primary resistance starters
primary resistance starters
(OP)
how do they operate
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
primary resistance starters
|
primary resistance startersprimary resistance starters(OP)
how do they operate
Red Flag SubmittedThank you for helping keep Eng-Tips Forums free from inappropriate posts. Reply To This ThreadPosting in the Eng-Tips forums is a member-only feature.Click Here to join Eng-Tips and talk with other members! |
ResourcesWhat is rapid injection molding? For engineers working with tight product design timelines, rapid injection molding can be a critical tool for prototyping and testing functional models. Download Now
The world has changed considerably since the 1980s, when CAD first started displacing drafting tables. Download Now
Prototyping has always been a critical part of product development. Download Now
As the cloud is increasingly adopted for product development, questions remain as to just how cloud software tools compare to on-premise solutions. Download Now
|
RE: primary resistance starters
1) Appropriate Resistance is introduced in series with each winding to start.
2) After a suitable time delay the resistance are bypssed and the motor reaches full speed.
3) Alternatively the series resitance is gradually reduced (like a reheostat) and finally the full voltage is across the winding.
This way the primary winding current is limited till the full speed is reached and back emf is prodcued.
marvin
RE: primary resistance starters
RE: primary resistance starters
NYedison is correct in his description, but I woulld like to add the following:
1. the voltage across the motor terminals is able to be calculated by ohms law and is a function of the value of the resistance and the motor impedance.
2. As the motor accelerates, it's impedance changes. The intirial power factor is very low and the effective resistance is also low. As the motor acelerates, the impedance gradually increases and the power factor improves.
3. The changing impedance of the motor during aceleration, results in an increasing voltage on the terminals of the motor, giving an increasing torque relative to an constant voltage starter such as an auto transformer starter.
4. The power disipated in the primary resistors during start is very high and is of particular problems for generator starting.
skogsgurra. The single phase control method also introduces a significant twist in the current vectors and a resultant increase in negative sequence currents. Not to be used on higher inertia or frequent starting loads.
Best regards
Mark Empson
http://www.lmphotonics.com