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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
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