Working on a Casino job and plan to use harmonic mitigating transformers for feeding my slot machine panels due to the nonlinear loads. Does anyone have any suggestioons or advice on design or recommended manufacturers? I did another project earlier on for a temporary facility at the same Casino and I used a K-rated transformer due to the harmonic load. This transformer runs a tad warm (could cook breakfast on it). Luckily the transformer was oversized due to a reduction in the slot machine load and there have been no issues and it is not a real concern as this is a temporary installation. Any thoughts would be appreciated.
Harmonic Mitigating Transformers
- Thread starter bfletcher
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kingpb
Senior Member
- Location
- SE USA as far as you can go
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- Engineer, Registered
Any Delta/wye transformer will not pass harmonics; they are trapped (e.g. circulate) in the delta winding.
The fact that the transformer is running "hot" could be a sign that the transformer is over sized, or that the k-rating is matched to a single load and not to the total contribution of the loads, or even worse if it was both too big and to high a k-factor.
Transformers feeding devices that produce harmonics should be sized at the actual running load and k-factor based on total load harmonics.
The fact that the transformer is running "hot" could be a sign that the transformer is over sized, or that the k-rating is matched to a single load and not to the total contribution of the loads, or even worse if it was both too big and to high a k-factor.
Transformers feeding devices that produce harmonics should be sized at the actual running load and k-factor based on total load harmonics.
A typical delta-wye transformer supplying nonlinear loads will have increased system losses and decreased efficiency, which calculates to increased power costs. The overheating of the transformer will also shorten the life-span of the unit. I want to cancel the harmonics, not leave them trapped inside the delta. That is why I'm looking into the Harmonic Mitigating Transformers.
gar
Senior Member
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- Ann Arbor, Michigan
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- EE
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kingpb:
Why is an oversized transformer going to run hotter than one sized to the load?
The magnetizing current will be approximately the same at no-load as at full-oad. The magnitizing current will be higher on the larger transformer because of more iron. But relative to full load magnetizing current is not a dominate factor. The I^2*R losses for the same output load will be less on the larger transformer because of the lower resistance.
What are the balancing factors?
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kingpb:
Why is an oversized transformer going to run hotter than one sized to the load?
The magnetizing current will be approximately the same at no-load as at full-oad. The magnitizing current will be higher on the larger transformer because of more iron. But relative to full load magnetizing current is not a dominate factor. The I^2*R losses for the same output load will be less on the larger transformer because of the lower resistance.
What are the balancing factors?
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kingpb
Senior Member
- Location
- SE USA as far as you can go
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- Engineer, Registered
Used Mirus filters before, not sure if the HMT's are any good.
http://www.mirusinternational.com/downloads/H-TG01-A1 Harmony Technical Guide.pdf
There are some good articles out there that dispel some of the myths about harmonics, make sure you look before you leap. You get a lot of cancellation between the branch loads. I'd gather some field data on the install you did and see what is really taking place.
Don't forget to add your O&M costs for the HMT's and look at MTBF. A small amount of downtime in a casino can't be cheap.
http://www.mirusinternational.com/downloads/H-TG01-A1 Harmony Technical Guide.pdf
There are some good articles out there that dispel some of the myths about harmonics, make sure you look before you leap. You get a lot of cancellation between the branch loads. I'd gather some field data on the install you did and see what is really taking place.
Don't forget to add your O&M costs for the HMT's and look at MTBF. A small amount of downtime in a casino can't be cheap.
The main transformer manufacturer's do offer harmonic mitigating transformers. Square-D, GE, Cutler-Hammer. These are also nicknamed "zig-zag" transformers.
There's a manufacturer that's been advertising at the A/E firms here a lot which is called PowerSmiths Transformers. Take all of their LEED claims with a grain of salt. They also offer some equipment to add to an existing system to reduce harmonics. If you do a retro fit job then talk to someone who lives/eats/breathes harmonics because location of equipment matters a lot.
There's also a type of transformer that does phase shifting by 30 degrees or something. I haven't ever used these but I think it will cancel out a couple more harmonics when you have multiple transformers off the same panel.
There's a manufacturer that's been advertising at the A/E firms here a lot which is called PowerSmiths Transformers. Take all of their LEED claims with a grain of salt. They also offer some equipment to add to an existing system to reduce harmonics. If you do a retro fit job then talk to someone who lives/eats/breathes harmonics because location of equipment matters a lot.
There's also a type of transformer that does phase shifting by 30 degrees or something. I haven't ever used these but I think it will cancel out a couple more harmonics when you have multiple transformers off the same panel.
brian john
Senior Member
- Location
- Leesburg, VA
A standard K-XX rated transformer is not harmonic mitigating but designed to handle the distortion imposed on it by the loads.
There are delta-wye/wye, and there are harmonic mitigating products available, BUT in my experience (and I am NOT an engineer) a properly sized K-rated transformer should fit the bill.
Additionally (ONCE AGAIN JUST MY EXPIERENCE) an over sized transformer will be a benefit not a hindrance. Bigger can handle the heat that may be generated due to the load.
There are delta-wye/wye, and there are harmonic mitigating products available, BUT in my experience (and I am NOT an engineer) a properly sized K-rated transformer should fit the bill.
Additionally (ONCE AGAIN JUST MY EXPIERENCE) an over sized transformer will be a benefit not a hindrance. Bigger can handle the heat that may be generated due to the load.
- Location
- Illinois
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- retired electrician
I have heard about this company, but don't know anything about them. There were a couple of trade magazine articles about them a few years ago.
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dbuckley
Senior Member
- Location
- Canterbury, New Zealand
K rated trannies do run hot. The harmonic currents are dissapated as heat, is my understanding.
A K-rated transformer is just extra insulation to handle the heat generated by harmonics. An over-sized transformer would have the same result. An over-sized transformer can reduce the efficiency because the efficiency is dependant on the percentage of load. As the percentage decreases so does the efficiency. This is not a linear relation though. Decreasing lower than 30% load can be a sharp drop off in efficiency.
A harmonic mitigating transformer will slightly reduce the total power consumed. Energy is not wasted in the form of heat.
A harmonic mitigating transformer will slightly reduce the total power consumed. Energy is not wasted in the form of heat.
wirenut1980
Senior Member
- Location
- Plainfield, IN
don_resqcapt19 said:
I have heard about this technology as well. It sounded very interesting. The one I heard about works by installing the unit at the transformer secondary feeding the harmonic loads between X0 and ground. It apparently is a filter that appears as a very high impedance to 3rd harmonic currents (180 Hz) only, and thus prevents them from flowing at all. No K-rated transformer necessary.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
The fact that higher harmonic content in the current causes higher eddy current loss in winding conductors and structural parts linked by the transformer leakage flux field and, consequently, higher operating temperatures. This is why the original install is running hot.
However, the answer is not to simply oversize as there is a negative effect in oversizing due to a lower ohmic resistance on the load harmonics that can cause the neutral line current to actually increase. The same effect is present when you use too high of a k-factor rating because with typical k-factor transformers reactance goes down when k-factor goes up.
At or near transformer full load is best and is where a k-rating may be necessary to prevent overheating since transformer losses vary with the square of current, therefore the losses for an over sized transformer with reduced loading has more negative impact, and also since transformers are most efficient around the 70-80% of their capacity. At full load is also where the transformer reactance will have the most effect in reducing the harmonics.
There are multiple transformers used for harmonics - K-factor, isolation, delta-wye isolation, phase shifting, auto, ferroresonant, and zig-zag. Each does something a little different.
In the end, the proper determination for the transformer should be done in accordance with IEEE C57.110.
However, the answer is not to simply oversize as there is a negative effect in oversizing due to a lower ohmic resistance on the load harmonics that can cause the neutral line current to actually increase. The same effect is present when you use too high of a k-factor rating because with typical k-factor transformers reactance goes down when k-factor goes up.
At or near transformer full load is best and is where a k-rating may be necessary to prevent overheating since transformer losses vary with the square of current, therefore the losses for an over sized transformer with reduced loading has more negative impact, and also since transformers are most efficient around the 70-80% of their capacity. At full load is also where the transformer reactance will have the most effect in reducing the harmonics.
There are multiple transformers used for harmonics - K-factor, isolation, delta-wye isolation, phase shifting, auto, ferroresonant, and zig-zag. Each does something a little different.
In the end, the proper determination for the transformer should be done in accordance with IEEE C57.110.
weressl
Esteemed Member
bfletcher said:
Why don't you explore the active harmonic mitigation methods? They work like the noise cancelling headphones, injecting opposing harmonic components to negatie the 'noise'. Eaton is one of the sources. excellent for variable loads.
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