Dahlander Motors 1

[FBW]

Hello All,

Having a few issues here on a dual speed motor running a fan, and i think im getting close to the answer, but i need a bit more insight from some experts.

After a bit of research, I've come to the understanding that what I'm dealing with is a Dahlander motor, which essentially doubles the poles in the motor to change speeds at the same voltage, with the help of a particular type of motor starter (NOT a Delta-Wye motor, which has nothing at all to do with changing speeds, which seems to be causing a lot of confusion for some people).

My question is this: having studied the circuits for both the high and low speed, it seems to me that i should expect to see a substantial current drop in high speed, as what was once 2 windings in series (1 pole) has essentially become 2 windings in parallel (2 pole). Am i correct in assuming this?

If so, that would explain what im seeing, as high speed current is measuring quite a bit lower than low speed current, which seems counter-intuitive to people whom i dont think understand how the motor works.

However, the motor nameplate has FLAs that are near identical for both speeds. So, as you can imagine, its causing some debate on whats going on, not to mention that the motor is not only pulling more that the FLA in low speed, for reasons no one can seem to figure out.

Can anyone shed a bit of light on this for me?

Cheers

 

[KuanYau]

To LionelHutz (Electrical)

1. "Do you have proof that the motor at 25% load operates at "very low efficiency"?"

Reference to Motor application and maintenance handbook by Robert W. Smeaton
page 3-47 Fig 33 Typical efficiency curves of 1Hp to 10kHp from 25% to 100% load; for 1800rpm normal-torque low-starting-current polyphase induction motors. Values will vary for a specific design......
e.g. for a 10Hp motor %Eff//%load: 76/25, 83/50, 86/75, 87/100
Note: 1. the efficiency curve is expected to turn down sharply from 25% to 0% load.
2. see also page 3-11 Fig 2 as an indication of the trend from 25% to 0% load.

2. In FBW (Industria) case, assuming 30Hp is required for 1780rpm, then 15Hp would be far over-rated for 880rpm. which needs only 3.11Hp. The motor would be load to 20.7%.

3. "I have doubts this would be a 2-winding 2-speed motor because the frame size would likely be larger. It is difficult ..."
FBW had stated in his post dated 24th July that "After a bit of research, I've come to the understanding that what I'm dealing with is a Dahlander motor,".

4. No-load high/low speed currents are NOT required during the engineering nor for components sizing. It is also NOT informative during commissioning/trouble-shooting, because very often the no-load current may range from 60% up to 80% of full-load current, with a healthy motor. Do not be alarmed. This is caused by the low power-factor and low efficiency while the other constant losses remained unchanged; when running on no-load.

 

[zlatkodo]

Hi, Kuan Yau,
Your explanation does not answer the question what causes a high amps at low speed.
- Obviously, the wrong external wiring could not be the cause, because Amps will be significantly higher in that case,
- Whether the connection is D / YY (8/4 pole) or Y / YY is not important if the rated power is enough for 8 pole load (if you ignore the efficiency and power factor).
Amps will not increase if the motor is underloaded.

very often the no-load current may range from 60% up to 80% of full-load current, with a healthy motor

8 pole motor of 15 HP with NLA from 60-80 % of FLA: that would be very bad design rather than "healthy motor".
- No-load current is important because it helps to determine whether an issue is related to the motor winding or load.
I am quite convinced that something can be improved during the first rewinding (For example: select the 8/4 pole winding that at 8 pole has a higher fundamental winding factor and lower differential leakage coefficient. That will cause a lower NLA and FLA even with same turns per phase ).
FBW

Right now we've adjusted the OL's up a bit, but it's not a solution in my opinion.

If it is an only consequence , it's OK. Just consider that your motor has the SF = 1.10

 

[LionelHutz]

So, your proof was from the wrong speed of motor. Anyways, it shows an efficiency change from 76% to 83% if you changed from a constant torque to variable torque motor? I learned something new. Apparently 83% is a good efficiency and 76% is a very poor efficiency. Your curve data also must be rather dated. A 30hp motor these days will have an efficiency that peaks around 92% to 94%, not 87%. Also, the efficiency question is in regards to a 880rpm motor and not a 1800rpm motor. The lower speed motors tend to have an efficiency that peaks around 50%-70% load and that doesn't start to fall off quickly until a lower speed than a 1800rpm motor does. So, I still don't agree with your dire warning and it does nothing to explain the issue with the low speed current current anyways.

No matter how many times you claim no load amps is irrelevant, it can still be useful when troubleshooting an odd case such as this. What would you say if the NLA was >90% of FLA? Is that still normal?

I've troubleshot field cases with both a very high NLA and a very low NLA and in those cases the abnormal NLA immediately eliminated the load as the cause of the issue. It can be a very useful troubleshooting tool for certain field issues.

 

[EngRepair]

A very interesting discussion. Thanks to all.

 

[KuanYau]

zlatkodo (Electrical)

1 "Your explanation does not answer the question what causes a high amps at low
speed."
What I wish to stress is when N1>N2, kW1>kW2 and I1>I2. There is something wrong when N1>N2 with I2>I1.
Suggested possible causes:
a) wrong winding termination e.g. wrong terminal selected in a tapped winding etc...,
b) wrong starter circuitry e.g. wrong contactor switching sequence/arrangement etc...,
c) wrong circuit selection e.g. YY/Y wired in Y/YY or D/YY wired in YY/D etc...,
d) wrong shorting-link termination.

2. " Whether the connection is D / YY (8/4 pole) or Y / YY is not important if the rated power is enough for 8 pole load (if you ignore the efficiency and power factor)".
A 8/4 pole motor even with enough Power(kW) rating would NOT be suitable for this case. The speed would be too low. It is very important and MUST be a 4/2 pole machine.

3. "8 pole motor of 15 HP with NLA from 60-80 % of FLA: that would be very bad design rather than "healthy motor".
No-load current is important because it helps to determine whether an issue is related to the motor winding or load."
NLA may reach 80% of AFL. This is so especially on small and low speed motors.
The NLA is NOT a good indicator of the health of the motor. For this reason, the value isNOT stated in the name-plate and NOT listed in the catalogue. Only the OEM (not the agent) has this datum in hand.

4. "I am quite convinced that something can be improved during the first rewinding (For example: select the 8/4 pole winding that at 8 pole has a higher fundamental winding factor and lower differential leakage coefficient. That will cause a lower NLA and FLA even with same turns per phase )".

Rewinding it to 8/4 pole would NOT reach the required rpm/static pressure, irrespective of the power rating.

 

[KuanYau]

LionelHutz (Electrical)

1. " ....A 30hp motor these days will have an efficiency that peaks around 92% to 94%, not 87%. Also, the efficiency question is in regards to a 880rpm motor and not a 1800rpm motor. The lower speed ..."
My post dated 1st August
Reference to Motor application and maintenance handbook by Robert W. Smeaton
page 3-47 Fig 33 Typical efficiency curves of 1Hp to 10kHp from 25% to 100% load; for 1800rpm normal-torque low-starting-current polyphase induction motors. Values will vary for a specific design......

2. " No matter how many times you claim no load amps is irrelevant, it can still be useful when troubleshooting an odd case such as this" .
Please see my post dated 3rd August point 3, addressed to Mr zlatkodo.


3. "What would you say if the NLA was >90% of FLA? Is that still normal?"
Have you actually come across NLA >90% of FLA?
My point is the NLA is no indication of the health of the motor. A wattage measurement would indicated the constant losses even though it is not stated in the name-plate nor listed in the catalogue.

4. "I've troubleshot field cases with both a very high NLA and a very low NLA and in those cases the abnormal NLA immediately eliminated the load as the cause of the issue"
Your claimed "Very high" or "very low" NLA is your own perception as you have NO basis to substantiate your perception. Did you obtain the NLA from the OEM ?. I would agreed with you (the motor is faulty) if the NLA differs "significantly" from that given by the OEM, after taken the permissible tolerance and the voltage differences between OEM testing and the actual voltage at site, when NLA measurement is taken. Do NOT trust the value from the motor agents. They DO NOT have this datum in most cases.

5. Suggested possible causes:
a) wrong winding termination e.g. wrong terminal selected in a tapped winding etc...,
b) wrong starter circuitry e.g. wrong contactor switching sequence/arrangement etc...,
c) wrong circuit selection e.g. YY/Y wired in Y/YY or D/YY wired in YY/D etc...,
d) wrong shorting-link termination.

 

[waross]

Given that the pitch of a Dahlander motor is chosen to allow consequent poles to form and not for greatest efficiency, the efficiency curves for standard induction motors may not apply.

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

 

[KuanYau]

Dear friends and experts

After much elaboration, I would like to suggest the following preliminary conclusion based on motor name-plate rating N1/N2=1780/880rpm, kW1/kW2=30/15Hp, I1/I2=29/28A.

1. There is some thing wrong when running N2=880rpm but I2>I1
Suggested possible causes:
a) wrong winding termination e.g. wrong terminal selected in a tapped winding etc...,
b) wrong starter circuitry e.g. wrong contactor switching sequence/arrangement etc...,
c) wrong circuit selection e.g. YY/Y wired in Y/YY or D/YY wired in YY/D etc...,
d) wrong shorting-link termination.

2. Check the "fan Law" for the required Power for N1 or N2 speed.
a) if N1 required about 30Hp, then 15Hp would be too high for N2 speed. Result: low efficiency,
b) if N2 requires about 15Hp, then 30Hp would be too low for N1 speed. Result: over-loading.

3. Present motor with N1/N2=2 and kW1/kW2=2 is a total "misfit" for "fan drive"/load application.

4. Ask the (motor+fan) assembler for reasons why the "constant torque" application motor is been selected instead of the "fan drive" type.

5. For long-term "economical" operation reasons, replace the motor with "fan drive" type that fits the required power rating for N1 and N2 speeds. It can be a "two-windings" or "Dahlander wound" type , no issue.
The essence here is the motor with a "fan drive" characteristic/rating is preferred.

 

[LionelHutz]

KuanYau - You don't need to repeat yourself over and over. It does nothing to help and just becomes an annoyance. We ALL know that the low speed current should not be that high. This has been well established early in this thread.

As for the NLA - why is this so difficult to understand? I NEVER posted that the abnormal NLA means the motor is bad. I posted that it eliminates the load. I would bet money in this case that if the NLA was found to be >90% then it's not the connected load causing the high low speed current. YES, I have used both atypically high and atypically low NLA in the field to help narrow down a power source or motor issue. Yes, I have troubleshot a field application with the NLA > 90%. On the flip side, I have also used a reasonable NLA as an indication that there was a load issue. As a smart person who has dealt with many motors, I will make a reasonable guess as to the NLA I expect for the motor in question. This is how you deal with things in the field when you don't have all the book numbers. The only way I can fathom someone having so much difficulty understanding this would be due to that person never actually having done field troubleshooting.

"It is very important and MUST be a 4/2 pole machine." - This statement and the others about the 4/2 pole you follow with make no sense.

Bill - there are likely exceptions but the efficiency data I've seen on these motors is similar to a single speed motor.

 

[waross]

Thanks for the insight Lionel. Does this imply that the high current may be mostly reactive? If so, could the reason be related to the formation of the consequent poles?
The last Dahlander I worked on had all the wire identification missing. I spent some time with a truck battery and a compass. I eventually got it running with no drama. The currents were unremarkable.
I have not noticed high no load current on the few Dahlanders I have worked on and I am following this thread with interest.


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

 

[zlatkodo]

The NLA is NOT a good indicator of the health of the motor. For this reason, the value isNOT stated in the name-plate and NOT listed in the catalogue.

Any responsible manufacturer shall submit such information.
Here are the data for a similar two speed motor:

Other way:
If the data for efficiency & power factor (for 100% load and some partial load) are known, then a no-load current could be estimated with a very high accuracy:

Winding Data Calculations

 

[LionelHutz]

Bill - Lower speed motors typically have higher inductive VAR's and require more capacitors to correct the power factor when compared to higher speed motors.

 

[FBW]

Ive been pulled away on some other jobs for the time being but i'm hoping to get back at this issue as soon as possible, just need to talk an electrician into coming to have a look at things with me again. Been a great learning experience so far, and I will definitely update when i find out more, or hopefully, a solution.

 

[waross]

Thanks Lionel. I was aware that lower speed motors tend to have greater VAR demands. I wondered if the consequent pole formation tended to further increase the VAR demands.

KuanYau
Your technical knowledge is good.
Your ability to work in groups is abysmal.
Some of our best and most experienced Gurus seem to have dropped out of this discussion. Your loss.
And, no matter how long you work with electricity, there is always something new to learn.

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

 

[FBW]

Update,

Took the belts off of the fan today and measured the no load current. On high speed it dropped, from about 20A to around 14. In low speed, there was almost no change, still pulling around 32A. It has a lot of people scratching their heads.

Cant see anything wrong with the wiring, but as a last ditch effort, when i get the next chance, im going to go scrutinize the starter circuits and wiring in agonizing detail. I just cant see how the wiring could be wrong and not burn something or trip something, or have the thing running at the wrong speeds, or something.

Im going to try and get in touch with Baldor and see if they can give me some more details about this motor....

Suggestions?

 

[zlatkodo]

Hi, FBW,
Thanks for useful update.

Cant see anything wrong with the wiring, but as a last ditch effort, when i get the next chance, im going to go scrutinize the starter circuits and wiring in agonizing detail

The wiring could not be the cause, because in case of incorrect wiring the Amps would be much higher, even in both connections.
High NLA indicates a very bad design, as I noted above.
Suggestions:
read my post of 30. July.

http://winding.wix.com/design