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STAR Configured Fan Motor for DOAS
3

STAR Configured Fan Motor for DOAS

STAR Configured Fan Motor for DOAS

(OP)
Hi,

Is it allowed to use a DOL starter to run a 3KW STAR(WYE)Configured Fan Motor for Dedicated Outside Air System (DOAS)? What is the technical reason behind if DOL starter is not allowed?

RE: STAR Configured Fan Motor for DOAS

There are lots of reasons. Generally, it's specific to the application. Could be the driven load, source or noise limitations.

RE: STAR Configured Fan Motor for DOAS

How else can you start a wye connected motor other than DOL? (ignoring soft starters and VFD's etc)

If the motor is delta connected with all 6 leads of 3 phases brought out, then wye/delta starter can be used.

Muthu
www.edison.co.in

RE: STAR Configured Fan Motor for DOAS

> What is the technical reason behind if DOL starter is not allowed

I believe the most common reason for prohibiting DOL start would be that it creates an intolerable system voltage dip during DOL start. The utility may impose this requirement.

There are more possibilities as Lionel mentioned. None of them have to do with the motor being wired in wye. As Edison mentioned, wye connection does prevent you from using a common reduced voltage start method (delta-wye), but of course it doesn't prevent dol start.

It's not clear exactly what you're really trying to get at with your questions.




RE: STAR Configured Fan Motor for DOAS

KikoRamos06 (Electrical)(OP)25 Oct 23 08:22
"...#1..Is it allowed to use a DOL starter to run a 3KW STAR(WYE)Configured Fan Motor for Dedicated Outside Air System (DOAS)? ....#2. What is the technical reason behind if DOL starter is not allowed?"
1. All motors irrespective of the wattage rating are manufactured that allow DOL starting, for indoor or outdoor usage. Whether the mechanical load can take the starting torque and whether the outdoor enclosure is suitably for the environment are to be taken in consideration, but does not restrict DOL starting. In most cases, 3kW (considered a very small motor) DOL is the preferred and most economical.
1.1 If reduced voltage starting is imposed by the utility or the power supplier which you have to comply with, a Y configured motor may use resistor/inductor, auto-transformer, soft starter or VFD. All these are possible alternatives, but which are 4-10 times the price of DOL.
2. DOL at 3kW may be not allowed in case:
a) where the supply line is of very small conductor and of long distance.
b) private generators of very small capacity and with small conductors and long distance.
c) very unlikely that the load is unable to take the high starting torque.
2.1 The main reason for the restriction is DOL starting the starting currant is 6-8 times the rated current, which cause voltage drop (I x R) that may affect the system voltage to lowered below the limit or light flickering; that affect all consumers.
Che Kuan Yau (Singapore)

RE: STAR Configured Fan Motor for DOAS

3kW is a small motor, I cannot imagine a reason not to start a 3kW fan DOL. the configuration of the windings inside of the motor is irrelevant to anyone other than the motor manufacturer.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: STAR Configured Fan Motor for DOAS

Besides the soft starter and VFD, there are other ways to start this motor.
It's important to keep in mind that this is a fan motor.
Attached are a few shots from a nearby service center that show a five-step speed control transformer regulator for the fan.
The speed is controlled solely by selecting the output voltage.
Such a regulator can be applied during the fan's startup, for example, starting at 230 V and then reaching the full voltage of 400 V.
This example is a manual regulator, although an automatic version is also possible.
What's interesting is that the speed of the three-phase fan can be altered using two (not three) transformers. These transformers are likely of the autotransformer type.
The main advantage of this method, as opposed to a soft starter and VFD, is that the motor receives a pure sinusoidal voltage.

RE: STAR Configured Fan Motor for DOAS

Respectfully I would class that device as a speed control rather than a reduced current starter.
The only reason for reduced current start in a tiny 3 kW motor is if it is driving an extremely high inertia load such as a centrifuge.
And given such a theoretical high inertia load, the motor would likely not survive long the jump from 50% voltage to full voltage.
I agree with jraef, just start this tiny motor DOL and get on with life.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: STAR Configured Fan Motor for DOAS

In my experience of testing externally driven centrifugal blowers from 1 KW to 50 KW, reducing the voltage does not reduce the starting inrush which is still 4 to 6 FLA and it only increases the starting time. DOL is the shorter I2t pain for such fans.

Muthu
www.edison.co.in

RE: STAR Configured Fan Motor for DOAS

Actually, leaving out VFDs because that is totally different, reduced voltage starting does not fundamentally change the “thermal pain” for an AC induction motor. The area of the curve for the energy it requires to accelerate a given load is the same no matter what. The only thing RV starting does is to trade the height of the curve for the width. I have argued in the past that stretching out the time allows more of that thermal energy to be dissipated during the acceleration process, but someone pointed out that the thermal resistivity of a motor is so high that it makes almost no real difference if it takes 2 seconds or 30 seconds to accelerate.

This issue came up in discussions as to whether using RV starting can allow an increase in the number of starts-per-hour a motor is capable of. There was a camp who said it did, because it lowered the peak current and thereby the peak heat, others felt that stretching out the start time caused MORE heat in the motor. The answer was what I said above, that the energy curve area is exactly the same size, so the answer is no. It doesn’t help, nor hinder.

Reduced voltage starting has only two benefits; reducing excess torque applied to a load that doesn’t need it, and reducing current when the supply is limited. I cannot imagine a situation where the 3 phase supply is unable to handle the starting current if a 3kW motor, and centrifugal fans are very easy to accelerate, so I can’t see starting torque as being an issue.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

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