ABB 500 Series, Руководство строителя

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104
Requirements
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The relays are designed for a maximum ambient temperature of 55
°
C at rated voltage.
The permissible ambient temperature stated for a relay refers to the average temperature
surrounding the relay itself and not the temperature in the control room, where the re-
lay’s cubicle or panel is located.
If a relay is mounted in a cubicle, case or other sealed enclosure, consideration must be
given to the increase in temperature, resulting from the power losses in the equipment.
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The maximum permissible ambient temperature for relays mounted in a case or cubicle
is, in reality, less than the specified 55°C due to temperature rises in the case and cubi-
cle.
The temperature rise must be considered when designing control rooms. The tempera-
ture rise for the room ambient temperature compared to the relay ambient temperature
could as high as 15°C if the maximum permissible power losses given in
table 60 are
applicable.
The actual power losses will generally be less than the maximum permissible values
and the temperature rise will be less than 15°C. With the maximum permissible room
ambient temperature corresponding to +55°C, the permissable relay ambient tempera-
ture could be +40°C.
If the room temperature is higher, it is necessary to keep the increase less than 15°C.
This can be acheieved either by mounting the equipment in several cubicles or cases in
order to reduce the supplied power losses per cubicle or case, or by improving cooling
through increased natural ventilation or by forced ventilation using a fan.
The total power losses of the relays incorporated in a case or cubicle are usually too low
to cause a 15°C temperature increase. However, there are two situations when it may be
necessary to observe the total power losses and to rearrange the relaying equipment. It
may then also be necessary to reduce the total losses per frame or cubicle.
The first situation is when the auxiliary voltage supply is 220 or 250 V dc for several
voltage or current measuring relays (2-3 pcs) with a fairly high power consumption, po-
sitioned in the same equipment frame or in equipment frames mounted close to each
other. It is not possible to fill all positions in a cubicle or a rack or otherwise to pack the
above relays too closely and still stay within the 15°C rise in the air surrounding the re-
lay.