isoltion transformer
- Thread starter himooo
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jcormack
Member
- Location
- Pennsylvania
Uses are many
Uses are many
Isolation transformers are used for many reasons
1. Reduce/limit available short circuit current
2. Change voltage
3. Buck or boost voltage
4. Provide isolated ground or neutral
5. Reduce harmonics
6. A resistor could be added to the neutral to ground connection and you then have an isolated "high impedance" grounded system for just this portion.
One example could be a VFD...VFD's prefer to not have high incoming voltage. So if a plant tends to have voltage run "high" for extended periods a "Buck" transformer can be used to lower the input to the drive. This transformer would also provide a reduced SC available that could help protect the electronics during a fault. Using a Delta-Wye would also reduce the harmonic content seen by the rest of the system.
Uses are many
Isolation transformers are used for many reasons
1. Reduce/limit available short circuit current
2. Change voltage
3. Buck or boost voltage
4. Provide isolated ground or neutral
5. Reduce harmonics
6. A resistor could be added to the neutral to ground connection and you then have an isolated "high impedance" grounded system for just this portion.
One example could be a VFD...VFD's prefer to not have high incoming voltage. So if a plant tends to have voltage run "high" for extended periods a "Buck" transformer can be used to lower the input to the drive. This transformer would also provide a reduced SC available that could help protect the electronics during a fault. Using a Delta-Wye would also reduce the harmonic content seen by the rest of the system.
L
Lxnxjxhx
Guest
Isolation is another word that gets abused in the industry.
Basically all transformers are isolation transformers (separate primary and secondary coils).
A "true" "isolation transformer", I guess, would be a 120V to 120V transformer used purely for isolation purposes.
Basically all transformers are isolation transformers (separate primary and secondary coils).
A "true" "isolation transformer", I guess, would be a 120V to 120V transformer used purely for isolation purposes.
mdshunk
Senior Member
- Location
- Right here.
Because some tele and data guys think they have magical properties.
crossman
Senior Member
- Location
- Southeast Texas
Article 517 has some locations where an isolated power system is allowed or required. The point in this case is to obtain the advantages of an ungrounded system in anesthetizing areas and other patient care areas. These isolated systems have their own NEC color code, and ground monitoring is required.
I seem to remember that certain types of cranes require an isolated power source, but am too lazy to look it up at the moment. Again, the point is to get the advantages of an ungrounded system as to not shutting down the power if there is a ground fault, and to eliminate the sparking which may occur with a ground fault. With the cranes, I suppose there may be a lessened shock hazard from the lifting cable under certain fault conditions.
I seem to remember that certain types of cranes require an isolated power source, but am too lazy to look it up at the moment. Again, the point is to get the advantages of an ungrounded system as to not shutting down the power if there is a ground fault, and to eliminate the sparking which may occur with a ground fault. With the cranes, I suppose there may be a lessened shock hazard from the lifting cable under certain fault conditions.
Actually we de believe that and have the data to back it up. Your plane jane dry type transformer provides a minimum of 40 decibels of common-mode-rejection-ratio (CMRR) or 10,000:1. A special type called feroresonat isolation transformer made specifically for the purpose has 160 db of CMRR, or 10,000,000,000,000,000 : 1mdshunk said:
Only one thing can do a better job and that is a true dual conversion UPS.
Engy,
You don't know how difficult to get this across to those who I receive call from regarding transformer applications and sales. I really have to ask a lot of questions so that I can understand what they are asking for.
Drive isolation transformers is a very common term that can start as a simple transformer that has separate primary and secondary winding to those the a K-rated with 200% neutrals and an electrostatic shield between the primary and secondary winding.
The goal in the common transformer application in an electrical distribution system is to reduce the voltage to usable values. Two winding transformers establish a new system and, as such, provide isolation between the primary and secondary by default. It comes with the transformer
If the transformer is neither step-down nor step-up it basically has no value in the distribution system other than the benefit of isolating the load from the line and there are many reasons to want to do so from harmonic and noise to protecting against electric shock.
You don't know how difficult to get this across to those who I receive call from regarding transformer applications and sales. I really have to ask a lot of questions so that I can understand what they are asking for.
Drive isolation transformers is a very common term that can start as a simple transformer that has separate primary and secondary winding to those the a K-rated with 200% neutrals and an electrostatic shield between the primary and secondary winding.
The goal in the common transformer application in an electrical distribution system is to reduce the voltage to usable values. Two winding transformers establish a new system and, as such, provide isolation between the primary and secondary by default. It comes with the transformer
If the transformer is neither step-down nor step-up it basically has no value in the distribution system other than the benefit of isolating the load from the line and there are many reasons to want to do so from harmonic and noise to protecting against electric shock.
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
mdshunk said:
They do
It is very simple, and only applies to 3-phase. A delta fed transformer will cancel triplen harmonics generated on the secondary by non linear loads wye connected from backing up on the primary side. In other words the triplen harmonics are trapped in the transformer and dissipated as heat. In most cases a "K" rated transformer is chosen to accomplish this because the grounded circuit conductor is oversized therefore able to handle the extra heat generated by the triplen harmonics.himooo said:
When to use the approach is strictly a design issue, but typically used in situations where the transformer will be used to feed sensitive equipment like that found in a data center where all the loads are non linear.
If you will pick up a copy of IEEE Emerald Book it will answer all the questions you have been asking.
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Himooo ? When you made your inquiry the second time you identified harmonics (very ubiquitous term) but you did not identify your loads. You should throw some application details in because having read through this thread I see you have drawn some big guns out. What are you working on? Single/Three phase? What?s your Primary/Secondary voltage? Load type(s) - Motor/lighting/other?
The commentary on triplens by our moderator is great (thank you) so let me create a scenario with two identical loads that generate harmonic "current" multiples of 6+/-1 on the AC supply, one with and one without an isolation transformer:
1000HP pumping requirement
Available power is 3P, 480V
Process allows for and plumbers are savvy enough to build a system with 2 x 500HP pumps
2 x 500HP VFDS with 6 pulse front ends are selected
A 480/480V isolation transformer is connected ahead of one VFD. A line reactor with similar impedance is connected in front of the other
Merits:
Pumps & Motor availability fit schedule, subsequent service improved for I hope obvious reasons
Power conductors, conduits and related components far more manageable
We reduced the available short circuit current
Running at reduced capacity on one pump should the other fail
Isolation transformer phase shifts input power 30 degrees to one VFD cancelling the 5, 7, 17, 19, 29, 31, etc harmonic currents generated on the AC supply when running at the same load as the other VFD.
Not one loss inserting high priced harmonic filter was required
And so on ........
jcormack Bob: you could add an item 7 to your list, something about dI/dT, because after my family, dogs & golf, inductors are my favourite thing on this planet.
The commentary on triplens by our moderator is great (thank you) so let me create a scenario with two identical loads that generate harmonic "current" multiples of 6+/-1 on the AC supply, one with and one without an isolation transformer:
1000HP pumping requirement
Available power is 3P, 480V
Process allows for and plumbers are savvy enough to build a system with 2 x 500HP pumps
2 x 500HP VFDS with 6 pulse front ends are selected
A 480/480V isolation transformer is connected ahead of one VFD. A line reactor with similar impedance is connected in front of the other
Merits:
Pumps & Motor availability fit schedule, subsequent service improved for I hope obvious reasons
Power conductors, conduits and related components far more manageable
We reduced the available short circuit current
Running at reduced capacity on one pump should the other fail
Isolation transformer phase shifts input power 30 degrees to one VFD cancelling the 5, 7, 17, 19, 29, 31, etc harmonic currents generated on the AC supply when running at the same load as the other VFD.
Not one loss inserting high priced harmonic filter was required
And so on ........
jcormack Bob: you could add an item 7 to your list, something about dI/dT, because after my family, dogs & golf, inductors are my favourite thing on this planet.
brian john
Senior Member
- Location
- Leesburg, VA
Buck Boost transformers are not isolation transformers, there is a connection in common to the primary and secondary.
jcormack
Member
- Location
- Pennsylvania
Not so fast my friend....
Not so fast my friend....
That is only true if the Buck-Boost is an Auto-Transformer. If it has separate primary coils and secondary coils then it is an isolation transformer. (that is what I buy for VFD iso).
Not so fast my friend....
brian john said:
That is only true if the Buck-Boost is an Auto-Transformer. If it has separate primary coils and secondary coils then it is an isolation transformer. (that is what I buy for VFD iso).
- Location
- Massachusetts
jcormack said:
What kind of buck boost is not an Autotransformer?
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
When you connect the typical two-primary/two-secondary (or single windings, of course) as a buck-boost, it becomes an autotransformer. Only if you use one as a step-down (or up) is it isolated.jcormack said:
Even an old-fashion ignition coil is an autotransformer. (Note: 'Auto' means self, one, etc., as in . . . never mind.)
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jcormack
Member
- Location
- Pennsylvania
Terminology
Terminology
If you go back to my original post I said to buck OR boost not meaning a traditional buck-boost voltage regulating set-up. I guess I was not clear in my reponse. It mainly comes down to local terminology I suppose. In my area AN & BN (above and below nominal) transformer taps are always refered to as "Bucking" and "Boosting" taps. If one wants to provide a small increase or decrease in the voltage at a point in the system or a plant then these transformers may be purchased with taps that only boost the voltage above incoming or only drop the voltage - but not change the voltage "Class". Examples would be to take a low 215 volt input and boost it to 240 volts for a peice of equipment that required the voltage to be at 240. Or one may have over 500 volts on his nominal 480 buss on low load days that was causing occasional DC buss overvoltage trips on a VFD, a transformer could be used to buck this voltage to 470, where the VFD is happier. In both of these cases the nominal system voltage is not changing (240 & 480) as you would in a traditional step-down/up stiuation where you change nominal system voltage - like a 4160 volt to 480 volt transformation. I have been doing this for 27 years and a transformer making a small voltage change, plus or minus, that did not change the nominal system volatge has always been called a boosting or bucking transformer. these may be autotransformers or isolatation transformers depending on your needs. I did not say buck-boost in my original post & did not mean that in my second response.. I do realize these are step-up or step-down......but still in the same nominal voltage class.I use buck-boost ferroresonant units for contant voltage apps @ 480, 240/120 & was not meaning that in my posts.
So, I say tomatoe..................
Terminology
If you go back to my original post I said to buck OR boost not meaning a traditional buck-boost voltage regulating set-up. I guess I was not clear in my reponse. It mainly comes down to local terminology I suppose. In my area AN & BN (above and below nominal) transformer taps are always refered to as "Bucking" and "Boosting" taps. If one wants to provide a small increase or decrease in the voltage at a point in the system or a plant then these transformers may be purchased with taps that only boost the voltage above incoming or only drop the voltage - but not change the voltage "Class". Examples would be to take a low 215 volt input and boost it to 240 volts for a peice of equipment that required the voltage to be at 240. Or one may have over 500 volts on his nominal 480 buss on low load days that was causing occasional DC buss overvoltage trips on a VFD, a transformer could be used to buck this voltage to 470, where the VFD is happier. In both of these cases the nominal system voltage is not changing (240 & 480) as you would in a traditional step-down/up stiuation where you change nominal system voltage - like a 4160 volt to 480 volt transformation. I have been doing this for 27 years and a transformer making a small voltage change, plus or minus, that did not change the nominal system volatge has always been called a boosting or bucking transformer. these may be autotransformers or isolatation transformers depending on your needs. I did not say buck-boost in my original post & did not mean that in my second response.. I do realize these are step-up or step-down......but still in the same nominal voltage class.I use buck-boost ferroresonant units for contant voltage apps @ 480, 240/120 & was not meaning that in my posts.
So, I say tomatoe..................
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