IEC 60079-0 - Explosive atmospheres -- Part 0: Equipment - General requirements EN 60079-0 - IEC 60156 - Insulating liquids - Determination of the breakdown voltage at power frequency -
General
Liquid immersion protection involves submerging Ex Equipment or its components in a protective liquid, ensuring that any explosive gas atmosphere present above the liquid or outside the enclosure remains unignited.
The Ex Equipment is designed to maintain the required level of protective liquid, which is crucial for safety This is accomplished through the use of monitoring devices, indicators, or level control safety devices that feature an automatic shut-off mechanism, tailored to the specific Equipment Protection Level needed.
In compliance with IEC 60079-0, it is assumed that all electrical equipment meets the necessary industrial requirements The IEC 60079 series of standards serves to enhance these industrial requirements.
Levels of protection and requirements of electrical equipment
Level of Protection
Electrical equipment with liquid immersion “o” shall be either: a) Level of Protection “ob” (EPL Gb or Mb); or
IEC 60079-6:2015 © IEC 2015 – 9 – b) Level of Protection “oc” (EPL Gc)
The requirements of this standard shall apply to all levels of protection unless otherwise stated.
Requirements for Level of Protection “ob”
Electrical circuits and components that are liquid-immersed in accordance with this standard are deemed non-ignition capable during normal operation and anticipated malfunctions, and are classified with a Level of Protection “ob” (EPL Gb or Mb).
A liquid level indication according to 4.7 is required
Switching devices with a liquid immersion level of protection "ob" must meet specific requirements: a sealed enclosure must pass an overpressure test at four times the prescribed pressure Electrical equipment with switching devices rated at 2 kVA per contact or less is exempt from further testing, while devices rated above 2 kVA must demonstrate that pressure increases or excessive decomposition products do not compromise their protection, as per tests outlined in section 6.1.5 Additionally, the equipment should be rated for a prospective short circuit current of 32 kA, unless otherwise indicated.
Disconnectors and manual tap selectors, above 1 000 V, shall be lockable and provided with a warning according to 7 i) In addition, information on their use shall be included in the instructions.
Requirements for Level of Protection “oc”
Electrical circuits and components that are liquid-immersed in accordance with this standard are deemed non-ignition capable during normal operation and expected occurrences, and are classified with a Level of Protection “oc” (EPL Gc).
Ex Equipment containing switching devices operated in the protective liquid, rated at 10 kVA per contact or less, are permitted without further test For switching devices rated above
10 kVA per contact, neither pressure increases nor excessive decomposition products shall invalidate the type of protection as demonstrated by tests in accordance with 6.1.5.
Switching device
Switching devices are only permitted for a.c circuits where the working voltage of the switch does not exceed the values given in Table 1 Switching devices for d.c circuits are not permitted
Level of Protection “ob” “oc”
Working voltage of switching device 1 000 V r.m.s a.c 6,6 kV r.m.s a.c.
Creepage and clearance
Electrical circuits and components designed for immersion in protective liquids must comply with industrial standards for creepage and clearance distances in air prior to immersion In cases where the industrial standard allows for different pollution degree options, pollution degree 2 should be assumed.
Liquid containment enclosures
General
The chemical resistance against the protective liquid shall be documented by the manufacturer
NOTE It is not a requirement of this standard that conformity to the chemical resistance against the protective liquid be verified
The enclosures shall be subjected to the type tests as specified in Clause 6 for sealed and unsealed enclosures respectively
Connection bushings provided for termination of the electrical conductors shall be considered as part of the enclosure and subject to the requirements of this clause.
Sealed enclosures
Sealed enclosure covers can be either continuously welded or secured with a gasket, and when using a gasket, the cover must include special fasteners in compliance with IEC 60079-0.
Equipment featuring a sealed enclosure must include a pressure-relief device, which the manufacturer sets to operate at a minimum pressure of 10 kPa Enclosures that are permanently sealed during manufacturing should show visible signs if opened Additionally, the enclosure must be marked according to the specified guidelines.
NOTE Suitable techniques that can provide visible evidence of being opened are, for example, welding, soldering, cemented joints, rivets, cementing of screws, or lead-seal safety-wiring of screws.
Unsealed enclosures
An unsealed enclosure must be designed to allow gases or vapors from the protective liquid to escape through a breathing device equipped with an appropriate drying agent It is essential for the manufacturer to outline the maintenance requirements for this drying agent.
Outlet of breathing device or pressure relief device
The breathing device outlet for unsealed equipment and the pressure relief device outlet for sealed equipment must be oriented downward and provide a minimum protection rating of IP66, as specified in IEC 60529.
Enclosures intended to be opened
Enclosures intended for access must feature sealing methods that can be renewed without causing damage during equipment repairs, refills, and resealing Additionally, these enclosures should be clearly marked in accordance with section 7 d).
Determination of the maximum/minimum criteria of the protective liquid
The following criteria shall be specified: a) the maximum and minimum level of the protective liquid; b) the maximum working angle, from the horizontal, of the equipment;
Immersion depth
Live components of electrical equipment must be submerged to a specified depth as outlined in Table 2, ensuring they are fully immersed in the protective liquid at the lowest possible liquid level, regardless of the internal equipment's orientation.
No switching device With a switching device
≤ 13 640 V 50 mm – a When determining the required values for depth of immersion, the working voltage may be higher than the voltage in the table by a factor of 1,1 (see Note)
The factor of 1.1 acknowledges that in various locations within a circuit, the operating voltage matches the rated voltage Additionally, it indicates that several commonly used rated voltages can be effectively managed by this 1.1 factor.
Protective liquid level indication
General
Protective liquid level indicating devices must be installed to ensure that the liquid level in each individual liquid-filled compartment can be easily monitored during operation.
The permissible maximum and minimum protective liquid levels in normal service must be clearly marked, considering the effects of expansion and contraction due to operational temperature changes across the full ambient temperature range specified by the manufacturer.
The protective liquid level indicating device must be clearly marked to show the appropriate filling levels for electrical equipment, based on the manufacturer's specified filling temperature conditions Additionally, a nearby label should be included to provide complete details on the filling conditions.
The protective liquid level indicating device must be positioned to ensure that the minimum indicated level of the protective liquid remains above the level required to meet section 4.6 This positioning should consider the effects of expansion and contraction due to operational temperature variations across the entire ambient temperature range specified by the manufacturer.
The manufacturer shall prepare documentation to show that transparent parts will retain their mechanical and optical properties when in contact with the protective liquid
For non-sealed equipment, a dipstick can be utilized as long as it remains securely in its measurement position during normal operation and complies with the ingress protection requirements outlined in section 4.5.1 Additionally, a warning marking must be placed nearby in accordance with section 7 g).
Remote-indicating protective liquid level indicator
For a remote-indicating protective liquid level indicator, the switching element must be positioned lower than the sensing element by a specified dimension, as outlined in Table 2, or it must be safeguarded by an appropriate protection type If the manufacturer does not supply the remote-indicating liquid level indicator, the certificate number must include the "X" suffix in line with IEC 60079-0, and the Specific Condition of Use should detail all essential information needed for user compliance with the standard's requirements.
Safety devices for Level of Protection “ob”
For Level of Protection "ob" with switching devices, a protective liquid level safety device must monitor the protective liquid level and automatically disconnect power if the oil level falls below the minimum permitted threshold The switching element of the safety device should be positioned lower than the sensing element by at least the dimensions specified in Table 2, or it must be safeguarded by an appropriate type of protection for the application If the manufacturer does not supply the safety devices, the certificate number must include the "X" suffix as per IEC 60079-0, and the Specific Condition of Use must detail all necessary information for users to ensure compliance with this standard.
Safety devices for these applications typically exhibit a fault tolerance of 0 and a safety integrity level (SIL) of 1, as outlined in EN 50495 A project is underway to develop an IEC standard derived from EN 50495, aimed at establishing comprehensive requirements for these safety devices.
Temperature limitations
General
The maximum permissible temperature for equipment or parts of equipment shall be equal to the lower of the two temperatures determined by 4.8.2 or 4.8.3
Maximum Surface Temperature
The temperature at the surface of the protective liquid or any accessible point on electrical equipment in an explosive gas atmosphere must not exceed the specified limit for its temperature class or maximum surface temperature, with a maximum allowable temperature of 200 °C.
Flashpoint of the protective liquid
The stated minimum flash-point (closed cup) for the protective liquid used shall be at least
25 K greater than the temperature at the free surface of the protective liquid and the temperature of the internal components immersed in the liquid.
Field wiring connections to liquid immersion equipment
Liquid immersion is not a recognized method for protecting field wiring connections Instead, bushings must be utilized for connections that pass through the equipment wall, as direct entry is prohibited.
The field wiring connections shall be protected with a type of protection suitable for the application.
Constructional elements of enclosures
Operating rods, shafts etc
Enclosures containing operating rods, shafts, and similar components must adhere to specific testing requirements: tests 6.1.1 and 6.1.2 for sealed enclosures, and test 6.1.3 for unsealed enclosures These tests are essential to ensure compliance and safety.
IEC 60079-6:2015 © IEC 2015 – 13 – with such elements in place Operating rods or shafts used in a sealed enclosure shall be subject to a conditioning of 500 operations prior to the tests of 6.1.1 and 6.1.2
Devices for draining of liquid
Devices for draining the liquid shall be secured against inadvertent removal
Protective liquid specification
The protective liquid must be a mineral oil that meets IEC 60296 standards, a silicone liquid compliant with IEC 60836, a synthetic organic ester liquid of Type T1 according to IEC 61099, or any liquid that satisfies the specifications outlined in section 5.2.
NOTE The future use of natural ester liquids per IEC 62770 is under consideration.
Detailed alternative specification
The alternative protective liquid must meet specific criteria: it should have a fire point of at least 300 °C as per ISO 2592, and a flash point (closed cup) that is at least 25 K above its free surface temperature according to ISO 2719 Additionally, the liquid's kinematic viscosity must not exceed 100 cSt at 25 °C, determined by ISO 3104 It should also possess an electrical breakdown strength of no less than 30 kV, as specified in IEC 60156, and a volume resistivity at 25 °C that meets the required standards.
The electrical insulation resistance must be at least \$1 \times 10^{12} \, \Omega \times m\$ as per IEC 60247 The pour point should not exceed the lower limit of -30 °C or 10 K below the minimum ambient temperature of the equipment, determined according to ISO 3016 The acidity, measured as the neutralization value, must not exceed 0.03 mg KOH/g in accordance with IEC 62021-1 Additionally, the protective liquid should not negatively impact the properties of any materials it contacts Oxidation stability must remain below 0.15% sludge, as specified by IEC 61125 The sulphur content must be verified as non-corrosive according to IEC 62535, and the water content should not surpass 35 ppm, following IEC 60814 standards.
NOTE It is not a requirement of this standard that conformity to the specification of the protective liquid be verified.
Group I equipment
For Group I equipment, mineral oils are not acceptable.
Liquid contamination and gassing that may result from arcing
When switching devices are integrated into electrical equipment, they can contaminate the protective liquid Therefore, it is essential to establish maintenance guidelines that include procedures for cleaning, filtering, or replacing the protective liquid after a specified number of normal switching operations and after fault current interruptions.
Total volume of the protective liquid
The documentation following IEC 60079-0 must detail the total volume of the protective liquid, specifying both the maximum and minimum volumes necessary to uphold the required levels outlined in section 4.6.
Type tests
Overpressure test on sealed enclosures
For Level of Protection "ob" with a switching device exceeding 2 kVA per contact, an internal pressure equal to four times the pressure relief device setting must be applied For all other enclosures, the required internal pressure is 1.5 times the pressure relief device setting The test pressure must not be less than 150 kPa, and the pressure should be maintained for a minimum of 60 seconds Additionally, the entry of the pressure relief device must be sealed throughout the testing period.
The test is deemed satisfactory if the enclosure shows no damage or permanent distortion at its conclusion, ensuring compliance with section 4.6.
For these tests, it is essential to use a non-compressible hydraulic medium Utilizing a compressible medium, such as air or inert gas, can lead to the failure of the enclosure, posing risks of personal injury or property damage.
Reduced pressure test on sealed enclosures
The internal pressure of the enclosure must be decreased by at least the amount corresponding to the pressure change caused by lowering the protective liquid level from its maximum to minimum permissible limits, while also accounting for any specified ambient temperature variations.
At the end of 24 h, any increase in pressure shall not exceed 5 %.
Overpressure test on unsealed enclosures
A pressure equal to 150 kPa, with the breather sealed, shall be applied internally The period of application shall be at least 60 s
The test is deemed satisfactory if the enclosure shows no damage or permanent distortion that negatively impacts its compliance with sections 4.5.3 and 4.5.5.
For these tests, it is essential to use a non-compressible hydraulic medium Utilizing a compressible medium, such as air or inert gas, can lead to the failure of the enclosure, posing risks of personal injury or property damage.
Maximum temperature
A sample of “o” equipment shall be subjected to a type test to ensure that the temperature limits specified in 4.8 are not exceeded
For “o” equipment without an external load, the test shall be carried out in accordance with the temperature measurements of IEC 60079-0
For “o” equipment with an external load, the test shall be carried out for Level of Protection
“ob” by adjusting the current to 110 % of the rated current and for Level of Protection “oc” at
100 % of the rated current in normal operation and at the maximum rated duty cycle
Equipment with non-linear external loads, input power control, or complex failure modes presents challenges in determining maximum temperatures during malfunction conditions.
Switching Tests
Electrical switching tests must be conducted in accordance with relevant IEC industrial standards, ensuring that the equipment is in its design configuration and that the protective liquid is at a minimum level Upon completion of the tests, it is essential that there is no release of the protective liquid and that the required creepage and clearance distances remain intact Additionally, the protective liquid must demonstrate an electrical breakdown strength of at least 30 kV, as specified by IEC 60156.
Routine tests
Sealed enclosures
Each sealed enclosure must undergo two sequential tests: the overpressure test outlined in section 6.1.1 However, this routine test can be skipped for non-welded enclosures if the equipment meets the acceptance criteria in section 6.1.1 during type testing at four times the pressure relief device setting.
For testing, it is essential to use a non-compressible hydraulic medium to prevent personal injury or property damage, as using a compressible medium like air or inert gas can lead to enclosure failure Additionally, the test outlined in section 6.1.2 or a comparable accelerated test at a lower pressure must be conducted, with thorough documentation of calculations to ensure that the test meets the same leakage threshold as the 24-hour test.
Unsealed enclosures
Unsealed enclosures must undergo the testing outlined in section 6.1.3 However, for enclosures that are not welded, this routine test may be waived if the equipment meets the acceptance criteria specified in 6.1.3 during type testing at a pressure of 600 kPa.
For these tests, it is essential to use a non-compressible hydraulic medium Utilizing a compressible medium, such as air or inert gas, can lead to the failure of the enclosure, posing risks of personal injury or property damage.
Ex Equipment or Ex Components of liquid immersion "o" must be marked according to IEC 60079-0, including essential details such as the type of protective liquid, pressure relief device settings, and specific warnings regarding enclosure sealing Additionally, markings should indicate the minimum and maximum levels of protective fluid, filling conditions as specified by the manufacturer, and a warning for dipstick replacement after use If applicable, the permitted prospective short-circuit current of the external electrical supply should also be noted, particularly for equipment designed for short-circuit currents below 32 kA.
“Permitted supply short-circuit current: 10 kA”;
– 16 – IEC 60079-6:2015 © IEC 2015 i) “WARNING – Operate only at NO LOAD” according to 4.2.2
Ex Equipment or Ex Components must be labeled with "ob" for EPL Gb or Mb, or "oc" for EPL Gc, in accordance with the updated standards, replacing the previous "o" marking for EPL Gb as specified in IEC 60079-0.
All liquid-immersed “o” Ex Equipment must include instructions as specified by IEC 60079-0, detailing the frequency and type of protective fluid replacement, guidelines for disconnectors and tap selectors, maintenance requirements for the drying agent in unsealed enclosures, and procedures for cleaning, filtering, or replacing the protective liquid after a specified number of normal switching operations or following fault current interruptions.
Ex Equipment having type of protection “o” shall be installed in accordance with the following:
• Level of Protection “ob” equipment may be installed in locations requiring equipment suitable for EPL “Mb” “Gb” or Gc
• Level of Protection “oc” equipment may be installed in locations requiring equipment suitable for EPL Gc
• The field wiring connections shall be protected with a type of protection suitable for the application
• Liquid immersion is not an accepted Type of Protection for field wiring connections Direct entry is not permitted
NOTE The selection and erection of the equipment requirements are found in IEC 60079-14 and are the responsibility of the user Until IEC 60079-14 contains sufficient information, this Annex A provides information
The inspection requirements of IEC 60079-17 are supplemented by those shown in Table B.1
Check that: Grade of inspection
1 Equipment is appropriate to the EPL/Zone requirements of the location X X X
3 Equipment temperature class is correct X X
4 Equipment circuit identification is correct X X X
5 Equipment circuit identification is available X X X
6 Enclosure, glass parts and glass-to-metal sealing gaskets and/or compounds are satisfactory X X X
7 There are no unauthorized modifications X X X
8 There are no visible unauthorized modifications X X
9 Bolts, cable entry devices (indirect) and blanking elements are of the correct type and are complete and tight
11 Condition of enclosure gaskets is satisfactory X X X
12 Breathing and draining devices are satisfactory The manufacturer’s schedule for maintenance requirements for the drying agent are documented to have been followed
13 Sealed enclosure pressure-relief devices are satisfactory X X
14 Enclosures marked Permanently Sealed have no visible evidence that the enclosure has been opened X X X
The protective liquid must be maintained within specified limits, ensuring that its level remains at or below the maximum and above the minimum permitted thresholds Additionally, the equipment should operate at a maximum working angle to the horizontal that is deemed satisfactory for optimal performance.
16 Enclosures intended to be opened
The protective liquid in Type of Protection “o” electrical equipment must be refilled to the specified level and resealed according to the manufacturer's guidelines.
17 When a dipstick is provided, the dipstick is secured in its measurement position and its seal is satisfactory X X X
18 remote-indicating protective liquid level indicating device operation is satisfactory X X X
19 switching device schedule for cleaning/filtering/replacement of the protective liquid following a given number of normal switching operations or interruption of fault currents is documented
NOTE The inspection and maintenance requirements are found in IEC 60079-17 and are the responsibility of the user Until IEC 60079-17 contains sufficient information, Annex B provides information
Repair, overhaul and reclamation is not applicable to Type of Protection “o” Ex Equipment with enclosures indicated as being sealed
Type of Protection “o” enclosures that are intended to be opened shall be subject to repair, overhaul and reclamation only as permitted by the manufacturer’s instructions
NOTE The repair and overhaul requirements are found in IEC 60079-19 and are the responsibility of the user Until IEC 60079-19 contains sufficient information, Annex C provides information
IEC 60050-421, International Electrotechnical Vocabulary – Chapter 421: Power transformers and reactors
IEC 60050-441, International Electrotechnical Vocabulary – Chapter 441: Switchgear, controlgear and fuses
IEC 60079 (all parts), Explosive atmospheres
IEC 62770, Fluids for electrotechnical applications – Unused natural esters for transformers and similar electrical equipment
EN 50495, Safety devices required for the safe functioning of equipment with respect to explosion risks