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Don't do that
Here will be shown some bad examples from workshops that should not be imitated at all.
Our intention is not to embarrass those who commit such mistakes but to warn all others in order to make an analysis in advance and avoid a big waste of work and copper.
Contact us at the right time if you have any doubts.
Analysis of 12 pole single-layer winding in 48 slots
(This example will show how important is an analysis-software )
Note:
The technician wasn't able to record a genuine connection and he tried with this one.
Is it correct?
What could be an outcome if this connection is applied?
Since each 12 pole winding in 48 slots is unbalanced by its nature, the analysis did show a small asymmetry in the MMF (amplitude and angle, see the picture ), as expected.
Also, the basic winding factor has good value.
Does this mean that the proposed diagram is good?
No.
Despite the fact that the internal connection diagram is formed in a proper manner, and that asymmetry is as usual, and that the basic winding factor is also good, though the analysis shows a significant presence of harmful harmonics (differential leakage coefficient - τd is more than 40%). This will cause excessive current (NLA & FLA) and overheating of windings, low efficiency and short life expectancy.
It is the worst single-layer 48 / 12p diagram that we have seen so far and should not be used at all..
There are :
- standard, single-layer winding with twice lower τd,
- double-layer winding with three times lower τd,
- NEW (OUR) single/double-layer winding with almost 8 times lower τd. Motor with such windings will have a significant reduction in Amps, increased power, efficiency, and life expectancy.
This example shows the big importance of analysis-software.
It is 3 phase, 12 pole winding in 48 slots. Notice: The technician wasn't able to record a genuine connection and he tried with this one. Is it correct ? What could be an outcome if this connection is applied?
Since each 12 pole winding in 48 slots is unbalanced by its nature, the analysis did show a small asymmetry in the MMF (amplitude and angle , see the picture ), as expected. Also, the basic winding factor has a good value. Does this mean that the proposed diagram is good?
Despite the fact that the internal connection diagram is formed in a proper manner, and that asymmetry is as usual, and that the basic winding factor is also good, though the analysis shows a significant presence of harmful harmonics (differential leakage coefficient - τd is more then 40%). This will cause excessive current (NLA & FLA) and overheating of windings, low efficiency and short life expectancy. It is the worst single-layer 48 / 12p diagram that we have seen so far and should not be
It is 3 phase, 12 pole winding in 48 slots. Notice: The technician wasn't able to record a genuine connection and he tried with this one. Is it correct ? What could be an outcome if this connection is applied?
Click on picture to enlarge.
Redesign of sinusoidal winding
REPLACING A SINUSOIDAL WINDING WITH A STANDARD ONE IS "GOOD" WAY TO DECREASE THE MOTOR EFFICIENCY, EVEN IF THE REPLACING WAS DONE ACCORDING TO RULES.
Diagrams and winding data calculations for sinusoidal windings are available.
Contact us if you have any issue with this kind of windings.
(36 slots, 4 pole is shown).
sinusoidal winding 36 slots, 4 poles
sinusoidal winding 36 slots, 4 poles
Example from Russia (Don't do that)
Wrong way to make a winding with 4 circuits.
Motor of 3150 kW, 6000 V, 4 pole, 72 slots
Example from Mexico (Don't do that)
Some kind of redesign have been made daily in the each service center. Frankly said the most common reason is to make the job easier. However, whether such changes can affect the motor operation?
Here is an example that relates to the 75 kW, 8 pole motor with 60 slots.
The original winding was "mixed", ie. single-double layer with span 1-8 (6 turns), 2-7 (3 turns) and 1-7 (6 turns). New winding is a single-layer with span of 1-10, 2-9, 3-8 and 1-10, 2-9 (6 turns / coil).
A technician at a service center claims he kept the same number of turns / slot because the winding factors of both windings are the same. Also, it is confirmed using well known redesign-software.
But, the customer complains due to increased currents (NLA and FLA) after rewinding.
Also, the winding is hotter than before .
How to explain it?
It is true that winding factor of both windings is the same and consequently the turns per coil, but new winding has almost four times higher diff. leakage coefficient representing the harmfull harmonic content.
Example from India (Don't do that)
Motor 440 V, 4 pole.
Wrong way to make a winding with 4 circuits.
(to much Volts/coil)
Example from US (Don't do that)
Wrong way to make a two-pole winding with 4 circuits.
Motor of 800 HP.
The picture shows an example of incorrectly recorded diagram of PAM winding with 54 slots.
Rewinding despite the doubts ( don't do that )
Often a problems and doubts arise when taking the data from the old winding .
Are you going to make a winding despite the doubts?
The wasted time and copper can be very expensive.
What we can offer in such cases?
You have the ability to ask for an analysis of your winding and make the necessary corrections before rewinding.
All you need to do is describe your concerns, draw a diagram of what you find and contact us.
The basic analysis includes checking of polarity , symmetry of angle and amplitude , calculating of winding factor of the fundamental wave ( distribution and pitch factor) .
The analysis can be extended to a complete analysis of whole spectrum of harmful harmonics (takes a little more time).
(The picture shows an example of incorrectly recorded diagram of PAM winding with 54 slots.)
Sinusoidal Winding ( a bad example from practice)
Example from practice:
- 4 pole concentric double-layer winding in 48 slots has a different number of turns/coil as follows: 8(1-13); 16(2-12); 14(3-11); 12(4-10).
Slot filling differs significantly ( see the photo).
Some of the slots are only half-filled.
What to do?
We can do the same winding as is or make a preliminary analysis to see what are the real characteristics of that winding.
Let's analyze this winding and compare it with the standard one with the same turns per coil.
There are five known procedures for obtaining an effective sinusoidal winding with the lowest possible content of harmful harmonics.
But, at first glance, this arrangement of turns/coil does not match any of them.
Remember, the goal of forming a sinusoidal winding is getting a minimal diff. leakage coefficient at maximal winding factor as is possible.
The attached table and graphs show that, although made by the manufacturer, the chosen solution is a very poor design of sinusoidal winding.
The winding, worse than the standard one (with same t/c) is obtained, because of:
- lower winding factor ( less power&torque),
- higher diff. leakage coeff. ( more amps & heat),
- significantly unequal slot filling ( low utilization of the core). Unfortunately, such cases are very common in practice.
What should be done?
You have an option to order a new calculation that will give you the best possible variant of the sinusoidal winding ( see the table) or make a winding as it was before.