Page 412 - Industrial Power Engineering and Applications Handbook

13/386 Industrial Power Engineering and Applications Handbook
periodically for any pitting or loosening. Such a the silver-plating is withered. Silver prevents
check is recommended at every six months of oxidation of copper contacts and also eliminates
operation and must be carried out meticulously, bimetallic corrosion.
particularly for aluminium busbar joints and cable
terminations. Aluminium is a highly malleable and Note
ductile metal and under high temperatures and Tarnishing (blackening) of contacts is a common characteristic of
pressures has a tendency to run out and loosen its silver-plated contacts. It is the formation of silver oxide film
grip. At locations that are critical, contaminated or which is a good conductor of heat and electricity is not a cause for
humid, or that are subject to vibrations, the period concern.
of maintenance checks may be reduced based on
experience. A logbook can also be maintained to - Clean and lubricate all the main incoming and
monitor the variance in important parameters and outgoing power contacts as well as the auxiliary
to take preventive measures during operation. sliding contacts at least once a year. Use of neutral
Draw-out components grease as noted in Section 13.6.l(iv) is recom-
- In a draw-out MCC all current-carrying compo- mended. A properly greased contact will also help
nents should be periodically checked for their to avoid a flashover.
silver-plating, proper contact area, spring pressure - For cleaning of contacts, use white petrol or carbon
and tightness of joints (this procedure can follow tetrachloride or perchloro-ethylene. Never use
the manufacturer’s maintenance schedule) or at sandpaper for it may damage the silver-coating
least during the six-monthly or yearly maintenance and also render the surface uneven which may
check ups of the busbars and the busbar joints as cause arcing and pitting during operation. While
noted above. The contacts or their springs may cleaning, care must be taken that the solvent does
be replaced when the contacts are worn out or not reach the insulating components.

Bottom frame of
the PCC or MCC

Foundation or
grouting frame

(i) Panel fixing by welding (ii) Panel fixing by bolting
Details of fastening at ‘D,’ (typical)

A ---/----

Switchgear Switchgear
assembly - - assembly
(rear) (front)
Details of fastening at ‘D2’ (typical)
Foundation frame
of the panel \

Figure 13.48(a) Illustration of a typical installation of high-rating switchgear assembly on a cable trench