Tettex MIDAS 2881, Operating Instructions Manual

Page: 156 / 164

146 Applications Guide
14.7.2 Live Tank Breaker
The test procedure for a Live Tank Breaker (e.g. SIEMENS 3AP1 type) is shown below:
Live Tank Breaker measurement connections
C
1T
= C
1B
+ C
G1
+ (PS
1
+ R
1
)
C
2T
= C
2B
+ C
G2
+ (PS
2
+ R
2
)
C
1B
, C
2B
: bushing stray capacitances (undrawn)
C
G1
, C
G2
: grading capacitors
C
TG
: insulation column capacitance
S
1
, S
2
: breaker switches
PS
1
, PS
2
: pre insertion switches
R
1
, R
2
: pre insertion resistors
Test Connections
DUT INPUT A
to INPUT B
to INPUT
HV GND
to Test Mode High Voltage
to Breaker
Status
C
1T
1 2 Floor GND UST A Tank (T) open
C
2T
1 2 Floor GND UST B Tank (T) open
C
TG
1 2 Floor GND GST gA+B Tank (T) open
C
1G
+ C
2G
1 2 Floor GND UST A+B Tank (T) open
Note: Test line #4 can be used to inter-check the measurement results. (#4 = #1 + #2). Additional
measurements in other test modes can be executed to inter-check the measurements results.
Although pre insertion resistors and their switches are included in the sum capacitances of the
interrupting chambers (C
1T
, C
2T
), the resistors R
1
and R
2
are normally very low resistive and the
switches S
1
and S
2
have very low capacitance compared to the bushing and grading capacitors.
Therefore the influences of these elements can be neglected.
Higher dissipation or power factor for the bushing/grading capacitor assemblies generally indicate a
degradation or contamination of the grading capacitors. The measurement could also be influenced
by surface leakage on the bushings. Abnormal capacitance values may be a sign of short-circuited
sections of the grading capacitor assembly.
High losses along the insulation column may be caused by surface leakage or moisture, which may
have condensed on internal tubes and rods.