Installing PLC in the Zone 2 Hazardous Area

[From:来自网络] [Author:admin] [Date:12-10-16] [Hit:]

Installing PLC in the Zone 2 Hazardous Area First of all, the PLC is best installed in the air conditioned room. But, there are some cases where the PLC needs to be installed in the outdoor hazardous area. Typically, when the PLC is installed in the outdoor application, it is because of the unavailability of the cooling system, to safe the wiring, and the application is in remote area. Installing the PLC in the hazardous area is not an easy task. It has some challenge such as ventilation, heat dissipation, the hazardous area certified component etc. This short article will tell us the detail method of the PLC installation assessment in the Zone 2 hazardous area. But please take a note that this assessment is for preliminary and education purpose only, the final assessment shall be done by the PLC panel vendor and the third party certification body. There are some step to install the PLC in the Zone 2 hazardous area. Identify all the component that is needed for the application Make sure that all the component is having a Zone 2 certification Arrange the PLC with all necessary component in the required enclosure Calculate the heat dissipation of all the component inside the PLC panel or PLC enclosure Compare the PLC heat dissipation with the maximum allowable heat dissipated inside the enclosure Calculate the temperature rise inside the enclosure (due to not ventilated and not air conditioned) and make sure that it is still 10% under the PLC maximum operating temperature. 1. Identify all the component that is needed for the application Lets say we have a skid package PLC just like in the “Calculation of the PLC Panel Power Consumption and Heat Dissipation”. Typcally we will have the following component in the PLC panel: - PLC Backplane/Chassis - PLC Controller - PLC I/O Card - PLC Power Supply - PLC Communication Card - Interposing Relay - Ethernet Switch - Human Machine Interface (HMI) - AC to DC Power Supply Converter - MCB - Terminal Block 2. Make sure that all component is having a Zone 2 certification Typcally the backplane/chassis, I/O Card, power supply, and also communication card is already Zone 2 certified as a complete PLC. The hazardous protection method is Ex nA which is the “Ex e lite” that will not produce spark or arc as long as it is enclosed in the enclosure with IP 54 at minimum to prevent the water entering the electronic part and causing a spark. The Interposing Relay, Ethernet Switch, AC to DC power supply converter, and also the MCB usually is also having Ex nA protection method and is suitable for Zone 2 application and shall be enclosed in the IP 54 enclosure at minimum. The terminal block usually having the Ex e protection method which is the protection method that will not produce spark or arc as long as it is enclosed in the Ex e enclosure which have IP 54 minimum. The HMI is quite complex, it is usually involving multiple protection method at the same time such as Ex d e nA. Eventhough like that it is suitable for installation in the Zone 2 application. 3. Arrange the PLC with all necessary component in the enclosure After we red all the component certificate of the PLC panel, we can conclude that the PLC panel is requiring an enclosure with IP 54 at minimum and also it has Ex e rating at minimum. Thus we will use Ex e rated enclosure which is always having IP 54 at minimum. Take a note every installation requirement in each hazardous area certificate of the component. Some of them are oblige the user to install the devices with certain distance, certain installation way etc. Thus we must sure that all the component certificate installation guidance has been followed. Otherwise we can break the complete system certification. Below is the typical arrangement for our example above: The selected Ex e enclosure is 1000 (W) x 400 (D) x 1200 (H) stainless steel. 4. Calculate the heat dissipation of all the component inside the PLC panel or PLC enclosure After we arrange all the PLC component in the enclosure, now we shall calculate the heat dissipation of all the component inside the PLC panel. For our example above, we have been calculate the panel heat dissipation in the “Calculation of the PLC Panel Power Consumption and Heat Dissipation”. The calculation result says that the PLC panel will dissipate the 234,69 watt heat from all the PLC panel component. 5. Compare the PLC heat dissipation with the maximum allowable heat dissipated inside the enclosure After we got the PLC panel heat dissipation value, next step is compare those heat dissipation with the selected Ex e enclosure maximum heat dissipation. The maximum heat dissipation of the Ex e enclosure is available in its hazardous area certificate (ATEX, IECEX etc). In our example above, the calculated heat dissipation of the internal component of the enclosure is 234,69 watt while the maximum heat dissipation for the selected enclosure (1000 (W) x 400 (D) x 1200 (H)) is lets say 500 watt from the hazardous area certificate or as informed by the enclosure manufacturer. Thus the PLC panel is safe for hazardous area Zone 2 installation. 6. Calculate the temperature rise inside the enclosure (due to not ventilated and not air conditioned) and make sure that it is still 10% under the PLC maximum operating temperature. The PLC and the other active electronic part is having a certain operating temperature limits. In typcial we shall make sure that the heat dissipated by the PLC inside the cabinet will not make the temperature inside the panel rise above the maximum operating temperature of the PLC. As a safety margin, we set the maximum temperature inside the cabinet shall not exceed 90% of the maximum PLC operating temperature. Typically, the PLC maximum operating temperature is 60 to 70 degree celcius. We can estimate the inside PLC panel temperature rise by using the following method. Qe = Qs (Heat dissipated inside the enclosure is equal to heat dissipated to the environment with certain temperature gradient) Qe = Heat dissipation inside the enclosure Qe = 234,69 Watt Qs = Heat dissipated to the environment Qs = k x A x (Ti – Tu) K = Heat Transfer Coefficient A = Effective heat loss dissipating-enclosure surface Ti = Enclosure internal temperature Tu = Maximum ambient temperature of the enclosure The selected PLC panel was the wall mounted stainless steel 1000 (W) x 400 (D) x 1200 (H). The heat transfer coefficient for stainless steel is 6.5 W/(m2K). The effective surface area is (2*(W*D)+(W*H)+(2*(D*H)) = 2,96 m2. Thus the (Ti-Tu) can be calculated as follows: 234,69 Watt = 6,5 W/(m2K) * 2,96 m2 * (Ti-Tu) (Ti-Tu) = 12,19 K = 12,19 Celcius If the maximum ambient temperature is 40 degree Celcius, then the temperature rise inside the enclosure caused by the PLC heat dissipation is 52,19 degree celcius. The 52,19 degree celcius is still less than 54 degree celcius (90% of 60 degree celcius which is the maximum operating temperature of the PLC). Thus we can say that the PLC panel is having a suitable operating temperature for the PLC system in the above example. WARNING: the above example doesn’t count the effect of direct sun radiation. Thus, the PLC panel shall be protected from the direct sun radiation. Further analysis shall be done if the PLC panel will be placed in the direct sun radiation.

Prev:Valves Classes

Next:

CONTACT US

SHANGHAI SANZHOU AUTOMATION DASH CO.,LTD
ADD:No.2651, Waiqingsong Road, Baihe Town Qingpu District, Shanghai, 201709, P.R.C.
TEL:86-21-59748861
FAX:86-21-59747999
Website:www.szvalves.com
E-mail:info@szvp.cn