Video: CAT – Wiring and test

Video transcript

How the CAT is wired to a circuit breaker, what every cable is for, and the order the job has to be done in. Four things before a single clamp goes on. The breaker is disconnected or separated from its circuit on both sides. The breaker is earthed to protective earth. The CAT is earthed too, with the cable supplied with it and no other. And the CAT is switched off while cables are connected or removed. And the order is not a preference, it is a rule.

Cables go to the CAT first and to the breaker second. Coming off, they leave the breaker first and the CAT second. The earth wire is disconnected last of all. If the instrument does not have the both sides grounded timing feature, the earthing is handled the conventional way, and it has its own sequence. This is the front panel, and these are the 6 connectors you will actually wire. Main contacts by phase, auxiliary contacts, coil control, coil supply, analog channels and the transducer.

And the 6 you operate. Mains in, the on off button, the earth stud, the touch screen, the START button, and the flash drive that takes the results away. The main contact cables come as one set per phase, and the whole colour code exists so that nothing has to be worked out on a ladder. Phase A carries a red ring over the connector, phase B a yellow ring, phase C a blue ring. Inside a set, the red clamp with a red label is the first break,

the red clamp with a blue label is the second, and the black clamp is the common. This is a live tank breaker with 4 breaking elements per phase, wired the conventional way. The instrument goes on the ground, earthed, and then the hookup is built phase by phase: A one and A two on the first two breaks, A 3 and A 4 on the next, and the black N clamp on the common side. And this is the same job on a dead tank breaker, with both sides grounded timing.

The earths stay on. A current cable with branch connectors feeds the whole line, and an AC clamp on each tank picks up the current that flows through the closed contact. In the yard it looks like this. The clamp goes on the terminal itself, and nothing about the connection is clever: what matters is that it is on the right terminal, tight, and on the right phase. The coil control wiring, on a breaker with 3 independently operated poles. Each coil control cable carries a close and an open, and the coil supply input cables come from whatever feeds the control circuit.

When the station battery is not available, or should not be used, an external source powers the coils and the spring charging motor instead. The CAT drives the close and open switches, and the supply comes from the unit beside it. This is the measurement everything else rests on: the current in the trip coil during one operation. Six things happen in it, and each one is a piece of the mechanism moving. Learn these 6 and you can read a breaker from one capture.

And with a transducer fitted, the travel curve. This is the contact actually moving, and it is where contact wipe, over-travel, rebound and average velocity come from. None of these can be measured any other way. The same instrument measures the resistance of the main contacts. Current cables on the outside, sense cables inside them, so the drop is measured across the contact and not across the test leads. And gas insulated switchgear, where there is nothing to clamp onto.

A test module sits next to the CAT, connects to it with one communication cable, and takes the current cables and the AC clamps out to the enclosure. Auxiliary contacts have 4 timing channels of their own, on inputs labelled one a, one b, two a and two b. They are what you put on the 52 a and 52 b contacts. Four analog channels take anything else worth recording alongside the operation: the station battery voltage, the motor current through a clamp, the motor voltage. They are isolated from everything else in the instrument,

and the panel supplies 24 volts for the clamp. Running the test itself is 5 steps, and 4 of them happen before anybody presses START. Two checks worth knowing, because they separate a wiring fault from a breaker fault. If the main contacts read wrongly, short the clamps together and run the test: what you should see is a closed contact on every channel. If a coil does not operate, check the coil supply before suspecting the coil. Circuit breaker testing, from Amperis.