A Diagnostic Service That Saves Money. It has been a longstanding, standard practice for maintenance personnel to perform fluid quality tests such as dielectric breakdown voltage to confirm an acceptable fluid condition when returning or placing oil-filled circuit breakers into service. Some utilities have also used these screening tests to continue monitoring fluid condition of in-service Oil-filled circuit breakers (OCB’s). Further assessment of in-tank condition required removing the OCB from service for internal inspections. Contact resistance measurements, and other intrusive maintenance activity.

In 1996, TJ/H2b began to search for a diagnostic marker for the detection of a particular failure mode in one type of OCB. The outgrowth of that effort was the development of the world’s first fluid-based OCB condition assessment tool, Breaker Oil Analysis (BOA®). By the beginning of 1998, BOA® had been successfully applied to thousands of transmission and distribution breakers as well as to oil-filled switches. The cost benefits from using BOA® are primarily achieved through the reduction of unnecessary maintenance activities.

Using traditional ASTM methodology and particle profiling, condition codes are generated by evaluating the relationships among the test data. BOA® provides information about coke formation, contact deterioration, fluid degradation, and interrupter deterioration (baffles, arc chutes housing, etc.). Application of this diagnostic tool allows maintenance personnel to depart from traditional time-based maintenance practices by monitoring the condition of units to determine when maintenance becomes necessary. BOA® also provides a guide for the maintenance practices by monitoring the condition of units to determine when maintenance becomes necessary. BOA® also provides a guide for the maintenance to be performed by indicating when components reach the end of their useful life or when abnormal conditions threaten the life or operation of the circuit breaker.

BOA® has been extensively field-tested and has proven to enhance equipment reliability. No false negatives have occurred with the BOA® service, which means that no tanks that have been assessed have been found to be in a poorer condition than indicated. Conversely, false positives are not a concern because BOA® has been designed to address the residual contamination of tanks from prior maintenance activities. This can occur when the used oil is replaced in the unit after repairs are made or when the unit is insufficiently cleaned and flushed after maintenance.

Consider the following case history

The breaker oil analysis for the unit in the table and figures below indicated a condition 4. Based on the BOA tank assessment, the breaker was scheduled for open tank inspection.

 

Dissolved Gas Analysis
Hydrogen
2251
ppm
Methane
2159
ppm
Ethane
887
ppm
Ethylene
6055
ppm
Acetylene
18490
ppm
Carbon Monoxide
1951
ppm
Carbon Dioxide
4758
ppm
Nitrogen
77485
ppm
Oxygen
1939
ppm
Particle Profile
Particles 5 to 15 um
1380250
cts
Particles 15 to 25 um
974690
cts
Particles 25 to 50 um
43710
cts
Particles 50 to 100 um
250
cts
Particles 100 um plus
30
cts
Oil Quality
Moisture
111
ppm
Dielectric Breakdown Voltage
23
kV

The inspection revealed (see figures below)

  • Interrupter assemblies that were generally found to be loose.
  • Excessive thermal wear in the baffles and arching nozzles with baffle and nozzle parts wear estimated to be greater than 76%.
  • Moving contact arching tip erosion estimated to be greater than 76%.
  • Signs of excessive heating on the stationary contacts with contact wear estimated to be greater than 50%.

All of the contacts and interrupters were replaced. Since the condition of the oil was poor, it was replaced after the overhaul.



Current distribution of condition codes for the utility industry

The Figures below represent baseline testing for a normal distribution of oil-filled circuit breakers:

Statistics for Utility Industry / Population Size: 15,000

Mix: 50% Transmission: 50% Distribution

Code 1: 69.0% Code 2: 26.0% Code 3: 3.0% Code 4: 2.0% Code 4: 1.0%

As a rough estimate, assume that all units with a condition code 4 require maintenance. According to the figures above, only 3% of the units would require immediate attention. For most utilities, this number will be significantly smaller than the number scheduled for maintenance on a time-interval basis.

Cost Savings Using BOA®Diagnostics for Condition Based Maintenance

Maintenance costs may be reduced by as much as ninety-two percent (92%) depending on the type of maintenance program currently being used. As an example, compare a six-year fixed-interval maintenance program to a condition-based program that results in an average maintenance interval of ten years. In this example, the annual average condition-based maintenance would be sixty percent of the maintenance performed using the fixed interval approach. Maintenance would be reduced by forty percent.

The table below indicates the savings that will be obtained by using the condition-based approach instead of a time-based interval. To find the savings, simply match the percentage of units that will require maintenance based on their condition code with the number of years in the fixed-time maintenance cycle.

Percent Savings in Maintenance
Fixed - Year Maintenance Interval (Years)
4
5
6
7
8
% of Units Requiring Maintenance Based on Condition Code
2%
92
90
88
86
84
3%
88
85
82
79
76
5%
80
75
70
65
60
7%
72
65
58
51
44
10%
60
50
40
30
20

The savings indicated in the table are impressive especially considering that equipment reliability is not compromised.

The BOA®Service is available exclusively at TJ/H2b Analytical Services.