Doble Power Factor Document

Together We Power The World

Basic Instruction Notes Doble Engineering Company 85 Walnut Street Watertown, MA 02472 Tel (617) 926-4900 Fax (617) 926-0528

Table of Contents 1

Doble Services

2

M-Series Safety Features & Practices

3

Power Factor Basic Theory

4

Transformer Overall Power Factor

5

Bushing Power Factor

6

Transformer Excitation Current

7

Transformer Turns Ratio

8

Insulating Fluids Power Factor Tests

9

Surge Arrestor Tests

10

Circuit Breaker tests

11

Grounded-Tank SF6 Circuit Breaker Tests Oil

12

Potential Transformers

13

Negative Power Factor

Doble Corporate Headquarters Telephone: (617) 926-4900 Fax: (617) 926-0528 www.doble.com

Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Doble Service & Equipment Agreement Mike Horning, Principal Engineer Doble Engineering Company

Doble Engineering Company

85 Walnut Street, Watertown, MA 02472

Doble Service & Equipment Agreement Overview of Services Included with Lease ¾ 24 Hour Technical Support ¾ Perpetual Warrantee ¾ Customized Training ¾ Doble Client Committees & Conferences ¾ Doble E-mail Forums ¾ Doble Knowledgebase ¾ Doble Laboratories

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1

Doble Service & Equipment Agreement Technical Support ¾ 24 hour support, 365 days a year ¾ Assigned Client Service Engineers (normal business hours) ¾ On-call Client Service Engineer (after hours, weekends, & holidays) ¾ Assistance with test procedures, data evaluation (written reports on request), and troubleshooting

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Doble Service & Equipment Agreement Perpetual Warrantee ¾ Client Service Engineers will assist with the troubleshooting and diagnosis of problems with Doble test equipment. ¾ Replacement of worn, damaged, or malfunctioning equipment. ¾ There are no additional costs for replaced equipment (unless client is negligent). ¾ Client is responsible for shipping costs. ¾ Overnight shipping is available.

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Doble Service & Equipment Agreement Customized Training ¾ Five (5) days of training per contract year. ¾ Training is tailored to clients needs. ¾ Client is responsible for travel expenses.

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Doble Service & Equipment Agreement Doble Client Committees & Conferences ¾ Any Doble client who is not an equipment manufacturer (or affiliate) may participate in the Doble Client Committees. Committee meetings are held twice annually (spring & fall). ¾ Any Doble client may attend the annual Doble Client Conference (spring). ¾ Committees and Conference Sessions fall into 8 categories: (1) Transformers, (2) Bushings, Insulators, and Instrument Transformers, (3) Circuit Breakers, (4) Arrestors, Capacitors & Cables, (5) Rotating Machinery, (6) Insulating Materials, (7) Protective Apparatus, and (8) Asset Maintenance Management. 6 of 9

3

Doble Service & Equipment Agreement Doble E-mail Forums ¾ Maintenance Engineers – an open form where clients may converse electronically about anything related to the power industry … system operations, safety procedures, maintenance/testing practices, equipment issues related to specific equipment, urgent equipment needs, etc. (open to nonmanufacturing clients only). ¾ DTA Users - an e-mail forum for users of the DTA software. ¾ SFRA Users – an e-mail forum for users of the Doble’s SFRA test equipment and software. ¾ TRX Users - an e-mail forum for users of the TRX software. ¾ PROTEST Users - an e-mail forum for users of the PROTEST software. 7 of 9

Doble Service & Equipment Agreement Doble Knowledgebase ¾ The Doble Knowledgebase is an electronic system that may be accessed through the Doble website (www.doble.com). ¾ The Doble Knowledgebase contains a large collection of information … Doble Conference papers, manuals and guides, frequently asked questions (from Maintenance Engineers e-mail forum), manufacture service advisories, etc.

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Doble Service & Equipment Agreement Doble Laboratories ¾ Doble’s HV laboratory and oil/material laboratories services are available to Doble clients at an additional cost. ¾ Doble has three oil/material laboratories: (1) Watertown, Massachusetts, (2) Indianapolis, Indiana, and (3) Kent, Washington. ¾ Contract includes $500.00 worth of laboratory services per year … an incentive to try our services.

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Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

M-Series Safety Features & Practices Michael Horning, Principal Engineer Doble Engineering Company

1 85 Walnut Street, Watertown, MA 02472

Doble Engineering Company

M-Series Safety Features Ground Relay. During normal operation, there are two grounds connected to the M4000; the #6 AWG ground lead and the ground provided by the 120V power supply. If the resistance between these two grounds exceeds 50-100Ω, then the ground relay will not pick up, thus preventing the operation of the test set. The purpose of the ground relay is to protect against hazards associated with differences in ground potential.

2

1

•

3

An Acceptable Method Power Cord Feeding the M4000

Ground Jumper From Specimen Ground 4

2

Improper method!

5

Safety Switches. Two safety switches are provided. Both must be depressed in order for test voltage to be applied. If either of these switches is released during test, then the test voltage will be immediately removed. The short safety switch is used by the “Operator”, and the long (extension) safety switch is used by the “Safety Lookout”. 6

3

Wrong!

7

Safety Beeper . (M4000 only) For the first few seconds after a test is initiated, the safety beeper will sound. This provides an audible signal that a test has been initiated. Safety Strobe. (M4000 only) Whenever voltage is being applied, the safety strobe will flash. This strobe has a magnetic base for convenient mounting. It should be positioned in a location that will alert all personnel in the area whenever a test is in progress.

8

4

9

Prepare the Specimen for Testing Conduct crew meetings, de-energize, ground, isolate, safeguard, etc., using your company’s established safe work procedures, and in compliance with applicable safety regulations (OSHA, NFPA, NESC etc). Grounding the Test Equipment The #6 ground lead should always be the first test lead connected and the last test lead removed. This ensures that the test set chassis is safely grounded, and it removes touch potential hazards.

10

5

Static and Induced Voltages Care must be taken to avoid exposure to static or induced voltages on ungrounded equipment. The following procedures will minimize the chance of exposure to static or induced voltages while applying and removing test leads: Before applying test lead connections, a ground should be applied to the specimen connection point. For Energized, UST, or Guarded circuits the ground should be removed after the test lead is connected and before initiating the test.* * Note: Proper protective equipment and live line tools must be utilized while applying and removing grounds. 11

• When applying connections, all test leads should be connected to the M4000 first and then to the specimen connection point. • Before removing test lead connections, a ground should be applied to the specimen connection point.* • When removing connections, all test leads should be removed from the specimen connection point first and then from the M4000. * Note: Proper protective equipment and live line tools must be utilized while applying and removing grounds. 12

6

Click picture

13

Safety During Tests Good Communication. A uniform system of communication between the operator and the safety lookout (and all other affected personnel) should be established in order to eliminate confusion during testing. The following is an example of common communication: 1.

Operator - “Ready?”

2.

Safety Lookout – Responds “Ready” if the connections are made and the work area is safe, or “No” if not ready and safe.

3.

Operator – “Going hot.”

4.

Safety Lookout – Echoes “Going hot” to acknowledge the operator.

5.

Test is initiated … completes.

6.

Operator – “All Clear.” Operator extends the operators safety switch at arms length with the button released for all to see.

14

7

Safety During Tests (continued) Safety Lookout. The Safety Lookout should position himself in an area where he can observe all terminals and access points to the apparatus under test. Safety Switches. The Safety Switches can be released at any time to terminate a test. This may be necessary if unauthorized personnel enter the area or if some other undesirable situation develops.

15

Safety During Tests (continued) Testing with Personnel on the Specimen. Testing with personnel on the specimen is strongly discouraged (i.e. on top of the transformer under test). Handling the HV Cable. Handling the HV cable during test, even when wearing insulated gloves, is strongly discouraged. If a flashover occurs while testing, transient voltages higher than 10kV can be developed resulting in a puncture in the cable’s insulation and a hazard to the personnel holding the cable.

16

8

Strongly Discouraged!

The Ladder Was NOT Tied-Up Either 17

Strongly Discouraged! - Do not hold high-voltage cable during a test.

Source: 1995 DCCM, Page Sec. 1-2.1, David Train and Lawrence Melia 18

9

Know the equipment under test!

19

Don’t be compared to this crew!

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Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Power Factor Basic Theory Mike Horning, Principal Engineer Doble Engineering Company

Doble Engineering Company

85 Walnut Street, Watertown, MA 02472

Capacitors, Resistors, & Inductors

E ↓ IC ↓

IR ↓

IL ↓

0

90

180

270

0

¼

1/2

3/4

0

1/240

1/120

3/240

360

1 Cycle 1/60 Sec

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1

Capacitors

εDielectric = CDielectric/CVacuum Vacuum Air Paper Oil Silicone Fluid Porcelain Water (20ºC)

C = Aε/4πd IC = E(2πf)C

ε Vacuum = 1.0 ε Air = 1.000549 ε Paper = 2.0 ε Oil = 2.1 ε Silicone = 2.75 ε Porcelain = 7.0 ε Water = 80 3 of 20

Capacitors (continued)

Question: Is an insulation system like a capacitor?

Answer = YES

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2

Capacitors (continued) A “Real” Capacitor is “Imperfect”

In a perfect capacitor, no current flows through the capacitor. Rather, the current IC flows back-and-forth from plate-to-plate through the source. A real capacitor is imperfect, and a small amount of current flows through. This current (IR) generates dielectric losses [watts]. P [watts] = IR2R As the insulation becomes contaminated or deteriorates… (1) the resistance (R) goes down, (2) the resistive current (IR) goes up, (3) and the dielectric losses (watts) go up.

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Power Factor

Power Factor = cos(θ) %PF = 100cos(θ) %PF = 100(IR/IT) = 100(W/VA) %PF = 100(IRE/ITE) =100(P/ ITE) Assuming E=10,000 volts, and converting IT from amperes to milliamperes this equation is simplified to %PF = 10P/IT = 10x[W]/[mA] 6 of 20

3

Changes in Power Factor Case 1 Starting Condition

Case 2 Contamination IR = 10 mA

E WLOSS = 10 C = 26,500 pF PF = 1.00% IT ≅ IC

06 mA

IC = 80 mA

IT = 100.

IT = 8 0.0

A 5m

IC = 100 mA

05 mA

IR = 1 mA

IT = 10 0.0

IC = 100 mA

IR = 1 mA

Case 3 Change in A, d, or ε

E WLOSS = 10 C = 21,200 pF PF = 1.25% IT ≅ IC

E WLOSS = 100 C = 26,500 pF PF = 9.95% IT ≅ IC

Except for extreme cases, contamination has only a small effect on the measured current IT. A significant change in IT is usually related to a change in capacitance; IT ≅ IC = EωC. Power Factor is affected by both contamination (watts) and capacitance (mA).

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Power Factor vs. Specimen Size IT2

IC2

IT1

IC1 θ IR1

IR2

Test Specimen #1, 5 MVA Transformer Specimen #2, 10 MVA Transformer

E %PF 0.5 0.5

MΩ 20 10

If specimen #1 and #2 are made with the same insulation, and the insulation is in the same condition, then the power factors will be the same. Power Factor measures the quality of the insulation, and it is independent of size. 8 of 20

4

Importance of Testing the Smallest Subsystem Subsystem Tests Case 1

0.5%

0.5%

•Four (4) subsystems of equal quality. •Each subsystem has equal power factor and they are equal to the total system power factor (power factor is independent of size).

Total System Test 0.5%

0.5%

•Each subsystem may have a higher meggar reading than the total system.

P.F.=0.5% 0.3% LV Circuit

0.2% Buswork

Case 2 •Four (4) subsystems of non-equal quality. •Each subsystem may have a different power factor.

1.1%

0.4%

HV Circuit

Bushings

•The total system power factor is a measure of the average quality/condition of all insulation included in the test.

It is important to test the smallest subsystem possible (economically feasible) in order to evaluate the quality of each individual subsystem. Otherwise, bad insulation could be disguised by good insulation (and vice-versa).

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Power Factor vs. DC Resistance Testing

For multiple layer insulation systems (i.e. condenser type bushings) AC tests, such as Power Factor, are much more sensitive to a single deteriorating layer than DC tests. 10 of 20

5

Test Modes M4100 High Voltage (HV)

Guard

Low Voltage (LV) Test Leads

mA &W Meter Meter = Measured Guard = Not Measured

Ground Test Lead

Kirchoff’s Current Law – All current leaving must return. Therefore, by KCL all current leaving the test set through the HV Cable must return to it … either through the LV Test Leads (red or blue) or the Ground Lead. Internal to the M4100, test leads that are connected to the METER will be measured, and test leads that are connected to GUARD will not be measured. We can choose to measure the RED LEAD, the BLUE LEAD, the GROUND LEAD, or ANY COMBINATION (any two, or all three) by specifying the correct TEST MODE. The TEST MODE is specified in the DTAF software. It is an instruction that tells the M4100 which test leads to connect to the meter and which leads to connect to guard circuit.

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Test Modes

TEST MODE Terminology GST = Grounded Specimen Test Measures anything connected to ground Measures grounded insulation. UST - Ungrounded Specimen Test DOES NOT measure anything connected to ground (ground is guarded) Measures ungrounded insulation (GST-) Ground or Guard - Describes the connection of the LV leads … either connected to the ground point (measured) or the guard point (not measured). (UST-) Measure or Ground - Describes the connection of the LV leads … either connected to the meter (measured) or the ground point (not measured).

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6

Test Modes - Ground Lead Only

M4100 B

Guard

mA &W Meter

C A

TEST MODE #1 GST DTAF “GND”

IA

Measures IA

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Test Modes – Ground and One LV lead M4100 IB Guard

B

C

mA &W Meter

A

TEST MODE #1 GST Ground Red DTAF “GND-R” Measures IA + IB

IA M4100 IB Guard

B

C

mA &W Meter

A IA

TEST MODE #2 GST Guard Red DTAF “GAR-R” Measures IA

M4100 IB Guard

B

C

mA &W Meter

A IA

TEST MODE #3 UST Measure Red DTAF “UST-R” Measures IB 14 of 20

7

Test Modes – Ground and Two LV leads M4100 B

Guard

mA &W Meter

C A

DTAF Abbreviation

Measures

#1 GST Ground Red, Ground Blue

Test Mode

GND-RB

I A + IB + IC

#2 GST Guard Red, Guard Blue

GAR-RB

IA

GAR-R

I A + IC

#4 GST Ground Red, Guard Blue

GAR-B

IA + IB

#5 UST Measure Red, Measure Blue

UST-RB

IB + IC

#6 UST Measure Red, Ground Blue

UST-R

IB

#7 UST Ground Red, Measure Blue

UST-B

IC

#3 GST Guard Red, Ground Blue

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Power Factor vs. Voltage, Tip-Up Voids

%PF

%PF @ L-G %PF @ 2kV

E Winding

Motor Insulation

2kV

Stator

L-G

In dry type insulation systems (i.e. generators, dry-type transformers) there may be gas pockets or voids in the insulation. As the voltage stress is increased, tracking may begin to occur across the voids. This results in a higher watts loss and Power Factor values. Tip-Up = %PF@VL-G - %PF@2KV When possible, it is also suggested to test at 110% or 125% of the line-to-ground rating. This may give an indication of what the future might bring. 16 of 20

8

Electrostatic Interference 60 Hz Lines

IE

60 Hz Lines

CE

H-V Test Cable

CE

H-V Test Cable

IE

CA

Test Set Step Up Transformer

CA

Test Set Step Up Transformer

GND Lead

Guard Point

GND Lead

Guard Point

IA

IA

IA-IE

IA+IE

Forward Polarity Test

Reverse Polarity Test

Interference current, IE, follows the path of least impedance to ground. The Line Sync Reversal method reverses the polarity of the test set applied voltage resulting in a reversed current, IA. The effects of interference are eliminated by calculating the average of the currents measured in the forward and reverse polarity tests. [IFOR + IREV]/2 = [(IA + IE) + (IA – IE)]/2 = (2IA)/2 = IA Note: If IE > IA, then the above equation is incorrect unless the polarity of the current is recorded. Therefore, when taking watts readings, it is important to check and record the polarity. The Line Freqency Modulation method conducts test at 57 Hz and 63 Hz and averages the results. By testing and measuring “off frequency” the effects of the 60 Hz interference are eliminated.

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Power Factor vs. Dissipation Factor

Power Factor = cos(θ) = IR/IT

Dissipation Factor = tan(Δ) = IR/IC

%PF = 100cos(θ) = 100(IR/IT)

%DF = 100 tan(Δ) = 100(IR/IC)

For values less than 10%, %PF ≅ %DF When %PF=10, %DF=10.05 As the values get smaller, they get closer. 18 of 20

9

Testing Below Freezing Whenever possible, it is desirable to have the apparatus temperature above freezing before conducting insulation tests. Ice has a volumetric resistance 144 times larger than that of water. If a specimen that is contaminated with water is tested below freezing (apparatus temperature), the effects of water contamination may be much less noticeable. The resulting watts loss and power factors may not be representative of the condition of the equipment when tested above freezing (i.e. testing the same specimen above freezing may yield significantly higher power factors). Alternative to testing below freezing: (1) Choose another day and/or time to test; (2) Test transformers immediately after removing from service before the oil temperature falls below freezing; (3) Construct a hasty shelter and apply heat with radiant or forced air heaters. 19 of 20

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Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Transformer Power Factor Tests Mike Horning, Principal Engineer Doble Engineering Company

Doble Engineering Company

85 Walnut Street, Watertown, MA 02472

Transformer Power Factor Test Voltages Liquid-Filled Transformers - Full Oil Level Rating, VL-L (KV)

Test Voltage (KV)

12 and Above

10

5.04 to 9.72

5

2.4 to 4.8

2

Below 2.4

1

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1

Transformer Power Factor Test Voltages Liquid-Filled Transformers – Drained or Reduced Fluid Level Delta and Ungrounded/Ungraded Wye Windings Rating, VL-L (KV)

Test Voltage (KV)

161 and Above

10

115 to 138

5

34 to 69

2

12 to 25

1

Below 12

0.5

SAFETY SEE NEXT PAGE!

Grounded/Graded Wye Windings and Single Phase with Grounded Neutral Rating, VL-L (KV)

Test Voltage (KV)

12 and Above

1

Below 12

0.5 3 of 21

Transformer Power Factor SAFETY Liquid-Filled Transformers – Drained or Reduced Fluid Level In the presence of oxygen, oil vapors and combustible gases can be ignited by an energy source such as an electrical arc or spark. Do not apply test voltage before determining - by direct measurement - that the gas space and insulating liquid contain safe combustible gas levels. Purging with dry nitrogen is recommended to reduce the oxygen level in the gas to less than 2%. Never apply test voltage to a transformer whose windings are under vacuum.

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2

Transformer Power Factor Test Voltages Dry-Type Transformers Delta and Ungrounded/Ungraded Wye Windings Rating, VL-L (KV)

Test Voltage (KV)

14.4 and Above

2 and 10

12 to 14.4

2, VL-G, and 10

5.04 to 8.72

2 and 5

2.4 to 4.8

2

Below 2.4

1

Grounded/Graded Wye Windings and Single Phase with Grounded Neutral Rating, VL-L (KV)

Test Voltage (KV)

2.4 and Above

2

Below 2.4

1 5 of 21

Transformer Power Factor

Load Tap Changers

H1

X1

H2

X2

If the transformer contains a LTC, then it should be moved to any non-neutral tap position for/during overall power factor testing. Certain LTC schemes contain non-linear resistor elements (surge protection) that may cause abnormal test results (high or negative power factors) if tested in the neutral tap position.

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3

Transformer Power Factor Physical Representation of a Three-Phase Two-Winding Transformer One of Three Phases Shown HV Winding

CH

CHL

LV Winding

CL

Core - Grounded Tank - Grounded

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Transformer Power Factor Short the Bushings for Each Winding H1

H2

X0

X1

H3

X2

X3

If the windings are not shorted, an inductance is introduced into the current reading. Instead of measuring IT, you will measure IT’. This will cause the calculated power factor to be higher than the true value, and the calculated capacitance will be lower than the true value. Use bare (non-insulated) wire for shorting. The neutral bushing, X0, must be ungrounded. Isolate the neutral bushing from any grounding resistors or reactors. 8 of 21

4

Transformer Power Factor Two-Winding Transformer – Dielectric Model H2

x2

x1

H1

H3

CHL

x0

x3

CL

CH TANK & CORE

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Transformer Power Factor Two-Winding Transformer Test Circuits

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5

Transformer Power Factor Two-Winding Transformer Test Table

Test No.

Mode

Energize

Ground

Guard

UST

Measure

1

GST

High

Low

-

-

CH + CHL

2

GST

High

-

Low

-

CH

3

UST

High

-

-

Low

CHL

4

Test 1 minus Test 2 (W, mA)

5

GST

6

GST

7

UST

8

Test 5 minus Test 6 (W, mA)

Low

CHL

High

-

-

CL+CHL

Low

-

High

-

CL

Low

-

-

High

CHL CHL

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Transformer Power Factor Liquid-Filled Transformers – Temperature Correction Factors

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6

Transformer Power Factor Liquid-Filled Transformers – Temperature Correction Factors Required Data for DTAF Software

1. 2. 3. 4. 5. 6. 7. 8.

Manufacturer KV Rating (Left Box, Primary KV) KVA Rating (Left Box, Base KVA) Coolant Type Year of Manufacture Tank Type Apparatus Temperature Ambient Temperature 13 of 21

Transformer Power Factor Three-Winding Transformer Test Table Test No.

Mode

Energize

Ground

Guard

UST

Measure

1

GST

High

Low

Tert

-

CH + CHL

2

GST

High

-

Low&Tert

-

CH

3

UST

High

Tert

-

Low

CHL

Tert

High

-

CL+CLT

4

Test 1 minus Test 2 (W, mA)

5

GST

6

GST

Low

-

Tert&High

-

CL

7

UST

Low

High

-

Tert

CLT

8

Test 5 minus Test 6 (W, mA)

9

GST

Tert

High

Low

-

CT + CHT

10

GST

Tert

-

High&Low

-

CT

11

UST

Tert

Low

-

High

CHT

12

Test 9 minus Test 10 (W, mA)

Low

CHL

CLT

CHT

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Transformer Power Factor Autotransformer – Shorted Bushings H1

X1

Y1

Y3

H0X0

X3

X2

Y2

H3

Tertiary Delta

H2

Autotransformer 15 of 21

Transformer Power Factor Autotransformer Test Tables Autotransformer Without Tertiary or With Buried Tertiary (i.e. no tertiary bushings). Test No.

Mode

Energize

Ground

Guard

UST

Measure

1

GST

High&Low

-

-

-

CH

Autotransformer with Tertiary (i.e. tertiary bushings available) Test No.

Mode

Energize

Ground

Guard

UST

Measure

1

GST

High&Low

Tert

-

-

CH + CHT

2

GST

High&Low

-

Tert

-

CH

3

UST

High&Low

-

-

Tert

CHT

High&Low

-

-

CT+CTH

4

CHT

Test 1 minus Test 2 (W, mA)

5

GST

6

GST

Tert

-

High&Low

-

CT

7

UST

Tert

-

-

High&Low

CTH

8

Tert

Test 5 minus Test 6 (W, mA)

CTH

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8

Transformer Power Factor Step-Voltage Regulator A step-voltage regulator is an autotransformer with a load tap changing switch. Test Voltages L

S

Rating (KV)

Test Voltage (KV)

12.47 and Above

10

4.16

5

4.16 and Below

2

Test Table ±10% Load Tap Changer

Test No.

Mode

Energize*

Measure

1

GST

S-L-SL

CH

1:1 Autotransformer

SL

* Short S, L, and SL bushings

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Transformer Power Factor Transformer Power Factor Tests – Evaluation of Results General •Whenever possible, compare to prior tests. •Significant changes in W, mA, %PF, or capacitance should be investigated. Liquid-Filled Transformers •New(er) – Expect power factors of 0.5% or less. •Service Aged – Expect power factors of 1.0% or less. •Investigate if one overall insulation power factor is significantly higher than the others (i.e. CH higher than CL and CHL). •Free-breathing designs tend to have higher power factors due to higher moisture content in the oil and cellulose insulation. •Lower voltage units (15 kV and below) tend to have higher power factors.

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Transformer Power Factor Transformer Power Factor Tests – Evaluation of Results Voltage Regulators •The expected power factors for voltage regulators vary according to the Manufacturer and Model. •On larger units, the LTC switch may be housed in a separate compartment (i.e. it does not share the same oil volume as the transformer). For these units, the expected power factors should be similar to those stated for liquid-filled transformers. Dry-Type Transformers •The power factor results for dry-type transformers are often very sensitive to humidity. Hence, cold units may need to be dried in order to obtain acceptable power factors. Ventilated Dry-Type Transformers •Expect CH ≤ 3%, CHL ≤ 2%, CL ≤ 4%, and Tip-up ≤ 0.5% Epoxy-Encapsulated Dry-Type Transformers •Expect CH ≤ 3%, CHL ≤ 1%, CL ≤ 2%, and Tip-up ≅ 0% 19 of 21

Transformer Power Factor Power Factors for Service Aged Transformers

Power Factor [%]

1.75 1.50 1.25 1.00 0.75 0.50 0.25 30Y

32Y

34Y

36Y

Transformer Age

38Y

40Y Current Test

42Y Future Test 20 of 21

10

Transformer Power Factor

Number of Transformers

CH Power Factors of Liquid-Filled Transformers

300 240

250

180

200 150

120 80

100 50

60 25 20 15

20

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

1.1

% Power Factor at 20 Degrees C

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11

Knowledge Is Power

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Apparatus Maintenance and Power Management for Energy Delivery

Bushing Power Factor & Capacitance Tests Mike Horning, Principal Engineer Doble Engineering Company

Doble Engineering Company

85 Walnut Street, Watertown, MA 02472

Typical Capacitance-Graded Bushing Center Conductor Sight-Glass Liquid or Compound Filler Insulating Weathershed Main Insulating Core Tap Insulation Tap Electrode Mounting Flange Ground Sleeve Tapped Layer Lower Insulator

2 of 57

1

3 of 57

Graded Bushing - Core Construction Semi-Conducting Paper Herringbone Pattern

Foil or Paint Core Wind

Core Wind

C2 Plate

C2 Plate

Common Construction

Distributed Capacitance GE Type U 4 of 57

2

ABB O + C Construction

C2 Plate

5 of 57

ABB O + C, 27 kV

Conductors 6 of 57

3

Graded Bushing – Electrical Characteristics

CA

Main Insulation C1

CB CC

Tap Insulation C2

CD CE

Center CA = CB = CC = CD = CE = CF = CG = CH = CI = CJ Conductor

CF CG

CENTER CONDUCTOR

CH CI CJ

Grounded Layer or Flange

CK

V1 = V2 = V3 = V4 = V5 = V6 = V7 = V8 = V9 = V10

Tap Electrode

CK

Line-to-Ground System Voltage

Voltage stress is evenly distributed across the insulation. As capacitive layers (i.e.. CA, CB, etc.) are shorted out the overall capacitance, C1, increases.

7 of 57

Adding Capacitors in Series 1 C1

C2

C3

CT

CN

1 =

C1

1 +

1 +

C2

1

C3

+…+

CN

CT Case 1: 3 Capacitors in Series

2

2

2

1

1 =

2

1 +

2

1 +

2 2

CT1 =

3 =

2

Shorting out a capacitor results in an increase in capacitance.

2

2

CT2 > CT1

CT1 CT1

Case 2: Shorted Capacitor

CT2 1 CT2

1 =

2

1 +

2

2 =

2

CT2 = 1

3

8 of 57

4

Test Taps vs. Potential Taps

Test Tap

Potential Tap 9 of 57

Test Taps vs. Potential Taps – “Typical” Differences Test Tap

Potential Tap

Test Voltage applied to Tap Electrode, Recommended Test Voltage = 500V Max Exception: Ohio Brass Type L = 250V Max

Test Voltage applied to Tap Electrode , Recommended Test Voltage = 2000V Max

Bushing Rated ≤ 69KV

Bushing Rated > 69KV

C2 ≅ C1 [capacitance]

C2 ≅ C1 x 10 …or… C2 >> C1 [capacitance]

In Service:Tap Grounded

In Service:Tap Grounded, Used as a Potential Source, OR Floating

C2 Plate is Outermost Foil

C2 Plate is Next Inner Foil Outer Foil Permanently Grounded

Tap Connected to C2 Plate by Friction

Tap Connected to C2 Plate by Solder, Clamp, or Other “Solid” Connection

Tap Cover 1 ½” or Smaller

Tap Cover 2 ½” or Larger

Tap Well Dry

Tap Well Dry or Oil/Grease Filled

Note: There are exceptions to most of the above statements. 10 of 57

5

Test Voltages Applied to Center Conductor Doble Recommended Test Voltages For Voltage Applied to Bushing Center Conductor Bushing Rating (kV) >8.7 8.7 5 4.3 1.2

Recommended Test Voltage (kV) 10 8 5 4 1

NOTE: The test voltages recommended for the bushing C1 UST test are applicable to spare bushings and for bushings installed in apparatus. For bushings in apparatus there may be unusual circumstances whereby the voltage rating of a bushing is greater than the voltage rating of the apparatus terminal to which it is connected; For example, the neutral terminal of a transformer winding. In such cases, though rare, the normal test voltage for the bushing C1 UST tests may have to be reduced to that which can be applied for the overall tests on the apparatus itself. 11 of 57

Bushing Test Connections HV Cable Short Shortthe thebushings bushings of ofeach eachwinding. winding. LV Test Lead

Only Onlyremove removethe the tap tapcover coverfrom fromthe the bushing bushingunder undertest. test.

Ground Lead Ground Groundwindings windings not notunder undertest. test. DO DONOT NOTFORGET FORGET to toreplace replacethe thetap tap cover coverafter aftertest! test!

12 of 57

6

Effects of Unshorted Bushings For apparatus containing windings, when the bushings are not shorted there may be a difference in potential at each bushing (due to winding inductance). If so, there may be a capacitive cross-coupling between phases which can result an increase in watts and power factor.

Incorrect (Unshorted) 0.80% = D 1.05% = I 0.76% = D

Phase A Phase B Phase C

Correct (Shorted) 0.39% = G 0.40% = G 0.39% = G

13 of 57

Bushing C1 Test, Routine Method - Connections HV Cable

C1 C1Test TestIncludes Includes •Core insulation •Core insulation between betweencenter center conductor conductorand and tapped tappedlayer. layer.

Test Mode: UST mA & W Guard

LV Test Lead

Ground Lead Apparatus Ground

C1 C1%PF %PFisistemperature temperature corrected correctedto to20°C 20°C using usingthe theaverage averageof of the theapparatus apparatusand and ambient ambienttemperature. temperature. Connection to Parent Apparatus 14 of 57

7

Bushing C1 Test, Routine Method HV Cable C1 Center Conductor

Test Tap

C2

Test Mode: UST

IC1

Ground Lead

LV Test Lead

mA & W Guard

CG

ICG

CG CG==Capacitance Capacitancefrom fromcenter center conductor conductorcircuit circuitto toground. ground. Includes Includesparent parentapparatus apparatus insulation insulationand andupper upperand andlower lower insulators insulatorsof ofbushings. bushings. 15 of 57

Typical C1 Test Data Description

Current (mA)

Watts

%PF

Typical Good Bushing

1.08

0.03

.28

Same Bushing, Contaminated

1.09

0.06

.55

Same Bushing, Shorted Condenser layers

1.19

0.04

.34

16 of 57

8

Bushing Temperature Correction Factor (Page 1 of 2)

17 of 57

Bushing Temperature Correction Factor (Page 2 of 2)

18 of 57

9

Bushing Temperature Correction Factor

DTAF Software – Required Fields 1. Manufacturer 2. Type 3. Ambient Temperature (Probe) 4. Apparatus Temperature Transformer – Top Oil Temperature Oil Circuit Breaker – Ambient (with discretion)

19 of 57

Bushing C1 Tests – Abnormal Results C1 Troubleshooting & Investigations ¾

Check connections. Ensure that all intentional connections have good metal-to-metal contact (no paint or oxidation). Verify that there are no unintentional grounds on test leads. Avoid using insulated wire for phase-to-phase shorts. Inspect test leads for damage. Verify proper test mode (UST).

¾

Clean and dry upper (and lower) porcelain and retest using Routine C1 method.

¾

Repeat test using a guard-collar to guard surface leakage on upper weathershed (see slide 19).

¾

Perform Inverted C1 test. This test is less sensitive to the effects of surface contamination (see slides 17-18).

¾

Perform Hot-Collar tests using both the GST-Ground and UST Methods (see slides 38-45).

¾

Perform reduced voltage test using Routine C1 method. 20 of 57

10

Resistive Path-to-Ground

Test Kv

mA

10

1.313

Watts -.007

Measure % Power Factor -.053 21 of 57

Bushing C1 Tests, Inverted Method - Connections LV Test Lead

Inverted InvertedMethod Method •Useful for •Useful for investigating investigatingnegative negative power powerfactors factors obtained obtainedusing usingthe theC1 C1 Routine RoutineMethod. Method.

Test Mode: UST 0.5 or 2 kV Test HV Cable

Ground Lead mA & W Guard

Apparatus Ground

•A •Acommon commoncause causeof of negative negativeC1 C1power power factors factorsisissurface surface contamination contaminationon onthe the upper upperor orlower lower insulators insulatorsof ofthe the bushings. bushings.

22 of 57

11

Bushing C1 Test, Inverted Method LV Test Lead

Test Mode: UST 0.5 or 2 kV Test

C2

Ground Lead CG

IC2 mA & W Guard

IC1

Center Conductor

Test Tap C1

HV Cable

Using Usingthe theC1 C1Inverted InvertedMethod, Method, the thecenter centerconductor conductorisis effectively effectivelygrounded groundedvia via connection connectionto tothe theLV LVTest Test Lead. Lead. Hence, Hence,there thereisisno no voltage voltagestress stressacross acrossCG. CG. 23 of 57

Bushing C1 Test with Guard-Collar HV Cable Guard-Collar Guard-Collar •May •Mayeliminate eliminatethe the effects effectsof ofsurface surface contamination contamination from fromthe thetest test result. result.

Test Mode: UST

mA & W Guard

LV Test Lead

Ground Lead Apparatus Ground

•Use •Useone oneguard guard collar collarpositioned positioned near nearthe thebottom bottom skirt. skirt. •Or, •Or,use use multiple multiple collars collarslocated locatedat at various variouslocations locations on onthe theupper upper weathershed. weathershed. Connection to Parent Apparatus 24 of 57

12

Bushing C2 Test - Connections LV Test Lead C2 C2Test TestIncludes Includes •Tap insulator •Tap insulator

Test Mode: GST-Guard 0.5 or 2 kV Test

•Core •Coreinsulation insulation between betweentapped tapped layer layerand andbushing bushing ground groundsleeve sleeve

HV Cable

•Portion •Portionof ofliquid liquid or orcompound compoundfiller filler

Guard

mA & W

•Portion •Portionof of weathershed weathershednear near ground groundsleeve sleeve Ground Lead C2 C2%PF %PFisisnot not temperature temperaturecorrected. corrected.

Apparatus Ground

25 of 57

Bushing C2 Test LV Test Lead

C1

C2

Test Mode: GST-Guard 0.5 or 2 kV Test

Center Conductor

Test Tap

HV Cable

CG

mA & W Guard

Ground Lead

IC2

IC1

26 of 57

13

Why Perform C2 Tests ?????

27 of 57

C2 TESTS •Internal Flashover Around the Main Core is a Real and Serious Threat to all Sealed Capacitance Graded Bushings •The C2 Power Factor Test has Been Shown, in Some Cases, to be a More Apparent Indicator of Internal Fluid Contamination Than the C1 Test

28 of 57

14

C2 TESTS GE Type U 230kV Bushing: C1

C2

Date 1/6/82

%PF Cap .31 508.8

%PF .28

Cap 4134

5/1/96

.58

2.26

4138

1/30/97

Failed in service

510.2

29 of 57

C2 TESTS Example: McGraw-Edison Type PA 23kV Bushings Bushing # X1 X2 X3

C1(%PF) 0.46 0.60 0.45

C2(%PF) 0.50 2.78 0.50

• X2 was removed from service and found to have highly contaminated fluid with low dielectric-breakdown strength 30 of 57

15

Bushing C2 Tests – Abnormal Results

C2 Troubleshooting & Investigations ¾

Check connections. Ensure that all intentional connections have good metal-to-metal contact (no paint or oxidation). Verify that there are no unintentional grounds on test leads. Avoid using insulated wire for phase-to-phase shorts. Inspect test leads for damage. Verify proper test mode (GST-Guard).

¾

Clean and dry tap insulator and retest.

¾

Add an additional ground to the bushing flange and retest. Poorly grounded bushing flanges can cause both high and low/negative C2 test results. If a poorly grounded flange is discovered, then corrective actions should be taken to ensure proper grounding before returning to service.

31 of 57

Doble Bushing Tap Adapters

32 of 57

16

Westinghouse Type O Bushing Tap Adapter

33 of 57

Westinghouse Type O+ Bushing Tap Adapter

34 of 57

17

Spare Bushing Tests Comments on Spare Bushing Tests ¾

Do not test in wooden crate or on wooden stand.

¾

Support bushing on a grounded metal stand if possible.

¾

Web slings may be used for tests. ™ Cleanliness of sling may affect test results. ™ Sling should be kept clear of energized points.

¾

Connect ground lead directly to bushing flange.

¾

Ground bushing flange to substation/building ground.

¾

Clean upper and lower surfaces before testing.

35 of 57

Bushing “Overall” Test HV Cable Test TestIncludes Includes •Main •MainC1 C1Core Core Insulation Insulation

Test Mode: GST-Ground

•Upper •UpperInsulating Insulating Weathershed Weathershed •Sight-Glass •Sight-Glass •Lower •LowerInsulator Insulator •Portion •Portionof ofLiquid Liquidor or Compound CompoundFiller Filler

mA & W Guard

Ground Lead

Bushing and Test Stand Ground

%PF %PFisistemperature temperature corrected correctedto to20°C 20°C using the ambient using the ambient temperature. temperature.

36 of 57

18

Bushing “Overall” Test HV Cable C1

IC1 C2

Test Mode: GST-Ground

CG mA & W Guard

Ground Lead

IC1+ICG

Center Conductor

Test Tap

ICG

Note: Note: For Formost mostbushing bushing types, types,the theC2 C2insulation insulation will willbe beshorted shortedout out(as (as shown) shown)via viathe thetap tapcover. cover.

37 of 57

DTA Spare Bushing Test Screen

38 of 57

19

Bushing C1, C2, and Overall – Evaluation of Results

Capacitance ¾

Suggested limits: ±5% of Nameplate Capacitance = Investigate

¾

Each shorted capacitance layer will cause an increase in C1 capacitance of 5% to 15%.

¾

If the tap electrode becomes disconnected from the C2 plate there may be a dramatic decrease in C2 capacitance. This may also cause a change in the C1 capacitance.

¾

Oil or compound leaks may cause a decrease in capacitance.

¾

Differences in factory and field test procedures and/or test conditions may result in differences in capacitances.

39 of 57

C2 Capacitance – Factory vs. Field Test “Conditions” C2 capacitance varies depending on the length of the outer condenser layer and the distance to the grounded test tank wall. C2 = C2A + C2B [pF]

C2A C1

Flange

Bushing Center Conductor

C2B

Test Tank Wall

Outer Condenser Layer

40 of 57

20

C1 Capacitance – Factory vs. Field Test “Procedures”

Haefley Type COTA Bushing Flange

Flange Potential Tap

Potential Tap Test Tap (burried)

Test Tap

C0 C2

C2 C1

C1

Center Conductor

Center Conductor

Factory C1 Test

Field C1 Test

Because the test tap is buried, the factory C1 test cannot be reproduced in the field. Using the nameplate capacitances, the Doble C1 capacitance may be calculated: C1DOBLE = (C1NP x C2NP) / (C2NP – C1NP) [pF]

41 of 57

Bushing C1, C2, and Overall – Evaluation of Results

Power Factor ¾

Most modern oil-filled condenser type bushings have C1 power factors of approximately 0.5% or less, and values exceeding 1.0% are questionable. Specific limits for various manufactures and types are given on the following slides.

¾

Bushings that exhibit a history of continued increase in power factor should be investigated and considered for removal from service.

¾

Power factors that are significantly lower than nameplate or prior tests may be the result of extreme contamination patterns and/or tracking conditions, and these results should be investigated.

¾

A common cause of high C2 power factors is moisture or contamination on the tap insulator. Cleaning and drying of the tap insulator will frequently correct the problem. 42 of 57

21

Bushing C1 & Overall Power Factor Limits

ASEA Type (* All Types) GOA 250 GOA OTHER GOB GOBK GOC GOE GOE GOEK GOEL GOF GOFL GOG GOH GOM

Description

Typical %PF 0.5% 0.45% 0.5% 0.5% 0.4% 0.45% 0.4% 0.4% 0.4% 0.45% 0.4% 0.45% 0.25% 0.45%

50% drying is recommended. Overly wet interruptors may swell resulting in binding and/or overstressing of clamping bolts. Overly dry interruptors may loose their mechanical strength or develop looseness of their plate structure.

8 of 14

4

OCB Test Analysis – Example 1

9 of 14

OCB Test Analysis – Example 2

10 of 14

5

OCB Test Analysis – Example 3

11 of 14

OCB Test Analysis – Example 4

12 of 14

6

OCB Test Analysis – Example 5

13 of 14

OCB Test Analysis – Example 6

14 of 14

7

Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Grounded Tank SF6 Circuit Breaker Tests Mike Horning, Principal Engineer Doble Engineering Company

Doble Engineering Company

85 Walnut Street, Watertown, MA 02472

Grounded Tank SF6 Circuit Breaker

Power Factor Test Procedure • Bushings (Hot-Collar) • Open-Breaker Tests (6 Tests) • Open-Breaker UST Tests (3 Tests) • Closed-Breaker Tests (3 Tests) for some multi-contact breakers • Diagnostic (questionable results)

2 of 10

1

Grounded Tank SF6 Circuit Breaker Recommended Test Voltages Breakers Rated Above 15KV Overall tests are performed at 10KV Breakers Rated 15KV and Below Initial Tests 1. Below corona inception, 2KV or less. 2. Rated operating (system) line-to-ground voltage, VL-G. 3. 10% to 25% above rated operating (system) line-to-ground voltage, VL-G. Routine Tests 10% to 25% above rated operating (system) line-to-ground voltage, VL-G. Use same voltage as first test.

3 of 10

Grounded Tank SF6 Circuit Breaker Test Procedure Test No.

Breaker Position

Test Mode

Bushing Energized

Bushing Floating *

1

Open

GST-Ground

1

2

-

2

2

1

-

3

3

4

-

4

4

3

-

5

5

6

-

6

6

5

-

1

-

2

8

3

-

4

9

5

-

6

1&2

-

-

11 **

3&4

-

-

12 **

5&6

-

-

7

10 **

UST

Closed

GST-Ground

Bushing UST

* Bushings of phases not under test should be floating ** Test 10-12 are supplementary tests for breakers containing internal support insulators (ie. those that are isolated when the breaker is open). In general, this applies to some circuit breakers with more than one break per phase. Some of these designs include: Brown Boveri / Gould / ITE, Types GA/GB High Voltage Breakers, SF6 Puffers Westinghouse, Type SFV (two interrupters/phase)

4 of 10

2

Grounded Tank SF6 Circuit Breaker Open Breaker GST-Ground Tests HV Lead

Included In Test Results: • Bushing • Any Support Insulation or Operating Rod on Same Phase & Side

Ground Lead

5 of 10

Grounded Tank SF6 Circuit Breaker Open Breaker UST Tests HV Lead

LV Lead

Included In Test Results: • Contact Assembly • Gas • Any Grading Capacitor(s)

Ground Lead

6 of 10

3

Grounded Tank SF6 Circuit Breaker Closed Breaker GST-Ground Tests HV Lead

Necessary to test operating rod and support insulation Ground Lead

Included In Test Results: • Bushings (Both) • “All” Support Insulation and Operating Rod on Same Phase

7 of 10

Grounded Tank SF6 Circuit Breaker Evaluation of Results • If current is greater than 300 μA evaluate % PF. • No temperature correction. • Compare to previous tests, similar breakers, and Doble’s tabulated data for similar breakers (TDRB). • Compare results: ¾ Tests 1, 3, and 5 ¾ Tests 2, 4, and 6 ¾ Tests 7, 8, and 9 ¾ Tests 10, 11, and 12 8 of 10

4

Grounded Tank SF6 Circuit Breaker Evaluation of Results (continued) • Tests 1 through 6 ¾ Dominated by bushing. ¾ Also includes operating rod and any support insulation. ¾ % PF generally 1.0 % or less. • Tests 10, 11, and 12 ¾ Dominated by bushings (tests both bushings). ¾ Also includes “all” operating rod and any support insulation (including those located between the breaks). ¾ % PF generally 1.0 % or less. 9 of 10

Grounded Tank SF6 Circuit Breaker Evaluation of Results (continued) • Tests 7, 8, and 9 (contact assembly without a grading capacitor) ¾ Condition of contact assembly and SF6 gas. ¾ Very low current, evaluate losses. ¾ Losses generally 0.010 Watts or less. • Tests 7, 8, and 9 (contact assembly with grading capacitor(s)) ¾ Dominated by grading capacitors. ¾ Condition of contact assembly and SF6 gas.

10 of 10

5

Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Potential Transformer Tests Mike Horning-Principal Engineer Doble Engineering Company

Doble Engineering Company

85 Walnut Street, Watertown, MA 02472

Common PT, Line-to-Line & Line-to-Ground H1 H2

H1

CH2

CH1 CHY

CH1

CHX

X1 X2 X3

CHX X1 X2 X3 Y1 Y2 Y3

H0

Y1 Y2 Y3

CHY CH0

CH = CH1 + CH2

CH = CH1 + CH0 2 of 12

1

Recommended Test Voltages Line-to-Line PTs (Liquid Filled)

PT Voltage Rating [kV]

Test Voltage [kV]

15 kV and Above

10.0

7.2 to 8.7

5.0

4.2 to 5.0

2.5

2.4

2.0

3 of 12

Recommended Test Voltages Line-to-Ground PTs (Liquid Filled and Dry-Type) Test Description

Any Test with H0 Energized

Any Test with H0 Not Energized

Test Voltage The maximum test voltage must be limited to the rated line-to-ground voltage of the H0 bushing (usually 5 kV or less), the rated line-to-ground voltage of the PT, or 10kV, whichever is lower. This statement applies to all tests except H1 CrossCheck Test #2 and H1 Bushing Test #8 (see Routine and Supplemental Procedures on following pages). The maximum test voltage should be limited to the rated line to ground voltage of the PT or 10 kV, whichever is lower. This statement applies to H1 Cross-Check Test 2 and H1 Bushing Test 8 (see Routine and Supplemental Procedures on following pages).

4 of 12

2

Recommended Test Voltages Dry-Type PTs (Line-to-Line and Line-to-Ground) Test Description

Test Voltage a. 2 kV b. Line-to-ground operating voltage.**

Overall *

c. 10% to 25% above line-to-ground operating voltage. a. 2 kV Cross-Check * b. Line-to-ground operating voltage.** Exciting Current *

a. Line-to-ground operating voltage.

* For line-to-ground applications, The maximum test voltage must be limited to the rated line-to-ground voltage of the H0 bushing (usually 5 kV or less), the rated line-to-ground voltage of the PT, or 10kV, whichever is lower. ** Calculate and analyze Power Factor Tip-Up by subtracting the 2 kV test result from the operating line-to-ground test result. 5 of 12

Test Procedures Routine Tests, Single-Phase PT Test No.

Test Mode

Energize

Ground

Guard

UST

Test Description

1*

GST

H1 & H0 (H2)

X1 & Y1

-

-

Overall (CH+CHX+CHY)

2

GST

H1

X1 & Y1

H0 (H2)

-

H1 Cross-Check

3*

GST

H0 (H2)

X1 & Y1

H1

-

H0 (H2) Cross-Check

4**

UST

H1

X1 & Y1

-

H0 (H2)

Excitation H1 to H0 (H2)

5*

UST

H0 (H2)

X1 & Y1

-

H1

Excitation H0 (H2) to H1

* Maximum test voltages for Tests #1, 3, and 5 must be limited to (1) the rated line-to-ground voltage of the H0 bushing, (2) the recommended test voltage based upon the kV rating of the PT, or (3) 10 kV, whichever is lower. ** For purposes of comparison, Test #4 should be conducted at the same voltage as Test #5.

6 of 12

3

Test Procedures Supplemental Tests, Single Phase PT Test No.

Test Mode

Energize

Ground

Guard

UST

Test Description

6*

UST

H1 & H0 (H2)

Y1

-

X1**

CHX

7*

UST

H1 & H0 (H2)

X1

-

Y1**

CHY

8

GST

H1

-

H0 (H2), X1, & Y1

-

CH1

9*

GST

H0 (H2)

-

H1, X1, & Y1

-

CH0 (CH2)

* Maximum test voltages for Tests #6, 7, and 9 must be limited to (1) the rated line-to-ground voltage of the H0 bushing, (2) the recommended test voltage based upon the kV rating of the PT, or (3) 10 kV, whichever is lower. ** For Test #6 the X circuit must be ungrounded. For Test #7 the Y circuit must be ungrounded.

7 of 12

Test Procedures Routine Tests, 3-Phase PT Test No.

Test Mode

Energize

Ground

Guard

UST

Test Description

1

GST

H1, H2, H3, & H0

X1 & Y1

-

-

Overall

2

GST

H1

X1 & Y1

H0, H2, & H3

-

H1 Cross-Check

3

GST

H2

X1 & Y1

H0, H1, & H3

-

H2 Cross-Check

4

GST

H3

X1 & Y1

H0, H1, & H1

-

H3 Cross-Check

5

GST

H0

X1 & Y1

H1, H2, & H3

-

H0 Cross-Check

6

UST

H1

X1 & Y1

H2 & H3

H0

Excitation H1 to H0

7

UST

H2

X1 & Y1

H1 & H3

H0

Excitation H2 to H0

8

UST

H3

X1 & Y1

H1 & H2

H0

Excitation H3 to H0

* Maximum test voltages for Tests #1 and 5 must be limited to (1) the rated line-to-ground voltage of the H0 bushing, (2) the recommended test voltage based upon the kV rating of the PT, or (3) 10 kV, whichever is lower. ** For purposes of comparison, Test #6, 7, and 8 should be conducted at the same voltage.

8 of 12

4

Temperature Correction Factors

9 of 12

Line-to-Ground PT, Internally Grounded H0 H1

CH1 CHX

X1 X2 X3

CH = CH1 + CH0 CHY CH0

Y1 Y2 Y3

H0

10 of 12

5

Test Procedures Routine Tests, Line-to-Ground PT with Internally Grounded H0 Test No.

Test Mode

Energize

Ground

Guard

UST

Test Description

1

UST

H1

H0

-

X1 & Y1

Line End of CHX+CHY*

2

GST

H1

H0

X1 & Y1

-

Excitation H1 to H0 and CH1

Supplemental Tests, Line-to-Ground PT with Internally Grounded H0 Test No.

Test Mode

Energize

Ground

Guard

UST

Test Description

1

UST

H1

H0 & Y1

-

X1

Line End of CHX*

2

UST

H1

H0 & X1

-

Y1

Line End of CHY*

* Because H0 cannot be ungrounded, the test voltage is graded across the H winding. Therefore the insulation at the line end of the winding is stressed while the insulation at the ground end is not. This is only a partial test of the insulation system CHX and CHY. 11 of 12

Potential Transformers Evaluation of Results 1. Overall power factor test results (test 1) should be compared to prior tests, similar units, tabulated data (Doble Test Data Reference Book), and manufacturer recommendations. 2. For most single-phase PTs, the cross-check test power factor results (tests 2 and 3) compare closely to the overall test results. However, in some units it is normal for one cross-check power factor to be higher than the overall. 3. The cross check provides useful supplementary data, particularly when the overall test results are questionable. For example, in a single-phase PT if the overall power factor is higher than expected, then the cross-check could help differentiate between a general condition (overall and both cross-checks elevated) or a problem localized in one bushing or a end of a winding (overall on one cross-check elevated). 4. The sum of the two cross-check tests’ current and watts should be approximately equal to the overall current and watts respectively. Failure of these results to agree could indicate winding problems (open circuits), poor connections at the bushings, or some other voltage sensitive problem (i.e. if the cross check tests are conducted at two different test voltages). 5. Tip-Up analysis may be performed on dry-type PTs. 6. For single-phase PTs the excitation current tests (tests 4 and 5) should provide similar results if performed at the same voltage. For 3-phase PTs, a excitation current pattern of two similar values and one lower value is expected.

12 of 12

6

Knowledge Is Power

SM

Apparatus Maintenance and Power Management for Energy Delivery

Negative Power Factor Mike Horning, Principal Engineer Doble Engineering Company

Doble Engineering Company

85 Walnut Street, Watertown, MA 02472

Negative Power Factor Theory

HV Cable

ET IT

Z1 EG

Test Mode: UST IT’

IG

Z2

RG ≅ ZG

mA & W Guard LV Test Lead

Apparatus Ground

Ground Lead 2 of 21

1

Negative Power Factor Theory Case 1 – Normal Conditions IT

Z1

ET

Case 2 – Low Resistance Path to Guard

Z1

EG Z2

EG IG

IT ’

Z2

mA,W

ETZ2

EG =

Z1 + Z2

IT’ = EG / Z2 =

IT ’

ZG

mA,W

EG =

IT

ET

ET Z1 + Z2

ETZ2||ZG Z1 + Z2||ZG

IT’ = EG / Z2 =

= IT

=

ETZ2 Z1Z2 + Z1 + Z2 ZG ET

Z1Z2 + Z1 + Z2 ZG

≠ IT

3 of 21

Negative Power Factor Theory Assuming Z1 and Z2 are primarily capacitive, and ZG is primarily resistive Z1 = 1/jωC1 = -j/ωC1 = -jXC1 Z2 = -jXC2 ZG = RG

EG =

IT’ =

ETZ2 Z1Z2 + Z1 + Z2 ZG ET Z1Z2 + Z1 + Z2 ZG

=

=

-jETXC1 – XC1XC2 – j(XC1 + XC2) RG ET – XC1XC2 – j(XC1 + XC2) RG

EG = EG α° 0° < α < 90°

IT’ = IT’

δ°

90° < δ < 180°

4 of 21

2

Negative Power Factor Theory -IG

IT IT’ EG

IT IG

α° ET

EG ET

0° < α < 90° 1. Applied voltage ET produces total current IT through RC network between HV hook and ground/guard. 2. Current IT produces voltage EG across the RC network between the leakage origination point and guard. EG is phase shifted α° due to the leakage resistance RG.

3. Leakage point voltage EG produces leakage current IG. Because the leakage current is predominantly resistive, IG and EG are shown in phase with each other. 4. The measured current IT’ is equal to the total current IT minus the leakage current IG. 5 of 21

Negative Power Factor Theory

IT’

IC’ δ°

IR’

ET

90° < δ < 180°

5. The measured current IT’ has resistive IR’ and capacitive IC’ components as shown. 6. The resistive current IR’ has a negative value. Hence, the measured watts value and calculated power factor are also negative. w = IR’ x ET / 1000

%PF = w x 10 / IT’ [currents in mA]

6 of 21

3

Negative Power Factor Theory Effects of Origination Location and Resistance IT’ = 100%

75%

IT ‘

100%

XC1

25%

75%

XC

50%

ET – XC1XC2 – j(XC1 + XC2) RG

XC2

Maximum XC2 / 4RG

50%

25%

RG

0%

0%

• If RG >> XC2 / 4 then no phase shifting

mA,W

• If RG is small then phase shifting everywhere 7 of 21

Negative Power Factor - Laboratory Test Effects of Origination Location and Resistance RG = 5 MΩ

RG

mA,W

RG = 11.5 MΩ

11

Node

mA

W

%PF

Cap

mA

W

%PF

Cap

10

1

3.66

0.02

0.05

971

3.66

0.02

0.07

972

9

2

3.65

-1.77

-4.84

968

3.63

-0.31

-0.87

962

8

3

3.64

-3.11

-8.54

962

3.60

-0.62

-1.72

955

7

4

3.63

-4.07

-11.18

958

3.60

-0.87

-2.41

953

6

5

3.63

-4.62

-12.72

954

3.60

-1.04

-2.90

954

5

6

1.88

-15.88

-84.47

265

3.58

-1.23

-3.44

948

4

7

3.62

-4.61

-12.71

953

3.58

-1.32

-3.67

950

3

8

3.63

-4.06

-11.18

957

3.60

-1.27

-3.53

953

2

9

3.65

-3.12

-8.55

964

3.63

-1.03

-2.83

961

1

10

3.66

-1.77

-4.83

970

3.65

-0.77

-2.12

968

11

3.67

0.02

0.05

972

3.67

0.03

0.07

974

Ten Doble TTR capacitors in series, approximately 10,000 pF each

8 of 21

4

Negative Power Factor - Slung Specimen Grading Capacitor for Alsthom Circuit Breaker, Dirty/Wet Sling C1

Sling

C2

RG

N.P. Capacitance 1200 pF

Test / Mode

KV

Test Mode: UST

mA

W

%PF

Cap [pF]

Slung / UST

10

4.5

-0.014

-0.03

1193

Mounted / UST

10

4.505

0.038

0.08

1194

Note: The slung specimen could also be a bushing, arrestor, stand-off insulator, etc. 9 of 21

Negative Power Factor - Bushing ABB Type O+C Bushing, Surface Contamination C1 C1-1

C1-2

RG

Test Mode: UST

Test / Mode

Test KV

mA

W

%PF

C1 / UST

10

1.313

-0.007

-0.053 10 of 21

5

Negative Power Factor - Bushing Surface Contamination – C1 Test, Routine vs. Inverted Method Routine Method

C1-1

Inverted Method

Weakest Coupling

Strongest Coupling

Strongest Coupling

Weakest Coupling

C1-2

C1-2

C1-1

RG

RG

11 of 21

Negative Power Factor - Bushing LAPP Type POC-A 34.5kV Bushing, Internal Tracking C1 C1-1

C1-2

RG Test Mode: UST Bonding tape loose shunting outer surface of bushing core to ground flange.

Test / Mode

Test KV

mA

C1 / UST

10

0.551

C2 / Guard

0.5

W

%PF

-0.18

-3.3

Test set tripped off 12 of 21

6

Negative Power Factor - Transformer Epoxy Encapsulated Transformer with Surface Contamination Surface Contamination HV Winding LV Winding CORE

Air Gap

CHL

CH-Air

CAir RHG

CL-Air RLG

Test Mode: UST Ground Potential

13 of 21

Negative Power Factor - Transformer Epoxy Encapsulated Transformer National, 3-phase, 2250 kVA, 34/0.48 kV, 1984 #

Insul.

kV

mA

Watts

%PF

Cap [pF]

1

CH + CHL

10

4.772

0.092

2

CH

10

1.522

0.120

0.79

403.5

3

CHL (UST)

10

3.252

-0.020

-0.06

862.5

4

CHL

3.250

-0.028

-0.09

861.5

5

CL + CHL

.5

15.230

3.059

6

CL

.5

11.990

3.051

2.54

3179

7

CHL (UST)

.5

3.254

0

0

863.2

8

CHL

3.240

0.008

0.02

861.0

1265

4040

14 of 21

7

Negative Power Factor - Transformer Transformer with Ground Shield, Interwinding Test HV Winding

Ground Shield

LV Winding

CORE

CHL

CH-GS

CL-GS RGS

Test Mode: UST

Note: If RGS=0, then mA ≅ 0 and Watts ≅ 0

15 of 21

Negative Power Factor - Transformer Transformer with Ground Shield McGraw Edison, 1250 kVA, 20.9/2.3 kV, 1984 #

Insul.

kV

mA

Watts

%PF

Cap [pF]

1

CH + CHL

10

13.040

0.477

2

CH

10

7.854

0.752

0.88

2083

3

CHL (UST)

10

5.189

-0.280

-0.59

1376

4

CHL

5.186

-0.275

-0.58

1377

5

CL + CHL

10

16.85

2.024

6

CL

10

11.67

2.322

1.83

3095

7

CHL (UST)

10

5.186

-0.290

-0.61

1375

8

CHL

5.180

-0.298

-0.63

1373

3460

4470

16 of 21

8

Negative Power Factor - Transformer Three-Winding Transformer, Interwinding Tests HV Winding

LV Winding

TV Winding

CORE

CHT H

L

T

CHL

CLT RB

Test Mode: UST Meas R, Gnd B

Note: If RB=0, then mA ≅ 0 and Watts ≅ 0

17 of 21

Negative Power Factor - Transformer Transformer with Poor Grounding, Interwinding Tests CHL

LV Winding

HV Winding

ICHL

CHL CH

CH

CL

EG

CL ICL

RG Poor Core Ground

RG

Poor Tank Ground Poor Test Lead Ground

ICHL + ICL wCHL + wCL

Note(1): wCL may be negative. Therefore the measured sum wCHL+wCL may also be negative. This would result in a negative power factor. Note(2): If RG=0, then EG = 0. Therefore ICL ≅ 0 and wCL ≅ 0.

9

18 of 21

Negative Power Factor - Transformer Transformer with Poor Core Ground (High Resistance) Trafo-Union, 58 MVA, 230/20.72 kV #

Insul.

kV

mA

Watts

%PF

1

CH + CHL

10

92

3.0

2

CH

10

29

3.7

0.95

3

CHL (UST)

10

63

-0.7

-0.11

6

CL

10

108

19.5

1.8

19 of 21

Negative Power Factor - Transformer Transformer with Poor Tank Ground General Electric, 7.5 MVA, 13.8/4.16 kV, D-Y #

Insul.

kV

mA

Watts

%PF

Cap [pF]

1

CH + CHL

10

57.050

1.844

2

CH

10

0.913

-0.46

-5.0

241.9

3

CHL (UST)

10

1.669

-0.76

-4.5

442.1

4

CHL

56.137

2.3

0.41

14892

5

CL + CHL

5

42.100

1.4

6

CL

5

0.399

-0.1

-2.5

105.9

7

CHL (UST)

5

1.542

-0.7

-4.5

408.5

8

CHL

41.701

1.59

0.38

11061

15134

11167

20 of 21

10

Negative Power Factor - Stator CAB

Coils

CA

CAB Insulation Outside Slots

CA

EG

ICAB

CB ICB

RG

CB Insulation Inside Slots

RG

ICAB + ICB

Core A Phase

B Phase

wCAB + wCB

C Phase

Note(1): wCL may be negative. Therefore the measured sum wCHL+wCL may also be negative. This would result in a negative power factor. Note(2): If RG=0, then EG = 0. Therefore ICB ≅ 0 and wCB ≅ 0.

11

21 of 21