How do I size a VFD for a motor?

Calculate the motor's full-load current (FLA), then select a VFD with a continuous current rating equal to or greater than the motor FLA. Add margin for overload capability — typically 110% for normal duty (variable torque) or 150% for heavy duty (constant torque).

What is the difference between normal duty and heavy duty VFD rating?

Normal duty (ND) is for variable-torque loads like fans and pumps — typically 110% overload for 60 seconds. Heavy duty (HD) is for constant-torque loads like conveyors and mixers — typically 150% overload for 60 seconds. The same VFD is often rated for a higher kW in ND vs HD.

Should I oversize the VFD?

It is common practice to select one frame size above the motor rating for: high starting torque requirements, frequent starts/stops, high ambient temperature, or altitude above 1000m. Oversizing by one frame also extends VFD lifetime.

What voltage should I select for the VFD?

The VFD input voltage must match your supply. Common ratings: 230V single-phase (small motors), 400V three-phase (Europe/Asia), 480V three-phase (North America), 690V (large industrial). The VFD output voltage matches the motor rating.

Can I use a VFD with any motor?

VFDs work best with inverter-duty motors (designed for PWM waveforms). Standard motors can be used but may need derating above base speed, and bearing insulation may be required for motors above 30 kW to prevent EDM bearing damage.

मुक्त अभियांत्रिकी साधन

VFD निवड कॅल्क्युलेटर

तुमच्या मोटरसाठी Variable Frequency Drive चे आकारनिर्धारण करा. rated current, overload margin सहित आवश्यक VFD current rating आणि शिफारस केलेला drive size गणना करा.

Normal / Heavy Duty ओव्हरलोड मार्जिन मानक आकार

मोटर rated power (kW)

पुरवठा व्होल्टेज (V)

मोटर power factor (cos φ)

मोटर कार्यक्षमता η (0–1)

ड्युटी प्रकार

ओव्हरलोड मार्जिन (%)

Quick presets

Results

आवश्यक किमान VFD current rating

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मोटर full-load current

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मोटर apparent power

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ड्युटी / ओव्हरलोड

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शिफारस केलेला VFD आकार

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मोटर full-load current

VFD current rating

इथे overload margin transient conditions आणि safety factor यांचा विचार करतो.

मानक VFD आकार

kW (400 V)	सामान्य FLA (A)	VFD फ्रेम
0.75	2.1	आकार A
1.5	3.8	आकार A
4.0	9.5	आकार B
7.5	17	आकार B
15	32	आकार C
22	46	आकार C
37	73	आकार D
55	106	आकार D
75	145	आकार E
110	210	आकार E

⚠️ Note: VFD निवड नेहमी उत्पादकाच्या datasheets विरुद्ध पडताळा. ambient temperature >40°C, altitude >1000m किंवा switching frequency >4 kHz साठी derate करा.

VFD Selection Calculator — Size Your Drive Free | Vibromera

Published by Nikolai Shelkovenko on फेब्रुवारी 15, 2026 मार्च 5, 2026

Results

मोटर full-load current

VFD current rating

मानक VFD आकार

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