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Asynchronous motor

Asynchronous motor

Constitution and principle of operation of an asynchronous motor

An induction motor has two parts:
The stator consists of three coils supplied by a balanced three-phase network; U voltage composed and line current I. It creates a rotating magnetic field in the rotation frequency: ns = f / p (p is the number of pole pairs)
The rotor rotates a rotational frequency n slightly less than ns.
A relationship connects these two parts slip g = (ns-n) / n = ns ns --- (1 - g).
describes in W the rotational speed of the rotor, it is expressed in rad / s.

Then W = 2.π.n (if n is rev / s) and W = 2.π.n / 60 (if n is r / min)
  The smallest voltage listed on the motor nameplate must be found across a winding. Next the three-phase network used, the coupling will be star or triangle.


  power to the stator

Power consumption: Pa = j U.I.√3.cos (electric power in W)

I: Line current (A)

cos j: motor power factor

Joule losses:

If R is the resistance measured between two phases of terminals: Pjs = 3 / 2.R.I² (electric power in W)
If R is the resistance of a winding, in which case account must be taken of the stator coupling
star connection: pjs = 3.R.I² (electric power in W)

the delta: pjs = 3.R.J² (electric power in W)

magnetic losses: pfs = Constant

Power transmitted to the rotor: Ptr = Pa - pjs - pfs

  power to the rotor

Joule losses: PJR g.Ptr = (electric power in W)

electromagnetic power: Pem = Ptr - PJR and Pem = Tem.W (mechanical power in W)

mechanical losses: ECP = Constant

Output: Pu = You .W and also Pu = Ptr - PJR - ECP


Engine Performance: h = Pu / Pa

vacuum testing (T = 0 N.m and n = ns) so we ECP + pfs = Pa0 - pjs0

Load Test: Tu = Pu / W = Tr steady

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