Slip RPM of Submersible Pump Set Rotor

The difference between the theoretical synchronous rpm and the actual shaft rpm is the slip. Please explain the actual purpose of your question.

It is common practice to monitor the kW load on a motor, which is a more accurate indicator of load than current because current also fluctuates with applied voltage. It is done by monitoring the phase angle of the applied voltage and comparing it to the phase angle of the current. That doesn't really indicate the slip however if you have empirical data on the motor performance you can extrapolate the approximate slip by comparing the kW loading to that test data.

What is your reason for wanting to know the slip speed on a pump?

Erudite??? I don't do erudite... I do SWAG

The idea is to develop a probeless digital meter to display the slip rpm or the actual rpm of the rotor of a submersible pumpset because the rotor shaft is inaccessible after installation and the only parameter that can be measured is the current drawn by the pumpset.

The idea is to develop a probeless digital meter to display the slip rpm or the actual rpm of the rotor of a submersible pumpset because the rotor shaft is inaccessible after installation and the only parameter that can be measured is the current drawn by the pumpset.

If you look at the phasor diagram for a single phase induction motor you will note that the stator current vector changes in both angle and magnitude as the torque on the motor and its slip varies. It is the case that the current increases in proportion to torque and probably slip for low slip levels.

If you know the characteristic of a given motor then electronics ought readily to be able to convert that supply current supply voltage relationship to either load torque or slip as required.

The link below is an example of what I am talking about, though it is not the particular diagram I had in mind.

http://www.ece.umn.edu/users/riaz/animations/imphasors.html

Trevor,

Fantastic diagram!

Having experienced difficult to diagnose problems stemming from a mis-wound (by a local motor shop) stator, the only readily apparent indicator was a drop in head pressure capabilities for a 60 Hp submersible pump. KW remained close to specs for that point on the curve.

The fact that the slip was other than normal was only proven by dynamic load tests with the motor (pump disassembled).

I wonder if this condition would have shown up in a reflected signal, injected into the power supplied?

The more load, the more current, the more slip.

Current level is an actual indicator of slip in motors as the rated speed is affected by any additional load.

Since Percentage slip = n_s/n_s- n_r/n_s x 100%. where n_s is synchronous speed and n_r rated speed.

So Ur percentage increase in current should reflect Ur percentage slip. The actual speed is calculated with the formula below.

Note f = n_s x p/60. where p is the number of pairs of poles

Having been equipped with the percentage slip and normal speed, Ur slip speed can be calculated with the slip formula.

Dickson.

Why? What will yo do with the date once you have it?