Need help in drives & motors

[Nelliyan]

Hi all,

I need some basic information in motors & drives

I tried studying but it confusing me a lot

what is the need for drive in motor operations , why cant the motors run in direct AC supply or DC supply...What is the advantage

The basic many will say to control the speed of motor , if we use voltage regulator by varying the 230 we can reduce speed & viceversa.

Pls give me a direct answer
\
Thanks & Regards,
Nelliyan.G

 

[balash]

the main purpose for drive is to regulate torque and/or speed. V/f regulation is a part of VFD but VFD is os much more, it can regulate current, it has built-in PID, protections aginast overloads, overcurrent, torque control, and many other useful possibility.

direct online start of AC motor, and since most of them are delta connected, draw a starting current up to 9x nominal, and that can be a big stress on power supply, cables, and protection equipment, especially at high current ratings, and where constant start stops are required.

 

[Tom Jenkins]

Variable Frequency Drives (VFDs) provide speed control for a standard induction "squirrel cage" motor. This type of motor is the most economical for a given horsepower, and is simple and reliable. For most other types of control you need a special motor of some sort.

You can't vary the speed of a standard three phase induction motor by varying voltage.

The advantages of drives depend on the load and the application. For many applications energy savings is the main justification for using a VFD instead of across the line operation. For other applications process control is the most important factor. In other cases, as stated above, reducing starting current and stresses is important.

 

[leitmotif]

Prior to Variable Freq Drive - in industry
90% of motors were 3 phase induction. They could run at only one speed - with a few exceptions which also had control issues. They were started DOL and reversed by stopping and then restart. Starting current in general was 4 to 9 times running current.

IF variable speed was needed - in the vast majority - DC motors were used. THe most common used was shunt. Series and compound were also used. Shunt was popular because it had only one field to control and was easy to control on Ward Leonard type drive systems. These varied the armature voltage to control speed and direction. They also controlled dynamic braking to allow for quick motor braking. Shunt field voltage and current was commonly supplied from an independent power supply and generally left alone. In a steel mill the main "blooming mill" drive motor was circa 5,000 HP.
DC equipment was quite labor intensive in that it required a lot of labor to do brush and commutator maintenance, controller maintenance including changing contact tips and voltage dropping resistors.

Nowadays with the VFD the whole picture has changed and many places are changing from DC drive to AC drive.

The reasons in priority - which of course is subject to argument
1. Lowered maintenance
2. Speed control of equipment
3. Lowered starting current
4. Dynamic braking
5. Energy savings when able to drive centrifugal pumps and blowers at reduced speed.

Dan Bentler

 

[DickDV]

It sounds to me like the OP needs to focus on studying how a three phase induction motor works. Only after that is fully understood will VFD technology make any sense.

 

[leitmotif]

It sounds to me like the OP needs to focus on studying how a three phase induction motor works. Only after that is fully understood will VFD technology make any sense.

Fully agree.

Dan Bentler

 

[Kataeb]

hy, where can i find some theory about dc drives? pdf files? thanks

 

[widelto]

Kataeb & Nelliyan.
This is Siemens place for learning.
Go to : http://www.eandm.com/Products/Content/Siemens/Training/Siemens_Courses.aspx

 

[Kataeb]

any other place where i can find general theory files about dc drives?

 

[Kataeb]

dc drive theory files

any other place where i can find general theory files about dc drives?

help !

 

[mdim]

Some essentials here:
http://literature.rockwellautomation.com/idc/groups/literature/documents/at/drive-at001_-en-p.pdf

After reading it, try google