GVPI Generators (failures & PD

issues)

Generators Users Group

Leopoldo Duque

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

GVPI Global Vacuum Pressure Impregnation

Stator three main components: core steel, copper and insulation

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

GVPI Global Vacuum Pressure Impregnation

The “green” coils or bars are often manufactured slightly oversized to ensure a tight fit (with dry mica paper or mica splitting tapes)

Green coils are then placed in the slots, simple wedging, end windings blocked and tied (prior to impregnation)

Then the entire stator is normally placed in a VPI tank and impregnated and baked for curing.

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

GVPI Global Vacuum Pressure Impregnation How get resin into groundwall?

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

GVPI Global Vacuum Pressure Impregnation How get resin into groundwall?

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

GVPI Global Vacuum Pressure Impregnation How get resin into groundwall?

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

PROS as per the Experts

Reduced cost

Process can be accelerated

Good performance

Mechanically very sound

Quality mainly dependant on the impregnating resin penetrating to the conductor stack in each coil - void free well bonded insulation system.

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

CONS as per the experts

Inadverted:

Small voids are left within the ground wall as a result of inadequated VPI.

Due to complex process of GVPI improper impregnation could happen in comparison with a conventional VPI or resin rich coils.

Making generators at lower cost has had a significant negative impact on the current fleet of generators, units less than about 15 years old or less had fail in service.

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

Case of study

“A” unit somewhere

Large unit, more than 15KV rated, 3600 rpm

Air cooled machine, GVPI

Almost 10 years of operation

Stator Failed to ground in service

B phase to ground - after investigation

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

Case of study the “A” unit

Unit Background

This unit has installed an on line PD (epoxy mica cap 80pF)

Very first PD Analysis was done 6 months prior the failure

PD patterns where identified as Voids in the slot section, electric slot discharge, Interphasal PD, low contamination, negative predominance (next test within 6 months), percentile ranking –moderate.

Unit was O3 Ozone producer

A couple of inspections prior to the incident, some minor repairs to some bars at the slot exit portion (grading and semiconductive paint)

2 sister units with same PD issues (Rank in moderate and high PD)

Bleaching semicond layers

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

Case of study the “A” unit Findings once the failed coil was removed for a partial rewind

GVPI Generators (failures & PD issues)

EE TE

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

Case of study the “A” unit Findings once the failed coil was removed for a partial rewind:

Evidence of PD activity and O3, off line test were carried out, high PD Activity

Off line PD values (inception PDIV @ 30% RATED VOLTAJE = 330nC and after 15 Max 750nC) Extremely high

IEC 60034-27 Off-line partial discharge measurements on the stator winding insulation of rotating electrical machines

Bar –slot section- showed evidence of voids between ground wall & copper strands.

Yellow powder Probably an indicative of severe PD activity

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

Case of study the “A” unit

Improper Impregnation Debonding PD copper vibration due Em forces ground wall deterioration then - vicious circle until coils gets grounded

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

Case of study the “A” unit

Improper Impregnation Debonding PD copper vibration due Em forces ground wall deterioration then - vicious circle until coils gets grounded

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

Case of study the “A” unit

The unit was partially rewound and get online after almost 1.5 months.

After a year unit was serviced for a generator swap

Now in service with a new winding design, no issues so far.

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

GVPI Global Vacuum Pressure Impregnation failures & PD issues

To avoid premature failures, the specifications are key for ensuring good manufacturing process and QC of modern generators.

Online & offline monitoring complemented with visual inspections with a support of experienced interpretation & diagnostics of the results may help to prevent big failures.

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

GVPI Generators (failures & PD issues)

Bibliography.

• STATOR MAGNETIC CORE DESIGN, DETERIORATION AND FAILURE

• PARTIAL DISCHARGE AS A STATOR WINDING EVALUATION TOOL

• IMPACT OF GENERATOR DESIGN ON COMPONENT DETERIORATION MECHANISMS

Clyde V. Maughan,

President Maughan Generator Consultants

Schenectady, NY, USA

• PROBLEMS WITH MODERN AIR-COOLED GENERATOR STATOR WINDING INSULATION

Gary Griffith - Florida Power and Light USA

Shelagh Tucker & Jason Milsom - National United Kingdom

Greg Stone -Iris Power Engineering Canada

• Warning given of serious PD problems on large turbo, with global VPI stator, followed by in-service stator failure

Company: National Power, UK

• Insulation System Materials and Processing for Motors and Generators

Dr. Nancy Frost

Krempel Insulation Technologies

2013 IRMC, New Orleans

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.

THANK YOU

•“All rights reserved, the information contained herein constitutes a trade, industrial and commercial secret, confidential and property of Compañía Mexicana de Gerencia y Operacion, S.A. de C.V.,

y/o Mitsui & Co. Power Development and Management Americas, S. de R. L. (in conjunction the "Proprietors"), therefore it is prohibited to distribute, disclose, reproduce, or give a different treatment

than the purpose of this presentation, without express and written consent of the Proprietors”.