FIELD OF THE INVENTION

The present invention generally relates to a method for stator winding, more particularly the method for a three phase, double layer jointless mush winding assembly for stator of electrical machine.
BACKGROUND OF THE INVENTION
Electrical machines are rotating or linear electromechanical energy conversation devices universally classified as motors or generators. These devices are considered very important because they are extensively used in many house appliances and also very vital at the core of most engineering process in industries. The development of electrical machine is one of the supreme successes of the present day energy conversation. However, these machines go into failure mode due to fundamental limitation of material lifetime, manufacturing lifetime, manufacturing defects, deterioration, and damages in operation or contamination.
Electrical machine faults are the defects or imperfections that disturb or affect the performance of normal operation on or in the machine. A few faults lead to several symptoms such as unbalanced line currents, unbalanced air-gap voltages, pulsations in torque and speed, decrease in efficiency and average torque, excessive heating and thus increased losses. These machines are often exposed to harmful or even non-ideal operating environments. These conditions comprise insufficient lubrication, overload, inadequate cooling, frequent motor starts/stops. Under these circumstances, electrical machines are subject to undesirable stresses, which put the machine under risk of faults or failure. The repair and refurbishing expenses of electrical machine might not be substantial, however the cost associated with down time is enormous. These faults cause production shutdowns, personal injuries, and waste of raw material which could eventually lead to heavy financial loss.
The constant running of a rotating machine causes continuous wear and tear which manifests further into failures in the machine components or faults. A few reasons behind such failures are the machines have their origin in design, assembly, manufacturing tolerance, working environment, installation, schedule of maintenance and nature of the load. These machines

are designed such that the interaction between these forces under normal condition leads to a stable operation with minimum vibrations and noise.
A stator is an important part of electrical machine. The stator includes a cylindrical stator core and a stator winding composed of a three phase stator winding portion constructed by connecting three winding phase portions and a neutral point. The Stator winding significantly decides the useful life of the machine. There are various types of configurations used for winding of rotating machines. The most commonly used configuration for three phase electrical machine is the double layer lap or wave winding. Depending upon the requirement, form wound coils or flexible conductor mush wound coils may be used for low voltage windings. The stator is subjected to some type of fault such as core faults and winding faults. The manifestation of winding fault is due to winding to earth, phase to phase and turn to turn short circuit, whereas core faults are due to rotor strike, core slacking and laminations short circuit.
Moreover, winding faults are related to turns of wires in stator of electrical machine. These faults are caused by slack core lamination, slot wedges and joints. Any failure in the stator winding can be fetal and may require large shutdown period along with huge cost of repair.
In the prior art, the conventional method of winding disclosed about the coils which are made outside the core using former and then coils are placed inside the slots one after another which creates faults as discussed later.
In the said prior art, fig –1 illustrates about the conventional stator winding with joints. The coils are placed in the stator core and then the coils are joined together to form the desired circuit. In this process various types of joints are required to be made in stator winding such as coil to coil connection, group connection, and then finally winding to cable connection. However, every joint in the winding has a direct relation to reduction in reliability of the machine as individual joints are generally brazed together which involves human effort and application of filler and flux. Any deficiency on the part of the human effort or material may lead to weak joints resulting in high resistance zone which may ultimately lead to failure over period of time.

Fig (1) illustrates the conventional stator winding with joints. All the electrical machine manufacturers use conductor jointing through brazing process of the stator windings. The disadvantages of making joints in the conventional stator winding are as follows:
1. The conventional process is time consuming and reduction in productivity.
2. Application of costly flux and filler
3. Increase in size of overhang leading to reduction in overall active material
4. Increased chances of failure due to weakness in joints
Therefore, there is a need of a method for a three phase, double layer jointless stator winding in electrical machine in such a manner, that, the above mentioned drawbacks are addressed.
OBJECTS OF THE INVENTION
It is therefore, the object of the invention to overcome the aforementioned and other drawbacks existing in prior arts.
The primary object of the present invention is to propose a method for a three phase, double layer, and jointless mush winding assembly for stator of ac electrical machine.
Another object of the present invention is to propose a method to make jointless winding to increase reliability and productivity for low voltage mush wound electrical machines.
SUMMARY OF THE INVENTION
One or more drawbacks of conventional arts for constructing jointless mush winding in an AC electrical machine are overcome, and additional advantages are provided through the present invention as disclosed. Additional feature and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.
In the embodiment of the present invention, a method for a three phase, double layer, jointless mush winding assembly for stator of ac electrical machines, the method comprising:

forming a first-phase winding by laying coils made of conductors starting from a designated slot of a plurality of slots of a first parallel path, wherein the first-phase winding comprises: a) laying the conductors starting from the designated slot and continuously moving in anticlockwise or clockwise direction till the coils of the first parallel path of the conductors are placed in bottom of the slot or top half of the designated slot; b)laying the conductors in a designated slots for next parallel path as in step (a); forming a second phase winding by following the steps of a) and b); forming a third phase winding by following the steps of a) and b).
In an embodiment, the conductors used for winding purpose are placed at top-half of the slots after the bottom of the slots are occupied. Among three phases winding, the first phase, the second phase and the third phase winding is selected from a group comprising a U-phase winding, a W-phase winding and a V-phase winding. The terminals and neutral ends of the conductors of three phases are taken to the terminal box such that said conductors have no joints.
In an embodiment, the length of the conductors used in winding purpose is calculated for making all coils of atleast one of a parallel path based on the relation by using of a plurality of parameters.
Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of shrouds that are consistent with the subject matter as claimed herein, wherein:

Fig 1(a) - illustrates the conventional stator winding with joints according to prior art.
Fig. 2(a) illustrates a three phase, double layer jointless mush winding assembly for stator of AC electrical machines according to present invention.
The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION OF THE INVENTION
While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
The figures illustrate only those specific details that are pertinent to understand the embodiments of the present disclosure, so as not to obscure the disclosure with details that will be clear to those of ordinary skill in the art having benefit of the description herein.
The present invention is directed towards a method for three phase, double layer, jointless mush winding assembly for stator of ac electrical machines, the method comprising: forming a first-phase winding by laying coils made of conductors starting from a designated slot of a plurality of slots of a first parallel path, wherein the first-phase winding comprises: a) laying the conductors starting from the designated slot and continuously moving in anticlockwise or clockwise direction till the coils of the first parallel path of the conductors are placed in bottom of the slot or top half of the designated slot; b) laying the conductors in a designated slots for next parallel path as in step (a); and forming a second phase winding by following the steps of a) and b);and also forming a third phase winding by following the steps of a) and b).

Figure 2 illustrates the present invention, where the conductors are placed at the top –half of the slots after the bottom of the slots are occupied. Among three phases winding, the first phase, the second phase and the third phase winding is selected from a group comprising a U-phase winding, a W-phase winding and a V-phase winding. The winding is started by putting conductors starting from first slot and then progressing in anti-clockwise or clockwise direction till all the coils of one parallel path of U-phase are placed in bottom of the slots. Same process of winding is followed for both W-phase and V-phase and the conductors are placed either at the bottom or at the top half of the slots as per the availability of the slots position. If the slot bottoms are occupied first, then, the coils are placed in the top half of the slot. Each individual phase required atleast two parallel path and once the parallel paths are completed, the conductor terminals for three different phases (U1,U1′), (W1,W1′) and (V1, V1′) and the neutral points of the different three phases (U2,U2′), (W2,W2′) and (V2, V2′) are directly taken to the terminal box such that there is no joints between the conductors.
Further, to calculate the length of the conductors, a relation is formulated and shown in below. The length of the conductors is calculated for making all coils of atleast one of a parallel path based on a technical relation of a plurality of parameters, wherein length of mean turn (LMT), number of turns per coil, number of coils in one parallel path, extra length for termination in terminal box are required.
Length of conductors in one parallel path=[{LMT x (number of turns per coil) x (number of coil in one parallel path)} + extra length for termination in terminal box].
Further, the length of mean turn (LMT) is calculated based on relation by using at least two parameters one of a core length of the stator and a winding overhang are required.
LMT=2(Core length + winding over hang)
Further, the winding overhang is calculated by using at least two parameters one of a pitch and a profile of the conductor while placing from one slot to the other. Again the number of turns per coil is taken from the coil design and the number of coils in one parallel path is

calculated by using the relation with the parameters as number of slots, number of phases, and number of parallel path.
No of coils in one parallel path = {(No. of slots)/ (No of phases)/ (No of parallel paths)}
The method for making jointless winding is demonstrated considering the following configuration,
1. Three phase, double layer, short pitch, flexible conductor mush winding
2. No of slots-72
3. No of poles-16
4. Slots/pole/phase-1.5
5. Throw-4/4.5
6. No of parallel paths-2
7. No of leads brought in terminal box-3 Main + 3 Neutral
By using the above parameters and also by using the formula, the following parameters such as length of conductors in one parallel path and LMT (length of mean turn) and also no of coils in one parallel path is calculated. The advantages of the present invention is discussed below.
Advantages of the present Invention:
The advantages of the joint less winding are given as follows,
1) As the coil formation is directly taking place inside the core, formers for making coils outside the core is not required.
2) Reduction in size of overhang leading to reduction in size of the machine.
3) Cost saving due to increase in productivity and no usage of expensive filler and flux for joints.
4) As the leads are directly terminal box, no cable is required.
5) Increased life of the machine due to reduction in chances of failure due to weakness in joints.

WE CLAIM:

1. A method for three phase, double layer, jointless mush winding assembly for stator
of ac electrical machines, the method comprising:
- forming a first-phase winding by laying coils made of conductors starting from a
designated slot of a plurality of slots of a first parallel path, wherein the first-phase
winding comprises:
a) laying the conductors starting from the designated slot and continuously moving in anticlockwise or clockwise direction till the coils of the first parallel path of the conductors are placed in bottom of the slot or top half of the designated slot;
b) laying the conductors in a designated slots for next parallel path as in step (a);

- forming a second phase winding by following the steps of a) and b);
- forming a third phase winding by following the steps of a) and b).

2. The method as claimed in claim 1, wherein the conductors are placed at the top –half of the slots after the bottom of the slots are occupied.
3. The method as claimed in claim 1, wherein the first phase winding, the second phase winding, and the third phase winding is selected from a group comprising: a U-phase winding, a W-phase winding and a V-phase winding.
4. The method as claimed in claim 1, wherein, the terminals of conductors (U1,U1′) and neutral end (U2,U2′) of the first phase are taken to the terminal box such that said conductors have no joints.
5. The method as claimed in claim 1, wherein, the terminals of conductors (W1,W1′) and neutral end (W2,W2′) of the second phase are taken to the terminal box such that the said conductors have no joints.
6. The method as claimed in claim 1, wherein, the terminals of conductors(V1,V1′) and neutral end (V2,V2′) of the third phase are taken to the terminal box such that said conductors have no joints.

7. The method as claimed in claim 1, wherein, the length of the conductors is calculated for making all coils of atleast one of a parallel path based on a technical relation of a plurality of parameters, wherein said parameters comprises: length of mean turn (LMT), number of turns per coil, number of coils in a parallel path, extra length for termination in terminal box, wherein the length of mean turn is calculated based on core length of the stator and a winding over hang, wherein the winding overhang is calculated by using at least two parameters one of a pitch and a profile of the conductor while placing from one slot to the other, wherein the number of turns per coil is taken from the coil design, and wherein the number of coils in one parallel path is calculated based on the relation with a plurality of parameters as number of slots, number of phases, and number of parallel path.