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Winding Redesign
Warning:
Please, read carefully about possible limitations, before you order any kind of winding redesign.
Each motor-redesign has some limitations that need to be considered before the redesign was done. If you ignore these limitations, you could get a motor that is unusable for a particular application. Will the new parameters ( speed, power, torque ) match the specific motor application , should be determined in consultation with relevant professional on site. It's up to you, only.
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Very often a some motor performance has to be changed.
Please, read carefully about possible limitations, before you order any kind of winding redesign.
Each motor-redesign has some limitations that need to be considered before the redesign was done. If you ignore these limitations, you could get a motor that is unusable for a particular application. Will the new parameters match the specific motor application , should be determined in consultation with relevant professional on site. It's up to you, only.
Just some examples of redesign limitations that often occurs in the rewind shops, will be briefly mentioned here.
For any questions here is our contact form.
General Limitation
Frequently, the calculated value of "turns / coil" after redesign is not a whole number.
Despite the change in the number of circuits, in span or winding connection, the result may remain the fractional number.
Then should be decided which number of " turns per coil " to choose.
That decision could significantly affect the motor performance ( primarily motor power and torque).
Voltage Change
It seems to be the simplest redesign, but there are also some limitations.
- If the voltage increases, the upper limit of "volts/coil" should not be overcome.
- If the voltage decreases, the problem with "fractional turns/coil" may appear.
In case of redesign from LV to MV or HV, lot od issues should be solved ( insulation issue, replacing the round wire with form-wound coils, connection issues, etc).
Speed Change
by
Pole Changing
If you want to change the number of poles, you need to be aware of certain limitations.
Some of them are:
- Not each "stator slot - rotor bars " combination is suitable for a new number of poles. In some rare cases, it happens that the new number of poles is not suitable for a particular number of rotor bars, which is impossible to determine in advance.
- Not each rotor is suitable for new circumferential speed.
- Pole changing causes a significant change in the main motor parameters:
the power and torque.
Usually:
- increase the poles will reduce the power at constant torque,
- decrease the poles will reduce the torque at constant power.
Will the new parameters match the specific motor application, should be determined in consultation with a relevant professional on-site. It's up to you.
Must be very careful doing so especially in a pump or blower application, as they follow the affinity laws, where the load increases with the cube of the speed..
Frequency Change
This redesign could be done in two ways, depending on whether you are making a constant power or constant torque change. When frequency changes, the speed is also changing.
The main limitations are similar to the previous case:
- Not each rotor is suitable for new circumferential speed.
- Speed changing causes a significant change in the main motor parameters: power and torque.
(For example: Don't expect same HP if you make redesign from 60 to 50 Hz. The HP will be roughly 15-20 % lower.)
Also, must be very careful doing so in a pump or blower application, as they follow the affinity laws, where the load increases with the cube of the speed.
Will the new parameters match the specific motor application, should be determined in consultation with a relevant professional on-site. It's up to you.
Span Change
or
from Single to Double Layer
from Double to Single Layer
Each span change or replacing the double layer winding with a single layer or vice versa, must be followed with the new value of turns per coil, according to the new value of the fundamental winding factor.
New winding could have a higher content of harmful harmonics, which also should be considered.
Such a motor will have new value of power and torque.
Will the new parameters match the specific motor application, should be determined in consultation with a relevant professional on-site. It's up to you.
Circuits Change
There are some reasons for circuit change:
- Sometimes, when a winding has only few turns per coil and many wires in hand, it could be easier to rewind, if the number of circuits is increased.
- Also, the calculated value of "turns / coil" after any other redesign may be a fractional number and because of that the number of circuits should be increased.
Limitations:
- There could appear a "volts/coil" limitation .
- If the winding is unbalanced, the number of circuits other then 1 is not recommended at all,
- also, if the new number of circuits is equal to the number of poles, then there is no more possibilities for skip pole or any long jumper connection that is crucial for high rated motors.
Generally, the maximum number of circuits is equal to number of poles, but...
- In case of odd grouping (fractional windings) it may not be the case (our WindingDraw software could give the list of possible circuits).
- Another exception, when is possible to make more circuits then the number of poles, is using a winding arrangement with more complex connections.
But, should be very vigilant, because that arrangement is not just obvious.
Since it is about a large motors and expensive repairs, is always good practice to check the diagram before the repair. Such a verification can be achieved using our software for winding analysis.
A verification could be requested here.
Some " rules of thumb" for such a situations are published. Although the publisher is very reputable , it appears that they are valid only in few cases.
A genuine verification must be done for any case.
Ignoring these facts can result in a completely unusable motor ( high circulating currents inside the parallel paths, locked rotor condition, lot of heat, premature failures and possible winding failure even in "no-load" conditions).
Stator Slots
vs
Rotor Bars
The relation between the stator slots and the rotor bars ( slots ) is very important information when the number of poles is changing:
- from one number of poles to another or
- from single speed to two speed motor.
You can request a check before the redesign using our contact form.
It's free.
Only few information are needed: stator slots, rotor bars ( or slots in case of wound rotor) and information whether the rotor bars or stator slots are skewed.
Single Voltage
to
Dual Voltage
This kind of redesign could be limited because of inadequate number of parallel circuits and fractional number of turns per coil.
Number of leads depends on the mode of motor operation and can be either 9 or 12 .
Power Change
The power rating could be increased by decreasing the number of turn/coil, but in this case, the FLA, NLA, core loss and copper loss of stator and rotor will also increase, because the flux densities in air gap, tooth and back iron are higher then previously.
Motor operating conditions become less favorable or completely unfavorable.
Then, is it possible at all to increase the motor power rating?
Yes, to a certain extent, but only in two cases:
- When there is a "core - reserve" ( with mandatory application of higher thermal class of insulation),
- When the new duty cycle (in terms of cooling time) is more favorable than the previous one.
But should be remembered that in both cases it is necessary to check the flux densities in the core i.e. make a core calculation (before redesign).
Core calculation can help in the evaluation of new power rating.
In addition, this redesign can be limited by mechanical issues with the shaft or bearings.
Single Phase
to
Three Phase
Any method of calculation using the old data of main and auxiliary winding is not reliable.
The only reliable way is to calculate the new three phase winding using a complete core calculation.
Such redesign is always desirable, because it gives more power, torque, reliability and easier maintenance.
When you have a three-phase electricity, always do that way.
Adjacent to Skip Pole
or Long Jumper
YES, if it's possible.
Skip Pole
or Long Jumper
to Adjacent Pole
NO.
Single-Speed to
Two-Speed
(Dahlander Wdg)
Sometimes you need to convert a single-speed to a two-speed motor (Dahlander winding).
Contact us if you need our recommendation which motor as a donor is the best choice?
For example, it is not irrelevant whether you will use (as a donor) a 2-pole or 4-pole motor , if you want to get a two-speed 4/2-pole motor. For constant torque application you should select a 4 pole motor . HP rating should be the same or higher then low-speed HP of two-speed motor.
Note that any other connection (variable torque or constant HP) should be considered in advance as well as selection of slot span.
Sinusoidal
to
"ordinary" winding
??
will be continued
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