Transformer Name Plate

[brian john]

On a Square D 75 kva transformer the following temperatures are noted

220 DEGREE C INS SYSTEM 150 DEGREE C RISE

I assume (possibly incorrectly) that the transformer insulation is rated 220 C or 428 Degree F?

And the second number is that the acceptable operating temperature above ambient or assuming 21 C or 70 F which takes us back to 220 C or 428 F???????????

 

[masterinbama]

You got it.

 

[templdl]

These are the three commonly available dry type distribution transformers that are available, all with 220degC class insalation:


This is a common transformer rating;
40 degC maximum ambient
150 degC maximum average winding rise
30 degC maximum hot spot in winding
220 degC ultimate temperature at hot spot

This is a 115degC rise transformer that allows for a 15% overload without exceeding its insulation rating.
40 degC maximum ambient
115 degC maximum average winding rise
30 degC maximum hot spot in winding
+35deg C which allows for the 115degC rating and a 15% overload before exceeding 220degC
220 degC ultimate temperature at hot spot

This is an 80degC rise transformer that allows for a 30% overload without exceeding its insulation rating.
40 degC maximum ambient
80 degC maximum average winding rise
30 degC maximum hot spot in winding
+70deg C which allows for the 80degC rating and a 30% overload before exceeding 220degC
220 deg ultimate temperature at hot spot

Also, don't overlook that fact that 25degC (77degF) is commonly the ambient temperature and the actual transformer ambient rating that the transformer is rated at is 40degC (104degF). As such there is an extra 15degC (27degF) to work with.
As such the game one plays is never to exceed the transformer insulation rating if at all possible. But that doesn't mean that you can't if you follow under loading rules. Overloads do sacrifice transformer life though which is dependent upon the overtemperature and the length of time of the overload.

 

[brian john]

Another question

Another question

Where or what is considered the maximum temperature, is this in the coils or the core?
I know when manufactures imbed temperature sensors in a transformer in the windings out of sight.

A better question would be when measuring maximum temperature, where do you measure.

 

[jim dungar]

Technically there are three temperatures in regards to transformers.

Ambient air
Insulation System
Hot spot

The hotspot temperature would occur internal to the transformer core and coil assembly. This is an all but theoretical value, typically a 30?C allowance is used. This allowance is 'subtracted' from the insulation's ultimate rating.

 

[templdl]

Where or what is considered the maximum temperature, is this in the coils or the core?
I know when manufactures imbed temperature sensors in a transformer in the windings out of sight.

A better question would be when measuring maximum temperature, where do you measure.

You can't measure it as it is done by testing transformer designs at the factory and using themistors within the windings with winding material that has 220degC insulation. This is how the transformer is listed and as such the user must accept it a part of the design itself. It is a matter of understanding how the 220degC temperature is not exceeded. You start of with 40degC ambient, then add the temperature rise sch as 150degC, then add for an allowable 30degC hot spot, 40+150+30= 220deg C. The be redicing the temperature rise at a give KVA the transformer runs cooler which can extend transformer life if the transformer is overloaded.

 

[brian john]

Ok assuming a resistive load (as harmonic loads would seem to have to many variables) is there a expected temperature increase as loads increase on a specific transformer?

 

[templdl]

Ok assuming a resistive load (as harmonic loads would seem to have to many variables) is there a expected temperature increase as loads increase on a specific transformer?

I guess if you are refering to specifically resistive loads I am missing your point.
As far as harmonics goes then the K-factor must be considered and the transformer designed as such. There will be more steel and often a higher grade of steel used in the core of the transformer to reduce the heating affects that are caused but the harmonics.

These are the "K" factors that are commonly available that also would include a 200% neutral:
Applications
K=4
Welders
Induction heating
HID lighting
Fluorescent lighting
K=13
Telecommunications equipment
Classroom facilities
Healthcare facilities
Production lines
SCR variable speed drives
K=20
Office buildings
Data processing equipment
Adjustable speed drives
Computer installations
Instrumentation
K=30
Computer installations
Office buildings
Data processing equipment
Adjustable speed drives
Instrumentation

 

[brian john]

I guess if you are refering to specifically resistive loads I am missing your point.
As far as harmonics goes then the K-factor must be considered and the transformer designed as such. There will be more steel and often a higher grade of steel used in the core of the transformer to reduce the heating affects that are caused but the harmonics.

Sorry for the confusion, assuming a resistive load is the temperature rise linear in regards to a increase in kw?

 

[templdl]

Sorry for the confusion, assuming a resistive load is the temperature rise linear in regards to a increase in kw?

Since neither in my many years as a sales and applications engineer that question nor have I had a need to address and as such I'm not sure if the question has any relevancy. I would have to ask a design engineer except that I no longer have access to any.

 

[Cow]

On a Square D 75 kva transformer the following temperatures are noted

220 DEGREE C INS SYSTEM 150 DEGREE C RISE

I assume (possibly incorrectly) that the transformer insulation is rated 220 C or 428 Degree F?

And the second number is that the acceptable operating temperature above ambient or assuming 21 C or70 F which takes us back to 220 C or 428 F???????????

Wouldn't that be a 70? C ambient?

 

[brian john]

Wouldn't that be a 70? C ambient?

An ambient of 70 C is 158 F and while some electric rooms may seem this hot I think temperatures like that are to be avoided.

I did repair a chiller starter once in a boiler room where the ambient was 127 F.

 

[Smart $]

...
220 DEGREE C INS SYSTEM 150 DEGREE C RISE
...
And the second number is that the acceptable operating temperature above ambient or assuming 21 C or 70 F which takes us back to 220 C or 428 F???????????

Wouldn't that be a 70? C ambient?

An ambient of 70 C is 158 F and while some electric rooms may seem this hot I think temperatures like that are to be avoided.

I did repair a chiller starter once in a boiler room where the ambient was 127 F.

I believe he is just saying that 220?C ? 150?C = 70?C. He and I do not see how you arrived at 21?C or 70?F...???

 

[brian john]

I believe he is just saying that 220?C ? 150?C = 70?C. He and I do not see how you arrived at 21?C or 70?F...???

With 21 C being the ambient (assumed or typical)?

 

[Smart $]

With 21 C being the ambient (assumed or typical)?

I've always assumed typical ambient for equipment to be 40?C... but that's irrelevant. We just don't see the connection you made in your statement, "And the second number is that the acceptable operating temperature above ambient or assuming 21 C or 70 F which takes us back to 220 C or 428 F???????????" You referred to the second number, 150?C rise, and 21?C plus that number doesn't take us back to 220?C.

We don't need to persue this, as I believe the answer has already been posted... :thumbsup:

 

[brian john]

I've always assumed typical ambient for equipment to be 40?C... but that's irrelevant. We just don't see the connection you made in your statement, "And the second number is that the acceptable operating temperature above ambient or assuming 21 C or 70 F which takes us back to 220 C or 428 F???????????" You referred to the second number, 150?C rise, and 21?C plus that number doesn't take us back to 220?C.

We don't need to persue this, as I believe the answer has already been posted... :thumbsup:

Rereading my post I see the issue. Sorry for the confusion.