What kinds of classification of traction motors
What kinds of classification of traction motors, the use of traction motors in our lives is still relatively widespread, for traction motors in fact, there are also classified, the principle of the use of traction motors is also a content that we need to understand, the following traction motors have what kinds of classification.
What kinds of classification of traction motors1In the locomotive or moving car used to drive one or several moving wheel axle motor. There are many types of traction motors, such as DC traction motors, AC asynchronous traction motors and AC synchronous traction motors. DC traction motors, especially DC series-excited motor has a better speed performance and operating characteristics, to adapt to the needs of the traction characteristics of the locomotive, has been widely used.
The working principle of the traction motor is the same as that of the general DC motor, but there are special working conditions: the space size is limited by the track gauge and the diameter of the moving wheel; in the locomotive running through the rail joints and turnouts to withstand considerable shock vibration; large and small gear mesh bad armature will produce strong torsional vibration; in the harsh environment, the use of rain, snow, dust and sand easily invasive and so on.
Therefore, the traction motor in the design and structure of many requirements, such as to make full use of the internal space of the body so that the structure is compact, to use higher level of insulation materials and magnetic materials, parts and components need to have a high mechanical strength and stiffness, the whole motor needs to have good ventilation and heat dissipation conditions and the ability to prevent dust and moisture to take special measures to cope with the more difficult to "change direction". Special measures should be taken to cope with the difficult "commutation" conditions to reduce the sparks under the carbon brushes.
There are two types of traction motor suspension. One is the traction motor and the dynamic wheel axle connected to the suspension, known as the holding axle suspension or semi-suspension. With this type of suspension, the impact vibration generated by the moving wheel through the rail joints and turnouts will be directly transmitted to the traction motor. Holding axle suspension is suitable for the structure of the rolling stock speed is less than 120 kilometers / hour. The other is the frame bearing suspension (or full suspension).
With this type of suspension, the traction motor is fixedly suspended on the bogie frame, and various elastic connecting elements are added between the traction motor shaft end and the small and large gears to reduce the impact of shock vibration. Frame bearing suspension is suitable for structure speed higher than 120 km / h rolling stock.
In the traction transformer step-down by silicon rectifier or high-power thyristor rectifier power supply to the DC series-excited traction motor, the voltage added to the traction motor for the pulsating voltage, so this traction motor is called pulsating traction motor. High-power pulsating traction motor "commutation" conditions are more difficult.
In addition, there are some additional losses within the motor, resulting in motor temperature rise, therefore, the pulse current traction motor in the design and structure of the special measures to be taken to solve the "commutation" and the temperature rise of the two outstanding issues. Dedicated to electric drive internal combustion locomotives, to supply traction motor power generator, also known as the main generator. There are two kinds of traction generators: DC and AC. DC traction generator directly to the DC traction motor power supply.
AC traction generator issued by the three-phase alternating current rectified by a silicon rectifier and then to the DC traction motor power supply. AC rectifier circuit is three-phase, the rectified voltage, although there are pulsations, but the amount of pulsation is relatively small, so the traction motor is also considered to be a general DC motor.
What kinds of traction motors are classified2Basic principles of traction motors
A traction motor is an electric motor that generates the traction power of a locomotive or a moving train. There are many types of traction motors, but they all have a characteristic that corresponds to the relationship between the traction force and speed of locomotives and rolling stock, i.e., the basic traction characteristics, which can either represent the performance of the locomotive or rolling stock, or can be converted into a relationship between the torque and speed of the traction motor through the relationship between the dynamic wheel diameter and the ratio of the vehicle's wheels.
The traction motor is the main motor that drives the vehicle's dynamic wheel axle, and is used for vehicle acceleration and braking. The stator winding of the traction motor is connected to a three-phase alternating current, which generates a rotating magnetic field in the stator space. The rotor winding in the rotating magnetic field will produce an induction motor and induction current, so that the rotor is subjected to the action of electromagnetic force and rotation.
Classification of AC traction motors and their respective characteristics
AC traction motors in the rated frequency and rated voltage under the conditions of constant, the natural operating characteristics of the given motor speed n, electromagnetic torque T, stator power factor cos φ 1 and the output power of the relationship between changes in P2, and the natural mechanical characteristics are The natural mechanical characteristic is the changing relationship between the motor and the rotational speed and electromagnetic torque. Commonly used AC traction motors have the following categories:
1, single-phase series-excited commutator motor
Input voltage is a single-phase, low-frequency alternating current (AC), usually only series-excited, and the natural operating characteristics of its direct (pulse) current series-excited motor is basically the same. It has more poles, plus the commutation problem is not perfect enough to solve, only some European countries in the low-frequency traction grid under the use.
2, three-phase asynchronous motor
(1) speed characteristics n = f (P2). In the speed range of stable operation, when P2 increases, the electromagnetic power Pem and rotor winding copper loss PCu2 also increases, and PCu2 than Pem increases slightly faster, that is, the rate of rotation s = PCu2 / Pem slightly increased. Therefore, the speed characteristics for a slight decrease in the approximate straight line, which indicates that the speed characteristics of the asynchronous motor is a hard characteristic.
(2) Torque characteristics T = f (P2). By T = CTΦI2 = T0 + P2 / Ω can be seen, three-phase asynchronous motor and direct (pulsating) current he excitation motor, torque characteristics for the upward trend of the approximate straight line.
(3) stator power factor characteristics cosφ1 = f (P2). No-load stator current is mainly the excitation component, so no-load is very low. As P2 increases, the rotor current's . . active component grows, the corresponding stator current active component also grows, and cosφ1 rises quickly. After P2 is increased to the rated load, the rotor leakage reactance sX02 increases due to the significant increase in the slew rate s. The reactive component of the relative stator current also increases, and cosφ1 decreases gradually instead. Therefore, the stator power factor characteristic is curved line.
(4) Mechanical characteristics n = f (T). In the range of stable operation, when T increases, the active component of the rotor current I2cosφ2 increases, indicating a slight increase in the rate of rotation s, the mechanical characteristics is a slight decrease in the approximate straight line. Thus, the mechanical characteristics of asynchronous motors are hard characteristics.
3, three-phase synchronous motor
(1) speed characteristics n = f (P2) and mechanical characteristics n = f (T). Because the synchronous motor for AC and DC bilateral excitation motor, its speed depends only on the armature current frequency and motor pole pair, and with P2 and T has nothing to do, speed characteristics and mechanical characteristics for the level of absolute hard characteristics.
(2) torque characteristics T = f (P2). By the "motor science" knowledge, electromagnetic power Pem with the increase in output power P2 and increase, due to its rotor synchronization angular velocity Ωr constant, torque characteristics of a straight line.
(3) stator power factor characteristics cosφ1 = f (P2). By the "motor science" knowledge, in the over-excited state of the synchronous motor will draw capacitive current from the power supply, in order to improve the cosφ1. no-load is mainly DC excitation, in the smaller excitation, power factor cosφ1 can be higher than the asynchronous motor. As P2 increases, it will be at larger excitation to make cosφ1 higher.
Figure 11-3 Operating characteristics of commonly used traction motors
(a) three-phase asynchronous motor; (b) three-phase synchronous motor
Figure 11-3 (a), (b) shows the natural operating characteristics of three-phase asynchronous motor and three-phase synchronous motor respectively. It can be seen that the three-phase asynchronous motor than three-phase synchronous motor characteristics have more obvious changes.
What are the advantages of three-phase AC traction motors
The advantages of the technical superiority of AC traction motors: Because AC traction motors do not have the commutator work surface circumferential speed limitations, and therefore can choose a high speed and large ratio, so that the weight of the motor can be significantly reduced to obtain a Larger power per unit weight.
The basic structure of the AC asynchronous traction motor advantages: asynchronous traction motor is mainly composed of two parts: stator and rotor. The stator is usually a shell-less laminated form, the core is equipped with thick pressure plate at both ends, between the pressure plate with a tie rod or steel plate fixed, with welding will be the pressure plate, core and tie rod, etc. welded into a whole.
In order to solve the DC and pulsating current traction motor "steering" problem, some countries have been using thyristors without commutator type traction motor and three-phase AC asynchronous inverter traction motor, and in the test of linear asynchronous motor as the driving force of the magnetic levitation high-speed vehicles.
The thyristor-less commutator traction motor consists of a synchronous motor and a set of thyristor inverters, with thyristors and rotor position detectors replacing the commutator and carbon brush structure of the DC traction motor.
Expanded:
In the use of traction transformer step-down silicon rectifier or high-power thyristor rectifier power supply to the DC series-excited traction motor, the voltage added to the traction motor for the pulsating voltage, so this traction motor is called pulsating current traction motor. High-power pulsating traction motor "commutation" conditions are more difficult.
The traction motor is usually powered by a frequency converter. The function and performance index of the test equipment puts forward high requirements:
1, the test equipment is required to have a wide bandwidth, and in a wide range of frequencies can be obtained within a high degree of measurement accuracy;
2, part of the test fundamental frequency may be lower than 5Hz, the conventional measurement instrumentation can not be stabilized readings;
3, the frequency converter switching frequency is low, harmonic content, and the signal is not strict. content is rich, and the signal is not a strictly periodic signal, Fourier transform, need a longer time window.
To make an accurate and stable measurement of the fundamental RMS value, the premise is that the output of the inverter is a periodic signal (Fourier transform for periodic signals). In practice, due to the low switching frequency of the traction inverter, when the switching frequency is not an integer multiple of the fundamental frequency, the output signal is not a periodic signal.