Schuetz Messtechnik GmbH

The great advantage of the PWR3A compared to many of the other instruments on the market is its simple set-up.

In most cases the required parameters must be looked up in tables on the basis of the vector group and the code number of the transformer to be measured, and set up at the instru-ment by means of rotary switches or keys. This often results in a wrong set-up or uncertainty regarding the set-up since some of the tables are confusing.

Such a manual set-up is not necessary with the PWR3A transformation ratio measuring instrument. You simply type in the vector group with the keys.

The only thing you have to do is to connect the transformer being off-line to the device and release the measurement; all three phases are measured consecutively, all connecting and short circuited procedures at the primary and secondary volt-age sides are performed automatically before each measure-ment. Of course it is also possible to measure just one phase, e g. H2.

An adjustable set value permits the display of an error or deviation of the measured transformation ratio. Further, an automatic control of the tap changer is provided. In this case all phases and taps are measured consecutively, and all the results are stored inside the instrument (using the trans-former specific memory), printed (if a printer is connected), and transferred to the PC (if connected).

Using the internal memory all results for all taps are written to a transformer specific area.

Furthermore, the transformer specific set point values, the vector group and additional information describing the trans-former (e.g. serial number, location …) are read from the memory when selected and displayed on the LCD. If set point values are present, an OK / NOT OK message with the corresponding information is displayed.

The transformer specific data can be easily programmed via a connected personal computer but it is also possible to input the transformer specific data via the internal keyboard.

The PWR3A transformation ratio measuring instrument is connected to the H.V. and L.V. sides via four connections each. It also powers the test object at selected voltage, supplied by an internal isolating transformer. However, an external excitation using different voltages and frequencies is also possible.

A special feature is the possibility to use three phase measur-ing voltage. Transformers have phase angles of n*30° where n is the vector number 0 to 11. Because all measurements are single phase all results will be 0° or 180° too together with eventually phase errors.

But there are some special transformers with phase angles of n*30° ± (0°..15°), e.g. 127.5°. To get this value (and not 0/180°) one need a three phase source to feed the transformer. A 3-phase line voltage is used for this purpose.

The PWR3A is supplied in a robust carrying case. All connections are provided at the front of the instrument and are locked in order to avoid unplugging during a measurement. An alarm set (a red lamp is on during the measurement) can also be supplied.

The connecting cables and clamps are 4-pole (Kelvin) on the HV-winding to avoid errors due to cable resistance.