Hazardous area motor/drive (SIEMENS_English)
- 25/07/2018/ 10:58:39
CÁC NGUYÊN TẮC BẢO VỆ ĐỘNG CƠ / ĐỘNG CƠ TỪ NGUYÊN TẮC / CHỌN LỰA CHỌN TỐI ƯU CỦA ĐỘNG CƠ PHÒNG NỔ
Abstract - This paper will provide an overview of hazardous area classifications including the implications of the latest IEC standards and the LV/HV motor & drive protection principles of ‘nonsparking’, ‘increased safety’, ‘flame proof’ and ‘pressurised’. The relative advantages for each technique will then be discussed for different scenarios such as atmosphere, overload, starting, inverter operation, size, weight, flexibility and cost.
Index Terms – Hazardous Area, Protection, Motors, Increased Safety, Flame Proof, Non-Sparking, Purge.
This paper will cover hazardous area basics, a description and comparison of motor Ex protection
types followed by advice on matching drives to Ex motors and a cost evaluation.
II. HAZARDOUS AREA MOTORS & DRIVES
A. Ex-protection in Electrical Apparatus
Three components are required to make a hazardous situation: - flammable material, oxygen and an ignition source.
B. Definition of Zones
Zones are defined on the probability of a hazard occurring in that area. Zone 0 which has a permanent threat of an occurrence is generally not suitable for any sort of electrical machine.
Risk minimization – basic principles according to EN 1127-1.Protection measures have to be undertaken in the following sequence:
Primary Ex-protection Prevent hazardous atmospheres
- Limit concentration of flammable material
- Inertization (add Nitrogen, Carbon Dioxide)
Secondary Ex-protection: Avoid every potential ignition source
Tertiary Ex-protection: Limit the consequences of an explosion to a harmless
Protection methods for electrical machines are part of the secondary precaution to avoid every potential ignition source
D. Classification of Electrical Equipment
In the Equipment Category designations M means Mines, G means Gases and D means Dust. This
paper will only focus on the G Gases category.
In approximate terms the Explosion Protection Levels (EPL) Ga, Gb, Gc correspond to the Equipment
Categories 1G, 2G and 3G which align with the Zones 0, 1 and 2. The latest IEC standards mean that nA
(non sparking) will become ec (for EPL increased - zone 2); e (increased safety) will become eb (for EPL
high - zone 1) and d (flameproof) will become db (for EPL high – zone 1). This terminology is mandatory
E. Classification of Gases and Vapours
Hydrogen is a very combustible gas but has a high ignition temp. The higher the gas combustibility the
lower the Minimum Ignition Energy (MIE) and the lower the Minimum Ignition Current (MIC) for intrinsic
safety circuits; and the smaller the Maximum Experimental Safe Gap (MESG) for Ex d machines.
The higher the ignition temperature; the higher the allowable surface temperature; and the lower the
permissible temperature class.
IIB gas group and T3 (200°C) temperature class motors are by far the most common.
Ingression protection to IP55 - dust protected and water jets is standard for all types of Ex motors which
is equivalent to NEMA 3. IP56 - dust protected and heavy seas are also common. Dust tight IP65 is
required for IIIC conductive dust and is possible for roller bearing HV motors.
F. Protection Classes
Electrical machines use different protection methods than monitoring devices. However motors may have
installed monitoring devices that require separate protection.
G. Non Sparking “nA” in future “ec”
According to EN 60079-15 this is an explosion protection type in which the risk of ignition sources
occurring during normal operation is minimised by utilising additional methods which can be:
nA – non-sparking
nC – enclosed break
nL – limited energy
nR – restricted breathing
nA is the most appropriate method of protection for electrical machines. In future nA (non sparking) will
become ec for Equipment Protection Level (EPL) - increased - zone 2. That is Ex n motors can only be
used in zone 2.
A rotor design ignition risk assessment is required for Ex n motors >100kw and other than S1 or S2
operating modes. A stator winding ignition risk assessment is required for motors >1kV and other
than S1 or S2 operating modes. (EN 60079-15)