Example Of Coolant Temperature Control For Condensation Prevention - Siemens SINAMICS G130 Engineering Manual

Fundamental Principles and System Description
Engineering Information
The coolant reservoir must provide adequate cooling of the coolant. Its geodetic head determines the static pressure
in the cooling system. The geodetic head must be at least 3 m to achieve the minimum required pressure of 30 kPa
(0.3 bar) at the suction side of the pump. The maximum system pressure of the cooling circuit to atmosphere must
not exceed 600 kPa (6 bar). The system pressure is displayed on the pressure indicator. The pump circulates the
coolant, whose flow area should be made of stainless steel. As regards the pressure difference between the inflow
and return flow, the criteria are the same as those applicable to closed cooling circuits.
Liquid-cooled SINAMICS S120 units in Chassis format: Recommendation for an open 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. To relieve the mechanical load on the SINAMICS
units and any motors connected to the cooling circuit, they must be connected by means of short insulating EPDM
9
hoses with an electrical resistance of > 10 Ω/m to the pipework of the cooling system. The cooling circuit of motors
and other units must, if connected to the same cooling circuit as the SINAMICS units, also be made of stainless steel
or another incorrodible material. Dirt traps retain dissolved solides of > 0.1 mm in size and prevent clogging of the
heat sinks in the SINAMICS units. The bypass valve is required for the purpose of temperature control (condensation
prevention).
1.16.6

Example of coolant temperature control for condensation prevention

With liquid-cooled units, warm air can condense on the cold surfaces of heat sinks, pipes and hoses. Condensation
water can cause corrosion and electrical damage, for example, flashovers in the power unit and, in the worst-case
scenario, can result in irreparable equipment damage. For this reason, it is essential to prevent condensation inside
the units.
As the SINAMICS units are incapable of preventing condensation when certain climatic conditions are present, the
cooling circuit must be designed such as to reliably prevent condensation. In other words, measures must be taken to
ensure that the coolant temperature is always higher than the dew point of the ambient air.
This can be achieved either by a relatively high, fixed coolant temperature that is set according to the maximum
potential ambient temperature and air humidity, or by temperature control of the coolant as a function of the ambient
temperature T and air humidity Φ, see diagram below.
a
The temperature control system adds a temperature difference ΔT to the ambient temperature T so as to ensure
L a
that the setpoint temperature T for the coolant is always at least 3°C to 5°C higher than the dew point of the
set
ambient air. The control system then compares the setpoint temperature T of the coolant with the actual
set
temperature T measured at the coolant inlet in the SINAMICS units (which is supplied to the control system via
act
parameter r0037[19]), and calculates the control deviation x. The value of x is passed to a 3-step controller which
operates in combination with an actuating motor M to regulate the flow by means of a 3-way valve (bypass valve) and
thus control the coolant temperature. The 3-step controller has three switch positions for controlling the actuating
motor:
● +y1 for forward motion
● 0 for standstill
● -y1 for backward motion.
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