6 types of 3 phase motor starters

OK, so here is the follow up question. Why would you choose one type over the other? One poster indicates that magnetic amplifiers are pretty much obsolete, why?

Now that my curiousity is peaked I'm going to have to look for a reference...

Sparkstation---

My hat is off to you

Thank you so much for that elusive bit of knowledge!

You know the net is a great place in general for info but when it comes right down to getting the right answer for a specific question---well you just can't beat the power of the people in these forums.

Hello quest, thank you for fast feedback response.

You're very welcome.

Learn much, help others = a good motto.....

There are two main types of induction motors a) Cage b)Wound rotor also known as slip ring motor.

For cage Starters available are Direct on Line (DOL), Star delta, Auto Transformer, resistance starter, Electronic Soft starter.

For slip ring type we have stator rotor starters wher the stator is DOL and rotor through a resistance which is 100% at stand still and gradually cut down to enable motor to accelerate.Rotor resistance can be liquid type or resistance in steps made of CI, Punched steel plates etc.

Thanks nesubra for that extra clarification--- that will go down in my notes

I wouldn't put Magnetic Amplifiers in the "most common" category. I haven't seen one used in 25 years and as far as I know there is only one company left in the world who is making them (for motor starting).

I would say that Part Winding motor starters are much much more common, at least in the US.

One could also argue that VFDs could fall into that category; they are used to start 3 phase motors after all, albeit also to change speed.

Point well taken JRaef,,,,

Thanks for the update

Three phase motors do not need starters. That's what's so neat about three-phase power! Single phase motors need starters because they don't know which way to go when the power is applied. Oh, you were just trying to catch us with this trick question, weren't you -- you devil! --jer

???

ALL motors need starters. How else would you turn them on or off and protect them?

You are maybe referring to Starting Capacitors? They are a completely different thing (and by the way, not ALL 1 phase motor designs need them).

The Motor Starters discussed here are used as " Power Switching device " which switches on Power to the motor. It is not the rotating magnetic force that provide the starting torque. They are devices that simply switches on Power to the motor.

1. Manually operated Motor Starters are used for starting fractional HP squirrel cage induction motors.

2.Direct on Line (DOL) starters are used for switching on( Starting) small capacity motors where starting current is not large. In few cases Large motors are also started with DOL starters where high starting current is not detrimental to the system.

3.In case of larger size Squirrel cage Induction motors auto transformer were used for starting where reduced voltage is supplied initially for starting and later full voltage is applied.These have become more or less redundant.

4. The later version is manual or Automatic star delta starters used for larger motors for starting where both ends of the windings are brought out and externally star connected while starting and later switched over to delta connection to limit starting current.

5.Resistance Starters are used for slip ring Induction motors for starting.In this case Resistance is connected to the rotor winding at initial starting and when the speed pick up they are manually or automatically reduced and finally rotor windings are short circuited when the motor picks up rated speed.

6.The Soft starters are the latest introduction with electronic voltage regulation for starting.They are energy saving starters

7. Magnetic Amplifiers are used for switching of SMPS ( Switch mode Power systems) They are not known to be used for motor starting purpose.

"7. Magnetic Amplifiers are used for switching of SMPS ( Switch mode Power systems) They are not known to be used for motor starting purpose."

Hello V.I.Abraham, and others,

Magnetic Amplifiers are sometimes still used for starting motors of 40MVA and above - the application of the motor was generally to be used, (with varied excitation), as a Synchronous Power Faction Correction Capacitor, used at a substation where supply lines exceeded 100 miles in length.

Very efficient in their day, many are still in use, and I saw my first one in 1962, helping to complete the installation of one, back in the days when the thyratron, (Who remembers the thyratron), was still around.

These days because more efficient methods are used, it would be rare to see one, except in the above specific type of installation.

To save me typing it all out here is some information for those interested:

[quote]

http://www.lmpforum.com/inforum/index.php?showtopic=257&view=findpost&p=693

Hereinafter is further information received from the manufacturer regarding the flux compensated magnetic amplifier (FCMA) soft starter. FCMA works on the principle of unsaturated core in the working zone, accordingly it does not generate harmonics, which is an advantage compared to the SCR soft starters.

FCMA is connected in series with the motor to provide stepless reduced voltage starter to ensure a constant low starting current with incremental voltage and torque to the motor to achieve smooth acceleration of the drive.

FCMA consists of main winding and compensating winding connected in phase opposition, so that the net flux in the core is difference between the main winding flux and the compensating winding flux.

The line current is limited and the motor voltage is reduced due to the impedance of FCMA.

As the motor speed increases, the compensating flux increases due to the counter emf feedback keeping the motor current constant, thus reducing the net flux and hence the impedance of the FCMA.

Due to the smooth decrease in FCMA impedance, the voltage across the motor increases in a gradual speed dependant ramp from the starting value (50-60%) to run value (94-98%). The increasing in motor voltage increases the motor torque to meet the load demand.

Then a bypass contactor closes to ensure full voltage running of the motor.[/quote]

So there is the distinct advantage of using the Magnetic Amplifier type of Motor Starter, refer to the absence of harmonic generation.

If you have ever seen a rotatable mass of some 40+ tons, go from standstill to around 1,000RPM in a few seconds, without "dipping the lights" you would agree that it was an interesting experience.

Kind Regards.....

Spark Station : Thank you for the information provided regarding "Flux Compensated Magnetic Amplifier " I wiithdraw my coments annd modify as "They are also used for Motor starting ".