Overhaul; Required Tools And Materials; Procedure; Preparations - ABB UC series Maintenance Manual

3. Overhaul

WARNING
Before any work is carried out on the on-load
tap-changer: Make sure that the transformer is
disconnected and that earthing is properly carried
out. Obtain a signed certificate from the engineer in
charge.

3.1 Required tools and materials

Necessary for the overhaul is the following equipment:
– Standard hand tools (keywidth up to 19 mm)
– Standard set of combination spanners
– Pipe wrench
– Thickness gauges (0.40; 0.50; 1.20 mm)
– Small hammer
– Sliding caliper
– Spring balance (10 N)
– Watch (with hand for seconds)
– Oil can
– Ohmmeter (1-30 Ohm)
– Air pump with pressure gauge (0-200 kPa) and connection
to R 1/8" male thread
– Telpher (at least 150 kg lifting force)
– Empty and clean barrels for transformer oil (calculate with
max. 225 l for each diverter switch housing)
– Oil draining and filtering equipment with connections
– Test equipment according to IEC 00156, 1995-08
– Two buckets (approximately 10 l)
– Rags (lint-free)
– 50 l of new transformer oil (class II according to IEC 00296,
2012-02)
– Standard lithium complex or calcium complex grease
with EP additive NLGI 2. Temperature range from -30°C
to +100°C. Suggested products: Dow Corning Molykote
Multilub, Gulf Crown EP 2 or similar.
– Oil (for plain ball and roller bearings)
– Degreasing agent
– Protective glooves, oil proof
– Dimension drawing for the on-load tap-changer
– Pen and note pad
– Set of spare contacts (see the spare parts list)
– Brass shims according to Fig. 7 (12 pcs)
– New O-ring for the cover (435x8)
When restoring the gas cushion. (section 3.17.5):
– Small oil pump with connection to the oil valve
– Empty and clean barrel for transformer oil ( ~ 15 l)
– Box wrench, 6 mm
14 Maintenance guide UCG | 1ZSE 5492-124 en, Rev 6
When measuring contact timing, add this equipment:
– See section 3.18
When replacing contacts (chapter 4), add this equipment:
– Universal pliers
– Pipe wrench
– 4 mm mandrel
– 5 mm brass mandrel, 320 mm long
– Steel ruler
– Round file
– Torque wrench (10 Nm)
– Piece of wood, 50 mm thick, 400 mm long

3.2 Procedure

The overhaul procedure includes the following points:
– Oil testing and oil draining
– Lifting and cleaning the diverter switch
– Cleaning the diverter switch housing and the oil filter (if any)
– Oil filtration
– Checking the breathers
– Checking the contact positions
– Checking the contact wear
– Checking the transition resistors
– Checking before lowering the diverter switch
– Lowering the diverter switch
– Checking the pressure relay
– Lubrication
– Checking the motor-drive mechanism (see the maintenance
guide for motor-drive mechanisms)
– Oil filling
– Check of contact timing
– Putting into operation

3.3 Preparations

If the on-load tap-changer is oil filled under
atmospheric pressure, a waiting period of three
hours is needed before energizing. To save out of
service time of the transformer, carry out all work on
the on-load tap-changer and the oil filling before the
maintenance of the motor-drive mechanism is started.

3.3.1 On-load tap-changer position

Note the position of the on-load tap-changer to enable restart
of the transformer in the right tap position.