ANSI/IEEE vs. IEC Generator Temperature Ratings

[rcw retired EE]

On a combined cycle power plant proposal, a vendor provided steam turbine and gas turbine generator ratings versus ambient air temperature charts that had different curves for "IEEE Class B Rise, 0.85 pf" and "IEC Class B Rise, 0.85 pf". It looked like the ANSI/IEEE curve had about 30C difference in the allowable temperature rise at the same MVA. For example at 250 MW, 0.85 power factor, the IEEE curve is 0C ambient air, but the IEC curve shows 32C ambient air. The curves take into account the approach temperatures for the fin-fan air to water cooler and the water to hydrogen heat exchangers on the generator.

What is the reason for the 30C difference in the allowable temperature rise bewteen the IEEE C50.13 and the IEC standard (# unknown). Is it hot spot allowances, different test methods or different definitions?

 

[ScottyUK]

Does this extract from IEC 60034 Part 3 help?

7.4.3 Temperature rise and temperature at base capability

For indirectly cooled windings, the temperature rises when operating at site shall be in
accordance with Tables 6, 7 and 8 of IEC 60034-1 as appropriate, adjusted as follows:

a) for primary coolant temperatures from 10 °C to 60 °C: add (40 – primary coolant temperature) K;
b) for primary coolant temperatures below 10 °C but not below –20 °C: add 30 K + 0,5 (10 – primary coolant temperature) K;
c) for primary coolant temperatures above 60 °C or below –20 °C, an agreement shall be reached;

For windings directly cooled by air or hydrogen the total temperatures when operating on site shall be in accordance with the limits of Table 12 of IEC 60034-1, adjusted as follows:

d) for primary coolant temperatures from 10 °C to 60 °C: no adjustment;
e) for primary coolant temperatures below 10 °C but not below –20°C: subtract 0,3 (10 – primary coolant temperature) K;
f) for primary coolant temperatures above 60°C or below –20°C, an agreement shall be reached.

 

[rcw retired EE]

IEEE C50.13 seems to include a hot spot allowance. IEC 60034-1 looks at average winding temperature. The limiting observable temperatures for both standards is 85C (measured by embedded RTD).

I will have to have the generator vendor explain why the capability curve is so different between ANSI and IEC for the same operating conditions.

 

[Hoxton]

I know that it is an obvious question, but are these curves for the same speed / Frequency? Years ago when I was a generator designer, we used to issue separate rating diagrams for 50 and 60Hz, 3000 and 3600 rpm. This was for clarity, as the standard curves showed ratings at 0.8 0.85 and 0.9 pf.

The electrical and mechanical designs were identical, just the speed change and different temperature rises etc defined in the specifications changed the rating criteria.

At the time, we offered 50Hz ratings to BS, IEC and other country specifications. For 60Hz applications we offered to ANSI.

This was because showing ratings for IEC and ANSI at the same frequency on the same piece of paper would potentially cause too many questions.........

 

[rcw retired EE]

Hozton- The curves supplied by Siemens are all on the same chart and same basis. It is just a graph of MW capability @ rated voltage, frequency and 0.85 power factor versus ambient air temperature. The curve accounts for the approach temperature differences across the fin-fan water-air coolers and the generator's water-H2 heat exchangers. Siemens has three curves on the chart: steam turbine output, "IEC Class B Rise 0.85 pf" and "IEEE Class B Rise 0.85 pf". The IEC rating curve exceeds the steam turbine MW, the IEEE curve drops below the turbine output curve for all ambients above 15C.

Maybe I can get the client to relocate the power plant to Europe where generators apparently run cooler?

 

[Hoxton]

I have the attached paper of the differences between C50.13 and 60034, following the 2006 update to C50.13. BUT note that C50.13 has just been updated, so not sure what the changes are, and which one your curve refers to. I suspect that the difference in rating comes from the hot spot limit in C50.13, but only Siemens can tell you. The situation used to be that in 60034, only the manufacturer would know if the temperature detector was in a hot spot or not.........

Please let us know what Siemens say