dga scoring system.pdf
TRANSCRIPT
-
7/21/2019 DGA Scoring System.pdf
1/31
Knowledge Is PowerSMApparatus Maintenance and Power Management
for Energy Delivery
DGA Scorin S stem
John Lapworth,Doble PowerTest Ltd
-
7/21/2019 DGA Scoring System.pdf
2/31
Dissolved Gas Analysis (DGA)
Ideal condition monitoring tool
Sensitive, broadband Cheap, on-line
Sampled by site staff and analysed by oil
laboratoryNeed to apply engineering experience for
interpretation
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
3/31
DGA Interpretation
Type and severity of fault - gas signature
Key gases
Loading, operational history
Development of fault
Action levels
Trend analysis
Scoring system
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
4/31
DGA - Key Gases
Fault Primary Secondary
ar a sc arge y rogen
Dielectric(Arcing/sparking)
HydrogenAcetylene
Ethylene
e ec r c(Power arc)
y rogen e aneEthylene
Acetylene
Temperature Ethane Monoxide
Thermal hotspot Ethylene Methane
OverheatedCellulose
CarbonMonoxide
CarbonDioxide
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
5/31
Difficulties of Using DGA
Deciding on an appropriate sampling interval
Ensuring accuracy not compromised by :
Poor sampling method
Deciding when a result is abnormal
Deciding on seriousness of a fault
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
6/31
Existing DGA Interpretation Schemes
Gas signatures and ratios
E.G. Rogers, IEC 599, Duval etcTrend anal sis
Normal and action levels
Expert systems
We will discuss pros and cons of these
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
7/31
Rogers Ratios
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
8/31
Gas Signatures and Ratios
Thermodynamic basis
Focus on diagnosing fault
e.g. Rogers Normal Deterioration(0000) code is rare
Triple zero syndrome
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
9/31
Trend Analysis
Increasing gas levels considered indication of
eve op ng au , u ...
Increase after de-gassing to equilibrium levels
Gas levels constant for inactive fault
Different interpretation for H2 and C2H2
May not have enough results for good trend
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
10/31
Normal and Action Levels
What level is significant ...
Statistical approach is problematic: What exceedance should be used - 90, 95 or
97% ?
important ?
unhealthy
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
11/31
Expert Systems
E. . Kohonen net cluster anal sis techni ue
Attempt to classify similar results
earc or en n orma on
Identify changes of stateRely on human expert to ascribe significance
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
12/31
New DGA Interpretation Scheme
Based on IEEE C57.104-1991 Key Gas Method
Combustible gas signature - bar chart
Percentage total combustible gas (%TCG)
CO, H2, CH4, C2H4, C2H6, C2H2
Used in IEEE to distinguish faults Used here to differentiate normal and abnormal
Faulty, normal and heavily loaded transformers
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
13/31
IEEE C57.104-1991
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
14/31
IEEE C57.104-1991
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
15/31
Faulty Transformers
100
60
80
CG
40
P
ercentage
0
20
TransformerA B C D E F G
CO H2 CH4 C2H4 C2H6 C2H2
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
16/31
Normal Transmission Transformers
100
60
80
CG
40
P
ercentage
0
20
Transformer1 2 3 4 5
CO H2 CH4 C2H4 C2H6 C2H2
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
17/31
Normal Generator Transformers
100
60
80
CG
40
P
ercentage
0
20
TransformerI II III IV V
CO H2 CH4 C2H4 C2H6 C2H2
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
18/31
New DGA Interpretation
High [ COCO ] ( 60-90 %TCG ) = normal
( Higher levels may be abnormal )
High [ C2H4C2H4 ] ( > 10 %TCG ) = abnormal
Significant [ H2H2 ] and [ C2H2C2H2 ] = serious
Significant [ CH4CH4 ] and [ C2H6C2H6 ] = not serious
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
19/31
Scoring System
NormalNormal < 60< 60
All normal results can be ignored
>>
Only suspect results need to be investigated
SeriousSerious > 100> 100
Winding and dielectric faults
Some can be discounted
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
20/31
Scoring System
Quality function
Importance of gas signature
Strength function
Importance of gas levels
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
21/31
Benefits of Scoring System
Normal results can be screened out (ignored)
Consistent, objective assessment of results
Resource focussed on deserving cases
Can ignore unusualcases
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
22/31
Use in Condition Assessment
CO ND ITIO N ASSESSMENT TEST RESULTS
Dielectric
9 8 3 2 4 8
DGA RFI MAG TTR PF AE PD
10 10
Thermal / Life
3 4 4 4 2 4 4DGA FFA H2O IRES ACID PF POL DP
5 10 10 5 10
8 4
FRA LRT CAP
SUMMARY
Dielectric
1 2 3 4 5 6 7 8 9 10
Thermal / Life
1 2 3 4 5 6 7 8 9 10
Mechanical
1 2 3 4 5 6 7 8 9 10
O VERALL
1 2 3 4 5 6 7 8 9 10
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
23/31
Application 1 - Core Earth Fault
30 year old 400 kV 750 MVA auto-transformer
Suspected core / frame to earth circulating
curren au
Core earth brought out and resistor inserted
Main tank de-gassed after work
Buchholz alarms subsequently at high loads
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
24/31
DGA History
Sample date H2 CO CO2 CH4 C2H4 C2H6 C2H2
16/4/96 10 140 757 14 16 5 0.4
14/8/97 11 271 1,463 27 28 9 0.7
Core earth brought out and resistor fitted. Main tank de-gassed
20/4/98 14 64 576 19 18 4 0.6
.
22/7/98 40 112 823 62 64 12 2.9
23/7/98 38 100 1,393 87 131 23 5.1
31/7/98 109 180 1,142 125 152 25 5.7
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
25/31
DGA Signature
100
80
G
40
Pe
rcentageT
20
0
16/04/96 14/08/97 20/04/98 22/07/98 23/07/98 31/07/98
CO H2 CH4 C2H4 C2H6 C2H2
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
26/31
DGA Score
140
100
120
60
80
DGAScore
40
0
20
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
27/31
Evidence
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
28/31
Application 2 - Puzzling Results
High CH4CH4 and C2H6C2H6in many new transformers
Some also have high H2H2-high scores
Seasonal dependence -H2H2 peaks in late
summer
Differenttransformer designs
Same oil
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
29/31
New Transformer DGA
250
150
200
100
PPM
50
01/01/94 01/01/95 01/01/96 31/12/96 31/12/97 31/12/98 31/12/99 30/12/2000
0
H2 CH4 C2H6
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
30/31
Effect of Oil Type on DGA
Oil type can change symptoms exhibited
Temperature and time effects-
How can we allow for this ? Need to know oil type
Need information on assin ro erties
Tailor scoring parameters for oil type
DGA Scoring System
-
7/21/2019 DGA Scoring System.pdf
31/31
DGA Scoring Conclusions
Scoring system has been valuable
More consistent and objective assessments
Resources focussed where deserved
Applicable to wider class of transformers ?
Further work required to confirm this
Oil type needs to be taken into account
Further work to understand effects on gassing
Vehicle for improving understanding ?
DGA Scoring System