7.1.1 General
Increased safety is an explosive-protection technique that may only be applied to electrical equipment which does not normally contain arcing or sparking devices, or hot surfaces that may cause ignition.
In order to reduce the possibility of arcing, sparking or hot surfaces being present to an acceptably low order of probability, AS 2380.6 and AS/NZS 60079.7 specify the following rigorous requirements:
(a) Superior insulation requirements.
(b) Minimum creepage and clearance distances to avoid arcing or tracking between live parts.
(c) Special requirements for internal connections and terminal arrangements for external connections to prevent them working loose and causing sparks and arcs.
(d) Protection against the ingress of foreign bodies or moisture.
(e) Stringent temperature limits for both internal as well as external surfaces of equipment.
(f) Additional requirements for specific equipment, such as motors and luminaires.
(g) Control requirements for specific equipment to avoid excessive temperatures, e.g. in motors.
(h) Specific testing to determine a safe stall-time ratio.
7.1.2 Arcing or sparking parts
If arcing or sparking parts or components are essential to the operation of equipment, safety can only be assured by the use of suitable types of protection, such as flameproof enclosures.
Such arcing or sparking parts should comply with the requirements of the appropriate Australian Standards, e.g. AS 2380.1 or AS/NZS 60079.0 and AS 2380.2 or AS/NZS 60079.1 for flameproof enclosures.
7.1.3 Insulation
Increased safety equipment should be designed so that the likelihood of arcs or sparks occurring in normal operation as a consequence of insulation failure is minimal. As a result, AS 2380.6 and AS/NZS 60079.7 specify strict creepage and clearance distances. The high level of protection against the occurrence or arcs and sparks in service is the basis of the increased safety protection technique, because no additional form of explosion protection is used to ensure safety.
7.1.4 Temperature
Unlike flameproof enclosures, the temperature rating ‘T’ assigned to increased safety equipment relates to the internal surface temperature of equipment, rather than the external surface temperature.
For certification purposes, the limiting temperature of increased safety equipment should be determined by taking into account the condition of maximum ratings, other factors according to the type of equipment and those conditions considered by the certification
There are some types of electrical equipment, such as rotating machines, that may require special techniques to ensure safety in respect to dangerous temperatures under conditions of duty that may be variable and onerous. Such special techniques include the use of thermal protection devices, which may be used directly or indirectly to disconnect equipment from the electrical supply in the event of a predetermined temperature being attained. This predetermined value for temperature should take into account the properties of the protected equipment (e.g. the winding insulation) in addition to limitations that may be imposed by the intended application (see AS 2380.6 and AS/NZS 60079.7 for further guidance).
7.1.5 Terminals and terminations
Increased safety equipment is largely installation dependent, in that the safety of such equipment, appropriately certified, can be compromised if due care is not taken during installation. Therefore, creepage and clearance distances should be maintained and it should be ensured that terminals cannot work loose and create an arcing situation. AS 2381.6 addresses these issues by placing strict requirements on the number of conductors for each termination and various torque values appropriate to each terminal clamping screw.
Reference should also be made to certification/approval documents for any special conditions that may apply.
7.2 OWNER/OPERATOR
Unlike Group I flameproof equipment, there is no advisory schedule for the periodic overhaul of increased safety equipment. In particular, mobile and transportable equipment in a harsh underground coal mines is subjected to considerable stresses. Historically, the increased safety explosion-protection technique was limited to connection or motor terminals boxes, but recently a broader range of increase safety equipment is being utilised in the environment.
Many operators appear not to have a clear strategy for periodic, detailed inspections or overhauls of increased safety equipment that does not have a flameproof part. Therefore, the owner/operator of increased safety equipment is recommended to seek the advice of the manufacturer for a timetable on overhauls. The owner / operator may schedule overhauls to coincide with process industry major shutdowns or coal mining long wall moves.
7.3 INSPECTION/OVERHAUL
Inspection should be carried out to ensure the following criteria is met:
7.3.1 Insulation material
The insulation materials used appear to be original and in good condition.
If not original, the service facility needs to carry out assessment/testing to determine whether the insulation materials meet the requirements of AS/NZS 60079.7.
There is no evidence of deterioration due to heating, physical damage or chemical degradation.
NOTE: Chemical degradation can be a major issue in some installations, e.g. at petrochemical plants.
7.3.2 Insulation clearances
Clearances are still within the constraints specified in the certification/approval drawings or manufacturer’s data.
NOTE: If the above data is not available, refer to the requirements in AS/NZS 60079.7.
7.3.3 Insulation creepage
Creepage distances are still within the constraints specified in the certification/approval drawings or manufacturer’s data.
NOTE: If the above data is not available, refer to the requirements in AS/NZS 60079.7.
7.3.4 Physical damage
The equipment needs to be fully inspected for any signs of physical damage and compared against the certification/approval drawings or manufacturer’s data.
If any type of physical damage is uncovered, its IP rating should be tested to ensure it has not been adversely affected in addition to correcting the physical damage.
NOTE: Physical damage includes degradation due to chemical reactions.
7.3.5 Temperature sensing devices
Temperature-sensing devices are to be tested for correct operation, including the operating temperature. RTD devices should be tested using a compatible test device to ensure correct operation over its operating range.
One method of achieving this is to place the equipment inside a temperature-controlled oven and raise the temperature at a controlled rate while observing the output of the temperature-sensing device.
These tests need to be carried out on all temperature-sensing devices, including bearing temperature sensors, which may not be nominated on the certification/approval documents.
7.3.6 Terminals and terminations
All terminals require examination to determine the following:
(a) They comply with the certificate of conformity.
(b) All creepage barriers are in place and not damaged.
(c) The surface finish of barriers is as original and not scratched, which may cause creepage.
(d) They are the correct size, complying with the enclosure’s specified heat loading.
(e) Retaining devices are present, in good order and comply with the certificate of conformity.
(f) Terminal lugs and lead wires are sized correctly and crimped in an approved manner.
(g) No corrosion or degradation has occurred, due to chemical or other means.
(h) They have not been subjected to undue mechanical stress.
7.3.7 Glands
If cable glands are supplied with the equipment, ensure that the glands are suitable for use with an increased safety enclosure.
The packing in the gland should be checked to ensure that it is in good condition and retains its flexibility. It is recommended that gland packing be replaced at the time of overhaul.
If the gland is of the compound-filled type and appears to be in good condition, there is no requirement to dismantle and perform further testing other than to ensure that its attachment to the enclosure is in good condition and does not compromise the IP rating and the certification/approval documents.
7.3.8 Seals and IP rating 7.3.8.1 General
It is essential that all seals are inspected to ensure that the IP rating of the equipment is not compromised. Inspection should look for signs of physical damage, including nicks and cuts within the seal.
Seals and their material should be examined to ensure compliance with the certification/approval documents, including mounting to the enclosure.
7.3.8.2 Rubber/Neoprene-type seals
These types of seals should be examined to ensure they are pliable and without a ‘memory’.
The attachment to the enclosure should also be verified. Any concern in this regard should prompt a full replacement of the seals.
7.3.8.3 Shaft seals
Shaft seals should be examined to ensure compliance to the certification/approval documents (including sizing and fixing to the enclosure).
7.3.8.4 Equipotential Bonding
Equipment comprising multi-section enclosures require examination and testing to ensure that all parts of the enclosures are earth bonded. This is a particular issue when sealing gaskets are used between equipment compartments. Refer to AS 60079.7 for rotating machine requirements.
7.4 SPECIFIC ISSUES FOR ROTATING MACHINES 7.4.1 Rotor
Rotors should be inspected for the following:
(a) They comply with the certificate of conformity.
(b) The stator rotor gap complies with the certificate of conformity.
(c) Integrity of windings/rotor bars.
(d) If faulty, cast rotors must be replaced in their entirety.
(e) Spigot gland is manufactured from the correct material.
NOTE: This is critical to ensure that no sparking will occur if the rotor bearing collapses.
For common tests relating to all rotating machines refer to Section 5.
7.4.2 Stator
Stator winding must comply with the original manufacturer’s design unless the repairer can demonstrate that an alternative design will comply with the certification/approval documents.
Windings and their insulation systems in Increased Safety machines have some specific requirements that are detailed in AS 60079.7, such as:
(a) That windings have, as a minimum, two layers of insulation.
(b) Impregnation methods and materials include requirements for double dipping when solvent-based varnishes are used.
(c) Minimum winding wire dimensions.
(d) Specific requirements for lead connections.
(e) Requirements for embedded temperature detection devices.
7.4.3 Fans
Fans used on Increased Safety machines should comply with the requirements listed in AS 60079.0. These include the following:
(a) Have a surface resistance of not less than 1 GΩ.
(b) Thermal stability.
(c) Clearances as detailed in the certification/approval documents.
7.4.4 Overloads
It is recommended that the associated overload detection equipment be assessed, curves verified as compliant with the Ex ‘e’ motor’s certification/approval documents when an Ex
‘e’ motor is overhauled.
7.5 REPAIR
7.5.1 Enclosure repair
If an Increased Safety enclosure is structurally damaged to the point where its IP rating is compromised, it is recommended to replace the enclosure.
If repairs are undertaken, the IP rating must be verified.
7.5.2 Winding replacement
The electrical construction of increased safety equipment decisively influences the explosion safety, and the overhaul service facility needs to be in full possession of the necessary information and equipment to enable equipment’s restoration to the original or certified condition.
Unless the overhaul service facility is able to meet all the requirements of AS/NZS 60079.7 and AS/NZS 3800, the rewind should be referred to the equipment manufacturer.
Information needed to carry out a rewind includes the following:
(a) Type of winding, e.g. single layer, double layer.
(b) Winding diagram.
(c) Number of conductors per slot, parallel paths per phase.
(d) Interface connections.
(e) Conductor size.
(f) Insulation system, including varnish specification.
(g) Resistance per phase or between terminals.
NOTES:
1 Copy winding is not acceptable unless a locked rotor test is conducted to verify the tE stall time complies with the certification/approval documents.
2 Winding data should be available from the manufacturer or the certified holder. Partial rewinding is not recommended.
7.5.3 Removal of windings
Refer to Section 5 for specific requirements on removing windings, including core loss testing.
7.5.4 Repair of rotors
Refer to Section 5 for specific requirements.
7.6 FINAL VERIFICATION
Tests as detailed in AS 3800 should be carried out and recorded to ensure that the equipment meets the certification/approval documentation and is fit for purpose.
7.7 PACKAGING AND DESPATCH
When packaging Increased Safety equipment for transport, additional care must be taken to ensure that no damage could occur during transport or storage, which could have an adverse effect on the physical construction or IP rating.
7.8 REPORTING
Reporting is to be carried out as detailed in the following documents:
(a) Appendix A.
(b) AS/NZS 3800.
S E C T I O N 8 E X ‘ i ’ I N T R I N S I C S A F E T Y