RIP vs OIP

Assessment of the Condition of

High Voltage Bushings

PAGE 4

Definitions

Dielectric Losses are caused by:

• Conductive losses •Polarization losses •Partial discharges 0.00E+00 5.00E-04 1.00E-03 1.50E-03 2.00E-03 2.50E-03 0 50 100 150 200 250 300 350 400 Serial Parallel Sum

Parallel circuit Serial circuit

RP CP RS CS tot R S S C R U U C R U U = ⋅ ⋅ = = ϕ ω δ cos : PF tan : DF | | | | cos : PF 1 | | | | tan : DF tot RP P P CP RP I I C R I I = ⋅ ⋅ = = ϕ ω δ PAGE 5

Capacitance Values

• Partial breakdowns between layers

• Incoming oil into cracks of solid insulation (RBP)

•Between transformer windings:

• Change of the geometry between winding

•Between windings and tank

• Displacement of the active part within the tank

•Between windings and core

• Displacement of the winding or the core (if the core

ground can be disconnected)

•Core to tank

• Movement of the core (if the core ground can be

disconnected)

PAGE 6

Power (Dissipation) Factor

•Bushings:

• Aging and decomposition of insulation • Water content

• Bad contacted electrodes or capacitive layers • Cracks in the insulation

• (Partial) discharges

•Transformers:

• Aging

• Water content in the oil and in the paper • Contamination by particles

PAGE 7

Condenser Type Bushings

RBP Resin Bonded Paper

RIP Resin Impregnated Paper

OIP Oil Impregnated Paper

PAGE 8

Limits

* at 1.05 Um/√3 and 20°C

Typ RIP OIP RBP Gas

Insulation Resin impregnated paper Oil impregnated paper Resin bonded paper SF6or other gases DF tan δ (RT) (IEC 60137) < 0,7% * < 0,7% * < 1,5% * -PF cos ϕ(RT) IEEE C57.19.01 < 0,85% * < 0,5% * < 2% * -Typical new values 0.3-0.4% * 0.2-0.4% * 0.5-0.6% * -Partial discharges (IEC 60137) Um 1.5 Um/√3 1.05 Um/ √3 < 10pC < 5cC < 5pC < 10pC < 5pC < 5pC < 300pC < 10pC < 5pC < 5pC < 0.7% < 0.7% <1.5% < 0.3-0.4% <0.2-0.4% <0.5-0.6%

PAGE 9

Capacitive Bushings (1)

Bushing Measuring Tap

PAGE 12

Measuring Taps

Measuring Taps

Measuring Taps

C-Tan Delta Progression of a Bushing

Year of Manufacturimg 1961, horizontal mounted, oil filled

0 5 10 15 20 25 30 T a n D e lt a x 1 0 -3 C h a n g e o f C a p a c it a n c e %

PAGE 16

Bushing Fault

Source: RWE

PAGE 18

• Not free of cavities – Partial Discharges

possible also at rated voltage

• Higher dielectric losses can feed to thermal

instability

• RPB has cavities and cracks in the

paper which are normally filled with the surrounding oil

• Increase of capacitance

• After a longer storage period this oil is running

out. The PD level is increasing and the capacitance is getting smaller

RBP - Bushings

RBP 220kV Bushing (1971)

RBP Bushing 220kV (1971)

RBP Bushing Oil-filled Cracks

PAGE 23

Micafil RBP Bushing 123kV

PAGE 24

Micafil RBP Bushing 123kV

Micafil RBP Bushing 123kV

Micafil RBP Bushing 123kV

• defective contact on the

measuring tap or

• defective connection between

the innermost layer and the HV conductor or

• partial breakdown between

layers

PAGE 27

Measurement Tap O.K.

Innermost Layer Was Not Properly

Dissipation Factor Measurement

Measurement of the Removed Bushing

Page: 31

Measurement of the Removed Bushing

Page: 32 0,0% 2,0% 4,0% 6,0% 8,0% 10,0% 12,0% 14,0% 16,0% 0 ,0 H z 5 0 ,0 H z 1 0 0 ,0 H z 1 5 0 ,0 H z 2 0 0 ,0 H z 2 5 0 ,0 H z 3 0 0 ,0 H z 3 5 0 ,0 H z 4 0 0 ,0 H z 4 5 0 ,0 H z DF (f) C1

Active Part of the Bushing

Page: 33

PAGE 34

OIP Bushings

• Paper of the OIP bushings ages particularly

at high temperatures

• Through aging the dielectric losses will

increase -> this increases the power factor

• Temperature dependent aging decomposes

the Paper and produces additional water -> this accellerates the aging

PAGE 35

420kV OIP Bushings

PAGE 38

33kV OIP Bushings

Tan Delta (T) at 50Hz (OIP Bushings)

0.10 1.00 10.00 20 30 40 50 60 70 80 °C 90 [%] 0.1-0.3% Water in paper 0.4-0.6% Water in paper 1% Water in paper

Source: ABB, Bushing diagnostics and conditioning

PAGE 40

Tan Delta (f) at 30°C (33kV OIP Bushings)

Tan Delta (f) A, B, C 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0 4 5 0 Hz % A B C A Removed B Removed C Removed PAGE 41

123kV OIP Bushings

123kV OIP Bushings

123kV OIP Bushings

PAGE 44

123kV OIP Bushings

123kV OIP Bushings

Aging of RIP Bushings

• Partial breakdowns between capacitive layers are rather seldom

• Decrease of the power factor with increasing test voltage can be an indicator for partial breakdowns

• Also defective connections of the measurement layer to the test tap or of the innermost layer to the high voltage conductor may be the reason for a decrease of the power factor with increasing test voltage

• Increase of the capacitance after a partial breakdown between two layers:

Cnew= Cold x n / (n-1) n= number of layers approx. 4-7 kV per layer

PAGE 47

220kV RIP Bushing Stored Outside

PAGE 48

220kV RIP Bushing Stored Outside

0.25 % 0.35 % 0.45 % 0.55 % 0.65 % 0.75 % 0.85 % 0.0 Hz 100.0 Hz 200.0 Hz 300.0 Hz 400.0 Hz 500.0 Hz T a n D e lt a 31.03.2004 15.07.2004 08.10.2004 Minimum Minimum Minimum PAGE 55 • The oil side of RBP and RIP bushings

doesn't need a housing

• Cellulose near to the surface can absorb water, if bushings are not stored properly • Incoming water, also from the ambient air reduces the dielectric strength – this causes an increase of the dielectric dissipation factor

Moisture in RBP and RIP Bushings

PAGE 56

Water in RBP and RIP Bushings

RIP wet RIP dry

Drying of RBP and RIP bushings is limited

PAGE 57

Micafil UTXF 24 (Drysomic)

RBP Bushings

• A,B,N humid after storage • C dryed

PAGE 58

New Micafil UTXF 24 RBP Bushings A,B,N

Stored Under Wet Conditions, C Dried

Messung bei 20°C DF (f) A, B, C, N 0.0% 1.0% 2.0% 3.0% 4.0% 5.0% 6.0% 0 .0 H z 5 0 .0 H z 1 0 0 .0 H z 1 5 0 .0 H z 2 0 0 .0 H z 2 5 0 .0 H z 3 0 0 .0 H z 3 5 0 .0 H z 4 0 0 .0 H z 4 5 0 .0 H z A B C N dryed humid PAGE 60

Drying of a 145kV RBP Bushing

PF Measurement

Drying of a 145kV RBP Bushing

2. Measurement after drying

1. Measurement before drying Drying:

1200h at 90°C / 200°F

PD

PAGE 63

PD Measurement

PD Measurement - Phase Resolved

Pattern @ 157kV

Separation of PD Sources in 3CFRD

3CFRD = 3 Center Frequency Relation Diagram

PAGE 67

PD Measurement Cluster 1

PD Measurement Cluster 2

PD Measurement Cluster 3

PAGE 75

50 Hz Tan

δδδδ

dependent on the Temp.

PAGE 76

Assessment and Interpretation

Indication RBP OIP RIP

increase of capacitance

oil in cracks

or partial breakdowns partial breakdowns partial breakdowns

high dissipation factor

partial breakdowns; insulator surface wet or dirty (clean the insulator); ageing of the inner

insulation; water in the inner

insulation;

partial breakdowns; insulator surface wet or dirty (clean the insulator); ageing of the inner

insulation; water in the inner

insulation;

partial breakdowns; insulator surface wet or dirty (clean the insulator); ageing of the inner

insulation; water in the inner

insulation; dissipation factor is

decreasing with increasing voltage

bad potential connections; partial breakdowns

bad potential connections; partial breakdowns

bad potential connections; partial breakdowns dissipation factor is strongly increasing with increasing temperature

high moisture in the insulation; high degree of ageing

high moisture in the insulation; high degree of ageing

high moisture in the insulation; high degree of ageing

partial discharges normal, if constant

Discharges produce gasses; Errosion of the cellulose;

production of x-wax

partial breakdowns; cracks or voids after electrical or mechanical

stress;

PAGE 77 • Periodical on-site measurements are essential to get a

picture of the aging status.

• With beginning of on-site measurements the fault rate could be continously reduced.

• A lot of information is necessary to assess the reliability of bushings.

• The tan delta measurement is an important tool. Particularly the tan delta sweep over a wide frequency range give a better indication of many kinds of faults. • RIP- bushings have become very common due to the

long life time expectation and a minimum of maintenance.

Conclusions

PAGE 78

Thank you for your interest !