Introduction Introduction to Doble Testing Testing for Bushings Doble Engineering Diagnostics Toolbox
Arturo H. Oropeza
Types of Bushings •
•
Capacitor/Condenser Type: –
Oil-Impregnated Paper Insulation
–
Resin Bounded Paper Insulation
Non-Condenser Type: Type: –
Solid
–
Alternate Layers of Solid and Liquid Insulation
–
Gas-filled
Types of Bushings •
•
Capacitor/Condenser Type: –
Oil-Impregnated Paper Insulation
–
Resin Bounded Paper Insulation
Non-Condenser Type: Type: –
Solid
–
Alternate Layers of Solid and Liquid Insulation
–
Gas-filled
Condenser Bushing Construction 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
Typical Condenser Bushing Construction CA CB
Core Wind
CC CD CE CF
R O T C U D N O C R E T N E C
Grounded Layer/Flange
CG CH CI CJ
CK
Tap Electrode Grounded Layer/Flange
Foil C2 Plate
Typical Condenser Type U Bushing Construction CA
Herringbone Pattern
CB CC
Core Wind
CD CE CF
R O T C U D N O C R E T N E C
CG CH CI CJ
CK
Tap Electrode Grounded Layer/Flange C2 Plate
Grounded Layer/Flange
Semi-Conducting Paper
ABB O + C Construction
C2 Plate
Unwinding the Main Core oil impregnated paper insulation
Components of a Typical Oil - Impregnated Capacitance-Graded Bushing 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
Typical Bushing Potential Tap Construction Center Conductor Tapped Capacitance-Graded Core Layer Liquid/Compound Filler Main Insulating Core Capacitance Graded Core Layers
Insulating Weathershed
Tap Cover Filler Plug Connection to Tapped Core Layer Tap Electrode Tap Insulation Mounting Flange Permanently Grounded Core Layer Ground Sleeve
Typical Bushing Test Tap Construction 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
Difference Between Power Factor Test and Potential Taps •
Power Factor test taps –
–
Bushings rated = < 69 KV C2 ~ C1 (except Lapp PRC s.n. > 00-189100)
•
Potential Tap –
Bushing Rated > 69 kV
–
C2 ~ C1 x 10 (C2 >> C1)
– –
–
Grounded in Service Doble Test Voltage: 500 V (except Ohio Brass Class L Bushing, to which no more than 250 Volts should be applied)
–
In Service: Floating, Supplying Voltage, or Grounded Doble Test Voltage: 2 KV (based on type up to 5 KV)
Standard Bushing Tests •
C1 Main Core Insulation (UST) –
•
C2 Tap Insulation Test (GST-guard) –
•
Tap to Flange
Hot Collar Test –
•
Center Conductor to Tap
Externally Applied Collar to Center Conductor
Overall (typically for Spare Bushings) –
Center Conductor to Flange
Investigative Bushing Tests •
Inverted C1 (UST) –
–
•
Tip-up Test (for C1 Standard) –
•
Repeat C1 Test at 2 and 10 kV or 2 and L-G kV if less than 10kV
Alternate C2 Test (GST-ground) –
•
Tap to Center Conductor DO NOT exceed Tap Voltage Rating
Tap to Center Conductor (C1 + C2)
Supplemental Hot Collar Tests –
Multiple Collars
Test Connections for Transformer Bushing Test 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
Bushing Test Set -Up Test Setup example (from our files): Which set of Bushings is Connected With the Winding Short-Circuited? Not shorted Shorted Phase A 0.60% 0.39% Phase B 0.65% 0.40% Phase C 0.56% 0.39% This is one of the most common sources of error in test results!
Bushing Test Set -Up •
•
•
Short-Circuit Windings (keep if already in place) Remove Test Tap cover from Bushing under test only Perform C1 (Main Core Insulation) test in UST mode –
–
•
Perform C2 (Tap Insulation) test in GST-guard mode –
•
•
•
Test Voltage 10 KV for ratings 15 KV and above Do not exceed line-to-ground Voltage for less 15 KV rating Test Voltage according to Tap type
Use Test Tap adapters Replace Test Tap Cover If results are questionable clean Bushings to minimize surface leakage
Main-Insulation C1 Test Standard Method High-Voltage Cable
Test Includes •Main C1 Core Insulation
Test Mode: UST Guard
Low Voltage Lead Ground Lead Bushing and Apparatus Ground
Main Insulation C1 Test Dielectric Circuit High Voltage Lead Test Tap Low-Voltage Lead
C1 C2
Test Mode: UST
C e n t e r C o n d u c t o r
Ground Lead
IC1 Guard I & W Meter
Test Ground
C1 Test Result Analysis Power Factor Modern Condenser Type Bushings in Acceptable condition •
– – –
•
Deteriorated Bushings –
•
Will depend on the manufacturer and type Generally the order of 0.5% Temperature correction to 20°C Generally Between 0.5% to 1.0%
Investigate Bushings –
Above 1.0%
Current/Capacitance Recommended Limits •
– –
+ 5% - Investigate + 10% - Investigate/Remove From Service
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
Tap- Insulation - C2 Test Standard Method 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
Tap Insulation C2 Test Dielectric Circuit Low Voltage Lead High Voltage Lead
C1 C2
Test Mode: GST-Guard IC2 Guard
Test Ground I & W Meter
C e n t e r C o n d u c t o r
C2 Tap Adapters
C2 Test Tap Adapter Westinghouse type O
C2 Test Tap Adapter Westinghouse type O+
C2 Test Result Analysis C2 Test results are heavily influenced by test conditions Power Factor Modern Condenser Type Bushings in Acceptable condition •
– – –
•
Deteriorated Bushings –
•
Will depend on the manufacturer and type Generally the order of 0.5% – 1.0% No correction factors available Generally Between 1.0% to 2.0%
Investigate Bushings –
Above 2.0%
Current/Capacitance Varies according to Bushing manufacturer and type, recommendations: •
– –
+ 5% - + 10% Investigate Greater than + 10% - Investigate/Remove From Service
Bushings Hot -Collar Tests 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
Single Hot Collar Test GST -Ground Mode 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
Single Hot Collar Test UST Mode 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
Single Hot Collar Test GST -Guard Mode Low Voltage Lead High Voltage Lead
Test Mode: GST-Guard Guard
Test Includes • Portion of insulating Weather shed sight-glass • Surface leakage from Collar to LV lead and to Bushing flange
Ground Lead
Bushing and Apparatus Ground
Doble Hot Collar Test •
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
Typical Hot -Collar Test Data
Description
Current (mA)
Watts
Typical Good Bushing
.090
0.02
Same Bushings, Contaminated
.095
0.31
Same Bushing, Low Liquid Level
.070
0.02
Client Recommended Bushing Cleaners •
Dry Clean Cloth
•
Water & Soap
•
Colonite
•
Windex with Ammonia
•
Apply Heat to Fully Dry all Surfaces
Do Not Use Evaporative Materials
Hot Collar Test Results Westinghouse , Type “S” General Contamination
Good Condition Bushin
Current
Watts
Bushin
Current
Watts
X1
110
A
0.06
X1
110
A
0.16
X2
110
A
0.04
X2
110
A
0.18
X3
110
A
0.05
X3
110
A
0.17
Physical Changes (X2) Bushin
Current
X1
110
X2
80
X3
110
A
A A
Watts
Defective Bushing (X3) Bushin
Current
Watts
0.06
X1
110
A
0.06
0.05
X2
110
A
0.05
0.05
X3
120
A
0.20
SPARE Bushings Testing Why? •
•
Bushings acceptance (in combination with the other Standard tests C1, C2, Hot-Collar) Overall test in GST-Ground will provide a quick test reference
•
Spares need to be ready at a moment notice
•
Benchmarking for future reference
•
Quick check on quality of manufacturing
Bushing Overall Test 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
SPARE Bushings Testing • • •
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
When Bushing Tests Are Doubtful •
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
When Bushing Tests Are Doubtful •
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
When Bushing Tests Are Doubtful •
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
Bushing Temperature Correction
Bushing Temperature Correction
Diagnostic Field Testing Standards •
IEEE Std. C57.152 – 2013 (Revision of IEEE 62 – 1995) Guide for Diagnostic Field Testing of Electric Power Apparatus – Part 1: Oil Filled Power Transformers, Regulators, and Reactors –
•
Section 3 Definitions – –
•
Section 6 Tests and test techniques – – – –
–
3.2 Bushing - power and distribution transformer 3.6 Power Factor - Dielectric 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
DTA Bushing Information •
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
Information on Bushings •
•
•
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
General Electric Company 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
LAPP Insulator Division 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%
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.
Ohio Brass Company Types 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
Typical %PF
Questionable %PF
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
0.8
2.0
On OCB and Inst. Trans. 69 kV and below (except Types S, OS, and FS)
1.5
3.0
Westinghouse 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)
