CIRCUIT BREAKER OPERATOR SIGNATURE ANALYSIS
Wesley R. Speed
TXU Electric USA
SUMMARY
Over the years utilities have experienced problems with slow operation, failure to trip or failure to close of circuit breakers. In recent years many of these problems have been traced to faulty lubrication of the circuit breaker operating mechanisms. While traditional diagnostic testing procedures are useful in determining the condition of the breaker insulation, contact resistance and operating time, they are not adequate to fully evaluate the condition of the breaker operating mechanism. The concept of measuring the control circuit characteristics of the circuit breaker during operation to evaluate breaker operator performance has been around for some time, but only in recent years has it become available in a lightweight, portable package that allows quick capture of data and analysis of results. TXU Electric has found circuit breaker operator signature analysis to be an extremely beneficial tool for evaluating the condition of breaker operating mechanisms, prioritizing the maintenance of circuit breakers, and minimizing equipment outages.
BACKGROUND
For many years electric utilities have relied on traditional diagnostic testing procedures (power factor, megger and time) to evaluate the condition of their circuit breakers. These tests provide information concerning the integrity of a breaker’s insulation system, contact resistance and main contact operating times. However, these procedures do not give meaningful insight into the condition of the operating mechanism except for overall speed. Since a large percentage of breaker problems can be attributed to the operator and related components, we were in effect looking for problems in the wrong places.
TXU Electric has experienced situations in which a breaker is suspected to be slow
(from a DFR trace or when a transformer is outaged on overload). Timing tests are then performed on the breaker, but it shows to be within specifications. At this point we have blamed the relaying system or other culprits. Another situation is a breaker that burns up a trip coil during a fault, and we blame a faulty trip coil.
Situations such as these may indicate a failure of the circuit breaker operating mechanism lubrication. Circuit breaker operators contain numerous mechanical components that rely on proper lubrication for their successful operation. However, many enemies of the lubrication, including age, temperature, airborne contaminates and improper or infrequent maintenance practices have left many circuit breaker operators prone to failure.

The Lubrication Guide of the Doble Circuit Breaker Committee [1] discusses these issues of lubrication and maintenance practices at length. An excerpt is taken from this guide as follows:
Transmission and distribution breakers have become a maintenance challenge because of their extended time in the field without relubrication … Circuit breaker failures have been traced to faulty lubricants and/or questionable lubrication practices. Many circuit breakers in use today are very old and continue to be lubricated with what the manufacturer specified many years ago. Many of these lubricants will not last. Some greases will separate, leaving only a dry thickener which can slow the breaker action. Some greases and penetrating oils can change in physical form, leaving what appears to be a varnish-like residue in bearings and other critical friction areas. [1]
The Lubrication Guide of the Doble Circuit Breaker Committee [1] also goes on to explain how the use of synthetic greases in lieu of petroleum based greases should provide longer service life of the breaker operator between lubrications.
Since traditional diagnostic testing procedures fall short of providing thorough data regarding the breaker operating mechanism, another means is necessary to provide this information.
Old Idea, New Package
The idea of measuring a breaker’s control circuit electrical information during operation to provide insight into the condition of the operating mechanism has been around for many years [2]. Graphical curves containing this electrical information can be plotted and analyzed. The electrical trace for a trip or close operation of a circuit breaker can indicate the health of the breaker operator. This shot can also be compared to other shots of the circuit breaker in order to track its performance over time. Operating mechanism problems are evidenced in changes in the characteristics of the electrical traces. In addition, shots of a breaker can be overlayed with shots of breakers with like operator types for comparison.
Previous technologies used to implement this concept required hard wiring of connection equipment into the circuit breaker. While the cost of equipment and installation was justifiable for breakers located at extremely critical system locations, it unfortunately became cost prohibitive to implement on a larger scale.
However, in recent years, lightweight, portable technology has become commercially available which does not require hard wiring to the breaker. Connection to the breaker control circuitry can occur safely while the breaker is still in service, and the whole process of testing the breaker only takes a few minutes. Information is immediately available from the portable device, and the data obtained can be downloaded to a computer for future in-depth analysis.

Monitored items include secondary CT currents, trip and close coil current, and DC voltage supply to the breaker. Analysis of the data provides insight into the overall condition of the breaker’s operating mechanism and lubrication, main contact operating time, trip and close coils, auxiliary switches, DC voltage supply and control circuit wiring.
One such product currently available which accomplishes the above is the Kelman
Profile P1 CB Analyzer. TXU Electric purchased this product and initiated a program to test system circuit breakers. The remainder of this paper discusses the experiences gained from utilizing this piece of test equipment.
IMPLEMENTATION
Connection
The connection of the breaker analyzer is extremely simple, consisting only of four leads, as indicated the Figure 1. First, two leads are attached to the DC voltage supply to the circuit breaker. Then, an AC clamp-on is connected to the secondary of one phase of the current transformers (providing main contact operating time). Finally, a DC clamp-on is connected to the trip and/or close circuit (providing DC current amplitude over time).
Figure 1 – Connection of Circuit Breaker Analyzer
A typical shot obtained from the breaker analyzer is shown in Figure 2. There are three main features – the main contact time, the DC supply voltage, and the trip / close coil current during the operation of the breaker. How the mechanical movement of the operator corresponds to the electrical trace is indicated in the Figure 2. When a trip signal is initiated to the breaker, the DC current through the trip coil starts to rise, moving the plunger inside the coil. The plunger moves until its hits the trip latch of the breaker. This is indicated on the electrical trace by the valley after the first hump on the curve. Up to this point, the breaker is stationary. For a proper breaker operation, the trip latch is

released, the energy in the stored energy mechanism starts in motion, and the breaker contacts start to move. At some point the main contacts break the current through the breaker, and an auxiliary contact opens and breaks the current in the trip circuit.
Meanwhile, the DC supply voltage is measured during the shot.
Figure 2 – Typical Trip Shot
Initial Program
For our initial program we tested 15kV, 25kV and 69kV circuit breakers. These voltage classes were selected because breakers of these voltages historically caused us the most problems. In phase 1 of this program, we were successful in identifying breakers in failure mode, and corrective action was taken. We feel that numerous equipment outages were avoided as a result of performing breaker analyzer testing. About six months later we initiated phase 2 of the program. During this time we refined our data collection and storage techniques, utilized the data to prioritize maintenance, documented healthy

breaker operators, identified “bad actors” by breaker type, and expanded our programs to include 138kV circuit breakers.
Examples of problems found while using the breaker analyzer were failed operating mechanism lubrication, damaged trip and close coils, dirty auxiliary switches, loose connections in the control circuitry, substation battery or battery charger problems, improper control cable sizing and tailsprings out of adjustment. In addition, while trip testing these breakers we found problems with reclosing relays, breaker closing motors, and RTU’s.
To perform the testing, we assigned two two-man teams who focused exclusively on breaker analyzer testing. Each team consisted of a person to run the breaker analyzer and a patrolman to perform the switching. The process of connecting the breaker analyzer to the breaker and running the tests took only about 5 minutes, plus time to switch the equipment out. Average testing, switching and travel time for each team was around 23 minutes per breaker. They averaged over 20 breakers per day, accomplishing testing on as many 50 breakers in a given day. It took these two teams about two months to test over
700 circuit breakers.
Shot Analysis
The process of analyzing the shots is a somewhat tedious process, but well worth the time considering the outages that can be prevented from finding problems. A process that seemed to work well was to first pull up trip shots for a particular breaker utilizing the breaker analyzer software. We would inspect the shots to see if they fell within the following general measurement criteria:
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Main Contacts < 50ms on trip shot (3 cycle breaker)
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Main Contacts < 200ms on close shot
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Breaker off latch < 17ms (1 cycle for a 3 cycle breaker)
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Voltage drop < 10%
Then we looked to see if the second shot was faster than the first. This is a good indication that the breaker was sluggish on the first shot due to faulty lubrication. The breaker would trip faster on the second shot since the breaker had been exercised and limbered up. This provided a good graphical representation (See Figure 3) of why in the past we would have a suspected slow breaker, trip the breaker to take it out of service to connect the timing equipment, and the breaker timed within specifications. In taking the breaker out of service, we were missing the all-important first trip. By using the breaker analyzer, we now have a means to capture the first trip.
After the breaker was compared to itself, we compared its shots to other breakers of the same operator type. These families of curves could be compared against each other to determine a prioritization of which breakers deserved the most immediate attention (See
Figure 4). We would also compare a breaker to one in which we had completely overhauled the operating mechanism – knowing it to be in the best possible shape. Shots

of each breaker are stored so that when future shots are taken we can compare them to the original baseline of the breaker – its signature – to see if the operator’s performance degrades over time.
Early in the program we focused on the breakers which showed large noticeable differences in their shots. These were our breakers in a critical failure mode. However, we began to realize the slight nuances between two shots from the same breaker could be significant and should not be overlooked. In other words, shots from a healthy breaker operator should have identical shots not only on their first and second trips, but on their trip shots compared over months or years of time.
An example of a breaker in which the DC supply voltage dropped more than 10% is shown in Figure 5. Other problems with the batteries or battery chargers could be picked in the shots as a 60Hz ripple superimposed on the DC trip current signal (See Figure 6).
In a couple of instances, the breaker analyzer shots indicated loose wires in the control circuitry (See Figure 7). Another item that can be identified with the breaker analyzer are a tailspring out of adjustment (fast trip, slow close). Adjustment of the tailspring has been used on occasion to speed up the trip on a slow circuit breaker, but this overlooks the root cause of the slow breaker is probably faulty lubrication. Other items found were trip coils on the verge of failure and dirty auxiliary switch contacts.
Figure 3 – Evidence of Faulty Lubrication in Breaker Operator

Figure 4 – Comparison of a Family of Curves
Figure 5 – Evidence of Battery Problem

Figure 6 – Evidence of Battery Problem
Figure 7 – Loose Connections in Control Circuit

Lessons Learned
We learned many lessons in the implementation of the circuit breaker signature analysis program. These are briefly described as follows:
Using the Breaker Analyzer
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For the most meaningful analysis, it is critical that thought be placed into how the data is managed. We purchased our breaker analyzers with a bar code feature that proved to be extremely helpful in maintaining consistent data.
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In order to obtain the best information about the breaker operator, it is critical to catch first shot. When a breaker with problems in the operator is not exercised in a relatively short period of time (as short as one month), the next breaker operation may be slow and sluggish. Once the breaker has been exercised, it frees up to a point and as long as the breaker gets off of the latch, the stored energy will mask the bearing problem temporarily. It is helpful to note the date of last previous operation on a breaker before using the breaker analyzer.
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In order to achieve consistency in where you connect to the breaker each time, and to make available the breaker analyzer testing duties to a broader range of employee skill levels, we found it helpful to use tape to color code the placement of the four leads within each breaker tested.
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Most breaker operators would show a difference in speed between the first and second shots if the lubrication was faulty. However, a few of particular type operators would be consistent on the shot information, even thought their lubrication was in bad shape.
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The breaker analyzer we used was sensitive to connection of the DC voltage supply leads to AC. It is a good practice to always check first with a voltmeter.
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The breaker analyzer we used had some memory limitations which necessitated downloading after completing tests on approximately twenty or thirty breakers.
Overhauling Breaker Operating Mechanisms
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Different maintenance crews may have different definitions of operating mechanism
“overhaul”. In order to completely address the problems associated with faulty breaker lubrication, breaker operating mechanisms should be fully disassembled, cleaned, lubricated, reassembled and adjusted.
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While a complete overhaul of an operating mechanism once seemed a daunting task, we have found that an experienced two man crew can generally perform a low voltage breaker overhaul within a day, and a high voltage breaker overhaul in two days.
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We found that in many cases the best practice is to replace all of the bearings when performing a breaker overhaul. Purchasing a full set of bearings for a breaker is often cheaper than attempting to clean and relubricate in the field. A complete set of bearings for a 15kV breaker is approximately $50, $300 for a 138kV breaker. Most bearings are available over the counter, except a few specialty trip latch bearings found on particular 138kV breakers. New bearings can be cleaned, lubricated and

placed in sealed plastic bag for installation in the field. Close attention should be paid to load bearing bearings. These can have flat spots that can cause a breaker to bind up during operation.
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If a complete operator overhaul is being performed, consideration should be given to overhauling all components associated with the breaker operation – for instance pilot valves on air systems.
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As experience is gained in overhauling breaker operators, we found that it was easier for some operator types to completely remove an operator from the breaker cabinet and overhaul it than to attempt to do it with the operator still in the breaker. Time savings can be incurred if a spare operator can be located, overhauled, then used for direct replacement in field.
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Due to manpower limitations, it can be difficult to overhaul all breakers identified in a short period of time. However, it is important to take necessary steps to minimize the chance of equipment outages. Since the trip latch is the weak link in the operation of the breaker, consider overhaul of the trip latch and light lubrication of the operator until such time a complete overhaul can be performed.
General
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The breaker analyzer does not perform all of the functions of a complete breaker timer (velocity, etc), but it does allow you to catch the first shot – which a breaker timer can not do.
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The consequences of faulty lubrication in vacuum breakers seem to be more severe than in oil breakers. The newer vacuum breakers require less stored energy to perform the breaker operation than older oil breakers did. However, the reduced stored energy becomes a disadvantage when bearing lubrication becomes faulty. Once a breaker is off the trip latch, the older oil breakers have more energy to overcome bearing problems than the vacuum breakers do.
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Manufacturers are still specifying petroleum-based greases in their breakers, and warranty considerations need to be taken into account when overhauling an operator.
Hopefully manufacturers will consider utilizing synthetic greases in future.
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There is benefit in a testing program in just being there. We found many problems that although they were not found by the breaker analyzer, they surfaced just because you were doing testing.
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The breaker analyzer is an excellent tool to help prevent customer outages.
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One disadvantage of the breaker analyzer we used is that it will not give a meaningful current trace for AC-close circuit breakers. However, the information from the main contact time and DC supply voltage to the breaker is captured.
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Another disadvantage of the breaker analyzer is that it does not easily accommodate testing of independent pole breakers.
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When you are doing your breaker analyzer testing, you will invariably run into problems that need immediate attention. Therefore, it is advisable to have access to the proper maintenance personnel during testing.
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Trip testing is the best, cheapest maintenance you can do.
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Failure mode is not linear for all operator types.

CONCLUSION
Circuit breaker signature analysis has proved to be an excellent innovation for assessing the condition of circuit breaker operating mechanisms and related components.
This is especially significant since a large percentage of equipment outages are attributed to circuit breakers. Circuit breaker signature analysis can also be utilized as an effective tool to prioritize the work to be performed – to identify the equipment that needs work, and also the equipment that does not need work. In the future, we plan to perform periodic breaker analyzer tests to see if there has been any deviation in the condition of the operator. We will also test any new circuit breakers that we install on the system to establish a baseline signature for the operator. In addition, we hope to track the performance of synthetic greases in the breakers that we have overhauled to track its performance in the field. We are not abandoning power factor, megger and timing tests of circuit breakers for they serve a different purpose. However, we believe that circuit breaker signature analysis can be used as an excellent tool to assess the condition of our breaker operators, prioritize maintenance and minimize equipment outages.
REFERENCES
[1] Doble Circuit Breaker Committee, Lubrication Subcommittee: Lubrication Guide of the Doble Circuit Breaker Committee, 1995.
[2] G. K. Nelson, C. A. Zimmerman, “Circuit Breaker Response Time Testing, An
Evaluation”, 1991 Transmission & Substation Design & Operation Symposium,
September 1991.
BIOGRAPHY
Wesley R. Speed is the Relay Support Manager at TXU Electric. Mr. Speed received a Bachelor of Science degree in Electrical Engineering at Texas A&M University in
1990. He worked six years in engineering as a substation project engineer and three years in field operations before transferring to System Protection in 1999.