Dry-type transformers are a part of most electrical installations. They range in size from small doorbell transformers to three-phase 25-kVA units installed in electrical closets to large, free standing units rated at several hundred kVA. Electro tehnical Officers on ship must know how to test for and diagnose problems that develop in transformers especially in the smaller, dry- type power-supply or control transformers.
Open Circuit problem on ship transformer
If one of the windings in a transformer develops a break or “open” condition, no current can flow and therefore, the transformer will not deliver any output.
The symptom of an open-circuited transformer is that the circuits, which derive power from the transformer, are de-energized or “dead.”
Use an AC voltmeter or DMM to check across the transformer output terminals.
A reading of 0 V indicates an open circuit.
Then take a voltage reading across the input terminals. If voltage is present, this indicates that one of the transformer windings is open. However, if there is no voltage reading on the input terminals either, then the open must be somewhere else on the line side of the circuit; possibly a disconnect switch is open.
WARNING!
Make absolutely certain that your testing instruments are designed for the job and are calibrated for the correct voltage. Never test the primary side of any transformer over 600 V unless you are qualified, have the correct high-voltage testing instruments, and the test is made under the proper supervision.
However, if voltage is present on the line or primary side and no voltage is on the secondary or load side, open the switch to de-energize the circuit, and place a warning tag (tag-out and lock) on this switch so that it is not inadvertently closed again while someone is working on the circuit.
Check ships transformers condition
Disconnect all of the transformer primary and secondary leads and check each winding in the transformer for continuity (a continuous circuit), as indicated by a resistance reading taken with an ohmmeter.
Continuity is indicated by a relatively low resistance reading on control transformers, while an open winding will be indicated by an infinite resistance reading (OL or 1). In most cases, such small transformers will have to be replaced, unless of course the break is accessible and can be repaired.
