Bushings Testing

Introduction to Doble Bushings Testing Doble Engineering Diagnostics Toolbox

•
Capacitor/Condenser Type: –
Oil-Impregnated Paper Insulation –
Resin Bounded Paper Insulation •
Non-Condenser Type: –
Solid –
Alternate Layers of Solid and Liquid Insulation –
Gas-filled

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

2

Main Insulation C1

Center Conductor

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

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

CK

Grounded Layer/Flange

Tap Electrode

Line-to-Ground System Voltage

The Condenser type bushing allows an energized conductor to penetrate a ground plane Voltage is stressed equally across each layer of the Condenser type bushing 89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

3

CA

CENTER CONDUCTOR

CB CC

Core Wind

CD CE CF CG CH CI CJ

CK

Tap Electrode Grounded Layer/Flange

Foil C2 Plate

Grounded Layer/ Flange

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

4

CA

Herringbone Pattern

CENTER CONDUCTOR

CB CC

Core Wind

CD CE CF CG CH CI CJ

CK

Tap Electrode Grounded Layer/Flange C2 Plate

Grounded Layer/Flange

Semi-Conducting Paper

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

5

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

6

Center Conductor Sight-Glass Liquid or Compound Filler Insulating Weather Shed

Main Insulating Core Tap Insulation Tap Electrode Mounting Flange Ground Sleeve Tapped Capacitance-Graded Layer Lower Insulator

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

7

Center Conductor Tapped Capacitance-Graded Core Layer Liquid/Compound Filler Main Insulating Core Insulating Weathershed Capacitance Graded Core Layers Tap Cover Filler Plug Connection to Tapped Core Layer Tap Electrode Tap Insulation Mounting Flange Permanently Grounded Core Layer Ground Sleeve 89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

8

Center Conductor Tapped Capacitance-Graded Core Layer Liquid/Compound Filler Main Insulating Core Insulating Weather shed Capacitance Graded Core Layers Tap-Cover Tap Insulation Tap Electrode Connection to Tapped Core Layer Mounting Flange Ground Sleeve 89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

9

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

10

•
C1 Main Core Insulation (UST) –
Center Conductor to Tap

•
C2 Tap Insulation Test (GST-guard) –
Tap to Flange

•
Hot Collar Test –
Externally Applied Collar to Center Conductor

•
Overall (typically for Spare Bushings) –
Center Conductor to Flange 89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

11

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

12

Take advantage of the Short Circuit in place for the Overall test (HV windings, LV windings, and Neutral Bushing disconnected from ground) to complete Bushings tests.

High Voltage Windings

CHL

CH CL Low Voltage Windings

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

13

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

14

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

15

High-Voltage Cable

Test Includes •
Main C1 Core Insulation

Test Mode: UST Guard

Low Voltage Lead Ground Lead Bushing and Apparatus Ground

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

16

Test Tap Low-Voltage Lead

C1 C2

Test Mode: UST

Center Conductor

High Voltage Lead

Ground Lead

IC1 Guard I & W Meter Test Ground

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

17

Power Factor •
Modern Condenser Type Bushings in Acceptable condition –
Will depend on the manufacturer and type –
Generally the order of 0.5% –
Temperature correction to 20°C

•
Deteriorated Bushings –
Generally Between 0.5% to 1.0%

•
Investigate Bushings –
Above 1.0%

Current/Capacitance •
Recommended Limits –
+ 5% - Investigate –
+ 10% - Investigate/Remove From Service 89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

18

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

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

19

Low Voltage Lead Test Includes •
Tap Insulator •
Core Insulation between tapped layer and Bushing ground sleeve •
Portion of liquid or compound filler •
Portion of Weather shed near flange High Voltage Lead

Test Mode: GST-Guard IC2 Guard I & W Meter 89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

20

Low Voltage Lead

C1 C2

Center Conductor

High Voltage Lead

Test Mode: GST-Guard IC2 Guard

Test Ground I & W Meter

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

21

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

22

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

23

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

24

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

25

When to perform Bushings Hot-Collar Tests •
•
•
•


Compound-Filled Bushings Solid Porcelain Bushings Gas-Filled Bushings Oil Filled Bushings not equipped with taps and Overall Test cannot be performed –
Single Hot-Collar Test on small Bushings 15 KV and below –
Several single Hot-Collar Tests for Bushings rated above 15 KV

•
To check Oil level on all liquid filled Bushings without liquid level gauges or sight glass •
To check Bushings with liquid level gauges whenever the gauge is suspect •
As supplementary tests when Overall, C1, C2 Tests indicate possible problem

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

26

Low Voltage Lead High Voltage Lead

Test Mode: GST-Ground Ground Lead

Guard •
•
•
•
•


Test Includes Portion of insulating Weather shed Sight-glass Core insulation in upper area Liquid or compound filler in the upper area Surface leakage from Collar to LV lead and to bushing flange

Bushing and Apparatus Ground

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

27

Low Voltage Lead High Voltage Lead

Test Mode: UST Ground Lead Guard Test Includes •
Core Insulation in Upper Area •
Liquid or Compound Filler in the Upper Area

Bushing and Apparatus Ground

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

28

Low Voltage Lead High Voltage Lead

Test Mode: GST-Guard Ground Lead

Guard

Test Includes •
Portion of insulating Weather shed sight-glass •
Surface leakage from Collar to LV lead and to Bushing flange

Bushing and Apparatus Ground

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

29

•
Test Voltage 10 KV •
Recommended Acceptable Limits: –
Watts < = 0.1 Watts (100 mW) –
Current: similar for same type Bushings

Hot Collar Test Results Analysis •
Increased Watts –
Contamination of the Insulation

•
Decreased Current (Amperes) –
Low liquid or compound level 89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

30

Description

Current (mA)

Watts

Typical Good Bushing

.090

0.02

Same Bushings, Contaminated

.095

0.31

Same Bushing, Low Liquid Level

.070

0.02

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

•
•
•
•
•


31

Dry Clean Cloth Water & Soap Colonite
Windex
with Ammonia Apply Heat to Fully Dry all Surfaces

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

32

Good Condition

General Contamination

Physical Changes (X2)

Defective Bushing (X3)

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

33

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

34

High-Voltage Cable Test Includes •
Main C1 Core Insulation •
Insulating Weather shed •
Sight-glass •
Lower insulator •
Portion of liquid or compound filler Guard Ground Lead

Test Mode: GST-Ground Bushing and Apparatus Ground 89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

35

•
DO NOT test Bushings in wooden crate or stand •
Support Bushing on a metal stand if possible •
Slings may be used for tests, observe the following: –
Cleanliness of sling may affect test results –
Sling should be kept clear of energized points

•
Connect ground lead directly to Bushing flange •
Ground both test set and specimen to substation ground •
Clean upper and lower surfaces before testing 89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

36

•
Re-Check All Connections, Including Ground Lead and Bushing Flange Ground •
Check Test Circuit Used •
Check Test Set and Test Set Leads •
Visually Inspect Bushing Sheds and Oil •
Clean and Dry All Surfaces

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

37

•
Check all connections including ground lead and Bushing flange ground •
Check test circuit used •
Check test set and test set leads •
Visually inspect Bushing and Oil (sight glass) •
Clean and dry all surfaces

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

38

•
Compare and analyze results of identical Bushings •
Research Bushing history of flashovers or line Surges •
Verify temperature correction factor was used for C1 and Overall Tests * •
Verify the necessary fields in the nameplate were used in order for DTA to identify the correct limit file * Note: C2 Power factors are not temperature corrected

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

39

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

40

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

41

•
IEEE Std 62 - 1995 –
Guide for Diagnostic Field Testing of Electric Power Apparatus – Part 1: Oil Filled Power Transformers, Regulators, and Reactors •
Section 3 Definitions –
3.2 Bushing - power and distribution transformer –
3.6 Power Factor - Dielectric

•
Section 6 Tests and test techniques –
–
–
–


6.2 Bushings 6.2.2 Visual Inspection 6.2.3 Oil Level 6.2.4 Capacitance, Power Factor, and Dissipation Factor

–
Annex B (informative): Bushings Power Factor measurements

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

42

DTA Bushings Tests Procedures (Useful tips for DTA users)

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

43

•
DTAF fields required To Activate temperature Correction Factor –
Manufacturer –
Type –
Ambient Temperature (Probe) –
Apparatus Temperature –
Transformer - Oil Temperature –
Oil Circuit Breaker - Ambient Temperature

•
DTA - Fields Required To Identify Correct Limit File –
Manufacturer –
Type –
KV rating

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

44

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

45

•
The following pages provide information about different Bushing Manufacturers and different types of Bushings •
Use as Guidelines for test results analysis •
Please send your tests results to Doble for further compilation and enhancement of Bushings Database

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

46

Type A* A** B* D F L LC OF S*

Description Through Porcelain High Current Flexible Cable, Compound Filled Oil Filled Upper Portion, Sealed Oil Filled, Sealed Oil Filled Upper Portion, Sealed Oil Filled Upper Portion, Sealed Oil Filled Expansion Chamber Force C & CG, Rigid Core, Compound Filled

Typical PF 3.0% 1.0% 5.0% 1.0% 0.7% 1.5% 0.8% 0.8% 1.5%

Questionable PF 5.0% 2.0% 12.0% 2.0% 1.5% 3.0% 2.0% 2.0% 6.0%

* Type S, Form F, DF & EF (flexible cable) redesigned as Types B, BD, and BE, respectively. Type S, no Form letter (through porcelain) redesigned as Type A

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

Typical C1 PF Type ERC (Epoxy-Resin-Core, Plastic or Oil Filled) Type PRC and PRC-A (Paper-Resin-Condenser Core)

0.8% 0.8%

47

Questionable C1 PF 1.5% 1.5%

Typical C2 power factors for older PRC design range from 4-15% due to injected compound used during manufacturing.

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

48

Types

Typical %PF

Class LK-Type A, 23 to 69 kV ODOF, Class G, and Class L Oil-Filled: Prior to 1926 and after 1938 Between 1926 and 1938

0.4

1.0

1.0-5.0

Change of 22% from initial Change of 16% from initial

2.0-4.0

Type S, OS, and FS On OCB and Inst. Trans. 69 kV and below (except Types S, OS, and FS)

Questionable %PF

0.8 1.5

2.0 3.0

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

Typical %PF

Questionable %PF

On OCB and Inst. Trans. 92 kV to 139 kV (except Types O, O-A1, OC and O Plus)

1.5

3.0

On Power and Dist Trans of all rating, and OCB & Inst. Trans. 161 kV to 288 kV (except Types O, O-A1, OC, and O Plus)

1.0

2.0

All Type D Transformer Bushings ( Semi-Condenser)

1.5

3.0

1.0

2.0

Type RJ (Solid Porcelain)

49

89 Years of Diagnostic Instrumentation and Services for the Electric Power Industry

50