Assembly Of Accessories; Retightening; Connection Of The Regulating Winding Of The Transformer - ABB UZE Installation And Commissioning Manual

4.1.3 Assembly of accessories

All details which have been removed for the transport are
specified on the packing list. The openings on the tap-
changer are then sealed by transport covers.
1. Remove the transport covers.
2. Check the O-rings. Make sure they are pressed into the
bottom of the groove on the flanges.
3. Assemble the accessories. Tightening torque for the nuts
as per section 1.7.

4.1.4 Retightening

When a gasket is subjected to the pressure from the flange
bolts it will change its shape or settle. This reduces the
pressure on the bolts, making them loose.
The settling effect will increase at higher temperatures. For
this reason retightening is required.
Retighten one day after assembly. Retighten again after the
transformer has been in service for about two weeks to let the
gaskets settle at service temperature. The retightening torque
should again be approximately 90 Nm.
Retighten the dome nuts with 42 Nm before oil filling. See
section 5.1.
Neutral connection
Fig. 8. Assembly of the neutral connection.
4.2 Connection of the regulating winding of the
transformer
On UZE the winding has to be connected from the rear.
On both UZE and UZF the cable lugs can be either crimped or
brazed. The free distance between the cable lugs for adjacent
contacts must be at least 7 mm. Tightening torque is 38 Nm.
For star point design, attach the neutral connection as shown
in Fig. 8 and the connection diagram.
On UZF the top cover is intended to be used when
connecting the transformer's regulating winding leads to the
tap-changer terminals.
Remove the cover and connect the leads. Tightening torque
is 38 Nm for the cable lugs. For star-point design, attach the
neutral connection as shown in Fig. 8 and the connection
diagram. Bolt on the cover. Tightening torque is 42 Nm for the
dome nuts.
If the oil conservator is to be installed on the top of the tap-
changer, connect the regulating winding leads before installing
the oil conservator.
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