9
User manual - Annex III
High Voltage Instrument Transformers | DDB/DFK/DDN/DFN
The Portable Transformer Ratio Meter (TTR) is commonly used
to measure the ratio, excitation current and polarity of windings.
The values obtained are a reference that the transformer is
in good condition and can be energized. They should not be
compared with the results of factory tests carried out in the
manufacturing plant laboratory.
Due to the high precision required for this measurement, the
actual uncertainty of the test must be taken into account when
testing on site.
The TTR contains 4 terminals (this confi guration may vary
depending on the manufacturer):
› H1: Black excitation terminal.
› H2: Red excitation terminal.
› X1: Black secondary terminal.
› X2: Red secondary terminal.
TRANSFORMER RATIO TEST
This test verifi es the transformer ratio and polarity, and displays
a “+” signal if correct, and a “-” signal if inverted. To carry out the
test, proceed as follows (fi g. 5.
› The excitation terminals (clamps marked “H”) will be connected
to the transformer’s primary circuit:
• H1 will be connected to the primary terminal of equipment A/H1.
• H2 will be connected to the ground terminal, located at the
base of the equipment.
› The clamps marked “X” will be connected to the transformer’s
secondary terminals:
• X1 will be connected to the beginning of the winding. When
the secondary has taps, you must connect X1 to the tap of the
secondary terminal which is to be tested.
• X2 will be connected at the end of the secondary winding.
• This test must be applied to each secondary separately;
in case the transformer has more than one secondary, the
secondaries which are not to be tested must be left open.
CAPACITIVE VOLTAGE TRANSFORMERS/
A/H1
H1
H2
X2
X1
a1 a2 a3
T.T.R.
n
›
Fig. 5