Blower Motor Question

CAMotorControls · Oct 11, 2004

I am installing a new motor control panel for a fume collection system. The main fan motor is 200HP and will be started WYE/DELTA. This will be the only WYE/DELTA setup we have. I'm new to this technology, although I understand it's actually quite old. My question is, at what point do you transition from WYE to DELTA? Are you looking for a certain RPM? Current? I notice that the contactors are controlled by a timer. I found tons of info. on how they work, but nowhere that tells when to switch. Is there just a 'rule of thumb' time value depending on the application and load or something? Thanks in advance guys!

Andy

tom_stalcup · Oct 12, 2004

The only reference I've been able to find said to set the timer up to switch over when the motor is up to 90% speed.....
control.com forum
I dug through a few different manuals lying around, and found(like you already said) a ton of information about how they work, how to wire them up, but nothing on when to switch over.
For anyone else running into this stuff for the first time, here is a decent discussion on wye-delta starters.....
ron's forum site

jrwb4gbm · Oct 12, 2004

wye delta timer

I don't know if this is the "correct" way or not.

Here is how I set the time value. I set the timer for a long period of time the first time starting up, while monitoring the current. As soon as the current makes a rapid drop, (near or below 100% nameplate value) I record how long that time period is, then stop the motor. I then adjust the wye-delta changeover timer to that value.

This is only my way, USE AT YOUR OWN RISK !!!

.

JesperMP · Oct 12, 2004

I would do as jrwb4gbm says. But I would add 30% extra time to allow for variations.
Be sure that you have the REAL conditions that the blower will experience when installation is finished.
Fume/dust extraction systems are often adjusted carefully to get the required air volumes at the varying suction points. That means that the load and thus the startup time will vary as well.
After an adjustment to the system, check the startup time again and readjust if needed.

DonsDaMan · Oct 12, 2004

I'm not certain what you're doing with the fumes, but when I've worked with forced draft and induced draft systems, I've found that air temperature also has a great effect on fan loads. Of course, we were blowing the air up 200 foot stacks, as well, so hot air was easier to push.

In addition, I'd try to get the proper gas mixture through the fan, as well. Perhaps the gassy air is lighter (or heavier) than the non-gassy air. These adjustments should be able to be made after initial setup.

Lastly, with Variable Frequency/Adjustable Speed Drives being so cheap, why go through the trouble of a Wye-Delta starter? If this unit stops and starts often, you're going to save money in the long run using a VFD. Any motor that's not disposable (say less than 25 Hp) is a candidate for a VFD, in my opinion.

Tom Jenkins · Oct 12, 2004

The horse may already have left the barn, but if not I agree with Don wholeheartedly. At the very least, Reduced Voltage Solid State Starters (RVSS) are easier on the motor, more flexible, smaller, and not much (if any) more expensive.

CAMotorControls · Oct 12, 2004

Unfortunately, I don't have any say so in this. The Engineer who bought this system claims a drive for this motor is more than twice the price of the WYE/DELTA contactors, and that since this thing runs 24/7 365 days per year, the hard starting effect on the mechanical components is negligible.
By the way, he doesn't know on the switching time either, he says if I don't find a definite answer to just set it to switch 5 seconds after the inrush current calms down.
Thanks for all the involvement, guys. Anybody have any prices on a drive vs. a wye/delta contactor set? We have drives from Reliance, ABB, Lenze, Yaskawa, and SEW now, so standardization is not an idea that has struck their minds yet.

Andy

CT782 · Oct 17, 2004

Andy,

Did you ever find the answer to your question? I am installing a similar application. 150HP Fan motor for a dust collection system started WYE/DELTA. I, too, fruitlessly fought for a drive, or even a soft start, to no avail. I have seen lots of equipment using this somewhat antiquated technology, but have never run across any reference material indicating when to switch. I usually allow the motor to accelerate to speed and the current to stabilize, then add a couple seconds. This would be a good one to hear DickDV's theory on!
Please keep us posted.

Chris

elevmike · Oct 17, 2004

The motor should be switched to Delta when it is a full speed. How long the motor takes to get to full speed greatly depends on the mass of the motor and the load. My advice would be to start the motor on Wye, and use a hand held tach to time how long it takes to make it up to the tagged RPM. If a tach is not available then another option would be to use an analog amp meter. Time how long it takes for the current to stabelize in Wye. My SWAG, is that youll have about 4 or 5 seconds.

However in my expierance, (I havent ever delt with any motors over 75 hp), a soft start is usually NOT anywhere near 2x the cost of a good quality Y-D setup, Overloads, Isolation Contactor, and RPR etc.. With such a large motor I woudnt skimp on controls anyway. We never install Y-D contactor anymore. Only Detla start or Soft starters.

My say..

Mike.

sandeeppatil1980 · Oct 17, 2004

aney

Hi,
you first calculate slip differance rated speep and actual speeb
you have set timer value such that if your motor rated speed is 1440
then what time required to reasched that kind of speed + current drop down time
thanks
sandeep patil

JesperMP · Oct 18, 2004

elevmike said:
The motor should be switched to Delta when it is a full speed. How long the motor takes to get to full speed greatly depends on the mass of the motor and the load. ... My SWAG, is that youll have about 4 or 5 seconds.

I think that 5 seconds is very optimistic. Think that the 'load' that the motor has to accellerate is the motor + impeller + air volume in ducts, chimneys, etc. A throttle element (*) can diminish the load of the air volume, but even with this I experience star-delta changeover times in the region of 30 - 60 seconds for this size fan motors used for dust extraction.

A star-delta starter is perfectly adequite for this type of application. It is simple and cheap. Normally I would advocate an 'eletronic' solution. But not for a start-once-in-a-day application.

*: A throttle element is sometimes used to ease the startup. It simply blocks the air from entering the fan. When changeover to delta is finished the throttle element is automatically opened.

rsdoran · Oct 18, 2004

I am not sure about ALL wye-delta motors but for some there are DONT's

1. Using part winding start the changeover should be in 2 seconds normally.
2. Some motors require the wye-delta change over within 30 seconds.

I prefer an electronic solution but for a 100HP or above motor the cost could be significantly higher than using a wye-delta starter. The cost of buttons etc wouldnt be a factor because in most cases they are or may be used anyway.

Personally I have never thought about it and when motor obtains rated speed and current I did the changeover.

The best bet is contact the motor manufacturer.

DickDV · Oct 18, 2004

At 150 and 200hp, a drive (inverter) is probably 4 to 5 times the cost of an electronic softstarter. So, that's not a real option.

An electronic softstarter, on the other hand, is very close to the same cost as an across-the-line mag starter in those sizes. Surely it would be less expensive than the two stage wye-delta starter. And, an added benefit would be the elimination of the starting inrush as well as the second inrush pulse that occurs when switching from wye to delta. The starting inrush would not be totally eliminated but typically reduced to about 3 times FLA.

On a fan, unless the motor is way oversized for the fan hp, the transition from wye to delta will have to be made under load which is undesireable from an inrush current standpoint. You cannot expect the fan/motor to get up to full speed in the wye configuration alone

elevmike · Oct 18, 2004

As Jesper pointed out, closing the dampers during the start would greatly reduce the starting load on the motor and may allow the motor to reach full speed. Using an aux contact on the Delta contactor could signal the controller to resume normal operatoion and re-open the dampers.

Just a suggestion.... Mike

DonsDaMan · Oct 18, 2004

I'd be extremely cautious with changing the load configuration with dampers.

I'd make sure the suction side ductwork can handle the suction pressure and the pressure side can handle the positive pressure.

I'd be more concerned on the suction side, personally.

Blower Motor Question

CAMotorControls

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tom_stalcup

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jrwb4gbm

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JesperMP

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DonsDaMan

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Tom Jenkins

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CAMotorControls

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CT782

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elevmike

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sandeeppatil1980

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JesperMP

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