Content
1. Introduction ..........................................................................................................................9
1.1 General .........................................................................................................................9
1.2 Maintenance schedule ..................................................................................................10
1.2.1 Inspection ...............................................................................................................10
1.2.2 Overhaul .................................................................................................................10
1.2.3 Contact replacement ..............................................................................................12
1.3 Tightening torque ..........................................................................................................12
2. Inspection .............................................................................................................................13
3. Overhaul ...............................................................................................................................14
3.1 Required tools and materials .........................................................................................14
3.2 Procedure .....................................................................................................................14
3.3 Preparations .................................................................................................................14
3.3.1 On-load tap-changer position .................................................................................14
3.3.2 Disconnection and earthing of the transformer ........................................................15
3.3.3 Oil volumes and lifting heights .................................................................................15
3.3.4 Recommended set of spare parts...........................................................................15
3.4 Oil testing and oil draining .............................................................................................15
3.5 Lifting and cleaning the diverter switch ...............................................................................16
3.6 Cleaning .......................................................................................................................17
3.6.1 Cleaning the diverter switch housing .......................................................................17
3.6.2 Cleaning the oil filter in the conservator pipe (if any) ................................................17
3.7 Oil filtration ....................................................................................................................17
3.8 Checking of the breathing device ..................................................................................17
3.9 Checking the contact positions .....................................................................................18
3.10 Checking the contact wear .........................................................................................20
3.11 Checking the transition resistors .................................................................................20
3.12 Checking before closing ..............................................................................................20
3.13 Installation of the diverter switch .................................................................................20
3.14 Checking and replacing supervisory equipment ..........................................................21
3.15 Lubrication of the on-load tap-changer and the drive shaft system ...................................22
3.16 Checking of the motor-drive mechanism .....................................................................22
3.17 Oil filling ......................................................................................................................22
3.17.1 Filling methods and restrictions .............................................................................22
3.17.2 Before filling ..........................................................................................................22
3.17.3 Filling at atmospheric pressure..............................................................................22
3.17.4 Oil level .................................................................................................................22
3.17.5 Restoring the gas cushion ....................................................................................23
3.17.6 Waiting period ......................................................................................................24
3.18 Check of contact timing ..............................................................................................24
3.19 Putting into operation ..................................................................................................24
