Siemens SINAMICS G130 Engineering Manual page 459

SINAMICS S120 Cabinet Modules
Engineering Information
S120 Cabinet Modules: Schematic diagram of the converter-side deionized water circuit and the Heat Exchanger Module
The pump pressure in the Heat Exchanger Module depends on the volumetric flow rate. The pressure difference
between the inflow and return flow lines of the deionized water circuit is therefore determined according to the
number of parallel-connected S120 Cabinet Modules in the circuit.
When the pump is switched off, static pressure develops in the converter-side deionized water circuit. This pressure
is generated when the deionized water circuit is filled in combination with the pressure compensation capability of the
closed pressurizer (pressure compensating air reservoir). So as to prevent cavitation damage to the pump, the static
pressure must not drop below a specific minimum value on the suction side of the pump. The recommended static
pressure for the pump of the Heat Exchanger Module is 210 kPa (2.1 bar).
When the pump is switched on, the pressure difference between the inflow and return flow lines of the deionized
water circuit is determined according to the number of parallel-connected S120 Cabinet Modules in the circuit. The
rated flow rate dV/dt (coolant requirement in l/min) required for specific S120 Cabinet Modules can be found in the
technical specifications in Catalog D 21.3. The heat sinks of the Chassis power units are designed for a pressure
drop of 70 kPa (0.7 bar). This is achieved by means of a baffle plate and applies when water (H2O) is used as a
coolant, i.e. with a pressure drop of 70 kPa (0.7 bar) at the heat sink, the rated flow rate specified in the technical
specifications of Catalog D 21.3 is reached when water is used as a coolant. For this reason, the minimum pressure
difference at the heat sinks of the Chassis power units should be at least 70 kPa (0.7 bar). The maximum pressure
difference at the heat sinks of the Chassis power units should not exceed 200 kPa (2 bar) because the risk of
cavitation or abrasion damage caused by high flow rates increases at higher differential pressures (pressure drops).
In addition to the pressure drops at the heat sinks of the Chassis power units, the pressure drops at the connecting
hoses to the flow piping (inflow and return flow), at the optional quick-release couplings (option M72) if these are
installed, and at the additional heat exchangers for units with degree of protection IP55 (option M55), must be taken
into account. These pressure drops can be similar in magnitude to the pressure drops at the heat sinks of the
Chassis power units, especially on devices with quick-release couplings or with degree of protection IP55. The
minimum pressure difference between the inflow and return flow lines of the deionized water circuit should therefore
be at least 100 - 150 kPa (1.0 -1.5 bar) when water (H2O) is used as a coolant.
The addition of anti-freezes increases the kinematic viscosity of the coolant which means that the minimum pressure
difference between the inflow and return flow lines in the deionized water circuit must be increased in order to
achieve the required rated flow rate dV/dt (coolant requirement in l/min) specified in the technical specifications of
Catalog D 21.3. It is possible to deduce the following calculation method for water containing the recommended anti-
freezes Antifrogen N, Varidos FSK or Antifrogen L from the diagrams in section "Liquid-cooled SINAMICS S120
units" of chapter "Fundamental Principles and System Description" which specify the pressure drop as a function of
the volumetric flow rate for anti-freezes in various concentrations: For water containing the minimum concentration of
anti-freeze, the pressure difference must be increased by a factor of around 1.3, and for water containing the
maximum concentration of anti-freeze, by a factor of around 1.7. This results in a minimum pressure difference
between the inflow and return flow lines of the deionized water circuit of around 130 - 200 kPa (1.3 - 2 bar) at the
minimum anti-freeze concentration, and around 170 - 250 kPa (1.7 - 2.5 bar) at the maximum anti-freeze
concentration. It can thus be ensured that a satisfactory volumetric flow rate through the deionized water circuit of the
S120 Cabinet Modules is achieved over the entire permissible temperature range of the coolant.
The pressure difference generated by the pump in the Heat Exchanger Module at very low volumetric flow rates is
around 600 kPa (6 bar). Since the pressure difference between the inflow and return flow lines of the deionized water
circuit must be between 130 and 200 kPa (1.3 - 2 bar) at the minimum anti-freeze concentration and between 170
and 250 kPa (1.7 - 2.5 bar) at the maximum anti-freeze concentration (as explained above), the pressure difference
between the inflow and return flow lines of the deionized water circuit can be reduced by a ball valve installed in the
the Heat Exchanger Module. By this means it is possible to throttle down the pressure in the deionized water circuit to
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Ó Siemens AG