ABB REC670 Applications Manual page 516

Section 17
Monitoring
510
140°C
130°C
120°C
110°C
100°C
90°C
80°C
10
12 2 4 6 8
Hours of the day
Normal life expectancy loading
140°C
130°C
120°C
110°C
100°C
90°C
80°C
10
12 2 4 6 8
Hours of the day
Long time energy loading
IEC15000441 V1 EN-US
Figure 216: 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.
Insulation aging or deterioration is a time function of temperature, moisture
content, and oxygen content. With modern oil preservation systems, the moisture
140°C
130°C
120°C
110°C
100°C
90°C
80°C
12 2 4 6 8 10
12
170°C
160°C
150°C
140°C
130°C
120°C
110°C
100°C
90°C
12 2 6 8 10
4 12
1MRK 511 401-UEN A
10
2 4 6 8 12 2 4
Hours of the day
Planned loading beyond nameplate rating
10
2 4 6 8 12 2
4
Hours of the day
Short time energy loading
IEC15000441-1-en.vsdx
Bay control REC670 2.2 IEC
Application manual
6 8 10
6 8 10