Emerson PACMotion VFD Series - Derating Information

88 PACMotion VFD AC Variable Speed Drive User Guide GFK-3111A
Derating Information
Derating of the drive maximum continuous output current capacity is required when:
• Operating at ambient temperature in excess of 40°C / 104°F for enclosed drives (Non UL Approved).
• Operating at Altitude in excess of 1000m/ 3281 ft.
• Operation with Effective Switching Frequency higher than 8 kHz for IP20 models and 4 kHz for
IP55/IP66 models.
The following derating factors should be applied when operating drives outside of these conditions.
Table 62: Derating for Ambient Temperature
Enclosure Type Maximum Temperature
Without Derating
(UL Approved)
Derate by Maximum Permissible Operating
Ambient Temperature with
Derating (Non UL Approved)
IP20 50°C / 122°F N/A 50°C
IP55 40°C / 104°F 1.5% per °C (1.8°F) 50°C
IP66 40°C / 104°F 2.5% per °C (1.8°F) 50°C
Table 63: Derating for Altitude
Enclosure Type Maximum Altitude
Without Derating
Derate by Maximum
Permissible
(UL Approved)
Maximum
Permissible
(Non-UL Approved)
IP20 1000m / 3281 ft 1% per 100m / 328 ft 2000m / 6562 ft 4000m / 13123 ft
IP55 1000m / 3281 ft 1% per 100m / 328 ft 2000m / 6562 ft 4000m / 13123 ft
IP66 1000m / 3281 ft 1% per 100m / 328 ft 2000m / 6562 ft 4000m / 13123 ft
Table 64: Derating for Switching Frequency
Enclosure
Type
Switching Frequency (Where available)
4 kHz 8 kHz 12 kHz 16 kHz 24 kHz 32 kHz
IP20 N/A N/A 20% 30% 40% 50%
IP55 N/A 10% 10% 15% 25% N/A
IP66 N/A 10% 25% 35% 50% 50%
Example of applying Derating Factors
A 4 kW, IP66 drive is to be used at an altitude of 2000 metres above sea level, with 12 kHz switching
frequency and 45°C ambient temperature.
From the table above, we can see that the rated current of the drive is 9.5 Amps at 40°C,
Firstly, apply the switching frequency derating, 12 kHz, 25% derating
9.5 Amps x 75% = 7.1 Amps
Now, apply the derating for higher ambient temperature, 2.5% per °C above 40°C = 5 x 2.5% = 12.5%
7.1 Amps x 87.5% = 6.2 Amps
Now apply the derating for altitude above 1000 metres, 1% per 100m above 1000m = 10 x 1% = 10%
7.9 Amps x 90% = 5.5 Amps continuous current available.
If the required motor current exceeds this level, it will be necessary to either:
• Reduce the switching frequency selected.
• Use a higher power rated drive and repeat the calculation to ensure sufcient output current is available.