How do you test a circuit breaker
Check the condition of circuit breakers
SIEGFRIED: There are various tests for evaluating the condition of circuit breakers. Can you name a few, please?
ARI: Yes of course. There are actually a variety of exams. I would divide these into three groups: electromechanical tests, electrical tests, and visual tests.
Visual inspections are used to determine visible damage, corrosion and gas, air or hydraulic leaks. Using thermal imaging cameras, for example, to determine whether the connections or the main contact unit are showing any abnormal signs of heat, which would mean that the connections / contacts are worn. Such checks are carried out approximately once a year.
Electrical tests are one of the classic tests on circuit breakers. They include: B. switching time measurements, tests of the static and dynamic contact resistance, analyzes of the coil and motor current and also minimal excitation tests. In the case of electromechanical tests, in addition to testing hydraulic or gas pressure or vibration during operation, especially movement / contact measurement should be mentioned.
Both the electrical and the electromechanical tests are usually carried out every 10 to 15 years. Sometimes, however, they also take place more frequently, especially if the circuit breaker has tripped due to a fault or something abnormal was found during the visual inspection.
SIEGFRIED: Which tests are carried out most frequently and which would you recommend?
ARI: I think the most common tests performed are:
- testing of static and dynamic contact resistance,
- the switching time check,
- the analysis of coil and motor current and
- the motion measurement.
Personally, I would recommend testing dynamic contact resistance along with a motion measurement.
SIEGFRIED: Could you please explain briefly what is behind these tests?
ARI: Of course. With the test of the static contact resistance, the status of the main contact is checked, i.e. whether it is able to transport the rated current without major losses.
When testing the dynamic contact resistance, the contact resistance is recorded during the operation of the circuit breaker. The data provide clues as to signs of wear on the main and erosion contacts. This is the only way to get information about the arcing contact without opening the interrupter chamber.
The switching time measurement is used to control the safe and reliable operation of a circuit breaker. For this purpose, the switching times and their synchronicity are evaluated per phase and between the phases. For the analysis of the coil current, its signature is recorded during the operation of the circuit breaker. Deviations can indicate electrical or mechanical defects in the switch-on and switch-off coil elements.
When analyzing the motor current, the current required by the motor to tension the spring or to increase the hydraulic or air pressure is recorded. Just like the analysis of the coil current, the analysis of the motor current is also used to detect possible deviations in the electrical or mechanical components of the motor.
The purpose of the motion measurement is to check the performance of the mechanism as a whole and to identify defects in the kinematic chain, such as B. a jammed mechanism or poor mechanical dampers to detect.
All of these measurements taken together therefore provide a good overview of the circuit breaker condition. The great thing about the CIBANO 500 is that these tests can be carried out without rewiring, while the circuit breaker is earthed on both sides, which significantly increases the safety of the testers.
SIEGFRIED: You recommend motion measurement. Why should this measurement be carried out?
ARI: As already said, the performance of the kinematic chain of the circuit breaker, which is of course very important for its functioning, can be checked as a whole. For example, a jammed mechanism can be detected as the cause of slowed switching operations or poor mechanical dampers that impair the behavior of the circuit breaker and can even lead to its failure.
In addition, you get information about the total distance, the overshoot, the springback and the speed. Using the result of the test of the dynamic contact resistance, you can also calculate the length of the erosion contact, for example to determine its wear.
SIEGFRIED: Is movement measurement complicated?
ARI: No, not really. Of course, you will need a little more time and a special adapter to attach a motion sensor to the circuit breaker to be tested. OMICRON is constantly expanding its range of adapters so that our customers can test the widest possible range of circuit breaker types.
A big advantage of the CIBANO 500 is that we deliver the devices with digital sensors. These sensors do not have to be calibrated before measuring and, thanks to their coding, the CIBANO 500 system recognizes them automatically so that it can configure the correct resolution and supply voltage for them.
SIEGFRIED: The main contacts are housed in the interrupter chambers. How can their path be measured?
ARI: That's right. In most cases it is not possible to get directly to the pole connected to the main contact and you have to find another access point to measure the movement. The access points depend on the type of circuit breaker. In most cases, the best access point is at the end of a drive shaft or on the gear shaft at the bottom of the poles, so a rotary encoder is needed to measure movement.
If there are multiple ways to attach the sensor, I would recommend checking with the manufacturer as they have already measured the contact path. In this way, you can compare your own measurement results with those measured at the factory. Then find a place to mount the sensor near the main contact so that the measured movement is as linear as possible.
SIEGFRIED: If you measure a rotational movement and the main contact moves in a linear direction, how do you get from a rotational to a linear movement?
ARI: One has to convert the rotational movement into a linear movement. With CIBANO 500 you have two options for this: If the rotary encoder and the main contact are mechanically coupled on only one level, a linear conversion factor provides a sufficiently accurate result. With this factor, the measured degree value can be converted into a millimeter value. If there are multiple levers, I recommend using a conversion table to be able to determine the nonlinear behavior with greater accuracy.
SIEGFRIED: Can I get help attaching these sensors to my specific circuit breaker?
ARI: We have created various videos for our CIBANO 500 customers that show step by step how the motion sensor is attached for some common circuit breaker types.
SIEGFRIED: Thank you for all of this information.
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