Industrial Yaskawa 200-230V Servo Drive SERVOPACK 750W CNC/ROUTER SGDA-08AP

 

 

 

 

 

 

When a current-carrying conductor is placed in a magnetic Weld, it experiences a force. Experiment shows that the magnitude of the force depends directly on the current in the wire, and the strength of the magnetic Weld, and that the force is greatest when the magnetic Weld is perpendicular to the
conductor.

 

In the set-up shown in Figure 1.1, the source of the magnetic Weld is a bar magnet, which produces a magnetic Weld as shown in Figure 1.2.
The notion of a ‘magnetic Weld’ surrounding a magnet is an abstract idea that helps us to come to grips with the mysterious phenomenon o fNSNSNSNSFigure 1.2 Magnetic Xux lines produced by a permanent magnet

 

Electric Motors 3
magnetism: it not only provides us with a convenient pictorial way ofpicturing the directional eVects, but it also allows us to quantify the ‘strength’ of the magnetism and hence permits us to predict the various eVects produced by it

 

 

 

 

 

 

 

Nearly all motors exploit the force which is exerted on a currentcarrying conductor placed in a magnetic Weld. The force can be demonstrated by placing a bar magnet near a wire carrying current (Figure 1.1), but anyone trying the experiment will probably be disappointed to discover how feeble the force is, and will doubtless be left wondering how such an unpromising eVect can be used to make eVective motors.

 

 

We will see that in order to make the most of the mechanism, we need to arrange a very strong magnetic Weld, and make it interact with manyconductors, each carrying as much current as possible. We will also see later that although the magnetic Weld (or ‘excitation’) is essential to the working of the motor, it acts only as a catalyst, and all of the mechanical output power comes from the electrical supply to the conductors on which the force is developed. It will emerge later that in some motors the parts of the machine responsible for the excitation and for the energy converting functions are distinct and self-evident. In the d.c. motor, for example, the excitation is provided either by permanent magnets or by Weld coils wrapped around clearly deWned projecting Weld poles on the stationary part, while the conductors on which force is developed are on the rotor and supplied with current via sliding brushes. In many motors,
however, there is no such clear-cut physical distinction between the ‘excitation’ and the ‘energy-converting’ parts of the machine, and a single stationary winding serves both purposes. Nevertheless, we will
Wnd that identifying and separating the excitation and energy-converting functions is always helpful in understanding how motors of all types operate.

 

 

Returning to the matter of force on a single conductor, we will Wrst look at what determines the magnitude and direction of the force,NS Force

Current in conductor
Figure 1.1 Mechanical force produced on a current-carrying wire in a magnetic Weld 2 Electric Motors and Drives before turning to ways in which the mechanism is exploited to produce rotation. The concept of the magnetic circuit will have to be explored, since this is central to understanding why motors have the shapes they do. A brief introduction to magnetic Weld, magnetic Xux, and Xux density is included before that for those who are not familiar with the ideas involved

 

 

 

 

How do you size a VFD drive for an application and feel confident it's going to work? First, you must understand the requirements of the load. It helps also if you understand the difference between horsepower and torque. As electrical people, we tend to think of loads in horsepower ratings instead of torque ratings. When was the last time you sized something based on torque?

Thus, both torque and horsepower must be carefully examined.
Torque. Torque is an applied force that tends to produce rotation and is measured in lb-ft or lb-in.
All loads have a torque requirement that must be met by the motor. The purpose of the motor is
to develop enough torque to meet the requirements of the load.

 

Actually, torque can be thought of as "OOUMPH". The motor has to develop enough "OOUMPH"
to get the load moving and keep it moving under all the conditions that may apply.
Horsepower. Horsepower (hp) is the time rate at which work is being done. One hp is the force
required to lift 33,000 lbs 1 ft in 1 min. If you want to get the work done in less time, get yourself
more horses!
Here are some basic equations that will help you understand the relationship between hp, torque,
and speed.
hp = (Torque x Speed)/5250 (eq. 1)
Torque = (hp x 5250)/Speed (eq. 2)
As an example, a 1-hp motor operating at 1800 rpm will develop 2.92 lb-ft of torque.

 

 

Know your load torque requirements Every load has distinct torque requirements that vary with the load's operation; these torques must be supplied by the motor via the VFD. You should have a clear understanding of these torques.
* Break-away torque: torque required to start a load in motion (typically greater than the torque required to maintain motion).
* Accelerating torque: torque required to bring the load to operating speed within a given time.
* Running torque: torque required to keep the load moving at all speeds.
* Peak torque: occasional peak torque required by the load, such as a load being dropped on a conveyor.
* Holding torque: torque required by the motor when operating as a brake, such as down hill loads and high inertia machines.

 

 

 

 

The dotted lines in Figure 1.2 are referred to as magnetic Xux lines, or simply Xux lines. They indicate the direction along which iron Wlings (or small steel pins) would align themselves when placed in the Weld of the bar magnet. Steel pins have no initial magnetic Weld of their own, so there is no reason why one end or the other of the pins should point to a particular pole of the bar magnet.

 

However, when we put a compass needle (which is itself a permanent magnet) in the Weld we Wnd that it aligns itself as shown in Figure 1.2. In the upper half of the Wgure, the S end of the diamond-shaped compass settles closest to the N pole of the magnet, while in the lower half of the Wgure, the N end of the compass seeks the S of the magnet. This immediately suggests that there is a direction associated with the lines of Xux, as shown by the arrows on the Xux lines, which conventionally are taken as positively directed from the N to the S pole of the barmagnet.