Siemens SINAMICS G130 Engineering Manual page 124

Fundamental Principles and System Description
Engineering Information
is required. The pump is necessary to circulate the coolant and its flow area should, ideally, be made of stainless
steel. The permissible differential pressure of the cooling circuit to atmosphere must not exceed a maximum of 6 bar.
This must be ensured by a pressure-relief valve. The pressure indicator works as a visual control of the differential
pressure of the cooling circuit to atmosphere. The pressure difference inside the cooling circuit between inflow and
return flow, which is produced by the pump, must, on the one hand, be large enough to reach the coolant flow rate
required for the cooling of the SINAMICS units. On the other hand, however, the pressure difference inside the
cooling circuit must not be unnecessarily large as the risk of equipment damage through cavitation and abrasion is
considerably increased by a high coolant flow rate. Therefore, the differential pressure across each heat sink should
be between 1.0 bar and a maximum of 2.0 bar. The liquid-cooled units are designed in such a way that a differential
pressure of 0.7 bar occurs when the rated coolant flow rate is reached
SINAMICS S120 Liquid-Cooled units in chassis format: Recommendation for a closed cooling circuit
The connecting pipes between the individual components of the cooling circuit should be made of stainless steel or
ABS plastics. The seals must be chloride, graphite and carbon-free. For mechanical decoupling the SINAMICS units
must be connected to the piping of the cooling system by short, felixible EPDM hoses. Ideally, the heat exchanger,
like the piping, should be made of stainless steel. However, if absolutely necessary, copper heat exchangers may be
used, as long as the cooling circuit is closed and the correct concentration of inhibitors or anti-freeze is used. Dirt
traps retain dissolved solides > 0.1 mm and prevent the blocking of the heat sinks in SINAMICS units. The inspection
glass is recommended for diagnosing clouding or discolouration of the coolant, which indicates that corrosion and
wear may have been occured. The bypass valve is required in case a temperature control is required for the
protection against condensation.
Open cooling circuit for SINAMICS S120 Liquid-Cooled units
The diagram on the next page shows an example of a typical open cooling circuit. This type of cooling circuit must
not be used with units with aluminium heat sinks, through which the coolant directly flows, due to high oxygen levels.
It can, therefore, only be used with units with integrated stainless steel heat exchangers.
The geodesic height of the coolant reservoir determines the the differential pressure to atmosphere in the cooling
circuit and must be at least 3 m, in order that the minimum pressure of 0.3 bar on the suction side of the pump can be
reached. The pump circulates the coolant, whose flow area should be made of stainless steel. With regard to the
pressure difference between inflow and return flow, the same criteria apply as for closed cooling circuits.
SINAMICS Engineering Manual – May 2008
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