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Changing of reading during the bushing normal operation is an indication of gas leakages or malfunction of the
instrument.
Each gas monitoring device is equipped with three change-over micro switches that provide signals for alarm
and tripping signals. Table 16 shows the micro switches purpose and the pressure set up (see Appendix 2 for
the exact contacts arrangement of each gas monitoring device).
The instruments are installed on DILO valves for easy disassembly without the need to completely remove the
gas from the bushing.
In addition, the electrical cables of all devices are wired in a junction box provided with DIN type terminal blocks
for easy assembly and maintenance (see Appendix 2).
Additional information about the gas density monitor devices are illustrated in Appendix 4.
NOTE: Due to the instrument principle of operation, the replacement of bushing gas from SF6 to a gas mixture
SF6 N2 is not allowed without replacing the gas density monitors with the proper type. In this case contact GE
Energy Connections RPV for support, instructions and approval.
NOTE: The instrument equipped with the electronic sensor cannot be subject to the 2 kV 1' on the
terminals of the electronic sensor (terminals marked + - and relevant wiring at the junction box terminals
X10 35 and 36) The application of such voltage to ground will cause an immediate failure of the
instrument.
11
Power factor tap
The bushing is equipped with one PF tap. This tap is used for capacitance, tan-delta and partial discharge
measurements during the tests and in operation.
In operation, it must be accurately closed with its screwed metal cap that ensures also the grounding connection.
HVDC TRANSFORMER BUSHINGS
Micro switch
Alarm 1
Low pressure level 1
Low pressure level 2
Alarm 2
Minimum operating pressure
Tripping
Too low pressure for operation
Table 16 – Alarm and tripping micro switches set-up
PF tap insulator
Screwed cap
Clip type contact
Contact pin
Figure 16 – Power factor tap
PHI 530.1425.2500
PHI 265.850.1500
Kepco project
Description
IS 2664 GB
Page 28 of 70
Pressure set up
[MPa abs]
0.58
0.55
0.52
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