Learn how to select a suitable frequency converter for the normal operation of machinery and equipment electrical control system is essential. When choosing a frequency converter, you should attention to the load torque characteristics, speed range, static speed precision, starting torque requirements and use of the environment, and then decide which frequency converter to use. The so-called proper use is to achieve the best cost-effective applications under actual production requirements and the using occasion.
I. Choose appropriate control mode of frequency converter according to load characteristic
There are more types of frequency converter on the market, and the functions are becoming stronger. So the performance of frequency converter has become the determining factor. In addition to the quality of manufacturing, the control is also very important for frequency converter.
II. Choose protective structure of frequency converter according to the installation environment
Frequency converter protective structure should adapt to its installed environment. It is necessary to consider the environmental temperature, humidity, dust, pH, corrosive gases and other factors, which could make a different in frequency converter long-term, safe and reliable operation. Most frequency converter manufacturers provide the following common protective structure for users to choose:
- Open type: It protects the body from touching the live parts inside the frequency converter. This kind of frequency converter is suitable for installation in a cabinet or electrical room screens, trays, shelves, especially when using multiple frequency converters. But, it requires a higher installation environment.
- Enclosed type: This type of frequency converter has protective structure housing, and it can be wall-mounted in a building. It is suitable for most indoor installations.
- Sealed type: It is suitable for industrial fields with worse environment.
- Hermetic type: It has dust-proof, water-resistant protective structure. This kind of frequency converter is for poor industrial site with water washout, dust and certain corrosive gas.
III. Choose the frequency converter according to load torque characteristics of mechanical equipment
In practice, people produce mechanical torque characteristics depending on the load, divided into three types: constant torque load, constant power load and fluid class load.
Constant torque load
In this type of load, speed and load torque TL independent of any speed n, TL always remains constant or substantially constant, with the increase of the load power load and linear speed increase. Conveyor feed mechanism mixer, extruder and mechanical equipment, such as friction and class load cranes, hoists, elevators and other gravity loads, all belong to constant torque load.
When the frequency converter constant load torque, the output torque at low speeds should be large enough and have enough overloads. If you need a long time low speed constant operating, it should be considered a standard cage asynchronous motor cooling capacity to avoid the motor over-temperature.
Constant power load
This kind of load torque TL is characterized by demand and generally inversely proportional to the rotational speed n, but that is the product of power but remains approximately constant. Metal cutting machine tool spindle and rolling mill, paper machine, film production line winding machine, uncoiler, etc., are constant power load.
Constant power load should be on the terms of the speed range. When the speed is low, by limiting the mechanical strength, TL cannot grow indefinitely, into the nature of constant torque at low speed. Constant power load and constant torque region has a great influence on the selection of the drive program. When the motor speed constant flux, the maximum allowable output torque constant, is constant torque speed; while in weak magnetic speed, the maximum allowable output torque and speed is inversely proportional to belong to constant power speed. If constant torque and constant power range of constant torque motor and constant power speed range is consistent with the load, the so-called “match”, the capacity and the capacity of the motor frequency converter are minimized.
It’s proportional to the square of the load torque and speed of this kind of power and speed is proportional to the cube. All kinds of fans, pumps and oil pumps, are typical of the fluid class load.
Fluid type load is controlled by frequency converter to adjust the amount of wind capacity and water flow, which can greatly save energy. Since the fluid class load is proportional to the third power demand growth at high speed too fast, the speed of the load side, it should not make such a load over frequency operation.