Månadsvis arkiv: juni 2016

Variable Frequency Drive vs. Servo Motor Drive

http://www.fasttobuy.com/Supply-delta-vfd_c421

A VFD (variable frequency drive) is generally used to control a squirrel cage type motor, where both stator and rotor are of a wound type to create the magnetic flux. Servo drives are used to control permanent magnet motors. Permanent magnet motor because they use rare earth magnets in the rotor, create a much higher magnetic flux for their given size. This enables the motor to be able to create more torque in a much smaller rotor and hence motor size. Giving the motor a lower inertia to accelerate and decelerate much more dynamically than that of the asynchronous squirrel cage type motor.
Servo motors are used for getting a constant torque on all the speed ranges. Normal Induction motor torque varies with speed. Servos are normally used with machines for better torque characteristics. Servos are in normally closed loop controlled. Induction motors can be controlled with vfd004el43a in vector & vector less control.

Servos have a higher bandwidth than VSDs as well as may be controlled at a lot much less than 1 rpm. They preserve the optimum present within the windings utilizing an algorithm that calculates utilizing info from a really higher resolution positional feedback device (frequently a resolver) around the back from the motor. Their response occasions are a lot quicker (as they’ve extremely little inertia values) They are able to preserve correct speed and, position if a position loop is supplied by a motion controller, to extremely higher accuracy. VSDs have, at very best, an encoder around the motor and a lot reduce bandwidth

In reality a “servo drive” controls a “servo motor” there are many types of servo motor from dc to ac to brushless dc. A vfd110b43a cannot control a servo motor and a servo drive cannot control a servo motor. Calling a VFD, even with add on boards, as good as a servo drive is comparing apples to oranges. They are not the same, and not meant to be used for the same type of applications. A VFD can substitute for a servo in non position critical applications, but I would challenge anyone who said that their VFD drive was capable on +/- 1 micron positioning in a CNC environment, that is what Servo drives are designed to do, position. You can take a servo to a desired position and hold it there, without a brake.

Generally speaking, If you want to control speed and tork only use a VFD. But if beside that, you want to control accurate position then you need a servo.

0 kommentarer

VFD Influence On Induction Motors

https://www.fasttobuy.com/Supply-vfd_c420

An induction motor feels most comfortable when it is supplied from a pure sine voltage source which mostly is the case with a strong commercial supply grid. In a perfect motor there are no harmonics in the flux and the losses are kept low. When a motor is connected to a VFD it will be supplied with a non-sinusoidal voltage, this signal is more like a chopped square voltage. A square shaped signal contains all orders of harmonics.

As these harmonics will induce additional heat losses that may require the induction motor to be de-rated, a margin between maximum output power and nominal-rated output power is required. The required power margin depends upon the application and the supplied equipment. When in doubt contact the local Flygt engineering office for details.

The performance of the VFDs has improved over the years and is still improving, and the out put signal is looking more and more like an ideal sine wave. This implies that a modern VFD with high switching frequency can run with a low or no power margin whatsoever, while an old one might need a margin of 15%. Unfortunately the extensive work needed to develop VFDs’ ability to reduce losses in the motor and in the VFD, tends to emphasize other problem areas. VFDs with high switching frequency tend to be more aggressive on the stator insulation. A high switching frequency implies short rise time for the pulses which leads to steep voltage transients in the windings. These transients stress the insulation material. Flygt recommends reinforced stator insulation for voltages 500 V and above.
Here Recommend You Delta VFD

The Delta VFD007B21A VFD-B series is a general purpose NEMA 1 drive and offers V/F, Sensorless Vector and Closed Loop Vector control. With its Constant Torque rating and 0-2000Hz output, the VFD-B is designed to handle most conventional drive applications found in the industrial manufacturing industry. The VFD-B series drives are used in many applications including: HVAC, Compressor, Crane Gantry, Elevator, Escalator, Material Handling, Water/Wastewater, and Woodworking to name a few.
Specifications:

Item Number: VFD007B21A
Manufacturer: Delta Products
Item Category: Drives
Subcategory: AC
Series: VFD-B
Nominal Input VAC: 208;240 Volts AC
Input Range VAC: 200 to 240 Volts AC
HP (CT): 1 Horsepower
Amps (CT): 5 Amps
Input Phase: 3
Operator Controls: Keypad Included
Max. Frequency: 400 Hertz
Braking Type: DC Injection;Dynamic Braking
Motor Control-Max Level: Open Loop Vector (Sensorless Vector)
 

Sizing Criteria
The data needed to determine the correct size of a
VFD are:
• Motor kVA rating.
• Nominal voltage
• Rated current
• Ratio max. torque/nom. torque

If the ratio between peak torque and nominal torque, Tp/Tn, is greater than 2.9 it might be necessary to choose a larger VFD. There are basically two reasons why a motor can have a ratio greater than 2.9:

1. The motor has a high magnetisation level
2. The motor has been de-rated.

Running Above Nominal Frequency

Sometimes there is a desire to run the pump at frequencies above the nominal commercial supply frequency in order to reach a duty point which would otherwise be impossible. Doing so calls for extra awareness. The shaft power of a pump will increase with the cube of speed according to the affinity laws. Ten percent over-speed will require 33 % more output power. Roughly speaking the temperature will increase by approx. 80%.

There is however, a limit to what we can squeeze out of the motor at over-speed. Maximum torque of the motor will drop as a function 1/F when running above nominal frequency. This is due to the fact that the vfd015b43a output voltage has reached its full value at nominal frequency and cannot be further increased. The area above nominal frequency is denoted as the field weakening range. The motor will be overloaded and drop out if the VFD can’t support it with a voltage that corresponds to that needed by the torque. In reality the VFDs’ over-current protection will trip after a short while if we try to run the pump too far into the field-weakening range. Running above nominal frequency is not recommended, but if required, use the following guidelines:

• Check rated power. Shaft power will increase to the power of three according to affinity laws.
• Check that the VFD is dimensioned for the load increase. Current is higher than nominal rated current (for nominal frequency) in this case.
• Change “Base frequency” of the vfd110b43a. Base frequency is the frequency where the VFD output voltage is the same as supplied nominal line voltage.

If possible, select a machine designed for a higher frequency. When running a pump designed for 50 Hz operation above nominal speed, select a 60 Hz motor.

NPSH-required increases, according to the affinity laws, when running above nominal frequency. Always check that NPSH-available is greater than NPSH-required in order to avoid cavitation.

0 kommentarer

Stepping Motor Theory

Stepper motors provide a means for precise positioning and speed control without the use of feedback sensors. The basic operation of a stepper motor allows the shaft to move a precise number of degrees each time a pulse of electricity is sent to the motor. Since the shaft of the leadshine dm556 moves only the number of degrees that it was designed for when each pulse is delivered, you can control the pulses that are sent and control the positioning and speed. The rotor of the motor produces torque from the interaction between the magnetic field in the stator and rotor. The strength of the magnetic fields is proportional to the amount of current sent to the stator and the number of turns in the windings.

1

The stepper motor uses the theory of operation for magnets to make the leadshine m752 shaft turn a precise distance when a pulse of electricity is provided. You learned previously that like poles of a magnet repel and unlike poles attract. Figure 11-57 shows a typical cross-sectional view of the rotor and stator of a stepper motor. From this diagram you can see that the stator (stationary winding) has four poles, and the rotor has six poles (three complete magnets). The rotor will require 12 pulses of electricity to move the 12 steps to make one complete revolution. Another way to say this is that the rotor will move precisely 30° for each pulse of electricity that the motor receives. The number of degrees the rotor will turn when a pulse of electricity is delivered to the motor can be calculated by dividing the number of degrees in one revolution of the shaft (360°) by the number of poles (north and south) in the rotor. In this stepper motor 360° is divided by 12 to get 30°.

2

Leadshine 42HS03 2 phase 1.8 degree (200 Steps/Rev) Hybrid Stepper Motor is a famous brand: Leadshine 42HS03, which has a good reputation. It is a 2 phase stepper motor. 2 phase stepper motor has an advantages: high reliability and low heating. Due to the fact that the stepper motor can not be connected to the power supply directly, you need to choose a driver for your stepper motor and download the free driver manual pdf from Aduino or Raspberry pi. It can work with the step angle of 1.8 degree (200 Steps/Rev), which means very high precision.

It allows for the holding torque of 0.47Nm / 4.8kg.cm / 67oz-in, which is one of the main specs of any stepper motor and a simple indication of the “strength” of the motor.You can contact us to get the complete series datasheet ppt/pdf or serach the internet site such as Aduino/Raspberry pi to learn other knowledge like tutoring, or stepper motor schematic.

Using a 1.8 degree, unipolar, 4-phase stepping motor as an example, the following will explain the theory of operation. Referring to Fig. 6-1, the number of poles on the stator is 8 spaced at 45 degree intervals. Each pole face has 5 teeth spaced at 7.2 degree intervals. Each stator pole has a winding as shown in Fig. 6-1.

The hybrid rotor has 2 sets (stacks) of laminations separated by a permanent magnet. Each set of lams has 50 teeth and are offset from each other by 12 tooth pitch. This gives the rotor 50 N and 50 S poles at the rotor O.D.

Fig. 6-3 illustrates the movement of the rotor when the phase sequence is energized.

In step 1, phase A is excited so that the S pole of the rotor is attracted to pole 1,5 of the stator which is now a N pole, and the N pole of the rotor is attracted to pole 3,7 of the stator which is a S pole now. At this pointthere is an angle difference between the rotor and stator teeth of 1/4 pitch (1.8 degrees). For instance, the stator teeth of poles 2,6 and 4,8 are offset 1.8 degrees from the rotor teeth.

In step 2, there is a stable position when a S pole of the rotor is lined up with pole 2,6 of the stator and a N pole of the rotor lines up with pole 4,8 of stator. The rotor has moved 1.8 degrees of rotation from step 1.

The switching of phases per steps 3, 4 etc. produces 1.8 degrees of rotation per step.

A step motor operates on a series of input pulses, each pulse caus-ing the rotor to advance one step. In this time the motor’s rotor must accelerate and then decelerate to a stop. This causes oscilla-tion, overshoot and vibration. There are some speeds at which the motor will not run. This is called its resonant frequency. The objective is to design the system so that no resonant frequencies appear in the operating speed range. This problem can be eliminat- ed by means of using mechanical dampers, external electronics, drive methods and step angle changes.

0 kommentarer