480 V 3phase dual winding motors help 3

[dsull]

I have a client that has 3 such motors. Two manufactored by Siemans-Allis and one motor by Newman electric motors Inc.

I wish to convert these motors from two stage (windings) to a vfd start and control. Is this possible and how would it be done.They motor drive positive displacement blowers.

I can not find the corporate office for either of the motor manufacturers. Does anyone have this information.

 

[rhatcher]

I interested to know the hp and speed of the two ratings. Out of curiosity, I looked at the nameplate of a two winding, two speed motor in our shop. The hp and speeds are 20hp @ 1800rpm and 6.7hp @ 600rpm. This tells me that both windings produce the same torque, which is not surprising as I think this motor is for a winch or something like that. I believe you will find that your motor is constant torque also since a positive dispacement blower is a constant torque device (ie takes the same torque to operate at 600rpm as 1800 rpm). Finally, this tells me that the motor has sufficient cooling for full torque output down to 600rpm.

If you applied a VFD to the 4 pole winding of this motor, you could duplicate the performance of the original two windings at the original speeds as well as operate it at any speed between.

There are two pitfalls to this approach. First, the motor may not be capable of operating at speeds below 600rpm without overheating. Second, the motor will (probably) not be constructed using inverter duty magnet wire or insulation, so it may not last very long on a VFD.

Anyway, this will give you an idea of what factors to consider. If you provide your specific motor data we can see if this applies to you as well.

 

[jbartos]

Suggestion: Depending on the size of the motors, it may be wise to seek a help from manufacturer at first, namely, try
Siemens Energy & Automation Inc., Motors & Drives Div.
3333 Old Milton Pkwy
Alpharetta, GA 30005 USA
Tel: 513-841-3100
Fax: 513-841-3290
Assets: 50M+ ($50,000,000 - 99,999,999)
Activity(ies): Manufacturer
Description: Adjustable Speed Drives & Drive Systems; Static
Excitation Systems.

 

[dsull]

These motors are 75 HP with a service factor 0f 1.15 and are 1775 rpm. The starters are two stage first stage turns the motor blower at a lower speed and then to full speed. A time delay (an agastat triggers the second set of starters)The system is at least 20 years old. I sincerely appreciate your comments.

 

[teco]

dsull :- it appears from the info given that the motors are single speed(4pole) and are part winding start.(motor wound in two sections first part will develop 37hp adding the second part of the winding will develop 75 hp).
if this is the case all you have to do is parallel the windings. the vsd can now be connected across the motor terminals. any drive supplier can assist you from here.
kind regds.

 

[electricpete]

From the arrangement you describe it sounds like one set of windings is used for starting only. One reason for this would be to limit motor rotor heating during starting. (I can't think of any other reason)

I believe this approach would be most common for a large fan with high inertia which creates severe starting duty.

Perhaps in your case it is the high starting torque demanded by the load which makes the starting duty severe from a motor heating standpoint?

 

[rhatcher]

dsull, I have to agree with teco and electric pete that you probably have a single winding motor with a reduced voltage starter. Examples of reduced voltage starters include wye-delta and autotransformer starters. (There are other types as well but these are more commonly encountered in my experience). Usually these are applied to systems where it is desirable to limit the inrush current during starting. This is necessary when the motor is relatively large compared to the size of the distribution system to which it is applied.

So, if this is the case, the question to answer if you want to upgrade the system is:
- do you want to upgrade your starter to a modern design of similar function?
- or -
- do you want to upgrade your system so that it is variable speed?

My guess is that you want a modern starter of similar function. If so, a solid state soft starter will accomplish that at less expense than a VFD. A VFD would only be desirable if you want variable speed operation of the blower.

 

[jbartos]

Suggestions:
1. Do you happen to have model or type numbers, serial numbers, etc. from the nameplates?
2. The motors may also be soft started over y-delta soft starter.

 

[rhatcher]

jbartos, it may be just a matter of terminology, but this is not the first time that you have referred to a wye-delta starter as a 'soft start'. Please note that although a solid state (soft) starter may be known as a reduced voltage starter, a wye-delta starter is not a soft start. To avoid arguing over terminology I will give my definitions and my reason for believing that they are different.

A reduced voltage starter is one that starts the motor with reduced voltage across the windings. The methods of accomplishing this include primary reactor, primary resistor, autotransfomer, part winding, wye-delta, and (of course) solid state starters.

The primary factor that distinguishes a 'soft start' from the other types of reduced voltage starters is the fact that a soft starter offers continuously variable voltage from start to full speed. Specifically, the starter begins at 0V (full frequency) and ramps the voltage up to full value (240V, 480V....) based on user selection of acceleration time. This is done using SCR's.

All other types of reduced voltage starter involve discrete steps in the voltage applied to the windings. In other words, the motor starts in steps beginning at, for example with a autotransformer starter, 65% voltage and 42% torque right away. After a fixed time delay, the starter switches to full voltage and full torque. Two steps...'half speed' and full speed. If you stand next to one starting, you will hear (and see on the ammeter) two distinct steps. It is possible for these types of reduced voltage starter to have more than two steps, but this is not common and is more costly for each step added. However, no matter how many steps you add, the result is that for each step the motor sees an step increase in voltage and as such has an inrush and a torque surge with each step.

A soft starter uses SCR's to ramp the voltage up to full value based on user settings for acceleration. The ramping of the voltage (and torque output) is continuous from 0V to full volts. If you stand next to one of these while starting, you will not notice steps in starting but will see a gradual increase in speed. This is the basis for the name "soft start".

 

[dsull]

There are two 75HP Seimans - Allis Motors
Models No.PE-21
SN 1-5141-lr46473-01 and 1-5141-lr46473-01
Type RGE
Design B
Service Factor 1.15
Frame 365T
460 VAC, 3 phase, 82 amps, 1775 RPM

The other motor is a 75 HP Newman Electric Motor
Model or Frame 4054U/DD3482BB
SN X.4440316
Design Class A
440 VAC 3 phase, 80 amps, 1770 rpm

I believe all three motors have a class F winding

Thanks for you kind assistance Dave Sullivan

 

[rhatcher]

dsull,

Please clarify whether you desire a new controller to functionally replace the old one or do you want to change the method of operation for your sysem fom single speed to variable speed.

 

[dsull]

The desire is to start and control the motor speeds with a VFD. The speed range will be from the max speed to about 1,000 to 1200 rpm.

As a matter of interest the motor speed (blower) will be a function of flow based on a 4 - 20 ma single with lower limits to assure that the system does not go below a minimum speed.

The existing system is just one speed but starts with a twi stage system that I believe is a low voltage system.

Thanks for all the kind assistance this forum is wonderful Dave Sullivan