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TitleDoble Power Factor Document
File Size2.7 MB
Total Pages117
Table of Contents
                            new cover.pdf
Table of Contents5.pdf
	Table of Contents
Doble Services.pdf
Safety.pdf
	An Acceptable Method
	Improper method!
	Wrong!
Power Factor Basic Theory2.pdf
Transformer Overall Power Factor.pdf
Bushing Power Factor.pdf
Transformer Excitation.pdf
Transformer Turns Ratio.pdf
Insulating Fluids.pdf
Surge Arrestors.pdf
Oil Circuit Breakers1.pdf
Grounded Tank SF6 Circuit Breakers.pdf
Potential Transformers.pdf
Negative Power Factor.pdf
                        
Document Text Contents
Page 1

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

Page 2

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

Page 58

19

37 of 57

Bushing “Overall” Test

Note: For most bushing
types, the C2 insulation
will be shorted out (as
shown) via the tap cover.

Note: For most bushing
types, the C2 insulation
will be shorted out (as
shown) via the tap cover.

Ground Lead

Test Tap Ce
n
te

r C
o

n
d
u
cto

r

mA & W

IC1+ICG

HV Cable

Guard

C2

C1

Test Mode:
GST-Ground

CG

IC1

ICG

38 of 57

DTA Spare Bushing Test Screen

Page 59

20

39 of 57

Capacitance

Bushing C1, C2, and Overall – Evaluation of Results

Suggested limits:
±5% of Nameplate Capacitance = Investigate

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

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.

Oil or compound leaks may cause a decrease in capacitance.

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

40 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]

Flange

Test Tank
Wall

Outer
Condenser

Layer

C2A

C2B

C1 Bushing
Center

Conductor

Page 116

10

19 of 21

Negative Power Factor - Transformer

# 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

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

20 of 21

Negative Power Factor - Transformer

# Insul. kV mA Watts %PF Cap [pF]

1 CH + CHL 10 57.050 1.844 15134

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 11167

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

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

Page 117

11

21 of 21

Negative Power Factor - Stator

CA CB

CAB
Insulation Outside Slots

Insulation Inside Slots

Core

Coils

A Phase B Phase C Phase

CA CB

CAB

RG

ICAB

ICB

ICAB + ICB
RG

wCAB + wCB

EG

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.

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