SWITCHED RELUCTANCE MOTOR APPLICATIONS
Switched Reluctance Motors and Drives can provide an effective alternative to induction motors in many situations where the operating conditions do not suit them. Disadvantages of these conventional induction motor based systems include:
- Induction motors with direct-on-line starting, draw very high starting currents especially where the initial torque is high
- Induction motors with soft starting have limited torque available to start loads
- Induction motors with variable frequency drives (VFD) are less efficient where there is regular acceleration , deceleration, stopping and reversal
The SRD is well suited to these situations, providing many advantages over the conventional approaches.
Typical applications include:
Textile machinery including: rapier looms, towel looms, etc.
The switched reluctance motor features a low starting current and high torque, with a fast-dynamic response. It can deliver variable speed weaving and other enhanced weaving processes
The starting torque of the SMR for textile machine could be up to 5 times the rated torque. It has a very fast start time; under load the SMR can accelerate from standstill to rated speed within 200ms, making it particularly suitable for textile machines. The spindle motor is designed with a direct drive and the motor can reach the set speed within a single rotation of its spindle. It is not ideal to use fan-cooling in the textile industrial, as the air duct can become blocked by fluff in the atmosphere. To avoid this, the SRM has an external heat exchanger/radiator for cooling.
• The SRM driving system is designed so that the motor is connected directly to the main spindle. There is no need for a clutch, reducing the need for maintenance
• An advanced algorithm is applied in the control system. With the help of this, there is no need for the start and stop marks in the fabric. Longitude finding and backward running of the machine is readily achieved and is realised through the control system.
• The control of different types of textile machine is facilitated by the comprehensive interfaces on the control system.
• With fast dynamic response, it is especially suitable for enhanced weaving technologies, such as variable speed weaving etc.
• The SRM can save energy through its high system-efficiency, facilitated by its direct transmission.
One of the many textile looms utilising a Kehui switched reluctance motor
Including: vertical pumps, beam pumps, well testing machinery
Many oil fields are still using beam pumping units, otherwise known as Nodding Donkeys. Using these, electricity costs can account for more than 25% of the cost of oil production, and the stroke adjustment is not optimal. Due to increasing cost and lower revenue, reducing energy consumption is a high priority, so an energy efficient pumping unit can be very beneficial.
The switched reluctance motor speed control system can facilitate a long stroke pumping unit. The motor directly drives the oil rod moving it up and down by using its ability to readily reverse its direction, simplifying the transmission. The overall efficiency is greatly improved compared to the original pumping unit. This includes a maintenance-free motor, ideal for the harsh environment in many oil fields and which is simple to commission.
- SRM is suitable for frequently direction changing. This removes the need for traditional reversing mechanisms, which greatly reduces the need for maintenance
- The efficiency is high across a wide range of speeds. The energy saving is substantial compared to beam pumping and well-testing machine which operate with continually varying load. This is particularly important at low speeds, where the motor produces less heat with no need for external cooling.
- The starting and overloading torque can be more than twice the rated torque. The pumping rod is moved directly by the motor, with no need for a counterweight as with a traditional beam pump or well test machine.
- Wide speed adjustment range and allowing the stroke frequency to be adjusted with a speed ratio of up to 50:1.
- Smooth direction changing with less mechanical impact and shake
- The power-factor of the SRM driving system is approaching 1 and its low starting current, the system has less effect on the power grid.
- The flexible control system interfaces are connected through digital and analogue signal cards, a PLC, touchscreen control and wireless communications making it readily expandable
- The simple structure of the SRM ensures its long-term reliability which is unaffected by frequently direction changing.
- Easy to commission, with low-maintenance, the SRM is ideal for harsh environments
The SRM is suitable for all types of mechanical presses, including screw presses.
The electric screw press is a major challenge for motor drive technology. It is required to manage heavy loads, frequent starts, rapid braking and impact resistance The switched reluctance motor has a high starting torque coupled with a low starting current and can be frequently reversed, while providing the required fast braking. The rotor has no coil or permanent magnet and is immune to the load’s shock and vibration. Additionally, there is a direct drive which makes gear chains and clutches unnecessary, therefore increasing the efficiency of the system. The control system can be readily interfaced with a safety grating to help to ensure safe operation.
The energy usage, the force delivered and frequency of the press operations are all controlled by the controller programme, which is managing the motor speed and the frequency of its starting and stopping. As the energy and force of the press can be closely controlled, the press can produce products with a high level of accuracy.
The system is highly automated, reducing the need for operator interaction.
- There is no clutch, friction belt, transverse axles or gears so the maintenance cost is greatly reduced and the efficiency improves reducing energy costs. Furthermore, the absence of dust-producing friction belt drives, improves the working environment
- The starting current is only 30% of the rated current even though the starting torque reaches 150%
of the rated torque.
- Dual-braking by the motor and the brake results in a fast emergency response time. Safety is further
enhanced by the interfacing of the safety grating
- The simple structure and the absence of a coil or permanent magnet on the rotor lead to the
mechanical strength being very high. The loss of one phase, running under-power or sudden
stopping of the motor, will not lead to it being damaged.
4. Mining machinery
Including: shearers, conveyors, winches, boring machines, ball mills, coal crushers
Switched reluctance motors are especially suitable for a variety of coal mining equipment, such as cutters, conveyors and coal ploughs. This type of motor provides a low starting current and a high torque (30% of rated current gives starting torque up to 150%). The simple winding-free rotor is ideal for high speeds and its mechanical strength is resistant to impacts, The stator has no overlapping windings, making short circuits unlikely.
5. Electric Vehicles
The low starting current, quick acceleration and extremely efficient direct drive associated with the switched reluctance motor make it ideal for electric vehicles as it minimizes the load on the battery and extends the driving range from a single battery charge. Its ability to cope with frequent starting, stopping and reversal is also beneficial for transport applications.
6. Miscellaneous Applications
- Machine tools: planers, vertical lathes, drilling machines
- General machinery: fans, pumps, compressors
- Food mixing machinery
- Lifting machines: lifts, winches, conveyors
- Power generation equipment: wind turbine rotor blade load control
- Plastic manufacturing: extrusion machinery, injection molding machines
- Paper mill machinery
- Metal rolling mill
- Coil winding and unwinding machinery