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HVDC TRANSFORMER BUSHINGS
PHI 530.1425.2500
IS 2664 GB
PHI 265.850.1500
Page 30 of 70
Kepco project
The divider is a passive unit so the loading capacity is limited. It must be used in conjunction with a suitable
electronic amplifier. The accuracy class is guaranteed for resistive loads ≥ 1 MOhm.
The connection between the two units is realized by a special cable provided with special BNC plugs equipped
with a special locking system that prevents the disconnection of the cable (see Figure 18).
Figure 18 – BNC connecting cable with security plugs
WARNING: The divider is not designed for the bushing or the transformer test voltages. In addition the presence
of surge arrestors can cause electric disturbances during the tests.
For this reason it is necessary to disconnect it during the electrical tests of the bushing or the complete
transformer. The PF tap must be closed with its own metallic cap or directly connected to the test instruments.
WARNING: Never operate the bushing with the PF tap open or without the cable connection between
the PF tap adapter and Voltage divider box. It's extremely dangerous for the integrity of the bushing,
with a high risk of explosion.
13
Composite insulators maintenance
Composite insulators manufactured by qualified and experienced suppliers, require very limited maintenance.
The silicone used for the sheds is highly hydrophobic and it has the property to transfer this characteristic to the
pollution layer.
Cleaning of the composite insulator is necessary only in case of heavy contamination.
Due to the installation on the bushing inside the valve hall, cleaning by washing is not possible. In this case
cleaning can be done only manually by using a sponge and demineralized water. The composite must be
accurately rinsed and then dried with clean cotton fabric pieces. In case of heavy contaminated areas, use a
solution of isopropyl alcohol, rinse with water and dry with clean cotton fabric pieces. Appendix 6 describes the
composite insulator cleaning procedure of the composite manufacturer.
In case of accidental damage of silicone sheds, the repairing procedure is illustrated in Appendix
6.
The
composite manufacturer can provide a repairing kit and a technical support for the repairing activity.
WARNING: Severe electrical shock risks are deriving by the fact that the composite insulator and the other main
parts of the bushing remain electrically charged at high voltage for a long period of time (hours) after the plant
de-energization and the bushing grounding. Before starting any work on the de-energized bushing, check the
discharge by touching all surface of the composite insulators and all other parts of the bushing with an insulated
grounding rod which length must be ≥ 3m. Operators must wear protective insulating gloves and boots and
helmet with protective transparent face shield.
WARNING: Bushing cleaning must be performed with the bushing de-energized.
WARNING: Inspection of the bushing with the plant energized must be done by qualified technicians fully in
accordance with the safety rules specific for the access to the valve hall.
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