Electric motors
Three-phase electric motors 2 poli/3000 RPM
Three-phase electric motors 4 poli/1400 RPM
Three-phase electric motors 6 poli/900 RPM
Three-phase electric motors 8 poli/750 RPM
Three-phase electric motors B5 variant
Three-phase electric motors B14 variant
Three-phase electric motors B3 variant
Electric motors which are used by far more often in combination with gearboxes are A.C. electric motors. The name asynchronous comes from the fact that the rotor does not rotate exactly at the same speed of the induced magnetic filed, but it rotates at a slightly lower speed.
AC electric motors can be three-phase or single phase; the technical parameter that especially characterizes a three-phase motor is the starting torque, i.e. the value of torque motor is able to supply the phase of starting when it goes from a situation of standstill to the running condition.
How to check that the order for an electric motor is correct and complete
It is necessary to know:
For three-phase motor:
- power
- number of poles (speed)
- voltage
- frequency:50 Hz sau 60 Hz (depends on the country where it is used)
- size (56, 63, 71, 80,100, 112, 132 etc)
- isolation class
- protection degree IP (IP 54, IP 55 etc)
- service (S1 – continuous, S3 – intermittent)
possible special features, such as: auxiliary ventilation, double shaft extension, protection of winding, usage of an encoder.
For single phase motors:
- power
- number of poles (speed)
- voltage (only one value)
- frequency :50 Hz or 60 Hz (depends on the country where it is used)
- size (56, 63, 71, 80,100, 112, 132 etc)
- isolation class
- protection degree IP (IP 54, IP 55 etc)
- service (S1 – continuous, S3 – intermittent)
- features of the capacitor
Motors with double polarity
Bothe three-phase and single phase motors can be manufactured even in the version with double polarity: 2/4 poli, 2/8 poli,4/8 poli etc.
These double polarity motors enable to operate at two different rated speeds, depending on which is the sequence of poles actually running at a specific time.
Double polarity motors allow a single voltage and not a double voltage as it occurs for motors with single polarity. In fact, star/delta connection cannot be done for them.
While double polarity motors keep the same standardization as far as sizes and housing are concerned, there is no standardization concerning power, and in relation to this, any manufacturer arranges his own range. However, it is important to point out that double polarity motors have even a double value of power, one related to high speed and the other related to low speed, the motor operating at any time with only one of the two power values.
Brake motors
Brake motors are alternate current three-phase asynchronous motors (very seldom single phase) , with single or double polarity, which inbuilt inside their houring an electromagnetic brake, located in the rear portion of the housing.
Brake motors are used for acting during the deceleration transient, in order to brake all the installation (all rotating and translating masses), within a time drastically reduced and repetitive. Braking time depend, among the others, on the braking torque, which is adjustable and governable. However, it must be noted that, the higher is breaking torque, the more stressed is the motor and especially all parts connected, mainly the gearbox.
For choosing the brake motor, it is necessary to know the following data:
- the brake is with direct or separate feeding
- should feeding be direct, it is needed to know whether it is direct current or alternate current
- should it be in direct current (D.C.), it is needed the voltage of the D.C. current coil
- should it be in alternative current (A.C.), it is necessary to know whether it is three phase or single phase, and the relevant voltage (if the motor is single -phase, there is only the option direct current for the brake)
- if there is separate feeding of the brake, it is necessary to know whether it is three-phase or single-phase and related voltage;
- in addition to all these, there must be mentioned that the braking torque of the brake is to be pre-set
- other non standard possible features.