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 Post subject: Closed door racking
PostPosted: Thu Mar 08, 2012 6:55 am 
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Hello everyone, I am new here but I've been reading the forum for the last couple of weeks and decided to join since I saw all the great help your experience offers.

I have a question for you guys. We are going to implement remote racking in our company, however the process we have to go through is lenghty and we need an interim soultion.
Our breaker coordination gives us no choice to cut back on incident energy. With the tools we have we keep the racking distance at 40 inches and still have an energy of 60Cal/cm2. My question is, if we do closed door racking of the 480V breakers will this help reduce the energy seen by the worker? I must note that the switchgear is not arc resistant. Do you think this will reduce the risk of injuries to a person exposed to an arc flash? We would still use our PPE for that level, I just want to know if this practice can reduce the damage to the person.
Thank you


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PostPosted: Thu Mar 08, 2012 10:14 am 
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Maybe, maybe not. There is just no way of knowing. Are all of your door fasteners in place? Do you have vents on the doors? What is the physical condition of the switchgear? Lots of variables.

There is also a theory that closed door racking can produce a different type of hazard by allowing pressure to build before mechanical failure of the door resulting in higher blast pressures. I believe IEEE 1584 group has been doing some research on that.

Arc Flash reduction, or maintenence switches on your mains may be a good solution to look into, it allows for temporary INST settings while racking out a feeder breaker and is very effective in reducing Ei. We do these retrofits everyday, it has become a very popular solution.


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PostPosted: Mon Mar 12, 2012 5:32 am 
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Thank you Zog.
I understand that it is almost impossible to predict what would happen in the event of an arc flash during racking with the doors closed, being not designed for this purpose. We put a rush in the remote racking and are trying to avoid any breaker racking operations until we get the new equipment.


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PostPosted: Mon Mar 12, 2012 6:03 pm 
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Be careful with aftermarket remote racking units. Many of them don't work at all and there have been several incidents where they racked a breaker and got it jammed. Even the OEM versions are sometimes pretty poor. They are not a panacea.

In addition, when the failure rates of rack mounted gear (IEEE 493 data) being roughly 10 times more likely to fail, and when 80% of failures are mechanical (CIGRE data), and given the fairly limited number of failure modes where rack mounted equipment improves reliability (when considering failure data, it seems to do the opposite in reality), when installing rack mounted gear, it might be time to reconsider doing it at all.

This may be extremely radical thinking especially in some circles. We've been looking at the stuff from Elastimold, Joslyn Hi Voltage, and others. A lot of SF6, solidly insulated, (and Tavrida's solid/air insulated) gear especially for underground equipment is made to be sealed for life. There are no user serviceable parts at all. Right angle seperable connectors provide a means for changing components out that is more reliable than rack mount. I have been giving serious consideration to the idea of not using rack mounted gear anymore. Whether that takes the form of a single "unitary" structure or perhaps a modular structure connected by cabling is still food for thought. With today's materials and designs, 25 year plus sealed, maintenance free (as in no way to do anything to it but check condition) is available now with much better reliability than rack mounted gear. The question in my mind is whether there is enough data yet to back up the thing that we don't yet know...will it last for 25+ years. Powell is already selling traditinonal rack mount gear that they claim 8 year maintenance cycles on. Thats long enough that the gear should only see 3 maintenance cycles for its enough life. The only plants I'm aware of where this is a limitation is some furnaces such very long campaigns such as float glass plants and coke batteries.


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PostPosted: Tue Mar 13, 2012 5:36 am 
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Remote racking should have multiple methods of overtorque protection to prevent any damage to the gear. There is no protection from Bubba cranking on the racking handle and over racking a breaker. A good remote racking system with proper torque settings can not only prevent damage but also be an indicator of the racking system needing service/lubrication.


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PostPosted: Wed Mar 14, 2012 8:41 am 
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Thanks for the input! I will be extra careful and keep everyone here well informed on the issues that can affect the remote racking systems.
We were considering a simple system that performs the rotating motion of a rod to do the racking, nothing invasive to the existing system. It's more of a human replacement during racking operations, rather than a whole system that changes the way things are done.
I think this approach is the safest bet in failure rates and it will not introduce new variables to the switchgear operation. What do you think? Am I making sense?


(A little background on me) I am new at this arc flash stuff, and the previous work experience I had was all low voltage residential and commercial installations and design. I have a solid understanding of power systems since it was my focus on college and I graduated two years ago, so the knowledge is still fresh. That's why some of my ideas and remarks might seem a bit off; from lack of experience. I appreciate all of your input and help. Thank you!


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PostPosted: Sun Mar 18, 2012 10:43 am 
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PaulEngr wrote:
Be careful with aftermarket remote racking units. Many of them don't work at all and there have been several incidents where they racked a breaker and got it jammed. Even the OEM versions are sometimes pretty poor. They are not a panacea.

In addition, when the failure rates of rack mounted gear (IEEE 493 data) being roughly 10 times more likely to fail, and when 80% of failures are mechanical (CIGRE data), and given the fairly limited number of failure modes where rack mounted equipment improves reliability (when considering failure data, it seems to do the opposite in reality), when installing rack mounted gear, it might be time to reconsider doing it at all.

This may be extremely radical thinking especially in some circles. We've been looking at the stuff from Elastimold, Joslyn Hi Voltage, and others. A lot of SF6, solidly insulated, (and Tavrida's solid/air insulated) gear especially for underground equipment is made to be sealed for life. There are no user serviceable parts at all. Right angle seperable connectors provide a means for changing components out that is more reliable than rack mount. I have been giving serious consideration to the idea of not using rack mounted gear anymore. Whether that takes the form of a single "unitary" structure or perhaps a modular structure connected by cabling is still food for thought. With today's materials and designs, 25 year plus sealed, maintenance free (as in no way to do anything to it but check condition) is available now with much better reliability than rack mounted gear. The question in my mind is whether there is enough data yet to back up the thing that we don't yet know...will it last for 25+ years. Powell is already selling traditinonal rack mount gear that they claim 8 year maintenance cycles on. Thats long enough that the gear should only see 3 maintenance cycles for its enough life. The only plants I'm aware of where this is a limitation is some furnaces such very long campaigns such as float glass plants and coke batteries.


You have some good points about drawout equipment failing much more than fixed mount equipment - you're exactly right. Your vision of the future probably has some merit for commercial and light industrial applications, although those of us in the process industries and not likely to adopt your approach for a few reasons:

- The purpose of drawout breakers for us is so we can keep the bus hot, take one circuit (or main or tie) out of service briefly to remove the breaker, install a spare breaker, and re-energize. This requires a 5-10 minute outage of the one circuit to change the device instead of a 30-60 minute outage on the whole bus. Since breakers are mechanical devices they have mechanical problems and fail occasionally. Ever had a breaker that wouldn't close, or wouldn't stay closed? In the process industries we remove it from the cell, put a spare in its place and get the circuit re-energized. Then we can take the problem breaker and repair it without process downtime. The impact of taking a bus outage due to a breaker problem is in the millions of dollars per incident, and breaker problems occur often enough when you consume 50 MVA or more on a single site that buying drawout breakers and spending money and training time of solutions to mitigate many of the risks of drawout equipment is quite attractive to us.

- For switchgear in process industries, semi-repairable equipment has a lower total cost of ownership (life cycle cost) than either equipment that can be completely torn down and rebuilt (gear from 40-50 years ago), or equipment that can be only minimally worked on and large sections of the equipment and run to failure and replaced (your example of the 25 year switchgear). Modern LV switchgear with composite frame drawout breakers is a good example of semi-repairable equipment. There's not a whole lot of work a tech can do on the breaker itself any more - many parts that were field replaced or repaired in previous generations of equipment are not replaceable any more. On the other hand, this is still drawout metal-enclosed equipment and bus faults, cable compartment faults, and breaker stab faults can be repaired without a week of downtime and a new $300k lineup of equipment. These repairs cost somewhere in the tens of thousands and take a few days.


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PostPosted: Tue Mar 20, 2012 3:34 am 
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First, I work in a process industry so believe me, I'm well aware of why one would keep the bus hot. I'm also well aware of the concept of why we have drawout equipment. And we pay a huge premium for that. Non-drawout "large" class breakers (1200 A plus) in a drawout configuration in medium voltage have been running around $25K-$50K for us whereas the same thing in a bolt in configuration is $5K-$15K depending on configuration. This is "all in" including the enclosures. So right away, I'm looking at what I get for my money.

- The purpose of drawout breakers for us is so we can keep the bus hot, take one circuit (or main or tie) out of service briefly to remove the breaker, install a spare breaker, and re-energize. This requires a 5-10 minute outage of the one circuit to change the device instead of a 30-60 minute outage on the whole bus. Since breakers are mechanical devices they have mechanical problems and fail occasionally. Ever had a breaker that wouldn't close, or wouldn't stay closed? In the process industries we remove it from the cell, put a spare in its place and get the circuit re-energized. Then we can take the problem breaker and repair it without process downtime. The impact of taking a bus outage due to a breaker problem is in the millions of dollars per incident, and breaker problems occur often enough when you consume 50 MVA or more on a single site that buying drawout breakers and spending money and training time of solutions to mitigate many of the risks of drawout equipment is quite attractive to us.

Leaving aside for a minute the safety argument (is one person's life really worth millions of dollars or not), which is in my opinion the weakest argument to stand on, drawout gear has a failure rate of around 10^-4 to 10^-5 whereas bolt in is 10^-6 or better. In the operation I work at a "replace a breaker" incident would run $20K per hour for a single unit, or around $200K per hour for "de-energize the bus". I've somewhat lowered both numbers to make it easy to do the math. With a factor of 10 in number of incidents it looks like we're talking comparable differences here. However, CIGRE numbers indicate that of those failures on newer equipment, 80% of failures are in the cell or cell/breaker connection itself which all necessitate powering down the whole bus anyways. So really we're only talking about being able to use the drawout function 20% of the time to save time/money. So unless the "pull the breaker" vs. "power off the bus" cost differential is 50:1 or greater, the process industry argument is flying in the face of economics.

Another view is that with the price differential being what it is, we can start getting creative with redundant equipment. Fully parallel buses/breakers such has double ended systems to the component level, a design which is estimated at 186% more expensive than the radial system in most of the engineering books turns out to be roughly even money when breakers cost you half as much. In this configuration the switchgear is fully parallelized so that you can literally shut down an entire bank of gear while still leaving the process energized. That is a trick that means the "80%" CIGRE number if it's real, becomes solvable.

- For switchgear in process industries, semi-repairable equipment has a lower total cost of ownership (life cycle cost) than either equipment that can be completely torn down and rebuilt (gear from 40-50 years ago), or equipment that can be only minimally worked on and large sections of the equipment and run to failure and replaced (your example of the 25 year switchgear). Modern LV switchgear with composite frame drawout breakers is a good example of semi-repairable equipment,

Again, little disagreement in the past but the economics seem to be dictating something else. A good example of what you are referring to even in the lowly molded case breaker is the Cutler Hammer "mining" breaker. This is a molded case breaker in every way except for one trick: the guts are fully repairable/replaceable. This actually makes it an insulated case breaker (slightly different UL category). It is realistically no more/less reliable and rugged than the standard molded case breaker. There is a massive premium for this capability but in a coal mining environment, contamination is a big problem with MCCB's. The premium is a factor of 3 in cost, and the replacement parts are about 25% of the cost of a complete new molded case unit. So unless MCCB's are routinely failing a LOT, the economics for use of this breaker are poor.

In the same respect, when total replacement of a vacuum contactor is now $5K-$10K even for large (over 600 A) units, the concept of "semi-repairable" is starting to fall apart. You can replace the bottles and even work on the linkage to some degree. In modern magnetic actuator units there's almost nothing mechanical left to work on. And when you consider some newer gear like S&C "Vista", ABB "R-Mag", Tavrida, Elastimold, etc., which is either sealed under an SF6 blanket or solid dielectric insulation thus not repairable, has roughly the same cost but effectively nothing replaceable or where the only thing you are preserving in a drawout configuration is the framework, semi-repairable is no longer cheap. In fact in the process industries, downtime cost is so large that breaker repair/replacement costs are almost meaningless. So if I have to spend twice as much for a "rebuild" (or outright replace) but I can reduce the number of downtime incidents by even a small percentage, more reliable wins every time.


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PostPosted: Wed Mar 21, 2012 10:50 am 
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Interesting discussion. I agree that many times the economics dictates the compromise we must make in safety and reliability. We don't want to spend a fortune to be over protected, but we also don't want to be cheap and have to do longer, more frequent and extensive maintenance every time. There must be a balance that accomplishes the desired objectives in maintenance and safety.
However our company does not want to change the working conditions to something that may or may not be better, they prefer to play it safe and keep the equipment that is working good. We just want to protect our workers the best we can, and since we can't change equipment, we rather try another approach to mitigate risk. Yes there will be more chance of racking equipment failures, and with aftermarket remote racking it can increase. But as long as the industrial safety can be guaranteed, we prefer to take the chance on the equipment than with people lives. (I know you said setting safety aside, but I just had to point my opinion here).


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