How to Document VFD Derating in a High-Altitude Pump Project Quotation

A high-altitude pump VFD quotation should state the exact site elevation, maximum ambient temperature, enclosure conditions, motor current and the derating rule used for selection. A supplier should not hide these assumptions inside a larger drive recommendation.

Thinner air can reduce cooling performance, but the final effect depends on the selected product documentation and installation. Altitude and temperature should be reviewed together.

What Information Is Required?

• Site elevation above sea level and maximum seasonal temperature.
• Motor voltage, current, power, frequency, speed and motor type.
• Continuous and peak operating duty for each pump.
• Indoor or outdoor enclosure, ventilation and mounting arrangement.
• Supply voltage, generator use and expected voltage variation.
• Number of VFDs in the panel and heat-dissipation constraints.
• Cable lengths, required accessories and applicable local standards.

Selection Example

A mountain water-transfer station is located at 2,400 m with a 30°C maximum panel-room temperature. One pump motor is 11 kW, 380 V, and its rated current is known. The RFQ asks three suppliers for an altitude-adjusted selection.

Each quotation should show the proposed drive current rating, the applicable altitude and temperature assumptions, and any required enclosure or ventilation conditions. The buyer can then compare equal scopes. A larger kW label without a documented current and derating basis is not a complete answer.

Common Mistakes

• Writing “high altitude” without stating the elevation.
• Applying a remembered derating percentage to every VFD series.
• Considering altitude but ignoring temperature and enclosure heat.
• Comparing quotations that use different environmental assumptions.
• Treating oversizing as permission to ignore installation instructions.

AUSENIST Solution

AUSENIST can review the site elevation, motor schedule and enclosure design, then document a YS620 or YS820 selection basis for engineering confirmation. The quotation can state the environmental assumptions, current margin and items requiring project verification.

No altitude rule should be generalized across unconfirmed models. If site temperature, ventilation or motor data is missing, the selection should remain provisional. Qualified personnel must design the panel cooling and electrical protection under the applicable documentation and local rules.

Send us the motor nameplate, quantity, voltage, application and project requirements. We can prepare VFD selection and quotation.