Handbook of Electrical Installation Practice - BeKnowledge

Rotating Machines 421
Flange mounted or vertical machines are usually erected on a specially designed
subframe or machined facing which itself forms the baseplate or foundation. Vertical
motors are often mounted on fabricated skirts, especially for pump drives, and
the skirts are treated as bedplates described above.
Alignment
Accurate alignment is an essential requirement if damage to bearings and flexible
couplings is to be avoided. Alignment between an electrical machine and its
prime mover or driven machine has to be established before the coupling may be
connected.
The faces of the coupling must be parallel and any separation dimension between
the faces established in accordance with coupling manufacturer’s recommendation.
The final coupling alignment would normally be established and checked using a
dial gauge (Fig. 15.24). If the machine is to be coupled to an internal combustion
engine it is necessary to remove engine spark plugs or injectors to facilitate alignment
so that the set may be turned easily by hand.
Two-bearing electrical machines are usually coupled to their prime mover or
driven machine by means of a flexible coupling. The purpose of a flexible coupling
is not to permit any misalignment but to minimise transmission of bearing shock
loadings.
Single-bearing electrical machines are coupled to their prime mover or driven
machine using a solidly bolted coupling. They cannot be connected by flexible couplings
because these are not designed for, or capable of, supporting the downward
thrust due to the weight of the machine rotor.
Mechanical erection is completed when the coupling halves are connected, but
some further checks are necessary before power can be applied. These should
include ensuring that cooling air flows are not restricted by obstructions to air
intakes or exhausts. Insufficient space between air intakes and adjacent walls can
cause overheating. Ensure that covers have been replaced and that any doors which
Fig. 15.24 Using a dial gauge to check the alignment of a flexible coupling.