Working Group on ATEX
ATEX_WG/15/1/04
OPINION ON ATEX WG/13/2/09:
Motor protection for Category 3 motors - DE proposal
Question from the Danish mirror ATEX standardisation committee to ATEX ADCO
Background:
In Denmark there has been a discussion on the issue of motor protection in relation to ATEX – or to be more precise: Is motor protection for category 3 motors covered by the ATEX Directive?
In 94/9/EC, Chapter 1, Article 1, 2nd paragraph, it is stated:
Here we normally regard intrinsic safe barriers, motor protections, thermistor relays, Variable Speed Drives (VSD) as “safety devices, controlling devices and regulating devices”.
In 94/9/EC Annex 1, 2. Equipment group II (c) it is stated:
Equipment in category 3 ensures the requested level of protection under normal operation.
The question raised by Denmark is:
Is an overload of a motor considered to be “normal” operation?
Answer: No with respect to the duty types S1 and S2, Yes with respect to duty types S3 to S10
The technical specification and requirement of the rotating machineof category 3 is given in the harmonised standard EN 60079-15:2010, item 8 “Supplementary requirements for non-sparking electrical rotating machines”, 8.1 “General”:
The duty type S1 and S2 is more or less defined as starting of the electrical machine not more than once a day.
According to the industrial standards IEC/EN 60034-series the manufacturer has to indicate the duty type on the name plate of the motor.
This requirement and specification is established over the last decades and the temperature tests of the electrical machines category 3 didn´t include the over temperature during starting or stalled conditions.
Within the TC 31 WG 27 “electrical machines” is was agreed that only for electrical machines with the type of protection increased safety “e” the additional temperature rise during starting and stalled conditions of the stator and rotor shall be measured and considered to determine the temperature class.
Other overload possibilities like reduced cooling through dirt or external sources of heat shall be covered by the user of the equipment (99/92/EC and not harmonized standards like EN 60079-14 and -17).
Additional remark:
The EN 60079-14 “Electrical installations design, selection and erection” requires in item 11 “Rotating electrical machines”,
11.1General
Rotating electrical machinery shall additionally be protected against overload unless it can withstand continuously the starting current at rated voltage and frequency or, in the case of generators, the short-circuit current, without inadmissible heating. The overload protective device shall be:
a)a current-dependent, time lag protective device monitoring all three phases, set at not more than the rated current of the machine, which will operate in 2 h or less at 1,20 times the set current and will not operate within 2 h at 1,05 times the set current, or
b)a device for direct temperature control by embedded temperature sensors, or
c)another equivalent device.
Applications of electrical machines in hazardous areasare protected against overload. The aforesaid protection devices for category 3 (zone 2) applications fulfil the common industrial requirements and are not to be considered safety device according to the ATEX directive.