Power Circuit Connections Of Fixed Circuit-Breakers; Earthing; General Recommendations; Assembly Of The Connections - ABB VD4 Installation And Service Instructions Manual

Fig. 9

7.6. Power circuit connections of fixed circuit-breakers

7.6.1. General recommendations

– Select the cross-section of the conductors according to the service
current and the short-circuit current of the installation.
– Prepare special pole insulators, near the terminals of the fixed cir-
cuit-breaker or of the enclosure, sized according to the electrody-
namic forces deriving from the short-circuit current of the installa-
tion.

7.6.2. Assembly of the connections

– Check that the contact surfaces of the connections are flat, and are
free of any burrs, traces of oxidation or deformation caused by
drilling or impacts received.
– According to the conductor material and the surface treatment used,
carry out the operations indicated in table T1 on the contact surface
of the conductor.
Assembly procedure
– Put the connections in contact with the circuit-breaker terminals,
taking care to avoid mechanical stresses (traction / compression)
on, for example, the conducting busbars on the terminals.
– Interpose a spring washer and a flat washer between the head of
the bolt and the connection.
– It is advisable to use bolts according to DIN class 8.8 Standards,
also referring to what is indicated in table T2.
– In the case of cable connections, strictly follow the manufacturer's
instructions to make the terminals.
T1
Bare copper
– Clean with a fine file or emery cloth.
– Tighten fully and cover the contact surfaces with 5RX Moly type grease.
Copper or silver-plated aluminium
– Clean with a rough dry cloth.
– Only in the case of obstinate traces of oxidation, clean with a very fine grain
emery cloth taking care not to remove the surface layer.
– If necessary, restore the surface treatment.
Bare aluminium
– Clean with a metal brush or emery cloth.
– Cover the contact surfaces again immediately with neutral grease.
– Insert the copper-aluminium bimetal with surfaces shined (copper side in con-
tact with the terminal; aluminium side in contact with the connection) between
the aluminium connection and the copper terminal.
42
Racking-in
Max 25 Nm
Racking-out
T2
Recommended tightening torque (1)
Bolt
Without lubricant
M6 10 Nm
M8 30 Nm
M10 40 Nm
M12 70 Nm
M16 200 Nm
(1) The nominal tightening torque is based on a friction coefficient of the thread of
0.14 (distributed value the thread is subjected to which, in some cases, is not
negligible).
The nominal tightening torque with lubricant is according to the DIN 43673
Standards.
(2) Oil or grease. The thread and surfaces in contact with the lubricated heads.
Take into account the deviations from the general Standards table (for example,
for systems in contact or terminals) as foreseen in the specific technical
documentation.
The thread and surfaces in contact with the heads of bolts must be slightly
oiled or greased, so as to obtain a correct nominal tightening torque.
7.7.

Earthing

For the fixed version circuit-breaker, carry out earthing by means of
the special screw marked with the relative symbol. Clean and degrease
the area around the screw to a diameter of about 30 mm and, on
completion of assembly, cover the joint again with Vaseline grease.
Use a conductor (busbar or braid) with a cross-section conforming to
the Standards in force.
7.8. Connection of the auxiliary circuits
Note: the minimum cross-section of the wires used for the auxiliary
circuits must not be less than the one used for the internal cabling.
Furthermore, they must be insulated for 3 kV of test.
7.8.1. Fixed circuit-breaker
Connection of the circuit-breaker auxiliary circuits must be made by
means of the terminal box (1) (fig. 10) mounted inside the circuit-
breaker and the cables must pass through the connector (2).
Outside the connector, the cables must pass through a suitable metal
protective cover (pipe, wiring duct, etc.), which must be earthed.
2
1
With lubricant (2)
4,5 Nm
10 Nm
20 Nm
40 Nm
80 Nm