EXPO MiniPurge D770/ET, Руководство пользователя

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Expo Technologies UK
T: +44 (0) 20 8398 8011
E: sales@expoworldwide.com
Expo Technologies US
T: +1 (440) 247 5314
E:sales.na@expoworldwide.com
Expo Technologies China
T: +86 532 8906 9858
E: qingdao@expoworldwide.com
Section 4: Description and Principle of Operation
The MiniPurge
®
system is pneumatic in operation, with electrical interfaces.
Purge and pressurization is a method of protection used in Zone 1 and/or Zone 2 hazardous locations to ensure
that the interior of an enclosure is free of flammable gas. Addition of a MiniPurge
®
system allows the electrical
equipment within the enclosure to be used safely in a hazardous location.
The principle of purge and pressurization is as follows:
• Clean compressed air or inert gas is drawn from a non-hazardous location.
• The interior of the pressurized enclosure is flushed to remove any hazardous gas or dust.
• This is introduced into the pressurized enclosure to keep the internal pressure at least 0.5 mbarg above the
external pressure.
• Whilst pressurized, flammable gas cannot enter the enclosure from the environment.
Prior to switching on the power to the electrical equipment, the enclosure must be purged to remove any
flammable gas that might have entered the enclosure before pressurization. Purging is the process of removal
contaminated air and replacement with air (or inert gas) known to be free from flammable gas. The duration of
this purge process is normally ascertained by performing a purge test.
At the end of the purge cycle the system automatically switches to leakage compensation mode. The Purge
Outlet Valve is closed and the airflow is reduced but remains high enough to compensate for the leakage of air
from the enclosure whilst maintaining the minimum over pressure state.
In the event of pressure failure within the pressurized enclosure the system will raise an alarm in the form of visual
indicators and a volt free contact depending on the specification of the system. The default action on loss of
pressurization is alarm and automatic disconnect of power (A&T - Alarm and Trip). This can be changed by the
customer to Alarm Only (/AO), please refer to section titled
Main Components .
The MiniPurge
®
system incorporates a Closed Loop Automatic Pressurization System (CLAPS). This allows the
system to detect a rise or fall of the enclosure’s internal pressure and adjust the leakage compensation rate
accordingly. Pressure variations are more likely during sudden start up of large rotating electrical machines but
can also be caused by changes in running temperature. This system has been specifically designed to maintain
a stable internal pressure within the enclosure.