Page 399 - Industrial Power Engineering and Applications Handbook

Switchgear and controlgear assemblies 13/373

Before the cabling After the cabling
Figure 13.33 Arrangement of gland plates

of cable running through the gland plate. In a segregated system, doors for the accessibility to the live parts:
the enclosure runs the full length of the conductors and provides (a) Doors which may not be opened for carrying
total shielding for the induced fields. Although the rating of cables out day-to-day operation or maintenance. Such
may not be high for the purpose of the proximity effect, the close doors may be almost the fixed type, as for a
vicinity of its phases, when not in a circular form, may cause busbar chamber or the rear panels of a front-
enough mutual induction between them, which can heat the gland
plate beyond safe limits. MS plates have been seen to melt as a operated assembly. They may be bolted to the
result of this effect leading to a severe fault. Hence the necessity frame so that, when required, they can be opened
for providing the gland plate of a non-magnetic material to eliminate only with the use of prescribed tools. This is a
the main heating constituents, hysteresis and eddy current losses. safety requirement for access to the live parts
For details on the proximity effect and magnetic shielding, refer to only by authorized persons. To provide an extra
(Sections 28.8 and 27.3.2). shroud between the door and the live buses/
parts in such cases is not mandatory.
Other requirements (b) Doors which may be opened often to carry out
1 Provision of a segregation between the adjacent day-to-day operation and maintenance. They
feeders in a modular design. should be the removable type and opened
2 Wherever a circuit breaker is to be housed, this should manually. In these cases, all parts that may still
be in a separate compartment. be live, even after the switching device has been
3 Shrouds and shutters are essential to cover all live turned OW, before opening the door must be
parts in a feeder module that may be exposed to the provided with a shroud or a shutter (this is a
operator when the feeder door is opened (see Figure mandatory requirement as discussed later under
13.3). This is a safety requirement for the operator interlocking schemes). Refer to Figure 13.3
attending the feeder. There may be two types of showing such an arrangement.