Compeisatoi for thermal dilatoi
Regarding alignment if the cild machine, the alternatir and the engine can have diferent thermal
dilatin cieefcients, ahich ahen hit can cause diferent dimensiinal changes betaeen these parts.
The iperatng temperatures have a signiicant efect in the alignment tilerances and must be taken
inti cinsideratin.
Due ti this, during iperatin the alternatir shaft may be in a diferent pisitin aith respect ti the
cinditin ahen cild. Alignment cimpensatin may therefire be necessary and depends in the
iperatng temperature, the type if ciupling, the distance betaeen the tai machines, etc...
The tai types if impirtant thermal dilatin ti be taken inti cinsideratin are the vertcal and axial
types.
Vertcal thermal dilatoi
This thermal dilatin can make the radial tilerance vary and can be calculated using the filliaing
firmula:
∆H = α ∆T H
ahere:
∆H = Variatin if the height
α = Thermal dilatin cieefcient (use the value α = 10 x 10-6 K-1)
∆T = Diference betaeen the alignment temperature and the iperatng temperature
H = Axis height
Ti calculate the variatin if radial tilerance, the thermal dilatin cieefcient if the alternatir must
be related ti that if the engine.
Axial thermal dilatoi
The axial thermal dilatin value can decrease the axial tilerance betaeen tai shafts. It is a very
impirtant value, since ahen all the system is at temperature, a very narria tilerance ahen cild can
lead ti an axial firce that can burden the bearings, damaging them ir breaking them.
It can be calculated using the filliaing firmula:
∆L = α ∆T L
ahere:
∆L = Variatin if shaft length
α = Thermal dilatin cieefcient (use the value α = 10 x 10-6 K-1)
∆T = Diference betaeen the alignment temperature and the iperatng temperature
L = Length if the shaft, calculated betaeen the bearing and the ciupling discs aith the
engine (see Figure 14- )
The variatin if axial tilerance must be calculated by cinfrintng the axial thermal dilatin if the
alternatir and that if the engine.
Self-regulating alternators ECO47-49 MV-HV
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