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Resin vs VPI: Coil Insulation Guide

This document compares the advantages and disadvantages of resin rich and VPI impregnated coil insulation systems. Resin rich coils use different resins in the slot and end winding areas to account for coil movement. They allow for partial repairs and on-site installation. However, they are more expensive and the end winding can contain voids. VPI coils are less expensive to manufacture but require additional processing and equipment. They provide homogeneous insulation but the rigid resin can cause cracking over time and bracing in the end winding can loosen. Both systems have tradeoffs between cost, repair ability, and insulation performance over the life of the machine.

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253 views2 pages

Resin vs VPI: Coil Insulation Guide

This document compares the advantages and disadvantages of resin rich and VPI impregnated coil insulation systems. Resin rich coils use different resins in the slot and end winding areas to account for coil movement. They allow for partial repairs and on-site installation. However, they are more expensive and the end winding can contain voids. VPI coils are less expensive to manufacture but require additional processing and equipment. They provide homogeneous insulation but the rigid resin can cause cracking over time and bracing in the end winding can loosen. Both systems have tradeoffs between cost, repair ability, and insulation performance over the life of the machine.

Uploaded by

supriya rakshit
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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RESINRICH

ADVANTAGES:
 Highly uniform impregnation of the resin in the slot portion reducing the risk of
partial discharge occurring
 Rigid resins are used in slot cell section of the coil and different resins with resilience
to coil movement are used in the end winding i.e. resin containing flexibilisers
 Capability to control partial discharge in the slot, and remedial action in service is
practical during insulation system life
 Partial repairs are practical i.e. coils which have failed can be replaced
 Coils can be installed on site as there is no requirement for further processing (i.e.
the VPI process)
 End winding bracing systems can be improved & made more robust to meet
operational requirements
DISADVANTAGES:
 The coils are more expensive (typically offset by the additional cost of the VPI
process)
 End winding can contain voids, but since the end winding surface becomes charged
to coil voltage, breakdown of internal voids is not a problem other than at the first
bend under the stress grading tape
 End winding insulation and blocking is not a homogeneous system therefore more
dependent on competence of winders
 Resin rich coils in the end winding can be more prone to chemical attack than VPI
windings (Our Resin Rich coils incorporate a sealant tape mitigating this risk)
VPI
ADVANTAGES:
 Reduced manufacturing cost (often offset by the cost of the VPI process)
 Fast to install due to high level of flexibility
 No scarf joint at end of coil slot straight meaning the straight length can be reduced
 Reduced risk of voids in the end winding
 Homogeneous insulation & bracing
 Gives good insulation resistance
 Inherently Resistant to moisture & chemicals
DISADVANTAGES:
 Cost of buying and maintaining the VPI equipment and materials such as tank and
resin
 Only one resin type can be used in the VPI process since the complete stator and
winding is impregnated in one process. To maintain stability of coil in slot the resin
needs to be a rigid thermo setting resin
 Multiple processing required for good surface finish
 After 15 -20 years’ service the rigid resin can cause cracking in the end winding
due to the frequency related movement
 Maintaining the coil parallel in the slot portion can be difficult (increasing the risk of
partial discharge)
 Due to differential expansion the coil to coil bracing in the end winding can result in
loosening of the bracing between coils which will require regular rectification during
the life of the machine
 There are a range of resins used in the VPI process The lower viscosity resins used
by manufactures are difficult to maintain and need a high resin turnover
 Retaining resin in the stator winding during curing generally requires stator rotation
during the curing process, which is easier for manufacturers who wind a stator core
pack before inserting the cured stator core pack into the stator case
 Since the complete stator needs to be processes the VPI vacuum/pressure vessel
needs to be large enough to accommodate the stator case
 Stators which have been VPI impregnated are very difficult to repair.
 Complete rewinds are more expensive due to difficulty of removing the old winding
This becomes a major issue for machines which can only be rewound on site

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