ABB REC670 Applications Manual page 515

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
IEEE C57.91-1995 standard has developed four different loading conditions
beyond nameplate to explain the risk involved in the higher operating temperatures,
see Figure 216. The four types of loading are:
• Normal life expectancy
• Normal life expectancy loading: The transformer loading is continuous
at rated output when operated under usual conditions.
• Sacrifice of life expectancy
• Planned loading beyond nameplate: Restricted to transformers that do
not carry a continuous steady load and it is a normal, planned repetitive
load.
• Long time emergency loading: Loading results from the prolonged
outage of some system element. This is not a normal operating condition,
but may persist for some time.
• Short time emergency loading: Unusually heavy loading for short time
due to occurrence of one or more unwanted events that disturb the
normal system loading seriously.
Section 17
Monitoring
509