Megger MTO106, User Manual

Page: 13 / 20

BN034794AE ZP-BN01E MTO106 13
4 SETuP AND OPERATION
tions" on page 12 are complete, the mains
power cord is connected to the power outlet.
5]
Set the "RANGE"selector to the required
test current, as high as possible but not more
than 10% of rated current (power transform-
ers, reactors, rotating machines). For a CT,
preferably use 1 A.
6]
For Single winding
Set switch "R2 SENSE" to "OFF" position.
For Dual windings:
Set switch "R2 SENSE" to "ON" position.
7]
Set switch "TEST CURRENT" to "ON", to initi-
ate current.
8]
The current and resistance values must be
observed on the display. Wait for the stabil-
ity reading to reach 100% and then note the
displayed resistance value in the supplied
reporting sheet or other location.
9]
When the measurement is finished set the
"TEST CURRENT" switch to "OFF".
The "DISCHARGE" lamp and sound will indi-
cate that the discharging is in progress.
10]
Discharge is complete when both discharge
indicator and "TEST CURRENT" lamp are off.
Warning
Do not disconnect any test leads until
the "DISCHARGE" light goes out and the
sound stops.
Note The discharge of a transformer after testing is
critical to prevent excessive voltage build-up
across the transformer bushings upon removal
the test leads. The MTO106 discharge circuitry
is built-in and will automatically initiate when
the current source is disconnected from the
transformer. It will also provide visual and
audible indication of discharging.
4.3 Testing Delta winding
resistance
Testing Delta winding resistance may be a very time
consuming procedure, in particular LV winding
deltas. The correct balance time can take up to 30-60
minutes for a large transformer, which far exceeds the
time restriction of many tests.
The method for quickly testing delta configurations
requires that both the high side and low side be
connected in series with the Transformer Ohmmeter’s
current source (see connection table 1). By using
both HV and LV windings to magnetize the core, the
effective test current increases with the turn ratio.
Table 1. Transformer connection schemes for
injecting test current and measuring two
windings
Vector
Group
Measurement setup
Current Connections
Meas
ch 1
Meas
ch 2
+ Current Jumper - Current + - + -
Dd0
H1 H3-X1 X3 H1 H3 X1 X3
H2 H1-X2 X1 H2 H1 X2 X1
H3 H2-X3 X2 H3 H2 X3 X2
Dyn7
H1 H3-X0 X1 H1 H3 X0 X1
H2 H1-X0 X2 H2 H1 X0 X2
H3 H2-X0 X3 H3 H2 X0 X3
Dyn1
H1 H3-X1 X0 H1 H3 X1 X0
H2 H1-X2 X0 H2 H1 X2 X0
H3 H2-X3 X0 H3 H2 X3 X0
YNyn0
H1 H0-X1 X0 H1 H0 X1 X0
H2 H0-X2 X0 H2 H0 X2 X0
H3 H0-X3 X0 H3 H0 X3 X0
Ynd1
H1 H0-X1 X2 H1 H0 X1 X2
H2 H0-X2 X3 H2 H0 X2 X3
H3 H0-X3 X1 H3 H0 X3 X1
Dy1
H1 H3-X1 X2 H1 H3 X3 X2
H2 H1-X2 X3 H2 H1 X1 X3
H3 H2-X3 X1 H3 H2 X2 X1
YNd7
H1 H0-X2 X1 H1 H0 X2 X1
H2 H0-X3 X2 H2 H0 X3 X2
H3 H0-X1 X3 H3 H0 X1 X3
Dyn5
H1 H2-X0 X1 H1 H2 X0 X1
H2 H3-X0 X2 H2 H3 X0 X2
H3 H1-X0 X3 H3 H1 X0 X3
Dy11
H1 H3-X1 X3 H1 H3 X1 X3
H2 H1-X2 X1 H2 H1 X2 X1
H3 H2-X3 X2 H3 H2 X3 X2
Dyn11
H1 H2-X1 X0 H1 H2 X1 X0
H2 H3-X2 X0 H2 H3 X2 X0
H3 H1-X3 X0 H3 H1 X3 X0