Release time：2018-07-23 Browse times :
Variable pole logarithmic speed regulation
This speed regulation method uses changing the wiring of the stator winding to change the number of stator poles of the cage motor to achieve speed regulation. Its characteristics are as follows:
1. Has relatively hard mechanical properties and good stability;
2. No slip loss, high efficiency;
3. Simple wiring, easy control, and low price;
4. Gradual speed regulation, with large step differences, cannot achieve smooth speed regulation;
5. It can be used in conjunction with pressure regulation, speed control, and electromagnetic differential clutch to achieve smooth speed regulation characteristics with high efficiency.
This method is applicable to production machinery that does not require stepless speed regulation, such as metal cutting machines, elevators, lifting equipment, fans, water pumps, etc.
Frequency Control
Variable frequency speed regulation is a method of adjusting the synchronous speed of a motor by changing the frequency of its stator power supply. The main equipment of the variable frequency speed control system is the frequency converter that provides variable frequency power. The frequency converter can be divided into two categories: AC-DC-AC frequency converter and AC-AC frequency converter. Most domestic users use AC-DC-AC frequency converters. Its characteristics:
1. High efficiency, no additional losses during the speed regulation process;
2. Widely applicable and suitable for cage type asynchronous motors;
3. Large speed range, hard characteristics, and high precision;
4. The technology is complex, the cost is high, and maintenance and repair are difficult.
5. This method is suitable for situations that require high precision and good speed regulation performance.
Cascade speed regulation
Cascade speed regulation refers to the use of an adjustable additional potential in the rotor circuit of a wound motor to change the motor's slip and achieve speed regulation. Most of the slip power is absorbed by the additional potential introduced in series, and then used to generate additional devices to return the absorbed slip power to the grid or convert it into energy for utilization. According to the absorption and utilization method of slip power, cascade speed regulation can be divided into motor cascade speed regulation, mechanical cascade speed regulation, and thyristor cascade speed regulation. Thyristor cascade speed regulation is often used, and its characteristics are:
1. The slip loss during the speed regulation process can be fed back to the power grid or production machinery, with high efficiency;
2. The device capacity is proportional to the speed regulation range, which saves investment and is suitable for production machinery with a speed regulation range of 70% -90% of the rated speed;
3. When the speed control device fails, it can be switched to full speed operation to avoid shutdown;
4. The power factor of thyristor cascade speed regulation is low, and harmonic effects are significant.
5. This method is suitable for use on fans, water pumps, steel mills, mine hoists, and extruders.
Wire wound speed regulation
The rotor of a wound asynchronous motor is connected in series with an additional resistor, which increases the slip rate of the motor and allows it to operate at lower speeds. The larger the resistance connected in series, the lower the speed of the motor. This method has simple equipment and easy control, but the slip power is consumed in the form of heat on the resistor. It belongs to graded speed regulation and has relatively soft mechanical characteristics.
Voltage regulation and speed regulation
When changing the stator voltage of the motor, a set of different mechanical characteristic curves can be obtained, thereby obtaining different speeds. Due to the fact that the torque of an electric motor is proportional to the square of the voltage, the maximum torque decreases significantly, and its speed range is relatively small, making it difficult to apply general cage type motors. In order to expand the speed regulation range, cage type motors with high rotor resistance values should be used for voltage regulation and speed regulation, such as torque motors specifically designed for voltage regulation and speed regulation, or frequency sensitive resistors should be connected in series with wound motors. In order to expand the stable operating range, feedback control should be used to achieve automatic speed adjustment when the speed regulation is above 2:1.
The main device for voltage regulation and speed control is a power supply that can provide voltage changes. Common voltage regulation methods include series saturation reactors, autotransformers, and thyristor voltage regulation. The thyristor voltage regulation method is the best. Characteristics of voltage and speed regulation:
1. The voltage and speed regulation circuit is simple and easy to achieve automatic control;
2. During the voltage regulation process, the differential power is consumed in the form of heat in the rotor resistance, resulting in low efficiency.
3. Voltage regulation and speed control are generally applicable to production machinery below 100KW.
electromagnetic speed regulation
The electromagnetic speed regulating motor consists of a cage motor, an electromagnetic slip clutch, and a DC excitation power supply (controller). The DC excitation power supply has a small power and is usually composed of single-phase half wave or full wave thyristor rectifiers. Changing the conduction angle of the thyristor can alter the magnitude of the excitation current. The electromagnetic differential clutch consists of three parts: armature, magnetic pole, and excitation winding. The armature and the latter have no mechanical connection and can rotate freely. The coaxial connection between the armature and the motor rotor is called the active part, which is driven by the motor; The coupling between the magnetic pole and the load shaft is called the driven part. When both the armature and the magnetic poles are stationary, if the excitation winding is energized with DC, several pairs of N and S poles will be formed along the circumferential surface of the air gap, and their magnetic flux will pass through the armature. When the armature rotates with the dragging motor, due to the relative motion between the armature and the magnetic poles, eddy currents are induced in the armature, which interact with the magnetic flux to generate torque, driving the rotor with magnetic poles to rotate in the same direction, but its speed is always lower than the speed N1 of the armature. This is a slip speed regulation method, and changing the DC excitation current of the slip clutch can change the output torque and speed of the clutch. The speed regulation characteristics of electromagnetic speed regulating motors:
1. The device structure and control circuit are simple, reliable in operation, and easy to maintain;
2. Smooth and stepless speed regulation;
3. No harmonic impact on the power grid;
4. High speed loss and low efficiency.
5. This method is suitable for production machinery with medium to low power, requiring flat sliding and short-term low-speed operation.
Coupling speed regulation
A hydraulic coupling is a type of hydraulic transmission device, generally composed of a pump wheel and a turbine wheel, collectively referred to as a working wheel, placed in a sealed housing. A certain amount of working fluid is filled into the shell. When the pump wheel rotates under the drive of the prime mover, the liquid inside it is pushed by the blades and rotates. Under the action of centrifugal force, it enters the turbine along the outer ring of the pump wheel and gives thrust to the turbine blades in the same direction, driving the production machinery to operate. The power transmission capacity of the hydraulic coupler is consistent with the relative liquid filling amount inside the shell. During the working process, changing the filling rate can change the turbine speed of the coupler, achieving stepless speed regulation. Its characteristics are:
1. The power adaptability range is large, which can meet the needs of different powers ranging from tens of kilowatts to thousands of kilowatts;
2. Simple structure, reliable operation, convenient use and maintenance, and low cost;
3. Small in size, capable of accommodating large;
4. Convenient control and adjustment, easy to achieve automatic control.
5. This method is applicable to the speed regulation of fans and water pumps.
ABB speed regulating motor
Variable frequency speed range: 5-100 Hz stepless speed regulation. Constant torque speed regulation below 50 Hz (60 Hz); Above 50 Hz (60 Hz) is constant power speed regulation.
*By using the voltage boost of the variable frequency device, the motor can ensure its rated torque output at 5 Hz
Do not cause the motor to burn out due to heating.
*At low speeds, the torque is smooth and there is no crawling phenomenon.
*The motor can withstand an overload of 160% of the rated torque for 1 minute
Equipped with variable gear transmission motor (friction wheel)
