Derating Calculator

Equipment Derating Calculator

What is Equipment Derating?

In electrical and mechanical engineering, derating is the practice of intentionally operating a device at less than its maximum rated capacity. This is necessary when environmental conditions, such as high heat or high altitude, reduce the device's ability to dissipate heat or operate efficiently.

Why Temperature and Altitude Matter

Most electrical equipment (like generators, motors, and cables) is rated at a "standard" ambient temperature (usually 40°C) and a "standard" altitude (usually 1000m). When these thresholds are exceeded:

• Temperature: High ambient heat reduces the temperature gradient, making it harder for the equipment to cool itself. This can lead to insulation failure or thermal shutdown.
• Altitude: As altitude increases, the air becomes thinner (less dense). Thin air is a poorer conductor of heat, meaning air-cooled systems cannot shed heat as effectively as they do at sea level.

How the Calculation Works

This calculator uses standard industry approximations for derating:

1. Temperature Derating: Typically 1% to 2% reduction for every 1°C above the reference temperature.
2. Altitude Derating: Typically 1% reduction for every 100m above the reference altitude.

Example: If a 100kW generator is used at 50°C (10 degrees above standard) and 2000m altitude (1000m above standard), its effective capacity might drop to approximately 80kW after applying both factors.

Important Considerations

While this calculator provides a high-level estimate, always consult the manufacturer's derating curves or datasheet for specific equipment. Different insulation classes (Class F, Class H) and cooling designs (forced air vs. natural convection) will result in different derating coefficients.