Electric Motors
VFD Motor Speed Calculator
Use VFD Motor Speed Calculator when the question is to calculate estimated motor speed from base speed and frequency ratio and the inputs come from one consistent source case.
Set up the VFD Motor Speed case
Use one VFD Motor Speed case at a time; save a new run when a condition changes.
Detail checks for estimated motor speed
VFD Motor Speed should distinguish starting, running, and overloaded motor conditions. A nameplate value is not always the same as a measured load value.
Keeping frequency ratio tied to the case
On VFD Motor Speed, confirm decimal placement and unit scale before using estimated motor speed; small prefixes can move an electrical result by orders of magnitude.
- Base speed. Example value: 1470 rpm. Enter base speed in rpm.
- Frequency ratio. Example value: 0.7. Enter frequency ratio.
Formula notes for VFD Motor Speed
A clean VFD Motor Speed result confirms the arithmetic for estimated motor speed; it does not prove the equipment rating or source data is the right one.
Only the entries shown on VFD Motor Speed feed estimated motor speed. If another correction factor matters, keep it in the notes or make a separate run.
The formula uses Base speed, and Frequency ratio to produce Estimated motor speed. Unit mistakes usually show up as an answer that is off by a factor of 10, 100, or 1,000.
Using the VFD Motor Speed answer
Read estimated motor speed together with the input values, not as a standalone fact. The same number can imply different decisions under a different equipment rating or operating period.
Changing base speed while leaving frequency ratio fixed is a useful way to see which assumption controls the answer.
Where VFD Motor Speed can break down
Slip and control mode affect actual speed.
- Starting current
- Drive settings
A short VFD Motor Speed audit
- Compare the result with the relevant rating or limit before acting on it.
- Keep the result note attached when copying the answer.
Detail checks for estimated motor speed
The arithmetic here is compact, but the use of estimated motor speed still depends on the condition represented by base speed. If that condition changes, make a new run instead of editing the old result.
Motor results should identify whether the case is starting, running, accelerating, or protected by a drive.
Documentation for VFD Motor Speed
Record the motor nameplate, supply voltage, enclosure, duty, and whether VFD Motor Speed describes running or starting.
| Input set | Base speed, and Frequency ratio |
|---|---|
| Result | Estimated motor speed |
| Condition note | Slip and control mode affect actual speed. |