Transformer TestsTransformer Tests

Oil tests and on-line monitoring can increase transformer life expectancy

By: William Morse

Morgan Schaffer Inc.

MORGANSCHAFFER

TM

Transformers – The Inside View

TransformersTransformers

The heart of a substation

Needed to transmit electricity over long distances

Steps up or steps down voltage

The Inside ViewThe Inside View

Ready to work again Ready for repair

Oil, the Blood of the TransformerOil, the Blood of the Transformer

Part of the Insulation System– Excellent dielectric

properties

Cools the transformer– Excellent heat transfer

properties

Ease of access

Standard ASTM Tests for Insulating OilStandard ASTM Tests for Insulating Oil

Description ASTM NumberDielectric Strength D-877/D-1816Acidity D-974Interfacial tension D-971Color D-1500Water Content D-1533Density D-1298Visual examination D-1524Power factor D-924Dissolved gas analysis D-3612Inhibitor content D-4768Furan Analysis D-5837Metals Analysis ICP

Dielectric StrengthDielectric Strength

Acceptable limit for serviced aged oil: 25 kV

Interfacial TensionInterfacial Tension

Acceptable limit for serviced aged oil: 18 dynes/cm

Water ContentWater Content

The Past And The Present

Limit for serviced aged oil: 35 ppm

Dissolved Gas AnalysisDissolved Gas Analysis

The most important test you can perform on your transformer

Dissolved Gas AnalysisDissolved Gas Analysis

High vacuum gas extraction apparatus– Extracts all dissolved

gases found in the oil sample

– Determines dissolved water in ppm as well

– Extraction of all gases in less than 2 minutes

Gas Chromatographic AnalysisGas Chromatographic Analysis

CH4CO

CO2

C2H4

C2H6

C2H2

Oil Breakdown ProductsOil Breakdown Products

Partial DischargePartial Discharge

OverheatingOverheating

ArcingArcing

Two More Important TestsTwo More Important Tests

Furan analysis– Determines the state of the solid insulation

Metals analysis– Used to pin point the location of a fault

Predictive MaintenancePredictive Maintenance

On-site analyzers– Increase the frequency of testing– More data points – Better decisions

On-line monitors– Needed for critical transformers– Warn of developing problems between routine

maintenance

PHA-1000 Hydrogen AnalyzerPHA-1000 Hydrogen Analyzer

Fastest way of screening transformers.

Analyzes Hydrogen - A key gas produced by all fault types

High sensitivity and wide range

Simple operation

Accurate H2 readings in 60 seconds

Analysis of H2 only = No cross contamination

No special training required

MYRKOS Fault Gas Analyzer

A Full DGA Lab in the field

Typical Gas Extraction Typical Gas Extraction ApparatusApparatus

High vacuum gas extraction apparatus– Fragile– Not very portable– Special training

required

The Shake Test Syringe

Syringe must be filled so thatmetering pin is completelyoutside of syringe cap.

Completely portable

No special training required

Eject the excess oil by pushing the piston until the metering pin hits the syringe cap.

An exact amount of oil is measured using a metering pin located on the syringe piston shaft.

Mixing the oil with CO2 free ambient air:

• Connect syringe to CO2 trap• Open syringe and CO2 trap• Slowly pull syringe piston to the end• Close syringe and CO2 trap• Disconnect CO2 trap

Ambient CO2 free air is pulled into the syringe which is then vigorously shaken to speed up gas diffusion from the liquid phase to the gas phase.

Method accepted by IEC 60567

and ASTM D-3612

Complete DGA in 2 minutes on-site

Once the test is initiated, automatic sampling occurs and outputs are obtained from both modules (A & B) simultaneously. Calibration is then performed at a click of the mouse button.

On-line MonitorsOn-line Monitors

Continuously measure gas concentration Store data and trigger alarms

CalistoCalistoDissolved Hydrogen and Water MonitorDissolved Hydrogen and Water Monitor

Intelligent Electronic Device IED

Highly Accurate and Precise

Monitors Oil-Filled Transformers

Designed for Extreme Environments

Communicates with the World

Oil circulation and gas extraction circuits

Gas Extraction TechnologyGas Extraction Technology

H2 detection cell

Specially designed thermal conductivity detector

Specific to Hydrogen

No interference from other gases

Gas extraction chamber

Primary Heat exchanger

Oil circulation pump

Water sensor

H2 detector port

CalistoCalistoDissolved Hydrogen and Water MonitorDissolved Hydrogen and Water Monitor

Continuous Hydrogen measurement

Two alarm levels

Data storage and trending softwareH2

Why Hydrogen?

Hydrogen is produced in all transformer faults. Calisto will detect the fault before the Bucholz relay is tripped.

Continuous dissolved water measurement

Two alarm levels

Data storage and trending software

Reported in ppm or %RS at 25CH2O

CalistoCalistoDissolved Hydrogen and Water MonitorDissolved Hydrogen and Water Monitor

Why water?

Along with polar compounds and acids water can adversely affect the dielectric properties of the solid insulation

InstallationInstallation

Salt River Project Phoenix, Arizona, USA GE 20 MVA 69 Kv

InstallationInstallation

InstallationInstallation

InstallationsInstallations

MPEB Bhopal, India DUBAL Dubai, UAE

CommunicationCommunicationEthernet

RS-232

Modem

Fiber Optic

Wireless

RS-485

Gas TrendingGas Trending

Case Study 650 MVA GSU Transformer Case Study 650 MVA GSU Transformer failure and Repairfailure and Repair

DGA results as of November 11th, 2001

Table 2: H2 generating rates from May 30th to Sept. 26th 2002 Dissolved water

Sudden increase in hydrogen generating rate

Nov. 2001Initial source of high electrical resistance (e.g. bad connection)

May 2002 to Sept. 17th 2002Resistive hot spot of increasing resistance (H2, CH4, and C2H4)

Between Sept. 17th and Sept. 30th (Sept. 27th ?)Additional energy probably through circulating currents

Burned high voltage lead

Source of incipient fault

Burnt Lead

Overheated Connector

Mirant GSU – Update as of February 19th, 2003

Constant H2 level at approx. 30 ppm

Preventive Maintenance It PaysPreventive Maintenance It Pays

Thank you