Single phase Equivalent circuit for induction motors

[hisham1986]

Dear All ,

I would like please to know if the single phase equivalent circuit for the induction motor works for both star and delta connected stators...
i.e: Does the equivalent impedance computed from the equivalent circuit is the same for star and delta? Zeq star=Zeq delta?

Thank you in advance

 

[GoldDigger]

Dear All ,

I would like please to know if the single phase equivalent circuit for the induction motor works for both star and delta connected stators...
i.e: Does the equivalent impedance computed from the equivalent circuit is the same for star and delta? Zeq star=Zeq delta?

Thank you in advance

The Zeq values for the two configurations must be different because they must result in the same load power but at different applied voltages (ie.line to neutral voltage compared to line to line voltage.

 

[hisham1986]

In star delta starting technique of an induction motor,the power delivered to the mechanical load in star at starting period is 1/3 of the mechanical power delivered in delta connection or DOL.

Question 1:

Is this due only to the reduction in phase voltage by 0.557 in star connection instead of line voltage in DOL starting? , i mean is it only and only because of the voltage??

Question 2:

If this is so , then it would mean that at starting (Standstill rotor )the equivalent phase impedance (Zeq) in (Star connected stator) is exactly the same equivalent phase impedance in delta connection . i.e :Zeq star at starting =Zeq Delta at starting.

Hope someone could help with clear correct elaborations please,

Thank you.

 

[Jraef]

Wait wait wait, how can you have a star OR delta connection on a single phase motor? Either term implies MORE than two connections!
or am I misinterpreting the question?

 

[GoldDigger]

Wait wait wait, how can you have a star OR delta connection on a single phase motor? Either term implies MORE than two connections!
or am I misinterpreting the question?

I think that you are misinterpreting the question, but it seems very easy to do given what the OP said.

The power consumption of a fixed three phase inductive-resistive load can be modeled by the power consumption of a single phase inductive-resistive load of suitable characteristic impedance.
But a motor will not represent a constant fixed reactance as it accelerates or as the mechanical load changes, so the idea of modeling a three phase motor by a single phase motor just does not make sense. At the least you would have to make some assumptions about the starting method of the single phase induction motor and what type it was, as well as what type the three-phase induction motor represented.

The OP's second set of questions seem to apply just to three phase motor characteristics, leaving out the whole single phase comparison.

Also, to some extent a motor or other load will exhibit an identical (variable) impedance to each of the three phases, allowing you to leave some of the three phase math out of consideration. But not the way the OP is doing it, IMHO.

 

[cadpoint]

US Motors

US Motors

I'd go read up at this web site that had 147 responses to your question of "single phase equivalent"

US Motors

 

[Besoeker]

But a motor will not represent a constant fixed reactance as it accelerates or as the mechanical load changes, so the idea of modeling a three phase motor by a single phase motor just does not make sense.

Not a single phase motor. A single phase equivalent circuit.
The Steinmetz model is commonly used.

 

[GoldDigger]

Not a single phase motor. A single phase equivalent circuit.
The Steinmetz model is commonly used.

Precisely.