1. Alabama Section Meeting IEEE
Monitoring &
Diagnostic Overview
Alabama Section Meeting IEEE
2/2018
Chris White (904)

2. The Transformer … A Complex System
Cooling
System
Tap changer
Main tank
Core
Coils
Oil
Control Cabinet
Bushings
P&C Education Seminar

3. Transformer Construction
Cooling
System
Oil
Tank
Bushings
Tap changer
Coils
Core
Control Cabinet
The core is the most massive part of the transformer. It is a stack of several hundreds, even thousands, of precisely cut sheets of milled soft iron. Its purpose is to direct and concentrate the magnetic flux generated by the coils. It is sometimes referred to as the “magnetic” circuit.
The coils are the “inputs” and “outputs” of the transformer. In most transformers we have three sets of two coils. Each pair make up a “phase” and are labeled “A,B,C” or “White, Blue, Red” or “1, 2, 3”. The two coils of each set are usually called “High Voltage” and “Low voltage”, or “Primary” and “Secondary”. However there are a wide variety of coil configurations and many other combinations exist.
The tap changer’s function is to control the output voltage of the transformer. In essence it is a voltage regulator. Some tap changers are operated manually for seasonal adjustment, always requiring to remove the transformer from service to make the adjustment. Others operate automatically to maintain the transformer’s voltage as the load varies and are called “On-Load Tap Changers (OLTC)”. The OLTC could be located in the same tank as the core and coils (in-tank), or in a separate tank attached to the main tank where the leads are connected to the appropriate winding through either tap head connections or a barrier board.
The transformer is a very efficient device and every effort is made in the design and construction of the transformer to minimize the amount of loss. However, even the most efficient transformer will have some losses which will generate heat. The cooling system consists of radiators or coolers, fans and pumps that recirculate the oil to remove the heat generated by the operation of the transformer.
Bushings are the connection between the transformer and the power grid. Many consist of a conductor, wrapped with several layers of paper, impregnated with oil, and contained in a porcelain shell.
Control cabinets contain the interconnection between the various control and monitoring elements of the transformer, such as the pumps and fans control, temperature display and gas relay alarms contact.
Oil is the heat carrier in the transformer. Its function is to carry the heat generated by the coils and the core during normal operation to the radiator. The circulation of oil inside the transformer is a very critical function. Oil also acts as an electrical insulator between the various elements of the transformer.

4. Transformer Failure Modes
Component Failure rates
Monitoring method (Not cost of failure)
Main Tank %
DGA monitoring of main tank
Winding & oil temperature
Acoustic PD
PD recognition algo from BMT300 (next Gen)
SFRA
Tap changer %
DGA of diverter and tap changer tanks
Tap Changer models
Motor torque monitoring
Acoustic signature analysis
Tap changer control
Bushing %
Tan delta
Partial discharge
Cooling System %
Cooling efficiency models
Cooling control
Oil flow
Source of data: The Hartford Steam Boiler Inspection and Insurance Co. 4

5. What is wrong inside this transformer?

6. First, What Is Transformer Dissolved Gas Analysis?
Sample Test Doc Diagnosis
Doctors extract information about our health from our blood. Technicians extract information about the health of our transformers from the oil via DGA. Substations are more challenging for this sampling process than a doctor’s office

7. Transformer Dissolved Gas Analysis, The Process & Logic
Duvall’s Triangle
Sample Test Tech Diagnosis
We prefer a clean sample with no issues detected, just as a blood test in a doctor’s office.
In the early 1970s a utility in the NW region of the United States had a transformer failure. They decided to take an oil sample and send it to a university in California to see if the chemistry department could make sense of it. It was then that dissolved gas analysis began its rise to prominence in the utility world.

8. Transformer Operating Temperatures
20 – 80 C?
First signs of gassing begins around 100 C with CO2 & CO.
First signs of hot metal gases begins around 150 C.
While the typical power transformer may operate in the 20 to 80 deg. C range, there are many factors that influence the operation of a transformer, which can and do affect the overall life of the transformer.

9. What Are The Relevant Gases?
“Paper & Oil Gases”
It is important to distinguish and categorize the gases. This is vital in our efforts to diagnose issues within a power transformer. While there’s more involved than simply knowing the starting point for each of the relevant gases, the starting point at which these gases generate is certainly a good place to start when attempting to understand DGA. How the gases behave and relate to each other is also another important piece of the puzzle.
“Hot Metal Gases”

10. Oil degradation – Typical oil MoleculeH H H H C C H C H H H H C
P&C Education Seminar

11. CO Paper degradation – gases developed CH2OH O C OH H Paper Molecule
CARBON MONOXIDE O
CHO H
WATER CO
CH2OH OH O H C
HOH
FURAN
HOH
HOH
Paper Molecule
P&C Education Seminar

12. Key DGA gasses, and what they indicate
Hydrogen
Nearly all fault conditions, low energy PD
CH4
Methane
Oil overheating between 200ºC and 500ºC
C2H6
Ethane
Oil overheating between 300ºC and 500ºC
C2H4
Ethylene
Oil overheating over 500ºC, possible formation of carbon particles
C2H2
Acetylene
High energy arcing, oil overheating over 800ºC, strong formation of carbon particles, metal melting CO
Carbon Monoxide
Paper insulation overheating
CO2
Carbon Dioxide
Oil oxidation, paper degradation O2
Oxygen
Oxidation, leak
P&C Education Seminar

13. Why Dissolved Gas Analysis?
By identifying which gas is increasing it is possible to determine the likely nature of the anomaly without having to shut down the transformer.
Enables operational decisions based on this information.
On-line DGA monitors with remote communications enable true Condition Based Monitoring (CBM) and decision making without going to site.
P&C Education Seminar

14. Diagnosing Transformer Main Tank Faults

15. Where’s The Problem? Nitrogen Sealed #1 – 36 MVA
Notice that the hot metal gas signatures listed here have the same pattern for each transformer, but the outcome will be completely different due to “where” each of the 2 faults are located, as will be noted on slide 11. The question here is “what” further data is needed to understand the location of the fault prior to entering the transformer to attempt repairs?

16. Where’s The Problem? Continued
Ratio of CO2/CO gases decreased from 7:1 to 5:1 after the event
Ratio of CO2/CO gases decreased from 117:1 to 2:1 after the event
The greater the amount of paper involved in a fault, the greater the impact on the CO2/CO ratio.
Note the impact on the CO2/CO ratio for each of these transformers as a result of a problem. In the example on the left, which relates to the example on the left on slide 9, a significant drop in the CO2/CO ratio is noted, which is an indicator of exactly how much paper was affected at the time of the event. In the example on the right, which relates to the example on the right on slide 9, the paper appears to be much less affected.
If paper is truly involved in both faults, and since both scenarios did have an impact on the CO2/CO ratio, can we determine if the paper involved is a reflection of an overheated lead, or something more sinister buried in the windings? The answer is yes, we most certainly can.
aaaaaaaaaaaaaaaaa
aaajjjjjjjjjjjjjjjjjaaaaaa

17. Where’s The Problem? Continued
Winding Failure #1
Primary Lead – Repairable #2
As you can see from the example on the left, which had the vast reduction in the CO2/CO ratio did in fact fail in the winding paper (this example relates to the examples to the left on slides 9 & 10). This transformer in fact tripped on a transformer differential, and failed.
The second example on the right was a primary lead (this example relates to the examples to the right on slides 9 & 10). This unit also tripped on a transformer differential, however it had a different outcome altogether. It is important to understand the information and correctly categorize the gases. Without this insight, it is impossible to know if the problem is more fatal, or repairable when attempting to diagnose via DGA. This is very important information to have prior to opening up the transformer for an investigation and possible replacement of a transformer.
Of course, the ideal situation is to locate these problems prior to a differential trip, which can be done.
Transformer Replaced
Transformer Repaired

18. Where’s The Problem? Found coked De-Energized Tap Changer (DETC). DATE
TDCG
CO2/CO
11/4/2009
235
12,771
68,988
686
277
2,879
228
1,523 52
3001
1/8/2010
268
14,477
81,770
986
369
4,063
323
2,196 54
4,238
2/23/2010
282
13,893
76,571
821
312
4,506
329
2,239 47
4,030
3/22/2010
272
13,034
71,225
834
284
3,200
302
1,892 33
3,617
5/6/2010
226
11,639
68,938
974
350
4,000
325
2,054 39
3,968
8/13/2010
134
11,897
59,148
1,138
298
3,451
337
2,358 14
4,279
1/12/2011
8,613
72,536
1,663
577
5,183
447
3,215
6,245
1/25/2011
256
9,233
67,438
1,151
491
4,979
421
2,443 16
4,778
2% Decline
Overall
38% Increase
Overall
DETC Coked
Found coked De-Energized Tap Changer (DETC).

19. Descending CO2/CO Ratios - 75 MVA, N2 Blanketed
DATE H2 O2
CH4 CO
CO2
C2H6
C2H2
C2H4
CO2/CO
30-Jul-12 ND
9715 1 64
453 7
6-Jul-11
1180 22
485 2
25-Jan-10
5893 17
439 26
9-Mar-09
1738
TRACE 4
475
118
26-Mar-08
2829 25
851 3 34
15-Feb-07
1667
816 37
With the exception of the 2009 sample (likely poor handling during sampling), a downward trend in the CO2/CO ratio is exhibited in the six years leading up to failure. This unit failed shortly after the July/2012 sample. Had this knowledge of a descending CO2/CO ratio been available at the time, there’s a good chance that this transformer would have been removed from service, repaired/processed and returned to service. It is worthy to note that NONE of the gases displayed would be considered a problem by any standard available today.
Sure, there are times when a transformer has reached its end of life, but wouldn’t it be nice to at least see it coming? You may not be able to save every transformer, but you can position yourself to have better planning tools and possibly avoid an unexpected outage. It is believed that the March/2009 sample was either not properly collected or work was performed on the unit, which drives home the point that when manual sampling is performed, always take great care to ensure all outside influences are mitigated while collecting the sample as well as maintaining good maintenance records. This transformer was manufactured in the 1960s.
Transformers do eventually find their end of life.

20. 15 MVA, 100 kV – Manufactured 1999 – Pre-Fault
Date H2 O2
CO2 CO
CH4
C2H6
C2H4
C2H2
CO2/CO
2011
<2
845
579 8 5 6 2
<1
72.3
2012
831
524 4 1
104.8
2013
509
226 3
75.3
2014
1092
178
29.6
2015
500
124 10
12.4
83% Drop

21. 15 MVA, 100 kV – Manufactured 1999 - Post-FaultH2 O2
CO2 CO
CH4
C2H6
C2H4
C2H2
CO2/CO
2015
<2
500
124 10
<1 1
12.4
2016 post fault
212
802
1188
414
210 72
372
422
2.8
77% Drop in
1 Year

22. 1999, 15 MVA, 100 kV, Complete Picture
Date H2 O2
CO2 CO
CH4
C2H6
C2H4
C2H2
CO2/CO
2011
<2
845
579 8 5 6 2
<1
72.3
2012
831
524 4 1
104.8
2013
509
226 3
75.3
2014
1092
178
29.6
2015
500
124 10
12.4
2016 post fault
212
802
1188
414
210 72
372
422
2.8
96% Drop

23. Analyzing Events via CO2/CO
In this example, the large increase in C2H6 that occurred in 2013 was accompanied by a similar increase in CO while CO2 exhibited a downward trend during this time, leading to a sharp decrease in the CO2/CO ratio. This method of analyzing the relationship that occurs between the carbon oxide gases and the generation of hot metal gases is not as consistent as the trending of the CO2/CO ratio over a given period of time. However, it has proven quite useful in situations such as a transformer trip event where large amounts of combustible gases are subject to being produced in a very short time frame.
This is a very good example of the importance of maintaining historical data. Without it, the sharp decrease in the CO2/CO ratio may go unnoticed, depending on the impact of the event. With historical data in hand, it is easily compared with the established trend, thereby allowing a more accurate diagnosis of the impact on the paper. For example, during this particular event in 2013:
CO2 = 1850 ppm
CO = ppm
Ratio = 9:1
This single ratio, in and of itself, really doesn’t tell us much. In fact, this ratio may be considered normal by many. However, when compared to the previous sample in 2011:
CO2 = 2136 ppm
CO = ppm
Ratio = 101:1
As you can see, this became a 91% drop during the 2013 event, indicating a major amount of paper involved in the event. Without this insight, the analyst may be inclined to return the unit to service without further investigation, and the consequences of these actions could be catastrophic.

24. Acetylene Is Problematic, But Is It Fatal?
Not always:
Is it present due to activity in the winding insulation, or is it bare metal?
The problem could be easy to get to and simple to repair.
Transformers have been discarded when the problem was a simple fix, but that was unknown at the time.
It can mean the difference between a few thousand dollar$ in repairs, versus a few million dollar$ in potential replacement costs.
Acetylene is obviously not a gas that we’d like to see in a power transformer’s main tank regardless of where the problem is. Having said that, it is important to be in a position to know whether or not it is present as a result of an issue in the main winding insulation, or perhaps a connection away from the windings. One is most assuredly fatal, while the other may be repairable on site.

25. Summary/Conclusion All internal faults are not fatal.
Know your fleet. It will only be beneficial in solving the diagnostic puzzles as they present themselves.
All faults are not as easily identified. Don’t give up, as there is an answer. Allow software help with the data analysis and direct you to the critical assets and information, which are now available.
Trending the fluctuations of gas concentration, rate of change and ratios is very important for understanding your transformers’ vital signs.
Know when to reach out for additional support, if needed.
We are all in this together.

26. Questions?