Reluctance motors 0,1 - 7,5 kW

Today's drive technology demands higher and higher precision and speed adjustment as well as exact reproducibility of once found adjusting values. With conventional controlling methods, the time necessary for measuring and controlling the speed increases overproportionately with increasing demands on the accuracy.

Kaiser reluctance motors have a speed deviation of 0% from the set point! The speed deviation therefore only depends on the accuracy of the applied frequency inverter.

Construction:

• non-excited synchronous motor
  
• squirrel-cage rotor with damper cage
  
• noise-tested anti-friction bearings (lifetime lubrication)
  
• no carbon brushes
  
• no permanent magnets
  
• standard motor housing IP 55

Special advantages:

• unrestrictedly suitable insulating system for inverter operation
  
• digital preselectable speed
  
• speed deviation 0% in entire operating range
  
• no long-term drift
  
• synchronous or asynchronous start possible
  
• basic torque during standstill
  
• higher insulation material classes (F, H)
  

Options

• separately driven fan
  
• special shafts (also tapered shafts)
  
• pulse generator
  
• brakes
  
• gearing
  
• temperature switch (ETW), PTC thermistor (ETF)
  
• grease quantity controller or oil lubrication
  
• high speeds (ca. 20 000 min¨¹)

Power:
Stated powers are permanent powers under the prerequisite that a constant torque is required in the whole speed adjusting range. Temporarily higher powers for acceleration procedures are possible on inverters which enable a 'boost'.
The lowest permanently possible operating speed at full torque depends on the adjusting possibilities of the inverter. In this case the voltage adjustment and voltage formation at frequencies below 10 Hz are important.

Motor selection The selection of a KAISER reluctance motor always depends on the necessary torque in the controlling range. The possible permanent torques differ according to max. operating frequency and type of ventilation. Other torques can be admissible with maximum and minimum frequencies which deviate from the standard frequencies. We recommend to ask us! Initial adjustment of inverter for M = const. Cu = U nominal / f nominal U20 = (22÷24) · Cu U5 = (7÷7,5) · Cu

Inverter adjustment
Adjusting stipulations for all inverters available on the market cannot be provided because the adjusting possibilities of the the various inverters considerably differ. At KAISER, the data included in this list have been measured on inverters with a free programmability of the i/f characteristic on three supporting points. For a constant torque starting with 5 Hz during permanent operation, characteristics then result for all motors. These characteristics comply with fig. 1 to a great extent. Slight corrections may be necessary for concrete applications.

Attention! The stated voltages on fig. 1 are measured actual values and not standard parameters adjusted according to inverter adjustments. Only the fundamental wave may be taken into consideration with the measured voltage. The measurement is of course carried out with an r.m.s.-responding instrument with a low critical frequency (soft iron).

Nominal current If the voltage frequency characteristic is adjusted acc. to fig. 2 so that the basic torque can constantly be transmitted at 5 Hz, a current rise of approx. 10-20% results with most inverters in the range from approx. 5 Hz with an idling motor. When loading with basic torque, the current decreases to the nominal value (refer to fig. 2). This fact must definitely be taken into consideration when selecting the inverter. KAISER reluctance motors are suitable for a permanent operation with the stated increased current.

Concentricity
With inverters of a good industrial quality, a concentricity adequate for many applications can presently be attained with frequencies starting with approx. 1,5 Hz. Preliminary tests on our testing station are definitely advisable in such cases before installing the series.

Noises
With noise-sensitive applications, inverters with a variable chopper frequency should be selected because, depending on the motor size and motor pole number, random resonances can occur.
A calculation of such resonances in advance is unfortunately not possible as seen from an economical point of view due to the complexity of the entire system. The installation of high-pulse inverters (10-20 kHz) with KAISER reluctance motors is unrestrictedly admissible, however the postal regulations must be observed.

Bearings
Only 100% noise-tested bearings of first class quality are installed in KAISER reluctance motors. A test run is effected on the completely assembled motor and subsequently a noise test is again carried out.

Grease
KAISER reluctance motors are lubricated with a highly loadable EP grease (Mobiltemp SHC 100). This grease enables lifetime lubrication also with the higher temperatures due to the speed control. A large selection of special greases is available for special applications.

Balancing
KAISER reluctance motors are balanced acc. to DIN ISO 8821 with half featherkey. If a balancing with a full featherkey is necessary, then this must be explicitly noted in the order!

Series 46 - only upon special request
KAISER reluctance motors of the series 46 (4-poles) have an improved power factor (CosPhi). This improvement is concomitant with a higher inclination to oscillations. These motors therefore should not be installed in plants with an extreme inertia moment and a temporary operation near to the no-load operation. With subsequent gearing with a transmission ratio > 15, an application is possible without any problems.

Motor protection
As with all variable-speed motors, KAISER reluctance motors definitely should be protected by installed PTC thermistors or thermo-contacts (option).

Construction
KAISER reluctance motors have a conventional three phase stator and a special 'reluctance' rotor. The reluctance rotor has 2p large reluctance grooves and, depending on the motor type, a different number of normal rotor grooves. All grooves and the cage rings are cast with aluminum in the die-cast procedure. An extreme robustness and stability against high speeds is attained by this rotor construction. (Refer to fig. 3)

Housing KAISER reluctance motors are installed in the normal three phase standard motor housings. Therefore the conventional foot and flange fastening devices as well as standard shafts can be used. All special designs also possible with KAISER standard motors can be supplied. Insulating system As with all KAISER motors, an insulation system of highest quality is used for KAISER reluctance motors. The winding is made out of varnished copper wire of the insulation material class H with a particularly high mechanical strength. In general three layer material is used as a groove insulation. All KAISER three phase motors (also the smallest sizes) are provided with inter-phase insulation. The complete windings are saturated with impregnating varnish in a vacuum. This results in a particularly high stability against voltage peaks as well as against moisture. Up to now, no winding failures have occurred caused by inverter operation when respecting the directives of electromagnetic compatibility.

Function
A different inductivity of the motor results through the reluctance grooves depending on the rotor position. As the rotor always tries to be positioned in the position of the lowest energy content (the highest inductivity), it runs synchronously with the stator rotating field as long as the maximum possible load torque (synchronous pull-out torque) is not exceeded. Due to the also existing asynchronous rotor cage an asynchronous starting is possible. At the same time, the asynchronous rotor cage serves as a damper cage against rotary oscillations. Theoretically, KAISER reluctance motors can be regarded as non-excited salient-pole machines (refer to fig. 3).

Operational performance The speed-torque characteristic of the KAISER reluctance motors consists of two ranges. In the first range, the characteristic corresponds to that of normal asynchronous motors, this range is only entered during the asynchronous starting. In the normal operating condition, the characteristic is a straight line from zero up to the synchronous pull- out torque at synchronous speed (ref. to figure).

If the motors are accelerated on a frequency ramp via a frequency inverter, only the second range is entered. During operation, KAISER reluctance motors behave as ideal speed stable motors, to which the load is coupled via a torsion spring, i.e. with a load, the shaft lags behind the rotary field by a load torque dependent angle. In the normal operating range, the dependency between load torque and load angle is first of all linear.

Synchronizing performance If KAISER reluctance motors are switched on at a fixed frequency, they first of all accelerate on the asynchronous characteristic up to the intersection with the load torque. At this point in time, the asynchronous torque is superimposed by a sinusoidal torque with slip frequency (refer to figure). A positive half-wave of this torque has to accelerate the drive by the slip speed in order to synchronize. This results in the fact that the synchronizing performance depends on the load torque and the load inertia. In comparison to permanently excited synchronous motors, KAISER reluctance motors can accelerate and synchronize much larger external inertia torque.

Pulling out of synchronism
The characteristic of the load torque over the load angle is practically sinusoidal. If the load torque is increased up to the maximum of the first sinusoidal half-wave, the rotor falls out of synchronism during the next stable working point. If the load torque is still too high, the motor further falls out of synchronism, it runs asynchronously. This operating condition can be recognized by a considerably fluctuating current and pulsating sounds. The motor is destructed during a longer asynchronous operation.

Oscillatory characteristics
As KAISER reluctance motors - as every synchronous motor - together with the load, form a spring-mass system, mechanical sympathetic oscillations are possible. Such oscillations particularly can occur in the operating range below approx. 25 Hz with the 2 and 4-pole motors with external centrifugal masses. In this case - as also previously mentioned with regard to the noises - it is advisable to carry out preliminary tests.