Current and Speed in AC Motors

Current and Frequency ?

Current and Speed ?

Both are different.

And whether in AC or DC -

Power = V.I = τω

So ω = V.I/τ

V = Constant

τ = Defined by load and may be constant of f(ω)

ω = Angular velocity of the rotor and may or may not be dependant of ω_elect

In AC additionally the loss currents and reactive currents will be there and those are f(ω_elect)

Your question is not very clear what you want.

There's a relationship between frequency and speed in AC motors, and there's a relationship between voltage and speed in DC motors.

If you understand that and want to know more, please advise.

thanks for your response,can there be a relation between voltage and frequency in an ac drive?

Not really. When the voltage becomes too low to force current through inductive windings, the motor will not run. When the voltage is high enough, it will tend to run at a speed related to the frequency of the line. Keep in mind that voltage and current are related via winding reactance. Torque is a function of current, and when voltage is just high enough to make the motor run, there's very little usable torque available to do work.

Also, there's a "trick" to reducing voltage by way of duty cycle. In DC applications, Pulse Width Modulation is used to effectively control speed without much reduction in motor torque, as it is presented with full voltage during the entire pulse width, which can be from 0 % to 100 % of the duty cycle (usually chosen to be many times less than the electrical and mechanical time constants).

The same general philosophy was/is employed in AC variable speed drives, among other ways, but things get a little more complicated, and I'm not going to attempt to explain it in this forum. A little research on the internet will do a lot to answer your questions.

Not very clear about the context.

The motor (Refer #1) has to meet the load (or it stalls)

If you see the EMF of the motor, the back emf is created by the load (depending on its power requirement)

Add to this the Voltage drops in the equivalent circuit (Resistive and Reactive) and you get the required voltage at its terminal.

The back emf is most likely dependant on the Load (KW) hence motor speed (and hence) line frequency

The Equivalent circuit - Resistance is dependant on electrical frequency (skin effect), eddy losses etc

Reactance of the circuit is also dependant on the electrical frequency (ie L is a function of ω_elect )

Additionally the ω_electL drop itself has the ω_elect as multiplier.

So the voltage to be fed to the motor (or conversely the current that is going to be drawn by it) will be dependent on the frequency.

But still don't understand the context (in some context the above logic may not hold ?)