IEC 60079-6:2015/AMD1:2020

IEC 60079-6 ®
Edition 4.0 2020-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 1
AM ENDEMENT 1
Explosive atmospheres –
Part 6: Equipment protection by liquid immersion "o"

Atmosphères explosives –
Partie 6: Protection du matériel par immersion dans le liquide "o"

IEC 60079-6:2015-02/AMD1:2020-02(en-fr)

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IEC 60079-6 ®
Edition 4.0 2020-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 1
AM ENDEMENT 1
Explosive atmospheres –
Part 6: Equipment protection by liquid immersion "o"

Atmosphères explosives –
Partie 6: Protection du matériel par immersion dans le liquide "o"

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.260.20 ISBN 978-2-8322-7866-6

– 2 – IEC 60079-6:2015/AMD1:2020
 IEC 2020
FOREWORD
This amendment has been prepared by IEC technical committee 31: Equipment for explosive
atmospheres.
The text of this amendment is based on the following documents:
FDIS Report on voting
31/1517/FDIS 31/1526/RVD
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the stability date indicated on the IEC website under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
_____________
1 Scope
Delete the Note.
Add, after the fourth paragraph of Clause 1, the following new text:
Additionally, for Level of Protection "oc", Annex D applies where the rated voltage exceeds
15 kV AC RMS or DC and up to 245 kV AC RMS or DC.
Annex D applies specifically to liquid immersed transformers and reactors, and other liquid
immersed equipment such as swivels for off-shore platforms, power regulators, tap changers
and earthing/switching resistors.
2 Normative references
Add the following new references:
IEC 60071 (all parts), Insulation co-ordination
IEC 60076-3, Power transformers – Part 3: Insulation levels, dielectric tests and external
clearances in air
IEC 60079-1, Explosive atmospheres – Part 1: Equipment protection by flameproof enclosures
"d"
 IEC 2020
IEC 60079-2, Explosive atmospheres – Part 2: Equipment protection by pressurized enclosure
"p"
IEC 60079-33, Explosive atmospheres – Part 33: Equipment protection by special protection
's'
IEC 60137, Insulated bushings for alternating voltages above 1000 V
IEC 62770, Fluids for electrotechnical applications – Unused natural esters for transformers
and similar electrical equipment
3 Terms and definitions
Add the following new terms and definitions:
3.11
oil-immersed swivel for HV connections
oil filled equipment to transfer power with coupling between two parts enabling one to revolve
and the other to remain stationary (fixed)
3.12
oil-immersed earthing resistor
equipment intended for system neutral earthing
3.13
oil-immersed switching resistor
equipment intended for inrush current limitation

– 4 – IEC 60079-6:2015/AMD1:2020
 IEC 2020
Insert the following new Annex D after Annex C:
Annex D
(normative)
Supplementary requirements for electrical equipment
with Level of Protection "oc" for voltages greater than 15 kV
and up to and including 245 kV
D.1 General
Annex D supplements and modifies the requirements of this document. Subclauses 4.3, 4.4
and 4.6 do not apply to equipment covered by this Annex.
The voltage of explosion protected electrical equipment was limited for Level of Protection
"oc" up to 15 kV RMS AC or DC. Application of higher voltages exists to supply offshore
plants that are a long distance from the coast. Voltage levels up to 245 kV AC or DC are
RMS
needed to allow power transmission up to some hundred kilometres from shore to offshore or
between locations on shore/offshore. This Annex can be applied to liquid immersed
transformers, reactors, power regulators, tap changers and other liquid immersed HV
electrical equipment without dedicated IEC standards such as oil-immersed swivels for HV
connections, oil-immersed earthing resistors and oil-immersed switching resistors.
D.2 Additional requirements
D.2.1 Safety devices
For Level of Protection "oc", the requirements in 4.7.3 for Level of Protection "ob" apply for
equipment or components according to this Annex.
Each individual liquid filled compartment shall have its own safety devices.
A pressure relief device shall be provided that automatically disconnects the power when the
pressure relief device activates. The electrical equipment or system associated with the
pressure relief device to activate the automatic disconnection shall be suitable for EPL Gc. If
the pressure relief device itself is not directed downward a guide system, e.g. a pipe, shall be
provided. The dimensioning of this guide system shall not compromise the functionality of the
pressure relief.
D.2.2 Protective liquid specification
In addition to 5.1, natural ester insulating liquids in accordance with IEC 62770 may be used
in higher voltage equipment along with the insulating liquids already identified in this
document.
NOTE Natural ester liquids per IEC 62770 are proven up to 245 kV considering the ambient temperature
limitation.
D.2.3 Liquid immersion depth
Instead of Table 2, the required minimum liquid immersion depths necessary shall be
specified by the manufacturer and verified by high voltage tests as specified in D.4.7. The
tests shall be done with the minimum liquid level.

 IEC 2020
D.2.4 Connections
Cables for field wiring connections greater than 15 kV shall be shielded to mitigate external
arcs and sparks caused by an external dielectric field. All HV cables above 15 kV shall be
armoured and shielded. Considerations shall be made to avoid circulating currents and
external arcs and sparks during energizing operation (Refer to the requirements of
IEC 60079-0 for circulating currents in enclosures).
The termination of the HV cable may be within enclosures using other Types of Protection
such as flameproof “d”, pressurization “p” or special protection “s”.
In the case of an enclosure in accordance with IEC 60079-1 Level of Protection “db” the
interface to the liquid immersion shall withstand the overpressure test of IEC 60079-1.
Termination in pressurized enclosures in accordance with IEC 60079-2 shall be Level of
Protection “pxb” or “pzc”.
Special protection “s” shall be in accordance with IEC 60079-33.
When bushings are used, the requirements of IEC 60137 apply.
D.2.5 On-load tap-changer (OLTC)
The on-load tap-changer shall be of type which does not produce arcs and sparks during
switching.
DC switching is not permitted.
NOTE OLTC according IEC 60214 can make switching operations up to several MVA/phase without sparking in
liquid when vacuum tap changers are applied. In a vacuum tap changer current switching takes place inside a
closed vacuum bottle and the current is limited by transition resistor or reactor during the switching.
D.2.6 Containment solutions
The liquid containment enclosure shall be sealed from the ambient environment in accordance
with 4.5.2.
Unsealed enclosures of 4.5.3 are not permitted.
NOTE 1 Sealing can be achieved by diaphragm/bladder/bag in conservator tank between the liquid and air or by
closed gas cushion (usually nitrogen) or by flexible fully filled tank (flexible corrugations or radiators).
NOTE 2 Because mineral oil, esters and silicone oil are hygroscopic, a sealed design in HV liquid insulated
equipment is considered as the only practical choice to increase maintenance intervals and reduce failure risks.
Expansion vessels with membrane are considered sealed.
D.2.7 Routine tests
D.2.7.1 Dielectric tests
Transformers and reactors test methods and voltages are given in IEC 60076-3. Test voltages
for transformers may be applied to other oil-immersed HV equipment or IEC 60071 may be
applied where there is no industrial standard for the type of equipment.
The following routine dielectric tests apply:
a) The test for phase to earth shall be conducted in accordance with the requirements of
IEC 60076-3 or IEC 60071.
b) The test for phase to phase shall be conducted in accordance with the requirements of
IEC 60076-3.
– 6 – IEC 60079-6:2015/AMD1:2020
 IEC 2020
c) The test of partial discharge measurement for long duration with pre-stress voltage and
measurement level shall be conducted in accordance with IEC 60076-3. The acceptance
criteria shall be applied.
d) The test for lightning impulse given in IEC 60076-3 is applicable for transformers and
reactors, and for other equipment according to IEC 60071.
Tests a) and b) shall be a routine test for all equipment. Test c) and Test d) shall be an
additional routine test for all equipment above 72,5 kV.
The Tests of c) and d) may apply with a voltage level lower than 72,5 kV as agreed between
the manufacturer and the purchaser.
The tests of a), b), c) and d) shall be done with the manufacturer’s specified minimum liquid
level.
There shall be no breakdow
...