1. FIELD OF THE INVENTION
The present invention relates to moulded insulating spacers for assembly in the end
zones of hydro generators to achieve requisite cooling air flow distribution in stator.
More particularly, it relates to design and fastening arrangement of moulded insulating
spacers suitable for in-situ installation at site on stator between stator bars and inlet of
pressing plates to achieve the desired cooling air flow distribution between core and
end zones of stator in hydro generators.
2. BACKGROUND AND PRIOR ART OF INVENTION
Conventionally, hydro generators are air cooled machines. The stator core is built up of
laminations with ventilation ducts provided at regular intervals along the length of
stator core, these being formed by steel spacers welded to adjacent stampings. The
segments are secured to the frame by dovetail notches engaging with corresponding
dovetail key bars welded to stator frame. Stator core is pressed between steel end-
plates through radial fingers welded to them. Pressing fingers are made of rectangular
steel sections and exert pressure on teeth of stator core also. Cold air in the end zones
flows through the openings between the pressing fingers. For purpose of cooling of
active zones, cold air is circulated by the rotor of hydro generator. For optimum cooling,
the cold air thrown into the air gap is required to be distributed between the stator core
and end zones in proportion to losses & heat in these zones.
Cold air flow distribution is governed by the hydraulic resistances of stator core and end
zones which are mainly dependent upon the geometry of air flow paths. For stator core,
hydraulic resistance depends mainly on the number and size of ventilating spacers and
their layout/ configuration whereas, for end-zones, it depends on the number and size
of openings between pressing fingers. It is, generally, observed that for 10 mm thick
ventilating spacers forming 10 mm high ventilating ducts, no special considerations are
needed for design of end zones to achieve requisite air flow in the stator core and end
zones. However, with smaller ventilating spacers of sizes 6 mm and less, the hydraulic
resistance of stator core increases substantially which necessitates special design
considerations for achieving optimum air flow between stator core and end zones. The
hydraulic resistance of end zones is required to be suitably increased by partially
blocking openings between pressing fingers so as to direct requisite cold air through the
stator core.
Conventional design envisages welding of steel strips at exit of radial pressing fingers of
stator core pressing plates at outer periphery of stator core during manufacturing to
increase the hydraulic resistance of the end zones by partially blocking air passages so
as to direct air to the stator core as estimated. These strips are welded on pressing
plate assembly during manufacturing. The prior art arrangement is such that the
locations where these steel strips are welded are inaccessible after completion of stator
assembly and there is no scope of readjustment of air flow distribution after the
machine is put into operation.

Being tailor-made machines, it is observed that hydraulic resistances of various air flow
paths of hydro generators are not predictable accurately and actual air flow and its
distribution during operation can be at variance with the estimation - more so for a new
size of ventilating spacers introduced in a new design. Air flow distribution
disproportionate to losses & heating leads to high temp, in that zone and the machine
cannot be loaded to its rated capacity. Introduction of 6 mm ventilating spacers in the
design of hydro generators for first time led to a situation where the actual air flow
distribution was not proportionate to losses and stator winding and core temp, were
high because of deficit air in the ventilating ducts of stator. Consequently, the machines
could not be loaded to their rated capacity. The conventional arrangement of welding
suitable steel strips at exit of radial pressing fingers is not feasible in-situ and,
therefore, any readjustment in air flow distribution is also not feasible.
The present invention seeks to make readjustment of air flow distribution feasible at
site with in-situ installation of moulded spacers wherever the need arises to overcome
the drawbacks of the prior art mentioned above.
3. OBJECTS OF THE INVENTION
It is therefore an object of the invention to make a provision in end zones (turbine and
exciter ends) where modification of the hydraulic resistances of air passages of the

ventilation system to air flow in these zones is feasible at site to achieve requisite air
flow distribution through stator core and end zones of hydro generators.
Another object of the invention is to provide insulating spacers which can be installed
in-situ at site at both end zones (turbine and exciter ends) between lower layer of
stator bars and inlet of stator core pressing plates.
Yet another object of the invention is to provide suitable fastening arrangement of
these insulating spacers with the stator bars for in-situ adjustments.
4. BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS:-
Fig.-1 - Shows pressing plate with steel strip welded at exit of fingers in prior art.
Fig.- 2 - Shows stator cross-section with pressing plates having steel strips welded at
exit of pressing fingers (prior art).
Fig.- 3 - Shows typical views from stator cross-section having conventional design
of pressing plates with welded steel strips (marked in figure 2).
Fig.- 4 - Shows the moulded insulating spacer in accordance with the invention.
Fig.- 5 - Stator cross-section showing installation of moulded insulating spacers at inlet
of pressing plates.

Fig.- 6 - Typical sections from stator cross-section for installation of moulded insulating
spacers at inlet of pressing plates (marked in figure 5).
Fig.- 7 - Photographic view of moulded insulating spacers according to invention
provided in hydro generators.
Fig.- 8 - Photograph of assembled moulded insulating spacers according to invention on
stator of hydro generators.
The invention will now be described in detail in an exemplary embodiment as
depicted in the accompanying drawings. There can however be other embodiments
of the invention, all of which are covered by this description.
5. DESCRIPTION OF THE INVENTION:-
The invention envisages provision of moulded insulating spacers (4.00) which can be
installed between lower layer of stator bars and inlet of stator core pressing
plates(1.02). These spacers are so designed that they partially block the openings
between pressing fingers (1.01) at inlet of stator core pressing plates and direct more
cold air to flow through stator core. The spacers are inserted on both ends (turbine and
exciter ends) of stator core and rest on the radial pressing fingers (1.01).
Each spacer would cover one pressing plate. Moulding from insulating material was
preferred to machining from glass textolite in view of large number of pieces and,
primarily, to achieve uniformity of the required accuracy.

These spacers are glued with insulating packing (5.01) so as to fill the gap and ensure
minimum leakage path for cold air. After insertion, these spacers are suitably tied with
the stator winding bars using braided glass sleeve for fastening.
By modifying the height of teeth of spacers; the openings between pressing fingers on
both ends of stator core can be regulated to increase or decrease air flow through end
zones in the stator core.
From analysis of electrical design, losses in various active parts are known which
determine the required proportion of cold air in each path. Ventilation calculations are
carried out to work out the hydraulic resistances of various paths for determining the
height of moulded spacers which would partially block openings between pressing
fingers at inlet of pressing plates. The advantage of using spacers is that
these can be suitably adapted at site or can be replaced in-situ as required.
In the conventional design as seen in Fig.1, steel strips (1.03) of smaller width than the
height of pressing fingers (1.01) are welded at exit of fingersduring manufacturing of
pressing plates (1.02). These steel strips are located at outer periphery of stator core
before the cold air enters the annuals between stator core and the frame. Number of
these pressing plates are assembled on both ends of stator core as shown in figure 2.

Views A & B of Fig.2 shown in figure 3 show the air passages thus blocked by the steel
strips (1.03) at exit of pressing fingers and openings left for air flow in the end zones.
After completion of stator assembly, these steel strips are not accessible and therefore,
regulation of openings for redistribution of air flow is not feasible at site after units are
put into operation.
The present invention envisages providing moulded insulating spacers (4.00) of special
design shown in figures 4 and 5 which are installed between lower layer of stator
winding bars and inlet of pressing plates after laying of stator windings. These
insulating spacers, best seen in Fig. 4, have a comb-like configuration, with a plurality
of teeth (4.01), which have openings (4.02) between adjacent teeth. These openings
are so dimensioned as to fit properly on the pressing fingers while the teeth partially
block the openings between fingers for flow of air.
In the proposed arrangement according to the invention, spacers are installed at
accessible location and, therefore, can be installed in-situ after complete assembly at
site. The spacers are fastened with the stator bars with braided glass sleeve which
makes it possible to replace the spacers in-situ after removing the sleeve.
Few details of fastening are elaborated below:-

As best seen in Fig. 4, for fastening at both ends, each spacer (4.00) has provision of
two grooves (4.03) with tapered edges to restrain the braided glass sleeve from
slipping. There is also an undercut slot (4.04) between the grooves to secure the
braided glass sleeve within the slot to restrain its movement. Details of tapered grooves
(4.03) and the undercut slot (4.04 in section A-A) between them are shown in Fig.4.
Braided glass sleeve fastening/bracing (5.02) is shown in Fig. 5 & 6.
Installation and fastening of insulating spacers with the stator windings is shown in
figure 5.These spacers partially block the air passages at inlet of pressing plates as
shown in sections c-c & d-d of figure 6 and thus the height of teeth of spacers regulate
the hydraulic resistance of air passages of end zones. Rgure 8 shows typical pictures of
such spacers installed on stators of hydro generator during an experiment conducted
with 42 MW hydro generator.
The moulded insulating spacers (4.00) according to the invention have proven
successful in an experiment conducted with 3 units of 42 MW each hydro generators.
These machines were experiencing problem due to high stator temperature.
The hydro generators involved in the experiment have 60 stator core pressing plates of
two variants on each end zone - 30 nos. of variant 1 having four pressing fingers (1.01)
each and 30 nos. of variant 2 having five pressing fingers (1.01) each.

Accordingly, two types of moulded spacers were used on both end zones i.e. 30 nos.
are installed on pressing plates having five fingers each and 30 nos. are installed on
pressing plates having four fingers each. After installation of these spacers, air flow
distribution met the design requirements and the machines could operate successfully
at 10% overload as per design specifications.
6. ADVANTAGES
The comb-shaped moulded insulating spacers (4.00) and arrangement of assembly in
the end zones of stator have the advantage of in-situ installation at site after the
machines have been put into operation. These spacers can be suitably adapted or
replaced to achieve the desired cooling air flow distribution between core and stator
end zones of hydro generators.
WeClaim:-
1. Moulded insulated spacers (4.00) for hydro generators having a comb-like
configuration with a plurality of teeth (4.01) and openings (4.02) positioned
between adjacent teeth, characterized in that the insulated spacers are installed
between lower layer of stator winding bars (3.01) and inlet of pressing plates
(1.02) to partially block the air passages at inlet of pressing plates in the end
zones of a hydro generator.
2. Moulded insulated spacers as claimed in claim 1, wherein height of their teeth
regulates the hydraulic resistance of air passage of end zones in a hydro
generator.
3. Moulded insulated spacers as claimed in claim 1, which can be installed
in hydro generators in-situ as required.
4. Moulded insulated spacers as claimed in claim 1, wherein the spacers are
inserted on both turbine and exciter ends of stator core of a hydro generators
and rest on the radial pressing figures (1.01).
5. Moulded insulated spacers as claimed in claim 1, wherein the spacers are glued
with insulating packing (5.01) to fill the gap and to ensure minimum leakage
path for cold air.
6. Moulded insulated spacers as claimed in claim 1, wherein the spacers are
fastened with stator bars with braided glass sleeve to enable replacement of the
spacers in-situ.
7. Moulded insulated spacers as claimed in claim 6, wherein the said spacer is
provided with two grooves (4.03) with tapered edge to restrain the said braided
glass sleeve from slipping.
8. Moulded insulated spacers as claimed-in claim 7, wherein an undercut slot
(4.04) is provided between the grooves to secure the braided glass sleeve
within the slot to restrain its movement.

Moulded insulated spacers (4.00) for hydro generators having a comb-like configuration
with a plurality of teeth (4.01) and openings (4.02) positioned between adjacent teeth,
characterized in that the insulated spacers are installed between lower layer of stator
winding bars (3.01) and inlet of pressing plates (1.02) to partially block the air passages
at inlet of pressing plates in the end zones of a hydro generator.