- The COMPANO 100 test set can output life-hazardous voltages and currents.
- Before operating any such electrical equipment, carefully read the Safety Instructions chapter in this manual (see Safety instructions).
| WARNING | ||
| Death or severe injury can occur if the appropriate safety instructions are not observed.
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With COMPANO 100 you can measure the resistance of a busbar joint or of a closed circuit breaker. Here, we give an example for the latter.
In order to avoid any influence by the contact resistance of the clamps that are connected to the breaker’s contacts, it is important to use the four wires (and four contact points!) technique. The current is injected using two wires, the voltage is measured using a second pair of wires.
| Because there is only a neglectable current flowing on the voltage path, there no voltage drop created by the clamps of the current injection; means: there is no voltage drop that could possibly have an impact on the measurement result. It is important to understand that the point of connection of the voltage clamps determines what part of the resistance is measured. |
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When doing breaker measurements, you have two possibilities to measure:
Option one is to only measure the resistance of the contact itself. This is the value that breaker manufacturers quote in the breaker’s datasheet. This option makes sense to verify the breaker’s specifications. It is furthermore useful for "trending", that is, for surveying changes in the breaker's characteristics over the years.
Option two is including the breaker’s connectors to the measurement. Additionally testing the breaker's connectors may prove beneficial for certain maintenance measurements because the breaker’s resistance being within the limits is of little relevance when the breaker’s connectors to the busbar overheat in case of a fault.
On high voltage breakers it is generally easier selecting connection points since all points are easily accessible for connecting clamps.
| On medium voltage breakers, for example breakers equipped with tulip contacts (see photo at the right), it is often not possible to access the breaker directly using the 4-wire technique since the fingers of the tulip contacts are interconnected high-ohmic, therefore ruining the result. |
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| Therefore, in order to measure the total resistance of the breaker, insert stubs substituting the connection points of the busbar (see photo at the right). |
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| To only measure the resistance of the breaker contact, the tulip contacts need to be removed from the breaker. In many cases it is then difficult to access the contact because there is literally only one single thread in a massive piece of metal. In such a case use a Kelvin screw (see photo at the right). A Kelvin screw makes a high current contact to the thread itself, and an independent voltage contact to the surface around the thread. Kelvin screws are available for several different threads that are common on breakers. |
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| Kelvin clamps also provide the possibility of establishing two independent connections using one clamp, only. The two brackets of the clamp are insulated against each other. Such clamps are ideal when connecting to massive conductors like busbars or connector plates (spades) of a breaker. |
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For the actual measurement, connect the high current cables to the I OUT current output, and the voltage sense cables to the IN 1 measurement input. Once the connection is properly done, the measurement itself is simple. Open the Micro-ohm application module, set the current, and press the Start/Stop key to carry out the measurement. Stop it after the result has stabilized.
Note that the IN 1 measurement input is put into a special mode in the Micro-ohm application module, suppressing AC noise on a hardware level much more than this is possible in QUICK or FLEX.
In case the output stops automatically because the high current drove COMPANO 100 to its thermal limit, the result is still valid.
