U
(A)
V
(B)
W
(C)
Voltage to U (A)
100%
66%
33%
Voltage to V (B)
50%
100%
50%
Voltage to W (C)
33%
66%
100%
The main function of the on load tap changer is to switch between
transformer taps without interrupting the current. The 2293
registers the current while tap changer is operated and records
the values at a defined sample rate.
Discontinuities or deviations between different taps are a sign
of tap changer fault.
TAP CHANGER - DYNAMIC RESISTANCE
The tap changer test with the 2293 is done automatically and
without reconnection. In addition, the tap changer control
accessory allows a complete automatic sequence without
human intervention.
Calculation of the main curve parameters like time to rise, time
to fall or delta, for failure detection, is automatically done.
Magnetic balance test is performed to detect faults in the
magnetic core. The test looks for changes in the reluctance
of the magnetic circuit caused by defects in the magnetic
core structure, shifting or shape changes in the windings or
inter turn insulation fault.
The test is performed on three phase transformers by
applying a voltage on one of the phases and measures the
voltage on the other two. The induced voltage will depend
on the limb position into the core as the following table.
The 2293 performs the magnetic balance test automatically
and without any reconnection. Test results are shown
graphically for a better understanding.
Imbalances will be graphically noted including the involved
phases.
Short circuit impedance is a routine test done to all
transformers after manufacture and specified in the
transformer nameplate.
Changes in the short circuit impedance along transformer
life is normally an indication of mechanical damages.
The 2293 automatically performs a short circuit impedance
test at reduced voltage on power and distribution
transformers and calculates the three phase equivalent
short circuit impedance for comparison with previous test or
with nameplate values.
After a power or distribution transformer is disconnected
from the power grid or when a DC current is applied to it, for
example during a routine winding resistance measurement,
the transformer core is likely to have some remnant
magnetism. This remnant magnetism will generate high
over currents when the transformer is reconnected to the
grid, and this is commonly known as transformer inrush
current.
In addition, magnetic remnant has an adverse effect on
other measurements like FRA or TTR.
The 2293 includes a fully automatic demagnetisation feature
which eliminates the magnetic remnant. Select the winding
where demagnetisation needs to be performed and press
start. The unit visualizes the whole demagnetisation cycle
and performs the correct core demagnetisation in seconds.
MAGNETIC BALANCE TEST
SHORT CIRCUIT IMPEDANCE
DEMAGNETISATION FUNCTION
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