Solid State Starters and Wound Rotor Motors

  • Thread starter Alvaro Rodriguez
  • Start date

Thread Starter

Alvaro Rodriguez

Hello all:

We would like to get feedback on the use of Solid State Starters with Wound Rotor Motors. Is it mandatory to keep Rotor resistors?


Alvaro Rodriguez
Responding to Alvaro Rodriguez' query:

Mandatory.. No! Probable... Yes!

General Comment,
The starting and operational characteristics of a wound rotor (WR) motor and a squirrel-cage (SC) motor are significantly different. Using VSD to
turn a WR motor into one having the performance of the simpler SC motor could be troublesome. WR motors fulfill a need... variable speed, or
relatively high starting torque with low starting current, or both. Standard SC motors can not readily meet the performance or WR motors.
However, I don't mean to imply that it can't be done.

You have to start with the question, "What are the reasons for the existing WR application?"

a) To satisfy starting duty constraints. Must driven machinery be protected against rapid acceleration? Does the electrical supply have

b) To meet a variable speed requirement. Is a wide-range of speed control required? A few of the VSD failures I have investigated could have been done more simply and economically with two-speed motors.

c) A combination of both.

Don't reinvent the wheel. I am of the old school. Ask someone who has done it... (got a job once based on that reply) but for a similar
installation with like characteristics. Toward that end I am sure that members of the List can provide you with a variety of answers. Give
clear, meaningful technical information regarding your installation. Be very specific as to your goal(s).

Also contact VSD manufacturers for their opinion regarding both the technical and economic merits of your requirements. Be wary of tradeoffs
between hardware and software. When forced to select, I always chose the former.

Phil Corso, PE
Trip-A-Larm Corp
(Deerfield Beach, FL)