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  » Products » Valiadis Motors » General Information » Fundamentals
General Information

Three phase current

Three phase current is characterised as following: the available three phase network carries individual alternating voltages of the same magnitude, but with a phase difference of 120° in time. The three supply connections of the three phase system are called L1, L2, and L3.
The same formulas apply to single phase motors, but without the factor 3.

Rated output

The rated output is indicated at the shaft of the motor :


Pn = √3 * Vn * In * cosφ * n [W]



Vn:   Rated motor voltage [V]
In:   Rated motor current [Amps]
Cosφ:   Rated motor power factor
n:   Motor efficincy at full load

Rated torque

The rated torque is calculated as following:


Mn = 9.55 * Pn/nn [Nm]



Pn:   Rated power [W]
nn:   Rated speed [Rpm]

to convert Nm to kpm you can use the formula 1Nm=1/9.81 kpm


The real speed of a motor corresponds to the synchronous speed less slip. The synchronous speed of the motor is depended only from the poles No and frequency according the following formula:


ns = f * 60/p [rpm]




f: Frequency [Hz]
p: Number of pole pairs


The nominal speed of the motor is then:


nn=ns*(1-s) [rpm]




s:   the motor slip
ns:   synchronous speed [rpm]
Athens, Greece: 18, Gr. Lambraki Str., 141 23 Likovrisi. Tel: +302102817217. Fax: +302102814277. valiadis@valiadis.gr