Physical Fundamental Principles - Siemens SINAMICS G130 Engineering Manual

3.6.2

Physical fundamental principles

All SINAMICS devices and system components which are designed for cabinet mounting, such as
·
line-side system components (switches, contactors, fuses, line filters, line reactors, etc.),
·
SINAMICS power units (G130 Power Modules, S120 Line Modules, S120 Motor Modules, etc.),
·
SINAMICS electronic components (Control Units, Terminal Modules, Sensor Modules, etc.),
·
Motor-side system components (motor reactors, dv/dt filters, sine-wave filters)
generate power losses in operation. These power losses (which are specified in the technical data in the relevant
catalogs and operating instructions) must be expelled from the cabinet in order to prevent an excessive heating-up
inside the cabinet and to allow the units and system components to operate within their permissible temperature
limits. Operation within the permissible temperature limits is essential in order to a) prevent shutdown on faults in
response to overheating and b) to protect the service life of components which can be shortened if they are operating
at excessive temperatures.
In the case of air-cooled SINAMICS drives (which are the focal point of discussion in this and following sections), two
different methods can be used to cool the converter cabinets:
·
Cooling by natural convection.
·
Forced air cooling using fans (forced ventilation).
These two different cooling methods and their characteristics when applied in air-cooled units are examined in more
detail below. Methods of cooling liquid-cooled units are described in section "Liquid-cooled SINAMICS S120 units" of
chapter "Fundamental Principles and System Description".
Cabinet cooling by means of natural convection
With the natural convection method, the power losses which develop inside the cabinet are dissipated to the external
ambient environment solely via the surface of the cabinet, as defined by the following equation:
Definition and meaning of the variables used in the equation:
·
P Power losses inside the cabinet
v
·
k Coefficient of heat transfer from interior to exterior of cabinet.
·
A Effective cabinet surface for transferring heat to external ambient air.
J
·
Temperature difference between interior temperature T
D
Typical values of heat transfer coefficients for converter cabinets made of varnished sheet steel are within the range
2
k = 3 W / (m • K) to k = 5.2 W / (m
value applies to circulating air inside the cabinet and still air outside the cabinet.
All heat sources inside the cabinet must be included in the calculation of power losses P
surface area of the cabinet for transferring heat to the external environment, which is dependent on the conditions of
cabinet installation, must also be taken into account.
Cabinet cooling by means of natural convection: Temperature distribution inside the cabinet and heat transfer
General Engineering Information for SINAMICS
= × D ×
P k A
V
2
• K). The lower value applies to still air inside and outside the cabinet. The upper
SINAMICS Engineering Manual – November 2015
Engineering Information
J
.
and exterior temperature T
c
Ó Siemens AG
J
( =T - T ).
D
a c a
. Furthermore, the effective
v
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