transformer winding hot spot temperature determination 2006 new mexico... · transformer winding...

Transformer Winding Hot Spot Transformer Winding Hot Spot Temperature DeterminationTemperature Determination

Weidmann-ACTI’s Fifth Annual Technical ConferenceNovember 2006

Albuquerque, NM

Manitoba HydroManitoba Hydro

W.W. McDermidMcDermid

Neoptix, Inc.

Jean-Noël BérubéJacques Aubin

Why Monitoring Temperatures ?Why Monitoring Temperatures ?

In power transformers, winding temperatures In power transformers, winding temperatures have a direct impact on insulation aginghave a direct impact on insulation aging

Proper monitoring of operating temperatures Proper monitoring of operating temperatures are essential to assess the value of insulation are essential to assess the value of insulation aging and resulting remaining lifeaging and resulting remaining life

Allows for better asset management and Allows for better asset management and revenue generation strategiesrevenue generation strategies

Limitations of TransformerLimitations of TransformerTemperature Rise TestsTemperature Rise Tests

“Heat Run” tests reveal “Heat Run” tests reveal averageaverage winding temperature winding temperature under rated loadunder rated load

What is of interest for insulation aging is the winding What is of interest for insulation aging is the winding hottest spot temperaturehottest spot temperature

Temperature is highest at top of windingTemperature is highest at top of windingOil is hotterOil is hotterStray losses in winding are higherStray losses in winding are higherWinding insulation often calls for more paper to provide better Winding insulation often calls for more paper to provide better insulation against voltage surgesinsulation against voltage surges

Correct knowledge of operating temperatures is needed Correct knowledge of operating temperatures is needed to evaluate insulation aging and remaining lifeto evaluate insulation aging and remaining life

Winding insulation Winding insulation sensitivity to temperaturesensitivity to temperature

0.01

0.1

1

10

100

1000

60 80 100 120 140 160 180

Hot-Spot temperature

Agi

ng A

ccel

erat

ion

Fact

or Normal KraftPaper (IEC)

Normal Kraft paper (IEEE)

.

Thermally Upgraded Paper

Winding Hottest Spot Winding Hottest Spot Temperature ModelTemperature Model


Winding hot-spot temperature

Top oil temperature

Temperature (oC)

Win

ding

Oil


Top-OilTemp.

Hot-SpotTemp.

AverageWindingTemp.

Hot-SpotRise


Winding hot-spot temp.

= Top-OilTemp. + Hot-spot rise

at rated load * (%Load)2m

For any load level, the hottest winding temperature is assumed to be:

For several decades, this method was a standard feature:

• IEEE C57.91 - 1995 “IEEE Guide for Loading Mineral Oil Immersed Transformers”

• IEC 60354 - 1991 “Loading Guide for Oil-Immersed Power Transformers”


This simplified method is now regarded as inadequate• To estimate the aging of transformers • Given increasing occurrences of overloads

IEEE and IEC are proposing new methods to take account of (neglected in the previous equation):

• True oil temperature in the cooling duct• Change in winding resistance with temperature• Change in oil viscosity with temperature• The effect of tap changers• Oil inertia in case of sudden overload of large magnitude


This evolution in calculation method indicates:• Methods used until now are not very accurate• New methods will require additional parameters

that are not always readily available• New models still rely on information provided by

the transformer manufacturer and not always validated

• Direct measurement of winding temperature with fiber optic sensor is recognized as the best method

Direct Temperature MonitoringDirect Temperature MonitoringDirect winding temperature measurement provides valuable information for design, heat-run testing, maximizing loading and maintenance

Safely maximizes transformer loading

Avoids catastrophic failure and emergency shutdowns by monitoring long-term, gradual transformer deterioration

Allows better timing for winding cooling requirements, Allows better timing for winding cooling requirements, to avoid overheating around hotto avoid overheating around hot--spot immediate areasspot immediate areas

Gathers valuable information for scheduling maintenance and replacement of units

Introduction to Fiber OpticIntroduction to Fiber OpticFiber optic (glass) is a method of carrying information, Fiber optic (glass) is a method of carrying information, as a copper wire. But unlike the copper wire, fibers as a copper wire. But unlike the copper wire, fibers carry light (photons) instead of electricity (electrons)carry light (photons) instead of electricity (electrons)

Some advantages of fiber optic are compared to RTD Some advantages of fiber optic are compared to RTD sensors and IR based sensors:sensors and IR based sensors:

Immunity to electromagnetic fieldsImmunity to electromagnetic fieldsAll dielectric material probe constructionAll dielectric material probe constructionCan be installed in harsh environmentsCan be installed in harsh environmentsRobust, flexible and chemically resistant probesRobust, flexible and chemically resistant probesTrue intrinsic safety in explosive environmentsTrue intrinsic safety in explosive environmentsMinimal thermal shuntingMinimal thermal shuntingRelative ease of installationRelative ease of installation

Operating PrincipleOperating Principle

Based on a well understood and Based on a well understood and reproducible phenomenon: the reproducible phenomenon: the variation variation in the in the absorption absorption spectrum spectrum of the semiconductor of the semiconductor GaAs with respect to GaAs with respect to temperaturetemperatureA A direct contactdirect contact temperature temperature sensorsensor

System DesignSystem Design

The system is very The system is very simple yet elegant and simple yet elegant and consists of a light consists of a light sourcesource, an optical , an optical couplercoupler, the , the probeprobeand a and a spectrometer.spectrometer.MultiMulti--channel models channel models use the same design use the same design but the number of but the number of component (other than component (other than the probe) is greater.the probe) is greater.

White Light

Source

Spectrometer

Optical Coupler

Probe

OilOil--Immersed Transformer ProbeImmersed Transformer Probe

Probe Design DetailsProbe Design DetailsDesigned to allow complete oil impregnation, rapid response time, high dielectric strength and chemical resistanceGaAs based probe characteristics:GaAs based probe characteristics:

Designed for a minimum life time of 25 yearsDesigned for a minimum life time of 25 yearsNo driftNo driftNo recalibrationNo recalibration

Ruggedized design allows for minimal probe Ruggedized design allows for minimal probe breakage and lost during installationbreakage and lost during installation

Probe DesignProbe DesignAn optical fiber delivers An optical fiber delivers white lightwhite light to the semiconductor crystalto the semiconductor crystalSome of the light is more or less Some of the light is more or less absorbedabsorbed----this absorption is this absorption is dependent on thedependent on the temperaturetemperature at the tip of the probeat the tip of the probeThe light is The light is reflectedreflected back by a dielectric mirror and returns back by a dielectric mirror and returns through the same fiber for through the same fiber for analysisanalysis

fiber coresemiconductor crystal

dielectric mirror

fiber cladding

Fiber Optic Sensor can be in Fiber Optic Sensor can be in Contact with ConductorContact with Conductor

Fiber Optic Sensor can Fiber Optic Sensor can Inserted in Disk SpacerInserted in Disk Spacer

Can be inserted between the last few disks near the top of the winding

Location in Disk Spacer Location in Disk Spacer is Adequateis Adequate

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0 12 24 36 48 60 72Time (h)

Tem

pera

ture

(°C

)

0.20.40.60.81.01.21.41.61.82.02.2

Load

(p.u

.)

FO Sensor in spacer

FO Sensor in contact with conductor (top of bundle)FO Sensor in contact with conductor (bottom of bundle)

Load

Optic Fiber Handling & TestingOptic Fiber Handling & TestingDuring transformer assembly, optical fibers are safely spooled and attached to the winding.

Bright colors, such as orange or blue, also help minimize breakage during installation.

A portable test unit can be very useful for testing probes as they are installed.

FeedFeed--Through ConnectionThrough Connection

Development in optical fiber technology allows for low loss connection and leak free operation (epoxy-less design)

Temperature sensor, inside transformer

Tip

Feedthrough for tank wall

Extension cable, to monitoring system

Interfacing & CommunicationInterfacing & CommunicationSystems are now available with open communication Systems are now available with open communication protocolsprotocols

No more proprietary communication schemes!No more proprietary communication schemes!

Some popular protocols include:Some popular protocols include:OPC (T/Guard+)OPC (T/Guard+)Modbus (T/Guard)Modbus (T/Guard)Others: CANopen, Profibus, DevicenetOthers: CANopen, Profibus, DevicenetAnalog outputs (4Analog outputs (4--20mA)20mA)

Hardware interfacing is also flexibleHardware interfacing is also flexibleRS232RS232RS422 RS422 –– RS485RS485TCPIP (Ethernet) emulationTCPIP (Ethernet) emulationAnalog outputsAnalog outputs

An Example: Monitoring System An Example: Monitoring System (T/Guard)(T/Guard)

Supports up to 16 channels in a single unitSupports up to 16 channels in a single unitRuggedized design for heavy industry applicationsRuggedized design for heavy industry applicationsRSRS--232 and analog output standard232 and analog output standardAssistantAssistant Windows™ compatible softwareWindows™ compatible software

--Options:Options:--Modbus protocolModbus protocol

--RS485RS485--Supports a Supports a network of 32 network of 32 T/Guard’sT/Guard’s

--TCPIP interfaceTCPIP interface

An Example: Monitoring and An Example: Monitoring and Controlling System (T/Guard+)Controlling System (T/Guard+)Supports up to 8 channels in a single unitSupports up to 8 channels in a single unit16 Type16 Type--C relays, can be set as type A, B or C relays)C relays, can be set as type A, B or C relays)Ruggedized design for heavy industryRuggedized design for heavy industryapplications; built with a PLC,applications; built with a PLC,galvanicgalvanic--isolated relays. isolated relays. RSRS--232 and analog output standard232 and analog output standardOPC Server builtOPC Server built--ininOptions: Options:

Communication: CANopen Profibus,Communication: CANopen Profibus,Modbus, Devicenet and Ethernet server.Modbus, Devicenet and Ethernet server.Data loggingData logging

OPCOPC--Based CommunicationBased CommunicationInternational Industry Standard OrganizationInternational Industry Standard Organization

280+ member companies280+ member companies1500+ total companies build OPC products = 7500+ products1500+ total companies build OPC products = 7500+ products

Fully supported by Microsoft (uses DCOM)Fully supported by Microsoft (uses DCOM)The Vision of OPC is the Adapted Standard for interThe Vision of OPC is the Adapted Standard for inter--OperabilityOperability

For moving information vertically from the factory floor For moving information vertically from the factory floor through the enterprise of multithrough the enterprise of multi--vendor systemsvendor systemsFor moving information between devices on different For moving information between devices on different networks from different vendorsnetworks from different vendorsNot just data but information…Not just data but information…

Reliable Reliable -- Secure Integration is builtSecure Integration is built--ininwww.www.opcfoundationopcfoundation.org.org

OPC and the T/Guard+OPC and the T/Guard+An example: direct logging to ExcelAn example: direct logging to Excel

Can monitor/set 500+ variablesCan monitor/set 500+ variables

Field ExperienceField Experience

–– Converter transformerConverter transformer–– ODAF coolingODAF cooling–– 107 MVA107 MVA–– Dorsey sub, Manitoba Dorsey sub, Manitoba

HydroHydro

Field ExperienceField Experience

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60

80

100

0 12 24 36 48 60 72Time (h)

Tem

pera

ture

(°C

)

0.20.40.60.81.01.21.41.61.82.02.2

Load

(p.u

.)

Prediction from manufacturer using IEEE modelMeasured value with FO sensor

Corrected Prediction

Load

Ambient

Economic Benefits of Accurate Economic Benefits of Accurate Temperature MeasurementTemperature Measurement•Transformers have inherently some overloading capability

•The loading capability is highly dependent on winding temperature

•Dependable measurements of winding temperatures allow to take full advantage of overloading capability

•Market opportunities can generate important benefits if extra load can be handled under safe and predictable conditions

Economic Benefits, Transformer Economic Benefits, Transformer Overloading, An ExampleOverloading, An Example

1.Transformer rated power (MVA) 100

2.Overloading margin made available by monitoring (%) 10

3.Probability of overloading opportunity (hr/year) 450

4.Financial benefit from energy transmitted ($/MWh) 80

Yearly benefit from extra loading (1 x 2 x 3 x 4 ) = $360,000

Economic Benefits, Transformer Economic Benefits, Transformer Overloading, An ExampleOverloading, An Example

5. Replacement cost of transformer ($) 2 000 000

6. Transformer normal life duration (hours) 150 000

7. Additional aging factor at 110% load (125°C) 3.4

Cost for additional loss of life ((5 / 6) x 7 x 3 ) = $20,400

Net yearly benefit from overloading : $360,000 - $20,400 = $339,600

Conclusions (1)Conclusions (1)•For operators and utilities, overloading of transformers is often a better alternative to more and/or larger transformers

•Aging of power transformers is mainly driven by winding temperature

•More frequent loading to full capacity has shown need for better control of winding temperature

•Recent developments in IEEE and IEC loading guides have shown that simple calculation methods used in the past are not fully dependable

Conclusions (2)Conclusions (2)

•Fiber optic sensors have reached a level of dependability that makes them a natural choice for this important function

•Interfacing to utility’s computers is now easier than ever, thanks to open communication schemes, such as Modbus, OPC, and other non-proprietary communication schemes.

Thanks!

transformer winding hot spot temperature determination 2006 new mexico... · transformer winding...

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