ABB Relion 670 Series Applications Manual page 481

1MRK 511 401-UUS F
•
•
•
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 221: 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.
Bay control REC670
Application manual
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
10
8 12 2 4 6 8 10
Hours of the day
10
8 12 2 4 6 8 10
Hours of the day
Short time energy loading
IEC15000441-1-en.vsdx
Section 17
Monitoring
475