ABB UNO-7.6-TL-OUTD-S-US-A Product Manual page 90

EXAMPLE – TEMPERATURE DERATING CALCULATION for an UNO-7.6/8.6-TL-US installed at 7500
feet:
• The maximum rated temperature, for full power operation at sea level, from the UNO-7.6/8.6-TL-US series
datasheet, is 122oF (50oC).
• The normalized temperature derating factor, from the graph in Figure 7 3, at an altitude of 7500 feet is .945.
• The maximum full-power temperature for operation at 7500 feet would be 122oF * .945 = 115oF --OR-
- 50oC * .945 = 47oC.
Voltage derating
The dielectric strength of air decreases with altitude, so the maximum DC input inverter voltage must be de-
creased at high altitudes to avoid unwanted electrical arcs. Figure 7 4 shows normalized voltage derating factor
with increased altitude.
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7 - Appendix