Dahlander Motors
Dahlander Motors
(OP)
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
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





RE: Dahlander Motors
I think the place your thinking is going astray is that there aren't really two windings in parallel. They are two electrically similar star-connected windings, but the two star points aren't (usually) tied together to form a true parallel connection. The windings certainly aren't in magnetic parallel because of their angular displacement on the stator core. If you neglect the magnetic circuit you're only doing a partial analysis of the motor, and in a pole-changing design it is essential to consider how the magnetic circuit changes in order to understand its operation.
RE: Dahlander Motors
The connections are changed so that all the poles are the same polarity. The opposite poles are formed between the wired poles. Not all winding pitches are suitable for consequent pole use.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Dahlander Motors
(OP)
1. " 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?
2. You have wrong concept of Dahlander connection.
2.1 It is NOT "as what was once 2 windings in series (1 pole) has essentially become 2 windings in parallel (2 pole)".
2.2 For two-speed fan loads, the windings are usually connected in YY/Y formation. There are also YY/D connection for highest output at both speeds etc.
3. "i should expect to see a substantial current drop in high speed"
3.1 NO, in all cases, higher speed connection will result to higher Power(kW) and higher current(A).
4. [i]" the motor nameplate has FLAs that are near identical for both speeds"
4.1 NO, usually the FLAs are NOT near identical for both speeds.
4.2 e.g.1 at 380V YY/Y connection: P1/P2=2/4poles; kW1/kW2=4.5/1kW; I1/I2=8.7/2.3A [suitable for fan load]
4.3 e.g.2 at 380V YY/D connection: P1/P2=2/4poles; kW1/kW2=1.3/1kW; I1/I2=3.2/2.7A
Note: P=No. of poles. 2poles is higher speed than 4poles.
RE: Dahlander Motors
On a Constant Torque version, the Low speed HP or kW rating is 1/2 of the High speed. Torque is the same, therefore current is close to the same in either speed.
On a Variable Torque version, the Low speed is typically 1/4 the HP/kW of the High speed rating, bbecause the torque it develops is typically 1/4 that of the High speed torque. That means the current will (should) be lower as well.
Variable Torque motor version are INTENDED to only be used on centrifugal pumps and fans because the nature of the LOAD profile is such that as the speed reduces, the power required by the load reduces at the cube power of the speed. So at 1/2 speed, the LOAD only requires 1/8 of the power it does at full speed, so having a motor only capable of delivering 1/4 power is still more than adequate. What it sounds like to me, is that you might have a situation wherein someone did not know these subtle differences and applied a Variable Torque version motor on a load that required a Constant Torque version. So because your load requires the same torque regardless of speed, your motor is instantly overloaded as soon as you go to low speed.
Diagrams are shown here, but like I said, the external connections are exactly the same, so there is no way of knowing what you have unless you read the subtle difference in the power rating on the nameplate.
https://www.joliettech.com/easa-electrical-enginee...
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Dahlander Motors
To start, give us a photo of nameplate or ALL nameplate details.
http://winding.wix.com/design
RE: Dahlander Motors
RE: Dahlander Motors
Based on the comments above, i would guess this to be a constant torque motor, given that low speed HP is half of high speed, and little change in current in either speed (28/29).
The motor is drawing around 20 amps in high speed, but in low speed its drawing 31-31 amps, which is over the nameplate FLA and hence, above the overload settings, so we were getting a lot of OL trips. These motors are running supply fans for air handling units. Right now we've adjusted the OL's up a bit, but it's not a solution in my opinion.
There are 5 units doing the same thing, and have been, to my knowledge, for a long time.....
RE: Dahlander Motors
I would not fully agree with that. That's another rule of thumb that often leads to confusion.
I think, it can not be argued that it is a constant torque connection only because the power ratio is approx. 1:2.
Power ratio of two-speed motors can vary much more than the mentioned rule shows.
Unfortunately, manufacturers, for some reason, are not required to mark an internal connection to the nameplate ( as well as they are hiding the NLA).
There is no any appropriate "external" way to determine whether the connection is Y/YY or D/YY. Only reliable answer is inside the winding.
Note that each two-speed winding can be realized in many different winding arrangements. Some of them gives a better winding parameters for low, some for high speed.
( "winding parameters" means : fundamental winding factor, symmetry, differential leakage coefficient, power ratio etc...)
For example, the power ratio will be changed if the winding pitch changes ( but not only power ratio).
Designer selects the winding arrangement that best suits to given application. Consequently, the both the connections are not of "equal quality", because such a design is always a matter of compromise. That could be a reason for your high amps in low speed ( if the load and voltage are within an allowed range). Probably, it is estimated that high speed is more important for such an application.
Winding Design and Calculations
RE: Dahlander Motors
If they're just some motors someone stuffed into the hardware then you should probably change pulley sizes or close a damper somewhere to reduce the load.
Could be there is a damper that is supposed to restrict the flow whenever low speed is called for and someone decided it was causing reduced air flow. (duh!)
Keith Cress
kcress - http://www.flaminsystems.com
RE: Dahlander Motors
(OP)
1. "... i would guess this to be a constant torque motor, given that low speed HP is half of high speed, and little change in current in either speed (28/29)".
Yes, where N1/N2 = kW1/kW2 = around 1/2 is usually classified as a "constant torque motor".
2. " The motor is drawing around 20 amps in high speed, but in low speed is drawing 31-31 amps"
No, there is some thing wrong. It is impossible with constant voltage(575V), (say similar P.F. for both speeds)to be operating on high speed(1780rpm) with lower current(20A), while on low speed(880rpm) at higher current(31A).
3. Check the connection diagram and the starter circuitry. They can be very confusing if the terminals are not properly marked.
4. For fan load, the Power(kW) required is proportional to the cube of the Speed(rpm)
5. Check the fan Power requirement curve to establish the Power(kW) required for high and low speeds.
The motor shall fulfils the Speed(rpm) and the Power(kW) per the fan curve.
It shall be N1/N2 = kW1/cube kW1 = I1/cube I1. Also if N1>N2; then Power kW1>kW2; and Current I1>I2.
Attention: Your present motor is NOT having this (fan load) characteristic. It can be used if the Speed and the Power rating fulfil the fan Power requirement curve.
RE: Dahlander Motors
High speed - Power to 6,4,5 and short 1,2,3
Low speed - Power to 1,2,3 and open 4,5,6
I would check the connection of the shorting contactor. Does it short 1,2,3 or 4,5,6? My guess would be the starter is configured for the constant HP connection and is shorting 4,5,6 when it should be shorting 1,2,3.
RE: Dahlander Motors
Then we can do more: analyze the winding, try to find the right cause and suggest some changes to overcome it.
Winding Analysis
RE: Dahlander Motors
(OP)
1. Your motor name-plate rating shows:
Hp1/Hp2 = 30/15 = 2
N1/N2 = 1780/880 = 2
I1/I2 = 29/28
V= 575V
This is a typical "constant torque application" motor; where N1/N2 = 1780/880 = 2
and Hp1/Hp2 = 30/15 = 2.
These "constant torque" motors can be wound with two separate windings or in Dahlander-connection.
2. Reference to the fan affinity law, when the N1/N2 = 2, Hp1/Hp2 = 2x2x2 =8.
Typical "fan drive application motors" with N1/N2 =2, Hp1/Hp2 = 4...7.7.
These "fan drive" motors can be wound with two separate windings or in Dahlander-connection.
3. Your present "constant torque" motor does NOT match with the "fan drive" application.
Even with N1/N2 is around 1780/880 rpm as required, but the Hp1/Hp2 =2 is a problem. It does NOT match with the "fan drive" application requirement; which needs a Hp1/Hp2 = 8.
RE: Dahlander Motors
Actually that doesn't matter in a fan drive application, provided that the power capability in high speed is adequate. True it's not a mathematical match, but it is a perfectly acceptable solution - the motor just has much more capability at the low speed than is required by the load. I agree it could have been specified differently from new, but in this existing application it is ok.
RE: Dahlander Motors
I found the fan curve for these units, and to my understanding(i've never had to read a fan curve until this started happening), even at free delivery, this fan should not require more than about 5hp at low speed.
I'm going to go have another look at the motor and starter circuit wiring and see if anything looks odd. Learning a lot about fans and motors here, thanks all..
RE: Dahlander Motors
(OP)
1. Your present motor is intended to operate on 1780/880rpm. The kW1/kW2=30/15 is a total mismatch.
Assuming 30Hp is rated for 1780rpm, the motor rated 15Hp would be far too high when running
on 880rpm. It does NOT cause any damages physically but financially as it would be running at very low efficiency and power-factor. Running with low efficiency is damaging financially while low power-factor may not, that depends on whether the utilities charges take the Pf into consideration.
2. You had reported that "im seeing, as high speed current is measuring quite a bit lower than low
speed current".
No, there is some thing wrong.
3. A typical 2-speed motor irrespective of whether ["constant torque" or "fan drive"],and with ["two separate windings" or "Dahlander-connection"]:
in general: when N1>N2, kW1>kW2 and I1>I2 (only exceptional cases with very low ratings I2>I1). The Eff1>Eff2 (only exceptional cases Eff2>Eff1) also Pf1>Pf2 (only exceptional cases Pf2>Pf1)
RE: Dahlander Motors
Note: "no-load" means uncoupled shaft.
RE: Dahlander Motors
1. "Another information (if any), might be useful: no-load Amps in low and high speed-connection".
Usually no-load Amps in low and high speed-connection are NOT useful. These data are not needed for engineering design. That is why these data are usually not listed in the catalogues.
2. The basic rating data are voltage(V)+ Fqc(Hz), N(rpm1/rpm2), current (I1/I2), and less important data are Fff1/Eff2, Pf1/Pf2, Is1/I1 Is2/I2, Torque ratios, moment of inertia and weight etc.
3. Motor ratings:
a) Voltage and Frequency data are to ensure that match with the power source ratings,
b) Speeds N1/N2 match with the delivery volume and static pressure,
c) Current I1/I2 for breaker/fuse, contactors, overloads and conductor sizing,
d) Torque rations, and moment of inertia are for starting-up time study,
e) Eff1/Eff2, Pf1/Pf2, Is1/I1 Is2/I2 and weight are of less important,
RE: Dahlander Motors
Most 3-phase induction motor data I've seen has motor efficiency curve that are reasonably flat from about 15% load to full load. I'd expect the motor might drop about 3% in efficiency at 25% load. I'm just not seeing how that is a very low efficiency or worthy of dire warning about it being the wrong motor. You're possibly looking at about 100W of extra power being used in low speed compared to the same rated efficiency variable torque motor.
I have doubts this would be a 2-winding 2-speed motor because the frame size would likely be larger. It is difficult to fit 2 completely separate windings into the same frame size that a motor with a single winding uses.
Also, the no load current can definitely be a help when troubleshooting a situation such as this. Measuring to much low speed current even without load would eliminate the fan as having any part in causing the high current.
RE: Dahlander Motors
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.
RE: Dahlander Motors
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.
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
If it is an only consequence , it's OK. Just consider that your motor has the SF = 1.10
RE: Dahlander Motors
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.
RE: Dahlander Motors
RE: Dahlander Motors
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.
RE: Dahlander Motors
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.
RE: Dahlander Motors
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Dahlander Motors
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.
RE: Dahlander Motors
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.
RE: Dahlander Motors
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
RE: Dahlander Motors
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
RE: Dahlander Motors
RE: Dahlander Motors
RE: Dahlander Motors
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
RE: Dahlander Motors
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?
RE: Dahlander Motors
Thanks for useful update.
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