Voc - Open Circuit Voltage - Voltech AT5600 User Manual

C H A P T E R 7 – T E S T S
7.37.

VOC - Open Circuit Voltage

Where Used
The AT5600 offers two basic alternative ways to confirm that the transformer has
been assembled properly, with the appropriate number of primary and secondary
turns.
Open circuit voltage measurements are the preferred tests for line frequency
transformers, designed to operate over the full extent of the B-H curve, including
the non-linear regions.
(For other transformers, such as pulse transformers and those used in switched
mode power supplies, a measurement of turns ratio is the preferred test.)
Clearly an open circuit voltage test cannot tell you the actual number of turns on a
winding, only the ratio between one winding and the next. You should therefore
also include a magnetizing current test in your program, to give confidence that
the absolute number of turns is correct as well as the ratio.
Measurement Conditions
Open circuit voltage is measured by applying an AC test voltage to a selected
winding (usually a primary winding), and measuring the resulting voltage
produced on another winding.
If, there are several windings to be tested, the program will execute more quickly if
the following points are observed:
Place all the open circuit voltage (VOC) tests consecutively at the same point in
the program.
Use the same energized winding, with the same test voltage and frequency for
each test.
If there is a magnetizing current (MAGI) test which has the same energized
winding and the same test voltage and frequency, place this immediately before
the first open circuit voltage test.
Specifying the Test Limits
The AT5600 offers you three ways to specify the test limits:
Using a normal AC (RMS) measurement.
Using a rectified (mean) measurement.
Using a DC (mean) measurement.
Generally, the AC (RMS) value would be used, but you could use the rectified
(mean) or DC (mean) measurements if, for example, you are testing transformers
fitted with a rectifying diode.
AT5600 User Manual 98-119 issue 14
A N D T E S T C O N D I T I O N S
Page 154