Friday, March 1, 2013

Tips for Specifying A.C Motors to work in Hazardous Classifying Areas


It is a fact that The National Electrical Code, as well as the international standards establishes the general characteristics and specifications to be done at the time of developing an A. C. motor specification (also see Motor Selection Guide), it is common that engineers only identify the rated values that usually appears on characteristics motors data, but turns up that motors that will be used in classify areas as oil and petrochemical industries standards dictated that they must have two identification – rated values plaques, the first with the rated operational values:
Speed, Voltage, Power Factor, efficiency, Full load current, service factor, frame, etc.  as in the following picture
GA--502
The other plaque brings very important data that experience have thought me must people do not mention any of this at the time of purchase a motor and then when the order arrive comes along with regrets since the motor can’t be used; the other plaque indicates the type of area that it have been made to work in.
Class, Division, work group. (E.g. Class 1, Division II Groups ABCD)
Protection Type IP.
Temperature class (It’s not the same that operation temperature of the motor), this is referred to the type of gas in the atmosphere that it’s around the pump – motor package.
Start Type: DOL (Direct on-line, soft – starter, VFD - Variable Frequency Drive)
GA 502 S
All this parameters al highly important for the specification of an A.C motor as well as the general rated values, and are this characteristics the ones that will make more or less expensive the motor but the cannot be omitted. Therefore that if your to specify the replacement of a motor that have suffer damage of as well if it’s the case that is for a new installation, Care and attention its needed when the rated values and plaques data it’s been indicated in the purchase order.

The most important specifycation to be made in A.C. motors in this cases is class temperature, now lets see what it is.


Temperature class: The maximum superficial temperature of and equipment or in this case an electrical motor can not reach the ignition temperature of the atmosphere potentially explosive that it is in. This ignition temperature it’s determined in labs, and it’s considered as the lowest temperature of the equipment case, where the inflammable substance that surrounds it begins to blaze in presence of air. The characteristics of the Gases that are in the area under normal condition and non desired condition as well shall be known in order to determine the ignition point. Once it is calculated the following table is used to specify the motor, and this specification must appear on the motor rated plaque.


Temperature Class
Maximum superficial temperature
Ignition Point of the combustible material
T 1
450 oC
> 450 oC
T 2
300 oC
> 300 oC
T 3
200 oC
> 200 oC
T 4
135 oC
> 135 oC
T 5
100 oC
> 100 oC
T 6
85 oC
> 85 oC


See Spanish Post

Standards that apply to the subject:
IEC – International commission electrotechnical
60079-10-1, 60079-10-2, 60079-10-2, 60079-10-2
NFPA – National Fire Protection Association
30, 45, 496, 497, 499
NEMA – National Electrical Manufactures Association
250
PDVSA - Petróleos de Venezuela S.A.
N – 252, 90619.1.101
API – American Petroleum Institute
RP 500, RP 505
ANSI – American National Standards Institute
12.01.01, 12.10, 12.12.01

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