Sawmills and lumber mills take freshly cut logs and process them into construction grade wood of all shapes and sizes. The process of turning a log into a usable piece of lumber has more or less stayed the same; the largest change to the manufacturing process is that it has become largely automated. In order to accomplish the advances in industrial automation, leading edge processors are incorporating variable frequency drives.
The metric system of units was introduced for the first time in 1793 during the French Revolution and is used even today in almost all countries worldwide. The metric round plug connectors are also based on this system of units and are a known standard in raw industrial applications.
Variable speed drives, due to their operating principle, produce a series of unwanted secondary effects, such as: motor winding isolation stress, bearing stress, acoustic switching noise in the motor and electromagnetic interference. In most applications these effects are at an acceptable level – but in some cases these effects need to be mitigated.
Electromagnetic interference (EMI) is the degradation of the performance of equipment caused by electromagnetic disturbance. An example of EMI, is the noise on a microphone, if there is a cell phone next to it doing a handshake with a communication tower to process a call. In this example the cell phone is the source of the interference and the microphone is the victim equipment.
Potential ways to save energy can be found in almost all sectors, like building services, conveyor belt systems or chemical processes. The life cycle costs of an application can be roughly divided into four parts: the initial investment cost, the cost for the operation and maintenance of the application, the cost of the energy required by the application and the disposal cost at the end of the life cycle of the application.
Electric motors account about 50% of global electrical energy consumption *). In Industrial applications the ratio is even higher. Depending on the region and the industrial area, 65-75% of electrical energy in industry is used for electric motors. Therefore, electrical drive technology holds a great deal of potential for reducing the worldwide energy consumption.
Machines can create potential or kinetic energy which we want to remove from the machine. The dynamic characteristics of some loads require 4-quadrant operation. A reduction in the stator frequency (and voltage) by the AC drive allows the motor to act as a generator and convert mechanical energy into electrical energy. Motors connected directly to the mains deliver the braking energy straight back to the mains.
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The major technical characteristics of a motor are found on its nameplate. The information shown is very relevant for the electrical installer because values for voltage, frequency and full load current are given, but important information for the mechanical design is missing and can be found in the datasheet, catalogue, or by direct contact to the motor manufacturer.
Read more: Facts Worth Knowing about AC Drives - Star and...
A general overview of the standard current control principles for Danfoss AC drives is illustrated in Fig. 3.26 Basic principles of current standard AC drive from Danfoss. The PWM switching patterns are calculated for the inverter using the selected control algorithm.
Read more: Facts Worth Knowing about AC Drives - AC Drives...
The inverter is the last of the main elements making up the AC drive. The inverter processes represent the final stage in terms of generating the output voltage and frequency. When the motor is connected directly to the mains, the ideal operating conditions apply at the rated operating point.
The AC drive guarantees good operating conditions throughout the whole speed range by adapting the output voltage to the load conditions. It is thus possible to maintain the magnetization of the motor at the optimal value.
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