can we replace any slip ring motor with an induction motor ?
There it's a 55 HP slip ring motor , i have to replace it , so can i replace it , what capacity in HP the induction motor is required & of how many poles ?
if you want to replace an existing slip ring motor connected to a load by a squirrel cage motor , the answer is 'no'.
remember slip ring motor is an induction motor.
slip ring motor has a different characteristics compared to squirrel motor at start.
again , i assume that when you say 'simple induction motor' it is sq,cage type.
By asking the same question more generally, it becomes even more unlikely to get a reasonable answer.
Referring to your original question: If the specific torque characteristic (or another property) of the slip ring motor is required for the application, you can't replace it by a different motor without this feature. Or you have to find a different way to provide it, ultimately use a VFD as starter.
Slip-ring motors with resistor starter have been a standard solution to achieve a kind of soft start, when either reduction of start motor current or torque is required, used for 50 years or so. You have most likely difficulties to get a slip-ring motor replaced when it can't be no longer reworked. Using a standard induction motor together with a VFD is one option to achieve the required starter operation (of course with better performance and additional features).
If soft start is all thats required, you can also get soft starters that come in contactor cases. A lot cheaper than VVVF and simpler to install. Existing contactor coil wires connect directly to the soft-starter and thats it. Auxiliary contacts many need to be implemtned with an extra auxiliary control relay
Yes, an industry standard soft starting device should be considered. It can work as a sufficient replacement for a slip-ring motor + resistors starter in many cases, at a very attractive price.