The bearings in an electric motor are used to support the rotor, to bear the forces that are created in the motor and to position the rotor in the stator. The accuracy of the bearing design must meet high criteria to guarantee trouble free electric motor operation. If an electric motor is connected directly to the driven equipment, the bearing of the electric motor often absorb forces created in by the driven equipment. Rotor nl® electric motors are equipped with axially pre loaded and located bearings as standard.
All rotor nl electric motors are dynamically balanced with half key in accordance with the IEC 34-14 (2003) standard. The letter H (for Half key) is specified on the rating plate and on the shaft end as a sign the motor was balanced with a halve key. The letter F (for Full key) means that balancing has taken place with the full key.
Brake type- single disc brake mounted by means of a special mounting kit.
Braking principle- by means of loose springs. The brake is lifted electro-mechanically with direct current voltage 205 V DC.
The rotor electric motors are supplied with a cable connection on the right side (pos. 1). The terminal box entry is 4 x 90 ° rotatable, which allows for cable entries pos. 2 (DE), pos. 3 (left) and pos. 4 (NDE). Rotor can also supply motors where the cable is already fitted in the terminal box or where the cable is connected directly to the windings, which leaves the terminal box superfluous.
Upon request any electric motor can be sprayed/painted in any of available colors. Rotor operates its own spray shop where special anti-corrosion coatings can be applied. These coatings consist of several layers of paint with different characteristics, which, in the correct combination, are resistant to a number of corrosive agents such as seawater, chemical fumes etc.
The Degree of Protection of rotating electric machines is defined as protection against the penetration of mechanical particles, dust and water. The Degree of Protection is defined in the following standard: IEC 34-5 (NEN-EN 60034-5).
Various insulation materials are used in electric motors and each has its own function. All these insulation materials are specified in thermal classes that are referenced using a letter (Y—A—E—B—F—H—C). Every thermal class has its own temperature limit specified (see table). An insulation material of a specific class needs to retain its mechanical and electrical properties within the temperature limit and have a reasonably long service life. The maximum permissible temperature rise (see table) of the winding is determined based on the thermal class temperature limits.
The rotor nl electric motors that have been fitted with open bearings, are supplied with a lithium based grease as standard. Grease types based on lithium with mineral base oil can be used for re-lubrication. Good quality high temperature grease should be the preferred choice. If an electric motor is fitted with a special bearing and/or special grease (upon request), the bearing/grease information would be specified on the rating plate as well as the re-lubrication period. Re-lubrication must be done accordingly.
The mechanical and electrical performance of the basic rotor nl electric motors is adapted for marine and offshore application. All rotor nl electric motors are tested after assembly to guarantee their correct operation and are subject to high-voltage insulation and no-load run tests. Additional tests can be performed in the factory test laboratory.
Totally Enclosed Fan Cooled electric motors (TEFC) are air cooled motors provided with an external fan that is fitted on the electric motor’s own shaft or independently driven. It is also possible that the electric motor is installed in an air flow without a fan (TEAO, Totally Enclosed Air Over). The air necessary for cooling of the motor is usually provided by the driven equipment. The Totally Enclosed Non Ventilated electric motors (TENV) have no fan nor are they subject of forced cooling. There TENV motors are in particular used for short term duty cycle (i.e. S2-10min duty).
All electric motors should be protected against overloading. Electric motors will develop a fault when overloaded as the temperature rises above the thermal limit of the insulation materials during the overload, which results in the loss of the mechanical and electrical properties.
The specified mounting must always be mentioned when ordering an electric motor. The actual motor mounting may influence the protection class and bearing design. Flange mounted electric motors need further specification of the required pitch circle diameter (dimension M) of the fixing holes in the flange (FF or FT type of flange). FF (Flange Free Holes) = free holes are in B5 flanges, FT (Flange Tapped Holes) = tapped holes are in B14 flanges. The pitch circle diameter (dimension M) is specified in the EN50347 standard in relation to the frame size for the FF (B5) flange and the FT (B14A) flange (up to 160 frame). The pitch circle diameter (dimension M) is not specified for FT (B14B) flanges in the EN 50347 standard, they however are specified in IEC 72-1 standard. The motor mountings and the positions are summarized in the IM code as per the table below. For detailed information please consult the IEC 34-7 (NEN 10034-7) standard.
The unit of power output is kW (1HP = 0.75kW; 1 kW = 1.34 HP). The power output values specified are based on maximum power at continuous load at what the thermal stability of the motor winding is attained. The continuous load is referred to as S1 duty cycle. The duty cycles (S1 to S10) have been defined in IEC 60034-1 standard indicating the run cycles of electric motors and in case of the intermittent duty also the frequency of the run periods. The power output limit up to which an electric motor can be utilized is determined by the maximum permissible temperature of the stator winding. The electrical and mechanical parameters of electric motors are based on duty cycle S1 - continuous operation.
Electric motors that are not continuously running (S1 duty), are usually provided with a standstill or space heater coils (SHC). The heaters switch on when the electric motor is not running and ensure that a constant temperature inside the motor housing is maintained. Sudden differences in temperature inside the electric motors cause water condensation, which is harmful and can shorten the service life of electric motors. The heaters keep constant temperature in motors after they have been switched off and prevent forming condensation.
For the position of the terminal box a choice can be made between on top or on either side left or right of the electric motor, facing the output shaft . The rotor nl® standard terminal box is on top (TOP). Conversion of a terminal box to the side (right or left) is often possible. Please contact us for further information.
The rotating speed of an electric motor can be controlled by frequency inverter. This variable rotating speed control provides many advantages such as optimization of production processes and energy saving. The speed and the power needed to drive the driven equipment can be tailored more accurately when a frequency inverter is utilized. Frequency inverter driven motors consume less energy than fixed speed drives with a different way of control.
The IEC 38 “standard voltages” standard (sixth edition) was published in 1983. This standard describes the standard voltages for the network, the equipment and the installations. This standard makes provisions for a “standard voltage” of 3 x 230V/400V - 50 Hz. As a result of this standardization, a larger area in which the same voltage dominates will be created in due course. This ensures fewer voltage variations in devices.
The assumption is usually made when constructing the electric motor that the electric motor will be coupled to a machine with a flexible couple or a V-belt transmission. However, electric motors are also often coupled to the machine directly. Therefore, the electric motor bearing is also directly loaded with axial and/or radial forces originating from that machine. Usually such a load is significantly larger than the load of the electric motor itself. The total axial and/or radial load in combination with the rotational speed and the applied bearing design must always be taken into account when calculating the bearing service life.
An electric motor is a commonly used device that transforms electrical energy into mechanical energy through the interaction of magnetic fields. The main two components of an electric motor are the stator and rotor. The stator contains copper windings which are designed to carry direct current and set up a magnetic field. The windings are alternately magnetized, creating a magnetic field in the stator. The rotor is levitated to one side by the magnetic field. Because the three windings are alternately magnetized, the rotor begins to rotate.