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Ing. Ricardo Rivero Energy Sector Power Distribution

Gestión inteligente de Transformadores estratégicos

CIGRÉ México, 15 de Junio del 2011

15-Jun-2011 Energy Sector / ED SE Ing. Ricardo Rivero

Agenda

A) General information

B) Regular and Advanced Diagnostic

C) Strategic transformer management program

D) Monitoring system on line

E) References


Mortality Rate by Age

•Source: CIGRÉ

0

5

10

15

20

0 10 20 30 40 50 60

Age of Transformer

% F

ailu

res GSU

Network

A) General Information



Transformer failures:

Winding insulation

Bushings

Tap changers

Other areas of concern:

Pollution, dust & debris affecting

bushings & cooling systems

Cooling System inefficiency



Brittle insulation increases failures

Overloading increases heat = aged insulation

O2 & moisture in oil break down insulation

Short circuits ‘overpower’ older designs

Why does insulation break down ?



Bushings

Inherent design (Type U)

Tracking (Dust)

Tap Changers

Mechanical linkages

Cooling Systems

Blockage leads to heating & inefficiency

Transformer not rated to nameplate


B) Regular and Advanced Diagnostics

Regular and Advanced Diagnostics

Routine Electrical Testing FRA (Mechanical movement of the

windings) DFR (Dielectric properties of insulation system) ADGA (Dissolved gas analysis using design characteristics)


Routine Electrical Testing

Insulation Power Factor

Insulation resistance of windings and core

Transformer Turns Ratio (TTR)

CT ratio & polarity

Winding Resistance

Winding Excitation

Infrared Scanning



Routine Oil Analysis

General Chemistry

Dissolved Gas Analysis (DGA), Concentrations of H2, ethane, ethylene, methane, & acetylene



FRA Frequency Response Analysis (FRA) is a method of measuring the transfer function of the windings of a transformer. Changes in the transfer function reveal a wide range of failure modes, for example:

Axial Winding Collapse

Hoop Buckling

Shorted Turns



FRA: Axial Collapse

Axial winding collapse is likely to have the following characteristics:

Produced within a transformer winding due to excessive axial forces during a fault Failure likely to be catastrophic if transformer continues in service


FRA: Hoop Buckling

Hoop buckling is produced within a transformer winding due to excessive compressive forces during a fault.


FRA: Hoop Buckling


FRA: Shorted Turns

Shorted turns in transformers are produced by turn-to-turn faults and may have the following characteristics:

Adjacent turns lose paper and braze/weld together They result in a solid loop around the core


DFR The Dielectric Frequency Response (DFR) test is a series of power factor measurements at multiple frequencies. It provides more information about the dielectric behavior of the insulation system. The method be used to diagnose the following conditions in transformers:

Moisture in the cellulose insulation

High oil conductivity due to aging or overheating of the oil

Chemical contamination of cellulose insulation

Carbon tracking in cellulose

High resistance in the magnetic core steel circuit



60

Distinguishing Between Aged Oil and Moisture

DFR


Fitting the Right Dielectric Parameters

60

DFR


Dielectric Response Fingerprint Function caused by a High

Core to Ground Resistance in Auxiliary Transformer

.01 .10 1 10 100 1000

Frequency, Hz

XV to Ground

XV to Ground after Repair

High Core Ground Resistance

DFR


Adv DGA

Close observation of dissolved gases in the oil and other oil properties provides the most valuable information about transformer health. DGA analysis tools takes the following into considerations:



3D Simulation Solutions of Field Problems

verifications of hot-spot

verification of electric field

analysis and solution of overheated bus-duct in large GSU’s

determining overload-ability.

Electrical field distribution over the winding / HV bushing insulation structures



A series of assessments to provide optimal asset decisions …

Phase I – Fleet Risk Screening

Phase II – Condition & Design Evaluation of Critical assets

Phase III – Life Profiling

Phase IV – Implementation

Prioritization of critical assets

Improved capital forecasting Reduced O&M spending Improved availability and reliability Improved operational efficiencies Improved environmental, public safety profile



130 units total



Plot of Risk of Failure versus Importance

Urgent = 10

Priority = 40

Normal = 80



30-50% OF MAINTENANCE ACTIVITY IS UNNECESSARY

(CIGRE-2000)

OVERSPENDING

OS

UNDERSPENDING

US

$ $ $ $

OS=US - balanced budget OS>US - lower maintenance $$$

TRANSFORMERS

RISK OF FAILURE PER TRANSFORMER

MAINTENANCE $$$ PER TRANSFORMER

Budget Expenditures vs. Risk



Transformador Cromatógrafo de Gases Análisis de Disolución de Gases

GAS-Guard 8

Internet

Cuarto de Control Existente

Sistema de Monitoreo Y Gestión de Activos Siemens

SMGAS

Gestión de Mantenimiento y Alarma en caso de contingencia

Avisos / Alarmas / Informes Acciona

F.O. ETHERNET

ETHERNET

DNP i

Switch

Firewall VPN

Firewall VPN



Transformador

Internet

Cuarto de Control Existente

Sistema de Monitoreo Y Gestión de Activos Siemens

SMGAS Software WEB UI, con alarma Y recomendación de acciones

Avisos / Alarmas / Informes Acciona

F.O. ETHERNET RS485 DNP3

Switch

Firewall VPN

Firewall VPN

F.O. ETHERNET ETHERNET



Respaldo de Monitoreo y en caso extremo respaldo de Control y Operación Hacia Acciona vía VPN



E) References

Repair and retrofitting through - Transformer Lifecycle Management Siemens AG 2010

Sitram - Monitoring - Transformer Lifecycle Management Siemens AG 2010

Energy automation Siemens 2011

Service Handbook for Power Transformers ABB 2006

IEEE C57.125 – IEEE Guide for Failure Investigation, Documentation, and Analysis fro

Power Transformers and Shunt Reactor

C. Sweeter and T. McGrail, “Sweep Frequency Response Analysis – A Technical Paper

from Doble Engineering”, Ver. 1.0 January 2003

McNutt, W.J. “CIGRE Survey on maximum Safe Operating Hot Spot Temperature”,

From EPRI Proceedings on Transformer Overload and Bubble Evolution, EL-5807-SR,

Junio 1988, pp. 5.2.1-5.2.4

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