Delta 4000 Instruction Manual download pdf (Page 92)

81331 Rev 01 Nov 2010

Turns Ratio Tests

Measurements of transformer winding ratio can be made with a high voltage

power factor test set when a TTR capacitor is available. Depending on the

voltage rating of the winding being energized, tests can be made up to 10kV.

The significance of this is that higher volts per turn can be applied to the

winding, stressing the winding turn-to-turn insulation more than low voltage

ratio test sets. This may be able to detect high resistance turn faults that may be

undetectable at lower voltage. The tests are performed one phase at a time on

three-phase transformers.

To enable this portion of the test form, select the Show TTR Tests checkbox at

the top of Page 1. A table for ratio test results will become visible near the end

of the form. You should select the Number of Tests based on how many

transformer taps you intend to test.

The first test must measure the capacitance of the Standard Capacitor, in pico-

Farads (pF).

 Connect the test set leads, the HV lead and the Red measurement lead,

directly to the capacitor.

 Initiate the test by right clicking on the blue field for the Standard

Capacitor.

Subsequent tests require the HV lead to be connected to one side of a HV

winding (e.g. H1/U/A) where the other side of the HV winding is grounded to

the tank (e.g. H0/N/N). The corresponding winding on LV side is grounded on

one side and on the other side is connected to Red lead via the capacitor.

By enter the winding voltage levels in the form, the assessment is automatic.

Exciting Current Tests

Measurements of the individual phase excitation current values are valuable in

determining defects in the transformer core and coils. Excitation current

measurements are generally performed on the high voltage winding only, to

minimize the amount of current required.

NOTE: All bushing shorting leads must be removed for exciting current

measurements. If the low voltage winding has a neutral, connect the

neutral bushing as it normally is in-service (grounded or ungrounded).

Measurements are usually made one phase at a time. Connections should be

documented in the fields provided at the top of the table. For initial or

commissioning tests, perform the measurements on each possible primary and

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Delta 4000 Instruction Manual Page 92