Bad Transformer
- Thread starter adavey
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Re: Bad Transformer
dry type transfromer or liquid insulated?
have you conformed proper over-current protection?
checked for dead varmits inside ?
I would not go so far as to say its not a sign for concern, however, a transformer rated 50o C over an ambient of 40oC is going to be close to egg frying temperature and still be within specs.
amazing creatures, they are!
dry type transfromer or liquid insulated?
have you conformed proper over-current protection?
checked for dead varmits inside ?
I would not go so far as to say its not a sign for concern, however, a transformer rated 50o C over an ambient of 40oC is going to be close to egg frying temperature and still be within specs.
amazing creatures, they are!
bphgravity
Senior Member
- Location
- Florida
Re: Bad Transformer
The term "extremely hot" is concerning. Excessive heat is a sure-sign of overloading or early transformer failure.
The term "extremely hot" is concerning. Excessive heat is a sure-sign of overloading or early transformer failure.
- Location
- Illinois
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- retired electrician
Re: Bad Transformer
Don
Remember that many dry transformers have a 150?C rise over a 40?C ambient. While this is the temperature of the internal windings, the surface of the case can have a 50?C (122?F) rise.
Don
bphgravity
Senior Member
- Location
- Florida
Re: Bad Transformer
Would you agree that at a surface/contact temperature of 60? C would both be excessive and a hazard per OSHA requirements?
Would you agree that at a surface/contact temperature of 60? C would both be excessive and a hazard per OSHA requirements?
Re: Bad Transformer
bph, I can't disagree with you at all because I don't have any knowledge of what OSHA might require in this regard. Someone more experienced in transformers might show me the error in my thinking, but the manuals I have show a case temperature not to exceed 50oc over 40c ambient. To me, thats extremely hot, but apparently not to "mr transformer". As I said before, I would sure question it but I'm not sure its a problem in transformer terms. Is there a maximum surface temperature for this per OSHA standards? I'd like to know for future reference.
bph, I can't disagree with you at all because I don't have any knowledge of what OSHA might require in this regard. Someone more experienced in transformers might show me the error in my thinking, but the manuals I have show a case temperature not to exceed 50oc over 40c ambient. To me, thats extremely hot, but apparently not to "mr transformer". As I said before, I would sure question it but I'm not sure its a problem in transformer terms. Is there a maximum surface temperature for this per OSHA standards? I'd like to know for future reference.
Re: Bad Transformer
There is no question that the common 150 degree C rise over 40 degree C ambient xfmr will be rather hot when fully loaded. I have seen them in the field that are rather hot when fully loaded. I didn't record any temperatures, though.
You did not mention any Amp readings. 480v. primary would be rated for about 36 amps max. What is the measured load.
There is no question that the common 150 degree C rise over 40 degree C ambient xfmr will be rather hot when fully loaded. I have seen them in the field that are rather hot when fully loaded. I didn't record any temperatures, though.
You did not mention any Amp readings. 480v. primary would be rated for about 36 amps max. What is the measured load.
- Location
- Illinois
- Occupation
- retired electrician
Re: Bad Transformer
Byran,
Don
Byran,
In terms of safety it is excessive, in terms of operating costs it is excessive, but in terms of normal operation of the transformer its not. I believe that OSHA considers anything over 120F to be a hazard (it could be 140F, I'm not sure).
Don
Re: Bad Transformer
30kva ,Indoor Dry type. 277/480 - 208 V 3 phase (step down).
I would like to share my practical things here,
1) please check what kind of load is connected.also check the starting current of the larger capacity of the connected load.because your transformer's rated current is 28.8 A (after deration).
2) The transformer would may unbalanced.
3) Please check out the terminals for any loose contact ,which leads to raise the temp.,in particular phase.
Jeyakumar
30kva ,Indoor Dry type. 277/480 - 208 V 3 phase (step down).
I would like to share my practical things here,
1) please check what kind of load is connected.also check the starting current of the larger capacity of the connected load.because your transformer's rated current is 28.8 A (after deration).
2) The transformer would may unbalanced.
3) Please check out the terminals for any loose contact ,which leads to raise the temp.,in particular phase.
Jeyakumar
- Location
- Massachusetts
Re: Bad Transformer
I must ask after what de-rating?
There is no code reason I am aware of to de-rate a transformer under normal operating conditions.
The primary current of this transformer could be 36 amps all day long.
Jeyakumar welcome to the forum.
I must ask after what de-rating?
There is no code reason I am aware of to de-rate a transformer under normal operating conditions.
The primary current of this transformer could be 36 amps all day long.
Re: Bad Transformer
Dear all...
I am like a kid in US based building design work.
As Thump rule i am considering 1.2 as multiplication factor for 277/480 service voltage.so
as the said transformer rating 30Kva ,the maximum extent what the transformer can be loaded is 30*1.2= 36A
But as a design engineer i never allow the transformer to load beyond 80 percent where it will give us the maximum efficiency.
so,the transformer is practically rated to load 36*0.8=28.8 A
If it is exceeds ,definitly the transformer is under overloaded.
Thanks and regards
Jeyakumar
Dear all...
I am like a kid in US based building design work.
As Thump rule i am considering 1.2 as multiplication factor for 277/480 service voltage.so
as the said transformer rating 30Kva ,the maximum extent what the transformer can be loaded is 30*1.2= 36A
But as a design engineer i never allow the transformer to load beyond 80 percent where it will give us the maximum efficiency.
so,the transformer is practically rated to load 36*0.8=28.8 A
If it is exceeds ,definitly the transformer is under overloaded.
Thanks and regards
Jeyakumar
- Location
- Massachusetts
Re: Bad Transformer
Around here we would call that a design decision.
A perfectly reasonable one.
However I take exception to saying this transformer is overloaded if it is used at any load above 80% of it's rating.
Around here we would call that a design decision.
A perfectly reasonable one.
However I take exception to saying this transformer is overloaded if it is used at any load above 80% of it's rating.
Re: Bad Transformer
when its like me, its when it doesn't take its medication but then I'm an inspector so I have to be a bit unbalanced.
I'm unaware of unbalancing becomeing a problem unless you load 1 phase of the 3 phase transf,. beyond 33% of the kva capacity. Perhaps we will learn something.
when its like me, its when it doesn't take its medication
but then I'm an inspector so I have to be a bit unbalanced.I'm unaware of unbalancing becomeing a problem unless you load 1 phase of the 3 phase transf,. beyond 33% of the kva capacity. Perhaps we will learn something.
Re: Bad Transformer
From my application notes some of which were provided to my by a retired DTDT design engineer state that there is a "rule of thumb" in the industry that allows the estimation of the percentage of temperature rise caused by unbalanced voltages. It is temperature rise approximately increases by double the square of the maximum voltage unbalance percentage.. As an example a 2% voltage imbalance would result in an 8% increase in temperature rise.
In my opinion voltage unbalance today is something to take more seriously because transformers are more likely to be loaded close to their ratings. There is no "cushion."
From my application notes some of which were provided to my by a retired DTDT design engineer state that there is a "rule of thumb" in the industry that allows the estimation of the percentage of temperature rise caused by unbalanced voltages. It is temperature rise approximately increases by double the square of the maximum voltage unbalance percentage.. As an example a 2% voltage imbalance would result in an 8% increase in temperature rise.
In my opinion voltage unbalance today is something to take more seriously because transformers are more likely to be loaded close to their ratings. There is no "cushion."
Re: Bad Transformer
It appears unbalancing is not a problem. However, the trans. is good for 83.3A (OCPD 100A 3P ) and during winter months is supplied w/ two electric heaters (DRAW APPROX 50A for both) that's causing the overload. Other loads are connected as well (fans, outlets, lights and misc. small loads). Since, there is a 277/480v panel and heaters are dual voltage we will relocate the heaters to the 277 v panel. NOTE: NO AC units. Thanks
It appears unbalancing is not a problem. However, the trans. is good for 83.3A (OCPD 100A 3P ) and during winter months is supplied w/ two electric heaters (DRAW APPROX 50A for both) that's causing the overload. Other loads are connected as well (fans, outlets, lights and misc. small loads). Since, there is a 277/480v panel and heaters are dual voltage we will relocate the heaters to the 277 v panel. NOTE: NO AC units. Thanks
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