Copyright © SEL 2017

Asset Management through Transformer Monitoring

Ed Atienza

Overview

• Transformer materials

• Thermal aspects of transformer life

• IEEE C57.91 thermal monitoring

• Through-fault monitoring

• Monitoring Using the SEL-2414

Transformer Materials

• Core steel

• Copper or aluminum coils

• Paper insulation

• Mineral oil insulating liquid

• Steel tank

• Bushings

Transformer MaterialsCore Steel

Transformer MaterialsCoils and Insulation

• Copper or aluminum coils

• Paper insulation

Other Transformer MaterialsBushings and Steel Tank

Transformer Failure Statistics1983 to 1988

• Core

• Winding

• Tap changer

• Bushing

• Terminal board

• Miscellaneous

1%

37%

22%

11%

3%

26%

Factors Affecting WindingInsulation Life

• Water – controlled by oil treatment

• Oxygen – controlled by oil treatment

• Heat – controlled by operating personnel♦ Chemical reaction rate doubles for

each 5° to 10°C increase in temperature (Arrhenius’ theory)

♦ Loss of degrees of polymerization reduces insulation efficiency

Internal CoolingMedium

Circulation Mechanism

External Cooling Medium

Circulation Mechanism

O = Oil (fire point < 300°C)

N = Natural convection A = Air N = Natural

convection

K = Insulatingliquid (fire point

> 300°C)

F = Forced circulation W = Water F = Forced

circulation

L = Insulating liquid (fire point not measurable)

D = Directed with force NA NA

Transformer Cooling Classes

i.e., ONAN, ONAF, and ODAF

Average Winding Temperature

• Calculable with winding resistance measurement

• Not directly used for transformer life calculations

2I

Winding Hot-Spot Temperature

• Calculated with thermal model

• Measured with fiber-optic probe

• Difficult to correctly locate

• Directly used for transformer life calculations

Winding Hot-Spot Temperature Graphic

2I

How Thermal Monitoring Works

Uses formulas from IEEE C57.91 to calculate transformer temperatures

Transformer Thermal Model

Thermal Model Responseto a Load Step Change

Insulation Aging

• Winding hottest-spot temperature above the limit damages insulation

• One hour at 120°C ages the insulation the equivalent of 2.7 hours at 110°C

• Thermal model calculates insulation aging and accumulated transformer loss of life

How Old Is Your Transformer, Thermally?• Typical loading

♦ Very light

♦ Cycles daily

♦ Fully loaded

♦ Overloaded

• Average ambient temperature♦ Cold

♦ Moderate

♦ Hot

• Type of cooling system♦ Fans and oil pumps

♦ Two-stage fans

♦ Single-stage fans

♦ Passive only

Purpose of Thermal Model

• Real-time loading capability

• Long-term loss-of-life tracking

Single Tank With Three-Phase WindingsETHERM:=1

Three Tanks With Single-Phase WindingsETHERM:=3

Single Tank With Three Sets of WindingsETHERM:=W

Hourly Thermal Reports

=>>THE H <Enter>SEL-2414 Date: 03/31/2009 Time: 10:00:00DEVICETransformer 1

Ambient Calc Measure LoadDate Time Temp Top-Oil Top Oil Hot Spot Current FAA03/31/2009 0800 15.0 58.4 59.9 94.6 0.96 0.9003/31/2009 0900 15.0 58.4 59.9 94.6 0.96 0.90Transformer 2

Ambient Calc Measure LoadDate Time Temp Top-Oil Top Oil Hot Spot Current FAA03/31/2009 0800 15.0 59.2 60.1 95.0 1.00 0.9503/31/2009 0900 15.0 59.2 60.1 95.0 1.00 0.95Transformer 3

Ambient Calc Measure LoadDate Time Temp Top-Oil Top Oil Hot Spot Current FAA03/31/2009 0800 15.0 61.6 61.0 95.4 1.01 0.9603/31/2009 0900 15.0 61.6 61.0 95.4 1.01 0.96=>>

Daily Thermal Reports

=>THE D <Enter>SEL-2414 Date: 12/21/2012 Time: 00:37:34DEVICETransformer 1

Max Max Max Max Max MaxDate Time AMBT TOILC TOILM LOAD HS FAA RLOL TLOL12/20/2012 0000 24.5 57.3 59.9 0.91 109.6 0.99 0.014 2.34512/21/2012 0000 24.5 58.4 60.9 0.95 110.8 1.10 0.015 2.360Transformer 2

Max Max Max Max Max MaxDate Time AMBT TOILC TOILM LOAD HS FAA RLOL TLOL12/20/2012 0000 24.5 57.3 59.9 0.91 109.6 0.99 0.014 2.34512/21/2012 0000 24.5 58.4 60.9 0.95 110.8 1.10 0.015 2.360Transformer 3

Max Max Max Max Max MaxDate Time AMBT TOILC TOILM LOAD HS FAA RLOL TLOL12/20/2012 0000 24.5 57.3 59.9 0.91 109.6 0.99 0.014 2.34512/21/2012 0000 24.5 58.4 60.9 0.95 110.8 1.10 0.015 2.360=>>

What Is a Through Fault?

Through-Fault Monitor – Why?

• Thermal stress – low-magnitude faults

• Mechanical stress – high-magnitude faults

Transformer Through-Fault Capability

• Through faults cause thermal and mechanical stresses

• Mechanical effects are cumulative

• Extent of damage depends on:♦ Current magnitude

♦ Fault duration

♦ Total number of faults

Transformer Categories Per IEEE C57.12.00

Category Single‐Phase kVA Three‐Phase kVA

I 5 to 500 15 to 500

II 501 to 1,667 501 to 5,000

III 1,668 to 10,000 5,001 to 30,000

IV Above 10,000 Above 30,000

Transformer Through-Fault Capability Curves (IEEE C57.12.00)

• Define through-fault withstand capability

• Apply to transformers designed per IEEE C57.12.00

• Six curves:♦ One each for Category I and IV transformers

♦ Two each for Category II and III transformers (frequent and infrequent faults)

1,668–10,000 kVA 1-Phase5,001–30,000 kVA 3-Phase

Source: IEEE C57.12.00-2010, IEEE Standard for General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers

Category III

Category IV

Above 10,000 kVA 1-PhaseAbove 30,000 kVA 3-Phase

Source: IEEE C57.12.00-2010, IEEE Standard for General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers

Through-Fault Monitoring

• Monitor measures and records through-fault currents

• Estimates I2t values per phase and provides alarm

• Helps finding transformer problems and prioritizing maintenance

• Helps detecting high external fault activity

Combined Effect of Thermal and Through-Fault Stresses

Through-Fault Settings

Through-Fault Events

=>>TFE

SEL-2414 Date: 02/25/2013 Time: 13:53:39DEVICE

Winding ETotal Number of Transformer Through Faults: 16Total Number of A Phase Through Faults: 8Total Number of B Phase Through Faults: 8Total Number of C Phase Through Faults: 8

Total Accumulated Percentage of Through Fault Capability:A-Phase B-Phase C-Phase59.81 38.56 35.64

Through Fault Alarm: 1 0 0

Last Reset: 02/25/2013 13:49:13

Through-Fault Events

# DATE TIME Duration IA IB IC A B C Alarm(seconds) (max primary kA) (Increment %)

1 02/25/2013 13:53:34.505 1.013 0.00 0.00 32.15 0.00 0.00 4.35 A2 02/25/2013 13:53:32.500 1.013 0.00 34.80 0.00 0.00 5.07 0.00 A3 02/25/2013 13:53:29.500 2.017 43.41 0.00 0.00 15.84 0.00 0.00 A4 02/25/2013 13:53:27.999 0.521 43.40 43.39 43.85 3.97 3.97 3.97 5 02/25/2013 13:53:10.702 1.013 0.00 0.00 32.16 0.00 0.00 4.35 6 02/25/2013 13:53:08.697 1.013 0.00 34.75 0.00 0.00 5.07 0.00 7 02/25/2013 13:53:05.697 2.017 43.40 0.00 0.00 15.85 0.00 0.00 8 02/25/2013 13:53:04.196 0.521 43.41 43.41 43.70 3.97 3.97 3.97 9 02/25/2013 13:52:24.175 1.013 0.00 0.00 32.15 0.00 0.00 4.35 10 02/25/2013 13:52:22.170 1.017 0.00 34.75 0.00 0.00 5.08 0.00 11 02/25/2013 13:52:20.174 1.013 43.41 0.00 0.00 7.92 0.00 0.00 12 02/25/2013 13:52:18.869 0.321 43.38 43.38 43.40 2.38 2.38 2.38 13 02/25/2013 13:50:23.241 1.013 0.00 0.00 32.35 0.00 0.00 4.35 14 02/25/2013 13:50:21.236 1.017 0.00 34.73 0.00 0.00 5.08 0.00 15 02/25/2013 13:50:19.206 1.042 30.38 0.00 0.00 1.96 0.00 0.00 16 02/25/2013 13:50:17.201 1.021 43.41 43.82 43.40 7.93 7.93 7.92

Through-Fault Monitor Logic

ETHRFLT(Setting)

4.75 • IFULLLOAD

4.5 • IFULLLOAD

IA

–+

–+

S Q

R

1 min

0

Enable 0

10 cyc

10-Cycle Timer

1-Minute Timer

Total Counter

A-Phase Counter

Archive

Start TimeStop Time

Maximum Current Calculation

2RMS _pu

0.25 •100%t(I ) •FREQ

+–

TFLTALATHFLTPU

SEL-2414Transformer Monitoring and Much More

• IEEE C57.91-1995 transformer thermal model

• Through-fault monitoring

• Flexible I/O choices

• Critical reporting and logging

• Extensive ac metering capabilities

• Powerful integration with SCADA

• Simple commissioning tools

Track Important Transformer Quantities

• Ambient temperature

• Top-oil temperature calculations and measurements

• Winding hot-spot temperature

• Per-unit load

• Loss of life

Analog Signal ProfilingVisualize Key Data

Tem

pera

ture

Additional FunctionalityUsing Settings or Design Templates

• Replacement of other devices

• Fan control and monitoring

• Load tap changer (LTC) control

Replace Other Devices

• Oil temperature gauge

• Hot-spot temperature gauge

• 63PR seal-in relays

• Discrete control relays

• Indicator lights and switches

Communications Protocols Single or Dual Ethernet

• Copper and fiber optic

• Modbus TCP

• FTP, Telnet, and Ping

• DNP3 LAN / WAN (optional)

• IEC 61850 (optional)

SEL-2414 Summary

• Communication via front-panel HMI, serial ports, and Ethernet networks

• Transformer monitoring♦ Thermal monitoring

♦ Through-fault monitoring

• Design templates♦ LTC control

♦ Fan control

Questions?