ELECTRICAL MACHINES WITHOUT EXCITATION WINDINGS AND PERMANENT MAGNETS

           Modern electrical machines (direct-current machines, synchronous machines, alternating-current converter-fed motors, universal commutator motors, and other electrical machines) contain two windings, that is, an excitation winding and an armature winding (in direct-current machines) or a stator winding (in synchronous machines and alternating-current converter-fed motors).

           To generate excitation magnetic field, current-actuated excitation windings or permanent magnets are used.
           Until the present time, an excitation system based on an excitation winding or permanent magnets for generating excitation magnetic field was considered as integral part of any electrical machine required for the normal machine operation.
           The energy characteristics of electrical machines depend, to a large extend, on the amount of electric losses occurring due to the flow of eclectic current through the excitation winding and the armature winding or the stator winding of the electrical machine, as well as on the amount of losses in the magnetic core, mechanical losses, and other losses in the electrical machine. The efficiency coefficient of the electrical machine is determined as follows:

where:

          P2 is the output (useful) power of the electrical machine;

          p is the total losses in the electrical machine.

           The basic electric losses in the electrical machine are losses in the excitation winding. Such losses amount to 20 … 50 percent of the total losses in the machine.

          The proposed electrical machine of unique design is without an excitation winding. The machine contains only an armature winding and a magnetic system of special design which allows the machine to properly operate without an excitation winding and permanent magnets. Since the magnetic system of the machine does not contain pole terminals with an excitation winding, the machine design is simplified, and overall dimensions and weight of the machine are reduced.

          So, the proposed electrical machine with the magnetic system of new design is characterized by the simplified machine design due to that the machine does not contain an excitation winding, by reduced weight and overall dimensions of the machine, and by reduced electric losses in the machine. Since the excitation losses in the machine are reduced, the energy characteristics of the machine, specifically the efficiency coefficient, are enhanced, the production cost of the machine is reduced, and the performance parameters of the machine are improved.

          The proposed electrical machine can be designed as a machine with a cylindrical rotor or a disc rotor, as an open-end machine, a machine with an internal or outer rotor, or a machine with contact elements (a commutator machine) or without contact elements (an alternating-current converter-fed motor).

          The range of application for the proposed electrical machine is the following:

            — appliances (drills, grinders, juice squeezers, kitchen units, washing machines, and other equipment);

            — water transport.

           The experimental motors of new design have been manufactured and tested. The results of the preliminary tests have demonstrated that the electrical characteristics and mass and dimensions parameters of the motors are improved.

          As an example an SL-369 direct-current motor is shown. The performance parameters of the motor were determined for the motor with an excitation winding (see Photo Illustration 1) and for the motor without an excitation winding (see Photo Illustration 2).

Photo Illustration 1
Photo Illustration 2
COMPARATIVE CHARACTERISTICS OF SL-369 DIRECT-CURRENT MOTOR WITH A SERIES EXCITATION WINDING AND SL-369 DIRECT-CURRENT MOTOR WITHOUT AN EXCITATION WINDING

 

Characteristic

Motor with an excitation winding

Motor without an excitation winding

Shaft power (W)

36.0

55.0

Voltage (V)

110.0

95.0

Consumed current (A)

0.909

0.94

Winding resistance (W):

 

 

— excitation winding

10.5

— armature winding

20.5

20.5

Electric losses in windings (W):

 

 

— excitation winding

8.68

— armature winding

16.04

18.11

Armature core losses (W)

19.38

19.58

Other losses (W)

45.0

36.55

Efficiency coefficient

0.55

0.615

Stator frame diameter (mm)

85.0

55.0

           In Photo Illustration 3, a BOSCH GSB 1300 drill is shown. The drill motor stator with excitation wining is shown in Photo Illustration 4, and the motor stator without an excitation winding is shown in Photo Illustration 5.

Photo Illustration 3
Photo Illustration 4
Photo Illustration 5