appartus maintenance interval management

Copyright © SEL 2006

Apparatus MaintenanceInterval Management

Jeff Pope

Schweitzer Engineering Laboratories, Inc.

Transformer Investment

Aging Leads to Failure

Aging Reduces Withstand Capability

Time, not to scale

Stress

Stress Encountered

Stress Withstand Capability

End of Life

Rate of Aging

Customer Concerns

Costly Replacement Power

Spare Transformer Ready

Relays Are Always There

Modern relays have processing and recording capabilities to keep track of power system assets

Transformer Monitoring

Ambient TemperatureTop Oil TemperatureHot Spot TemperatureInsulation Aging FactorsThrough-Fault MagnitudeThrough-Fault DurationAccumulated Through Faults

Timing Is Important

Time

oo

o

Device Operating Characteristic

xx

x

Sampling Interval

Val

ue

Transformer Temperature Dependent Upon Loading and Ambient

0 5 10 15 20 250

50

100

150

Oil

Conductor Hot spot

Ambient

Hours

Deg

rees

Transformer Loading

0 5 10 15 20 250.5

1.0

1.5

Per

Uni

t

Hot Spot CalculationTemp (°C)

Hottest Spot

Top Oil

Ambient

gθ

oθ

aθ

FAA vs. Winding Hot Spot

Insulation Aging Acceleration Factor

0.00010.001

0.010.1

110

1001000

10000

50 70 90 110 130 150 170 190Winding Hot Spot Temperature

Agi

ng F

acto

r, FA

A

Aging Jumps With Temperature

Time

Hot SpotTemperature

120 C

105 C

90 C

RelativeAging

1 X

135 C

16 X

2 X

4 X

8 X

32 X

64 X

128 X

256 X

Hot SpotTemperature

RelativeAging

Thermal Element Reports Loss of Life

0 5 10 15 20 250

0.01

0.02

0.03

0.04

0.05

0.06

0.07Loss of Life (LOL)

Hours

Perc

enta

ge

LOL Alarm Point

Acceptable LOL Limit

Measured LOL

Don’t Ignore Necessary Data

Relay Thermal Monitor Alarms

Top oil temperatureWinding hot spot temperatureCooling system efficiencyInsulation aging acceleration factor (FAA)Daily loss of lifeTotal loss of life

Thermal Profile ReportHourly and Daily Maximum

Ambient temperatureCalculated top oil temperatureMeasured top oil temperatureHottest spot temperaturePer-unit loadFAA

Thermal Report

Hourly Thermal Report

Daily Thermal Report

Thermal Overloads Are Not the Only Root Cause of Failure

Surges No Longer #1 Failure Cause

Close-In Fault

#1 Cause of Transformer Failure

Relay

Through-Fault Current

Can This Cause a Transformer Failure?

Sudden Failure

Through Faults ReduceTransformer Life

Time, not to scale

Stress

Stress Encountered

Stress Withstand Capability

End of Life

Through-Fault Report

Don’t Drive by the Rear View Mirror

Information Overload

Transformer Worth Protecting IsWorth Monitoring

In-Service Transformer Monitoring

RTDSignals

4–20 mASignals

EIA-232 Modbus

Spread Spectrum Radio EIA-232

Modbus®

Substation PC

TransformerMonitor

PLC Communications Processor

Relay

Simplified Transformer Monitoring

RTDSignals

Optical Fiber

RTDModule

Substation PC

CommunicationsProcessor

Relay

Relay Thermal Monitor

Relay Identification Date: 2/2/05 Time: 11:35 Terminal IdentificationThermal Element Condition : NormalPer Unit Load Current : 123.45In-Service Cooling Stage : 1Ambient Temp. (deg. C) : 123Calculated Top-Oil Temp. (deg. C) : 123Measured Top-Oil Temp. (deg. C) : 123HS Wdg. Temp. (deg. C) : 123Max. FAA for last 24 hours : 123.4Present 24-Hour Avg FAA : 123.4Rate of LOL (%/day)(1) : 99.99Total Accumulated LOL (%)(2) : 99.99Time-Assert TLL (days) : 12345

Relay

Communications Processor

Distribute Report Data Over WAN

Substation

SEL Relay

Control Room

Web ServerComputer With Browser

SEL Relay

SEL Relay

SEL RelayDatabase

SEL-2032 WANDMZ

One-Line Webpage

Thermal Monitor Webpage

Asset Management Makes a Difference

Monitor and understand apparatus health

Perform fact-based risk assessment

Schedule periodic equipment exercises to avoid preventive maintenance

Asset Management Pays for Itself

Increased device and system productivity

Reduced expenses lower total ownership cost

Justified, defendable business planning based on actual power system data

Increased availability, reliability, revenue, and performance

Documented resolutions to NERC / FERC recommendations and insurance companies