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d) Cleaning and checking the anti-ferroresonance circuit
• Make the plant you want to work on safe (follow the plant safety regulations);
• Make sure that the circuit-breaker is in the open position;
• Rack the circuit-breaker out from the service position to the test/isolated position;
• Manually close the earthing switch;
• Open the miniature circuit-breakers 25 (figure 146) positioned inside the low voltage compartment
to remove the auxiliary power supply to the panel;
• Carry out a visual inspection on the anti-ferroresonance resistance 27 (figure 142) and check for any
presence of dirt;
• Manually check correct insertion of the cabling.
Figure 142
27
7.3.2.5.3 Cleaning and checking of the fuses
• With the VT truck withdrawn, manually hook up the fuses contained in the resin tube of the voltage
transformers (figure 20);
• Carry out a visual inspection on the fuses and check for any presence of dirt;
• Remove any deposits of dust using a dry cloth that does not leave any deposits on the treated
surfaces (do not use woollen cloths).
7.3.3 Maintenance in circuit-breaker compartment
7.3.3.1 Visual inspection and lubrication of the isolating contacts
• Make the plant you want to work on safe (follow the plant safety regulations);
• Carry out a visual inspection on the top and bottom isolating contacts 21 (figure 143) in the circuit-
breaker compartment and check for any presence of dirt, humidity and signs of corrosion on the
moving parts;
• Remove any deposits of dust using a dry cloth that does not leave any deposits on the treated
surfaces (do not use woollen cloths);
• If necessary, grease the mechanical moving parts by applying a thin layer of mechanical grease for
moving parts.
Figure 143
27
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