Aluminum Bus 30C rise over 40C ambient explanation

[cjcoronel21]

Hello everyone,

I have been scratching my head for some time over the meaning "30C rise over 40C ambient". I have read this footnote under many, if not all, manufacturers' specification sheets when determining the ampacity of the busbar. Anyway, i am trying to determine what this actually means. IT may be simple and i may be over thinking it but hoping to get a confirmation.

I was thinking it could meean:

1) The busbar will maintain its rated ampacity for temperatures up to 70C amiben (40C+30C)
2) The busbar temperature will rise 30C when the ambient temperature is 40C under full load conditions

Thank you in advance for your input!

Best,
Chris

 

[davidbeach]

2).

 

[jghrist]

Both statements are correct and equivalent, assuming that "full load conditions" are the rated ampacity.

 

[che12345]

Mr Chris
" ...the meaning (of) "30C rise over 40C ambient"
It means that the busbar shall be rated for when the ambient* temperature is 40C, the temperature-rise** shall not exceed 30C. In this case, the busbar surface*** temperature shall not exceed 70C.
FYI:
1. The busbar can be tested in the open free-air (IP00) or enclosed in the switchboard (IPnn) etc.
2.1 Testing under IP00, the ambient* temperature in degC is measured at the same height as the busbar and at a distance of one metre away. This is to ensure that the temperature measured is the surrounding free-air(ambient) temperature, which is not affected by the temperature of the busbar under test.
2.2 Testing under IPnn, the ambient* temperature in degC is measured at half the height of the switchboard and at a distance of one metre away. This is to ensure that the temperature measured is the surrounding free-air(ambient) temperature, which is not affected by the temperature of the busbar enclosed inside the switchboard. The free-air temperature inside the switchboard is usually not measured and is not reported in the test report.
3. Temperature-rise** is the [busbar surface*** temperature - ambient* temperature]. In SI system , the unit is k (kelvin). Note 1k=1degC.
4. Busbar surface*** temperature in degC is the temperature measured on the surface of the busbar, irrespective of whether testing is conducted in IP00 or IPnn.
5. Irrespective of whether testing is conducted in IP00 or IPnn, the ambient* temperature of the testing station cell may be and is allowed to be lower than 40C. Therefore, the temperature-rise** can be higher than 30C or (30k).
Note: However, under any conditions; the busbar surface*** temperature in degC shall not exceed 70C.
Che Kuan Yau (Singapore)

 

[LionelHutz]

2) is correct.

Change 1) to say up to 40*C ambient and it would be correct.

 

[Skogsgurra]

che

We recently have had a few discussions about b and B as in bits and bytes. There was also one about m (milli) and M (mega). I think that we shall keep to standard terminology, where k means kilo and K means kelvin. Less confusion that way.


Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[cuky2000]

Below is a sample of bus ampacity rating for an outdoor AIS substation application.

Notice that the ambient temperature drive the allowable ampacity for a constant operating bus temperature (ex.70 oC rating).
It is a common practice in the utility industry to have a Summer and Winter rating to take advantage that the station can operate safely with larger ampacity in Winter due to the lower ambient temperature that help to dissipate the heat generated by the Joule effect.
I hope this help.

 

[che12345]

Mr Gunnar Englund
Thank you for pointing out the typographical error.
Yes, temperature difference in SI unit name is [kelvin] and the symbol is [ K ] (not) k.
BTW The temperature difference in SI unit is K (not) degK . The interval 1K=1degC.
Thank you
Che Kuan Yau (Singapore)