeding another. A feeder in SWBD1 is set to trip in 0.4 sec because it is feeding SWBD2, which has feeders set to trip in 0.3 sec., which feed breakers in downstream panelboards set to 0.2 sec. and further down at motor starters set to 0.1 sec. If the fault happens at a motor (lowest "fault zone"), the motor breaker trips first in 0.1 sec, preventing the upstream devices from having to see the mechanical stresses of that fault. But if the fault happens in between the first two SWBDs (higher fault "zone), then ZSI would lower the trip time at the SWBD1 feeder to 0.1 sec. because it did NOT see the fault at any of the SWB2 breakers or anywhere below that. Without ZSI (or if it loses communications to answer a previous question), the basic original coordination still applies, but SWBD1 would have to withstand the fault stress for 0.4 seconds; 4 times as long and a virtual eternity if the AFC is high and effectively the last ditch level you would see only if all of the downstream devices had failed to clear a fault at their level.
This paper gives a good story board for the idea. But there is no specific standard that applies, it is a "feature" of high-tech circuit breakers. That's why it does not supplant doing proper coordination, it just makes it better.
http://www2.sea.siemens.com/NR/rdon...5-750A3DACF22D/0/VLCircuitBreakerZSIGuide.pdf
Nuts & Bolts
Nuts & Bolts
Thanks for the responses, and I agree that this enhances coordination but does not replace it, however if there is no UL, or ANSI standard on how to apply this ?signal? or ?no signal? how would you specify this? As opposed to saying to ?apply ZSI? in your specs. How is this addressed? How is the fault detected thru the ct?s is the communications typically a twisted pair sending a ?restraint signal?? I understand the basics of how it works by interlocking the short time etc. But I guess I am just looking to understand the nuts and bolts and components required. Also how would one complete a arc-flash coordination study indicating ZSI as most engineering softwares do not accommodate this. Is there a ?curve? to indicate this and the response time to appropriately calculate the incident of energy? And it sound like there is no calibration required once you set the time delays, there would be no calibration until an alterations was made to the system.
Nuts & Bolts
Thanks for the responses, and I agree that this enhances coordination but does not replace it, however if there is no UL, or ANSI standard on how to apply this ?signal? or ?no signal? how would you specify this? As opposed to saying to ?apply ZSI? in your specs. How is this addressed? How is the fault detected thru the ct?s is the communications typically a twisted pair sending a ?restraint signal?? I understand the basics of how it works by interlocking the short time etc. But I guess I am just looking to understand the nuts and bolts and components required. Also how would one complete a arc-flash coordination study indicating ZSI as most engineering softwares do not accommodate this. Is there a ?curve? to indicate this and the response time to appropriately calculate the incident of energy? And it sound like there is no calibration required once you set the time delays, there would be no calibration until an alterations was made to the system.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Most people just ask for ZSI.
Because the ZSI method may be unique to each manufacturer, specifying a "no signal" trip will exclude manufacturers that only offer a "signal" trip. I have never seen anyone chose their gear manufacturer based solely on their ZSI offering.
ZSI operation
ZSI operation
After doing some further research it turns out multiple manufacturers accomplish this in different ways, I came across some manufacturers literature that states ?It is able to interlock Ground Fault, Short Time and Instantaneous clearing times? it does this by not only adjusting the time element of the short time band but also the current element of the instantaneous band pushing it out beyond the instantaneous of the breaker below it allowing it to trip, this seems more fail safe to me therefore for some reason if the ZSI failed or for some reason stopped working you would have an overlap in coordination in the instantaneous range until the problem can be solved however maintain fast clearing of the fault with the sacrifice of coordination though until the problem is resolved.
ZSI operation
After doing some further research it turns out multiple manufacturers accomplish this in different ways, I came across some manufacturers literature that states ?It is able to interlock Ground Fault, Short Time and Instantaneous clearing times? it does this by not only adjusting the time element of the short time band but also the current element of the instantaneous band pushing it out beyond the instantaneous of the breaker below it allowing it to trip, this seems more fail safe to me therefore for some reason if the ZSI failed or for some reason stopped working you would have an overlap in coordination in the instantaneous range until the problem can be solved however maintain fast clearing of the fault with the sacrifice of coordination though until the problem is resolved.
rcwilson
Senior Member
- Location
- Redmond, WA
Arc Flash Studies with Zone Interlock
Arc Flash Studies with Zone Interlock
Do two studies, one with all breakers set on their fastest curve setting and one with the setting selected for coordination purposes. If a fault occurs in a piece of equipment the next upstream breaker will be tripping at its fastest setting because no downstream device is sending an inhibit signal.
You might get away with just doing one study with all trip units set on the lowest setting.
One problem we have had with ZSI switchgear feeding large motor loads was the motor contribution back to an upstream fault was enough to pick up the feeder breaker's short time element, sending an inhibit to the upstream device so the main breaker did not clear the bus fault as fast as it should have. This was a setting/coordination problem and not a problem with the ZSI.
We have implemented and tested ZSI on medium voltage switchgear using programmable relays with cross wired inputs and outputs. Downstream relays close a contact when any short time or instantaneous element picks up. Those contacts are paralleled into an input on the Main and Tie breakers that inhibits the fast short time and instantaneous trips. We had to have some time delays to allow for relay processing times and we used the solid state outputs but the net result was faster clearing on bus faults at less expense than full bus differential protection.
Arc Flash Studies with Zone Interlock
Do two studies, one with all breakers set on their fastest curve setting and one with the setting selected for coordination purposes. If a fault occurs in a piece of equipment the next upstream breaker will be tripping at its fastest setting because no downstream device is sending an inhibit signal.
You might get away with just doing one study with all trip units set on the lowest setting.
One problem we have had with ZSI switchgear feeding large motor loads was the motor contribution back to an upstream fault was enough to pick up the feeder breaker's short time element, sending an inhibit to the upstream device so the main breaker did not clear the bus fault as fast as it should have. This was a setting/coordination problem and not a problem with the ZSI.
We have implemented and tested ZSI on medium voltage switchgear using programmable relays with cross wired inputs and outputs. Downstream relays close a contact when any short time or instantaneous element picks up. Those contacts are paralleled into an input on the Main and Tie breakers that inhibits the fast short time and instantaneous trips. We had to have some time delays to allow for relay processing times and we used the solid state outputs but the net result was faster clearing on bus faults at less expense than full bus differential protection.
- Status