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Help with VFD with Bypass on two speed motor

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Hoopengarner

Marine/Ocean
Apr 2, 2010
2
I am an electrical contractor and need some help.

We have installed ABB drives on board a ship in three different types of applications, centrifugal pumps, centrifugal fans and vane axial fans. Previously, these loads had two speed starters, would first start in low speed for about 5-8 seconds before switching to the high speed windings. The folks on board the ship are concerned that if the drive failed and we put it into bypass that the motor would have a problem starting from a standstill on the high speed windings. These motors are approximately 15 – 18 years old, but are high quality and in other similar applications have withstood VFD application and run for years.

The most concern seems to be with the Seawater Pump (centrifugal) application where we have the ABB ACH550-UH-125A-4 E-Clipse drive connecting to the ABB pump motor Type HXR 280 SMB 6/8 1190/892 RPM. Theses pumps were previously controlled with a two speed starter, where the low speed would start at 892 RPM on the low speed windings and then switch to high speed if required.

We think that the drive bypass contactors in the ABB can handle this since they are sized for the high speed winding ratings of 59.6 KW. What we are uncertain about is the motor and the existing power cables. We have the option of just connecting the existing low speed windings to the bypass, but the real question is the high speed windings and cables...After all there is less than 300 RPM difference and as I understand things the real load is reached at the high end of the RPM on these loads.

What is the best course of action to determine if we are OK to use the byapss on the high speed windings? Should I be more concerned with the pump application that the fan application?
 
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Bill - I have read that in theory that ratios like 2:3 and 3:4 are possible with dahlander connection but in my 25 years, am yet to come across one.

I once had an interesting case of a 8/4 pole dahlander motor. The original scheme was to start the motor (compressor load) under 8 pole and then changeover to 4 pole. The client wanted me to eliminate the 8 pole operation. So I rearranged the leads at the terminal box and the motor would not start at all. On investigating, I found the stator slot/rotor slot ratio would not allow to start the motor as 4 pole but would allow it start it as 8 pole.

Muthu
 
"Pole Amplitude Modulation" can apparently can achieve 2-speed motors with ratio's other than 2:1

Design of Rotating Electric Machines said:
There is also another method to create windings with two different pole numbers: pole
amplitude modulation (PAM) is a method with which ratios other than 1 : 2 may be found.
PAM is based on the following trigonometric equation:
sin pb? sin pm? = 1/2 [cos (pb ? pm) ? ? cos (pb + pm) ?] . (2.103)
The current linkage is produced as a function of the angle ? running over the perimeter
of the air gap. A phase winding might be realized with a base pole pair number pb and
a modulating pole pair number pm. In practice, this means that if for instance pb = 4 and
pm = 1, the PAM method produces pole pairs 4 ? 1 or 4 + 1. The winding must be created
so that one of the harmonics is damped and the other dominates.
But how it really works is a little beyond me.

=====================================
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Thanks Muthu and Pete;
For the problem at hand, ABB lists quite a few two speed motors specifically for fans. Most are two winding motors. Only a few are shown as Dahlander connections.
A two winding starter is quite simple. It is similar to a reversing starter with two, 3 pole contactors for wye connected motors. 4 pole contactors may be used for delta connected motors to open the delta on the unused winding.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
First of all, thank you all for the terific responses here...I have carefully read and re-read each response. I am new to this type of forum, so forgive me if I am not following expected protocal here.

In my orginal plea for help, I failed to mention that the voltage here is 440V...I also failed to mention that we are using the high speed contactor at the starter panel to power the newly installed VFD. The reason for this was to maintain the orginal safeties, such as emergency shutdown and fire/smoke damper end switches. We have configured the high speed contactor to be energized when the safeties are good. The start/stop functions of the original starter were re-used to to provide a start/stop to the associated new VFD. The bypass was an afterthought and added to the design late in the process.

We made the assumption that the motor's high speed windings would be able to handle a DOL start when the bypass was activated. Since the new VFD/Bypass unit provides for motor and cable protection, the exsiting thermal overload protection(range 80-110Amp-seawater pump example)was jumpered out on the existing high speed contactor....the fused (200Amp-seawater pump example)disconnect at the starter was left intact. (Low speed fuses were 100Amp)

There was also concern about the high speed contactor being able to handle this DOL start.

You have all given me great insight into the issue. Since the ship has redundency in place for each load, whether fan or pump, the odds of the ship employing any one of the bypasses is slim at best.

At this point I am inclined to test the bypass DOL on one the fans and have a fast peak-hold ampmeter setup prior to testing. I will make certain to follow up with the results.

Again, thank you all for your help here!
 
Please don't take offense if you already know this;
You can't just close a bypass breaker across a running VFD as you can on a soft starter.
The VFD must be out of the circuit before the bypass is closed.
You probably knew that, but if you didn't it will save you a lot of money.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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