Cubicle Calculations; Thermal Protection And Automatic De-Rating - Siemens MICROMASTER 420 Reference Manual

2.11

Cubicle Calculations

The MICROMASTER 420 will operate in a temperature of 50 °C without de-rating.
Ensure that the inlet and outlet ducts are not blocked, for example by cables.
Check also that the positioning of units inside the cubicle do not obstruct natural
ventilation.
It is very important to ensure that the maximum operating temperatures are not
exceeded inside a cubicle. When installing an inverter in a cabinet, it is necessary
to calculate the heat rise. Refer to Table 2-6 for the steps in calculating this rise.
Table 2-6
1. Calculate total heat loss (P loss ) for all units inside the cabinet.
Use manufacturers' data. (See paragraph 2.19 on Page 38)
2. For a sealed cabinet, calculate temperature rise using the formula:
T rise = P loss /(5.5 x A)
Where A is the total exposed area of the cabinet in square metres.
3. For a fan cooled cabinet: calculate temperature rise using the formula:
T rise = (0.053 x P loss )/F
Where F is the air flow in cubic metres /minute.
Add the Temperature rise to the external ambient temperature. If this is greater
than the operating temperature of the inverter, additional cooling will be needed, or
the units must be de-rated.
It will also be necessary to de-rate at altitudes above 1000m. (See Figure 2-15 on
Page 24)
2.12

Thermal Protection and Automatic De-rating

The MICROMASTER 420 has comprehensive hardware and software thermal
protection.
trip if the temperature reaches 110 °C.
frequency, and output frequency of the inverter will both be reduced to reduce the
losses and current in the inverter in an attempt to prevent overtemperature trip.
It is possible to prevent this reduction and select an immediate trip if desired. See
parameters P0290, P0292 for further details.
The inverter is further protected by an Inverter I
hot the Insulated Gate Bipolar Transistors (IGBTs) are and will reduce the current
limit (P0640) when this calculation reaches 95%. (User defined in P0294). If the I
continues to rise to 100% an Inverter I
Overtemperature in the inverter is usually caused by a high ambient temperature, a
faulty or blocked fan, or blocked air inlet or outlet. Refer to Chapter 6,
Maintenance Information, for details of fan exchange.
26

Cubicle Calculations

Fitted to the heatsink is a PTC resistor that will cause the inverter to
When the heatsink reaches within 15 °C of this trip level, the switching
2
t calculation that determines how
2
t trip will occur (F0005).
MICROMASTER 420 Reference Manual
2
t
Issue A1