Video: ADOC-3

Video transcript

How the ADOC-3 tells you, in about a minute, whether a distribution transformer can be put back into service: the connection, the test and the 3 possible answers. After a storm or a line fault, crews have to decide whether each distribution transformer can be reconnected. Closing in on a unit with a damaged winding can end in a violent failure as soon as it takes the load again. The answer is needed on site, before reclosing, and quickly.

The ADOC-3 measures at low voltage, AC and DC, by simple contact on the primary bushings, while the secondary stays connected to its loads. One test covers every winding and finds short circuits and open circuits in the primary, and short circuits in the secondary. There is no curve to interpret. It covers transformers from one kilovolt-ampere to 3 megavolt-amperes, rated from 1000 volts to 50 kilovolts, with 3 measurement channels, and a check takes about 60 seconds.

Everything is on the front. Three bright LEDs give the answer: short, OK or open. The display shows the configuration and the rating. The kVA and kV arrows set the transformer, the mode key chooses single-phase, Delta or Yn, and the round key starts the test. The measurement lead plugs into the top of the instrument. Three red clips, H one, H two and H3, go on the primary terminals, and the black clip, N ground, on the neutral. The lead is removable and stores on its hook-and-loop strap.

The kit comes in a semi-rigid case: the instrument in its rubber boot, the lead, a magnetic strap that holds the unit on the tank, and 4 standard AA batteries. Available as options: a spare 1.5 metre lead, a rigid case, and adapter pins for transformer elbows. Before connecting: the transformer is de-energised and disconnected from the line, following the site safety rules. The secondary stays as it is. Switch on, and the instrument tests itself.

Run the lead self-check, then set the configuration, the power and the voltage. On a single-phase transformer with one primary bushing, the black N ground clip goes first, to the neutral on the tank. Then the red H one clip goes on the primary bushing. Nothing is touched on the secondary side. On a three-phase Yn bank, the N ground clip goes on the common neutral, and H one, H two and H3 on the primary bushings of the 3 units. One single test then checks the whole bank.

On a Delta primary, the 3 phase clips go on the 3 primary terminals. Choose the configuration with the mode key. Set the power range with the kVA arrows and the rated voltage with the kV arrows. Press start. About a minute later, one LED lights and the tone confirms the result. The answer needs no interpretation. Red, short: there is a short circuit in a winding, and the transformer is not reconnected. Green, OK: the windings are sound and it can be re-energised. Yellow, open: the primary is open, and it stays out of service.

It is made for the pole and the pad: from minus 20 to plus 60 degrees, IP 40 and IK 06 inside its rubber boot, 8 hours of measurement on 4 AA cells, and it switches itself off after 15 minutes idle. It is used to check transformers after storms and line faults, in inspection campaigns on overhead networks and distribution substations, on three-phase banks, pad-mount and dry-type medium-voltage units, and for receiving inspection in the workshop. Transformer testing, from Amperis.