ABB Relion 670 Series Applications Manual page 508

Section 18
Monitoring
• Normal life expectancy
•
• Sacrifice of life expectancy
•
•
•
140°C
130°C
120°C
110°C
100°C
90°C
80°C
12
140°C
130°C
120°C
110°C
100°C
90°C
80°C
12
IEC15000441 V1 EN-US
Figure 250: Typical load cycles for example
Impact of the increased currents and temperature leads to premature transformer failure and
this may have an immediate short term effect or a cumulative long term effect.
• Short-term effect: Reduction in dielectric strength due to the possible presence of gas
bubbles which leads to super saturation of the oil and reduction in short circuit strength.
• Long-term effect: Continuous deterioration of the conductor reduces the transformer life.
Deterioration of insulation reduces mechanical strength and dielectric strength. Heating from
heavy overload or large electromagnetic force resulting from short circuit causes expansion
and unusual movement of conductors and it leads to turn-to-turn fault.
502
Normal life expectancy loading: The transformer loading is continuous at rated
output when operated under usual conditions.
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.
10
2 4 6 8 12 2
4
Hours of the day
Normal life expectancy loading
10
2 4 6 8 12 2 4
Hours of the day
Long time energy loading
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140°C
130°C
120°C
110°C
100°C
90°C
80°C
6 8 10
12 2 4 6
Planned loading beyond nameplate rating
170°C
160°C
150°C
140°C
130°C
120°C
110°C
100°C
90°C
6 8 10
12 2 4 6
1MRK 511 401-UEN Rev. K
10
8 12 2 6 8 10
4
Hours of the day
10
8 12 2 4 6 8 10
Hours of the day
Short time energy loading
IEC15000441-1-en.vsdx
Bay control REC670
Application manual