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8
Power factor taps
The bushing is equipped with two PF taps, one for the indoor side and the other for the outdoor side of the
bushing. These taps are used for capacitance, tan-delta and partial discharge measurements during the tests.
In operation they must be accurately closed with their metal caps that ensures also the grounding connection.
CAUTION: PF tap cap MUST be accurately closed. Missing the cap could be dangerous and it can cause an
electrical discharge at bushing energization.
9
Composite insulators maintenance
Composite insulators are 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.
For this reason it is not necessary to proceed with frequent washing operation which may progressively
weaken the ability of silicone to regenerate its hydrophobicity. Washing must be done only when strictly
necessary, i.e. in case of a heavy pollution of the composite insulator. Keep in mind that after washing, the
silicone recovers its hydrophobicity in one or two days.
The composite insulator maintenance and repair procedure is described into the component manual: see
reference in the summary prepared for the specific wall bushing.
The composite manufacturer can provide a repairing kit and also a technical support for the repairing activity.
Useful indications about the composite insulator maintenance plan main actions are shown in Table 2.
CAUTION: Severe electrical shock risks 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 after the plant de-
energizing and the bushing grounding. Before starting any work on the de-energized bushing, check the
discharge by touching all surface of both indoor and outdoor side 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.
CAUTION: Bushing washing must be performed with the bushing de-energized. Live washing is not allowed
due to the high risk of fatal electrical shocks and dangerous flashovers across the composite insulator.
CAUTION: Inspection of indoor side 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.
It is recommended to perform all Table 2 listed actions, as a reference starting point, at the first bushing
energizing.
Nuova Via di Piano Comprensorio Vulcano
Sesto San Giovanni, MI 20099 Italy
Tel. 02-24105.001
PF tap insulator
Screwed cap
Contact pin
Spring loaded contact
Figure 10 – Power factor tap
IS 2653 GB
Page 14 of 18
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