FIELD OF THE INVENTION
The present invention relates to a multi-layered looped field coil device for salient
pole synchronous machine.
BACKGROUND OF THE INVENTION
Salient Pole Synchronous machine finds wide application in Synchronous
generators, drive for pumps in lift irrigation and drive for compressor in refineries
and steel industries. In salient pole machines, according to speed of drive the
number of poles are selected and pole bodies are bolted to solid shaft on which
main rotor field coils are placed. These coils are then connected in series.
Coils are designed with copper strips with required dimensions keeping in view of
excitation requirements of machine and permissible temperature rise. In view of
stringent starting conditions and frequent start/stops, the field end connectors
should be stress free, reliable and designed to have minimum contact resistance
to eliminate any local heating in joints which may cause melting of connectors.
As per conventional practice, each turn is made from copper strips, is in-parallel-
joined by a jig-saw joint (Figure 1, detail X). These copper strips are produced by
male female dies of high accuracy to ensure clearance to allow the fluid brazing
material to penetrate thoroughly. End connectors are brazed to the flat strips
having V shape groove (see figure 1, detail Y).
Another conventional practice is looped coil construction (figure 2) with end
connectors as an integral part, formed by bending the end copper at start and
stop of coil. Dummy coils (profiled copper, Item 03, 04 and 05 of figure 2) are
then brazed at these end connectors for consolidation of coil.

However, the basic disadvantage of the prior art looped field coil device is that
the end connectors are often melted and dislodged from the machine due to
heat generation.
OBJECTS OF THE INVENTION
It is therefore an object of present invention to propose a multi layered looped
field coil device for salient pole synchronous machine, which eliminates the
disadvantages of prior art.
Another object of the invention is to propose a multi layered looped field coil
device for salient pole synchronous machine, which is provided with improved
end connectors to maintain a low contact resistance of brazed joint and restrict
rise of localized temperature in the joints.
A further object of the invention is to propose a multi layered looped field coil
device for salient pole synchronous machine, which is easy to manufacture and
assembled at a lower cost.
SUMMARY OF THE INVENTION
According to the invention, the basic concept is to reduce the contact resistance
of the field coil and end connectors, and to shift point of brazing from a
maximum stress region so as to eliminate crack initiation point. The proposed
construction of the looped field coil device reduces the contact resistance of the
joints so as to restrict localized heating of the joints which otherwise would here
resulted in opening of joints due to melting. Further, the present invention
considerably reduces time to manufacture the coils due to the fact that

dependency on skilled manpower for brazing including manufacture of profiled
copper is reduced.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 - Shows a schematic diagram of a conventional type copper strips
brazed by jig saw joint, parallel in each turn (Prior Art).
Figure 2 - Shows a schematic diagram of a conventional type looped coil and
dummy turn profile copper (Prior Art).
Figure 3 - Shows a schematic diagram of a looped field coil device according
to the invention.
DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE
INVENTION
As shown in figure 3, the lopped field coil device is made from flat copper strip
wound edgewise on a former to produce a coil which fits over the insulation of
the pole. Var 00 and Var 01 are two adjacent different pole coils. Start and end
points (01,02) of formation of coil. The number of turns is decided as per
excitation requirement. The coils turns are alternatively finned to increase the
heat transfer capability. End connectors (item 03 and 04) are then brazed at
straight portion of coil at start and end positions (01,02). These connectors
(03,04) are profiled copper of thickness identical to that of the field turn, and
carved out of a single copper sheet to match the profile of the coil.

WE CLAIM
1. A multi layered looped field coil device for salient pole synchronous
machine, comprising:
- a coil produced on a former through edge-wise winding of a flat
copper strip, the produced coil matchingly disposed over the
insulated poles, wherein the number of turn of the coil is selected
according to desired excitation value and wherein the coil-turns are
alternatively finned to increase heat transfer area; and
- at least two end connectors rigidly connected on straight portion of
the coil and formed of a profiled copper sheet with thickness
identical to the field turn of coil.

2. The device as claimed in claim 1, wherein the end connectors are brazed
at starting and end points of said straight portion of the coil.
3. The device as claimed in claim 1 or 2, wherein the end connectors are
profiled copper having a thickness identical to that of the coil to reduce
the contact area between the two.

ABSTRACT

The invention relates to a multi layered looped field coil device for salient pole
synchronous machine, comprising: a coil produced on a former through edge
wise winding of a flat copper strip, the produced coil matchingly disposed over
the insulated poles, wherein the number of turn of the coil is selected according
to desired excitation value and wherein the coil-turns are alternatively finned to
increase heat transfer area; and at least two end connectors rigidly connected on
straight portion of the coil and formed of a profiled copper sheet with thickness
identical to the field turn of coil.