119
Preventive Maintenance
3ADW000488R0101 DCS880 Service manual e a
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Check for tightness of heatsink terminals of units H8.
The thyristors together with the heatsinks are stacked. Every single thyristor is connected to the DC+ and
DC- busbars via flexible copper busbars. These busbars consist of 10 layers of pre-shaped sheet copper.
This construction is able to compensate for small changes in length caused by temperature rise when
current is flowing. The screw fixings between heatsink and flexible copper busbar have to withstand different
types of mechanical stress.
Therefore each fixing needs to be checked for correct torque.
Actions:
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Make sure all supply voltages are switched off, most important the supply for the power part
(armature), for the drive electronics (SDCS-POW-H01), for the converter fan and for other auxiliaries!
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Open the cabinet’s and module’s door; if needed secure them.
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Set a latching torque spanner to 25 Nm (18 lb-ft). A 17 mm nut is needed too.
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Check the torque of the screws marked within the next figure.
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Apply the torque spanner to the screw and turn right until the right torque is indicated.
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Don’t loosen the screws by a left hand turn!
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Put on a new marking, if appropriate.
