High voltage equipment terminal temperature rating 1

[Mudcat]

Does anyone know if there is a standard terminal temperature rating for high voltage equipment? I was thinking that it was 90°C but am not sure. I've tried looking at some IEEE standards but haven't found anything yet.

 

[prc]

IEC60943: 1998 Guidance concerning the permissible temperature rise for parts of electrical equipment, in particular for terminals.

 

[Mudcat]

I don't have access to that standard. Any chance you could give me a little more detail before I spend $400 to get a copy?

 

[guiyermo]

Mudcat,

If the installation is ruled by NFPA the answer is 90 °C.

As per NEC 2011 Article 110 (Requirements for Electrical Installations), Part III (Over 600 Volts, Nominal)see the following articles:

110.30 General. Conductors and equipment used on circuits over 600 volts, nominal, shall comply with Part I of this article and with 110.30 through 110.40, which supplement or modify Part I. In no case shall the provisions of this part apply to equipment on the supply side of the service point.

110.40 Temperature Limitations at Terminations. Conductors shall be permitted to be terminated based on the 90°C (194°F) temperature rating and ampacity as given in Table 310.60(C)(67) through Table 310.60(C)(86), unless otherwise identified.

Hope this helps

 

[stevenal]

C57.19.00 says 30K rise over 30C average 24 hr ambient, 40C maximum ambient.

 

[prc]

Your understanding of max temperature of 90 C for terminals to be connected to external conductors is correct. If the terminals are tinned or silverplated,limit temperature is 105C. In both cases temperature rise shall be limited to a max of 60 or 75 C.

In IEC, the above limits are specified in various product standards eg Table 2 of IEC 60137-2008 Transformer Bushings, Table 2 of IEC 60947-1:2010 Low Voltage Switch gear and Control Gear,Table3 of IEC 62271-1:2007 High Voltage switchgear and Control Gear Part 1 Common specifications etc.

IEC/TR 60943ed2.1: 2009 is the Technical Report on Guidance concerning the permissible temperature rise for parts of electrical equipment,in particular for terminals. This classic tutorial elabortae the theory behind above temperature rise limits.This 60 page document is value for money covering theory and application.Table 4 gives comparative values of contact resistance, and table 6 typical values of temperature rise and temperature limits for various connections-bolted,spring contcat etc.

I could not find appropriate IEEE std on the subject. Stevenal,I could not find the values in C57.19-2004.Clause 5.4.1 gives 75K/ 65K as temperature rise

 

[stevenal]

Section 4.1, Usual service conditions.
5.4.1 speaks of the thermal basis for the continuous current rating. 75 K rise is the hottest spot on the bushing, 65 K is for the oil the lower part of the bushing is immersed in.
I believe Section 4 is more appropriate for an application question, since 5.4 is more about how the current rating was derived.
Also see 4.2 for unusual service.

 

[prc]

Thank you Stevenal! I missed it.But 70C absolute temperature looks too low compared to IEC standards values of 90C (uncoated) and 105C ( Tinned or silver plated)