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:
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).
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.
The purpose of this research consists in experimental comparison of characteristics of commutator electric motors having different configuration of stator magnetic system and similar configuration and dimensions of the armature. In this research the armature of SL-569MU2 motor is taken as a basis.
This report is focused on studying and comparing the characteristics of the following commutator motor configurations:
— SL-569 MU2 electric motor with stator field windings (SL-569 (Coil));
— electric motor without stator field windings (SL-569 (stateless)).
- Commutator motor SL-569MU2
SL-569MU2 electric motor is a DC commutator motor that has two windings: a field winding and an armature winding. The motor is operated in a continuous mode. The windings are made of copper wire insulated with high-strength enamel coating. The electric motor is fabricated in aluminum housing, made by die casting method. General view of SL-569MU2 electric motor is shown in Fig.1, and its technical characteristics are given in Table 1.
Table 1 – SL-569MU2 electric motor technical data.
Parameter | Value |
Rated supply voltage, V | 110 |
Current consumption, A | 2.35 |
Rated power, W | 160 |
Rated speed, rpm | 3300÷4000 |
Rated torque, N×m | 0.465 |
Operating temperature range, °С | -40 to +40 |
Weight, kg | 4.5 |
Length, mm | 173.2 |
Diameter, mm | 112 |
2. Electric motor without stator field windings (SL-569 (stateless))
The innovative electric motor is built on the basis of the commutator and armature of SL-569MU2 commutator motor. This motor has no field windings on the stator which is made from electrical steel segments of a special configuration.
3. Experimental studies of two types of electric motors
Experimental studies of two types of electric motors were carried out on a special test bench. The bench (Fig. 2) consists of the following main parts: 1 – load generator; 2 – tachometer to measure the speed of the studied motors; 3 – frame, on which the studied electric motors and the load generator are fixed; 4 – rubber coupling for connection of the electric motor and the load generator; 5 – commutator motor (SL-569 (Coil)); 6 — electric motor without stator field windings (SL-569 (stateless)).
Fig. 2. A test bench for commutator motor SL-569 (Coil) (a) and electric motor without stator field windings (SL-569 (stateless) (b).
The tests of the studied electric motors were carried out in the following manner. DC voltage was connected to the tested electric motor. The value of applied voltage could be adjusted in the range Uin = 50÷110) V. After connecting the voltage to the electric motor terminals, its armature began to rotate thus driving the load generator 1 via coupling 4. Windings of the load generator were connected to variable active resistance, by changing which the load on the tested electric motor could be adjusted.
3. Comparison of results for two types of commutator motors.
During the tests, each electric motor was supplied with voltage, such that the input power for a given load was the same for both motors. Table 2 shows the basic parameters of two compared electric motors, i.e. SL-569 (Coil) with stator field windings and SL-569 (Stateless) without windings and magnets on stator. In the table below the data are given for input power equal to Pin = 132 W.
Table 2 – Parameters of tested motors
|
Параметр |
Опыт 1 |
Опыт 2 |
||
|
SL-569 (Coil) |
SL-569 (Stateless) |
SL-569 (Coil) |
SL-569 (Stateless) |
|
|
Outer diameter (mm) |
95 |
68,4 |
95 |
68,4 |
|
Axial length (mm) |
68 |
68 |
68 |
68 |
|
Air gap (mm) |
0,25 |
0,25 |
0,25 |
0,25 |
|
Weight of active part (kg) |
3,1 |
2 |
3,1 |
2 |
|
Electric motor volume, (cm3) |
481,8 |
249,7 |
481,8 |
249,7 |
|
Speed (rpm) |
3375 |
3093 |
3469 |
3469 |
|
Supply voltage (V) |
83,2 |
52,8 |
63,5 |
63,5 |
|
Supply current (A) |
1,6 |
2,5 |
1,55 |
2,65 |
|
Power input (W) |
133,1 |
132 |
180,0 |
158,8 |
|
Power output (W) |
75,3 |
73 |
69,9 |
83,2 |
|
Efficiency (%) |
57 |
55 |
39 |
52 |
|
Power density (W/cm3) |
0,16 |
0,29 |
0,14 |
0,33 |
|
Specific power (W/kg) |
24,3 |
36,5 |
22,53 |
41,61 |
When analyzing the test results, it should be noted that at the same input power (Test 1) the output power and efficiency of both types of electric motors are also the same. At the same time, the motor without windings has a smaller diameter of magnetic system and, therefore, its power density (W/cm3) is 1.8 times higher than that of the motor with windings, and the ratio of specific power to the weight of its active parts (W/kg) is 1.5 times higher. With the same rotation frequency (Test 2), the power density (W/cm3) in a motor without windings on the stator is 2.4 times higher than that of a standard SL-569 motor, and the power density referred to the mass of active parts (W/kg) is 1.8 times higher.
It should also be noted that the efficiency value of an electric motor without stator windings is approximately equal to that of a standard commutator motor.
Conclusions
- The power density per volume (W/cm3) for a collector electric motor without windings compared to an electric motor with windings on the stator is on average 2 times higher and, accordingly, 1.65 times higher the power density per mass of active parts (W/kg).
- The technology of manufacturing an electric motor without windings is much simpler than an electric motor with windings on a stator, and therefore much cheaper, which is of decisive importance in mass production.