IEC TR 62757:2015
(Main)Fire prevention measures on converters for high-voltage direct current (HVDC) systems, static var compensators (SVC) and flexible AC transmission systems (FACTS) and their valve halls
Fire prevention measures on converters for high-voltage direct current (HVDC) systems, static var compensators (SVC) and flexible AC transmission systems (FACTS) and their valve halls
IEC TR 62757:2015(E), which is a technical report, deals with fire prevention measures on converters and their valve halls for high voltage direct current (HVDC) systems, static VAR compensators (SVC) and flexible AC transmission systems (FACTS). It is intended to be primarily for the use of the utilities and consultants who are responsible for issuing technical specifications for new converter valves and valve halls. It concerns fire incidents in HVDC projects using line commutated converters (LCC) or voltage sourced converter (VSC) technology and it is from these projects that most examples of fires and fire incidents are taken. This technical report also addresses converter valves and valve halls for SVC and FACTS. This technical report provides general recommendations to be considered while preparing specifications for these systems. Specific requirements for a particular project need to be clearly specified and mutually agreed upon between the supplier and the purchaser.
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Standards Content (Sample)
IEC TR 62757 ®
Edition 1.0 2015-07
TECHNICAL
REPORT
Fire prevention measures on converters for high-voltage direct current (HVDC)
systems, static var compensators (SVC) and flexible ac transmission systems
(FACTS) and their valve halls
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IEC TR 62757 ®
Edition 1.0 2015-07
TECHNICAL
REPORT
Fire prevention measures on converters for high-voltage direct current (HVDC)
systems, static var compensators (SVC) and flexible ac transmission systems
(FACTS) and their valve halls
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 13.220.20 ISBN 978-2-8322-2788-6
– 2 – IEC TR 62757:2015 © IEC 2015
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Fire hazards in valves and valve halls . 13
4.1 General . 13
4.2 Possible causes . 13
4.2.1 Valve insulation failure . 13
4.2.2 Loose connections or high resistance joints in the power circuit. 13
4.2.3 Valve component failures . 14
4.2.4 Semiconductor device level connections . 15
4.2.5 Coolant system problems. 16
4.2.6 Failure of valve hall bushings . 17
4.2.7 Failure of surge arresters . 17
4.2.8 False operation of deluge system . 17
4.2.9 Other valve hall equipment . 17
4.2.10 Work in and around valve hall . 17
4.3 Assessment of possible consequences . 18
5 Valve hall layout and access. 18
5.1 Physical arrangements . 18
5.1.1 General . 18
5.1.2 Present practices . 19
5.1.3 Specific provisions . 19
5.2 HVDC valve hall construction . 19
5.2.1 General . 19
5.2.2 Valve hall construction . 20
5.3 Means of egress . 20
6 Supervision of valve components and other valve hall equipment . 20
6.1 General . 20
6.2 Supervision of valve components . 21
6.2.1 General . 21
6.2.2 On-line monitoring . 21
6.2.3 Off-line checks and inspection . 22
6.3 Supervision of other valve hall equipment . 22
7 Fire detection systems . 23
7.1 General . 23
7.2 Detection and operating principles . 23
7.2.1 General . 23
7.2.2 Air sampling systems . 23
7.2.3 Infra-red beam smoke detectors . 23
7.2.4 Arc detector systems . 24
7.2.5 Infra-red flame detectors. 24
7.2.6 Ultraviolet (UV) flame detectors . 24
7.2.7 Imaging video camera systems . 24
7.3 Guidelines for valve hall fire detection. 24
8 Fire suppression systems . 24
8.1 General . 24
8.2 Design considerations for an installed fire suppression system . 25
8.3 Types of fire extinguishing agents . 26
8.3.1 List of agents . 26
8.3.2 Carbon dioxide . 26
8.3.3 Inert gases . 26
8.3.4 Hydro fluorocarbons . 26
8.3.5 Other gases . 27
8.4 Installation requirements . 27
8.5 Guidelines for fire extinguishing agents . 27
9 Vent management . 28
9.1 General . 28
9.2 Design considerations . 29
9.2.1 General . 29
9.2.2 Natural ventilation . 29
9.2.3 Forced ventilation . 30
9.2.4 Design . 30
10 Control and integration of fire detection, fire protection and converter control
systems . 30
10.1 General . 30
10.2 Fire alarm classification . 31
10.2.1 General . 31
10.2.2 Classification by detection principle . 32
10.2.3 Classification by detection objective . 32
10.2.4 Detection system reliability . 33
10.3 Fire control system . 33
10.3.1 General . 33
10.3.2 Basic system functions . 33
10.3.3 Other system components . 34
10.3.4 Outline of system design . 34
10.4 Guidelines for integrated fire control systems . 35
11 Fire fighting and maintenance . 35
11.1 General . 35
11.2 Role of station and fire fighting personnel . 35
11.2.1 General . 35
11.2.2 Actions in case of a fire . 35
11.2.3 Fire fighting . 36
12 Guidance for purchaser specifications . 36
12.1 General . 36
12.2 Purchaser specification . 36
12.2.1 General . 36
12.2.2 Semiconductor valves . 37
12.2.3 Other valve hall equipment . 38
12.2.4 Valve hall construction . 38
12.2.5 Fire detection systems . 38
12.2.6 Fire suppression systems . 39
12.2.7 Vent management system . 39
12.2.8 Fire alarm and control systems . 39
Annexe A (informative) Valve hall fire hazards and survey of fire incidents . 40
– 4 – IEC TR 62757:2015 © IEC 2015
A.1 General . 40
A.2 Hazard categories . 40
A.3 Reports from HVDC users . 41
A.4 Reported incidents . 42
A.4.1 Overheating of valve components due to reduced cooling . 42
A.4.2 Valve component failures . 44
A.4.3 Loose or high resistance connections in the load current carrying circuit . 57
A.4.4 Failure of auxiliary circuit electrical connections . 58
A.4.5 Insulation failures . 58
A.4.6 Failures of equipment associated with the valve hall . 61
A.4.7 False alarms . 62
A.4.8 Unknown causes . 63
A.5 Conclusion and recommendations . 63
Bibliography . 65
Figure 1 – Types of ventilation . 29
Figure 2 – Possible arrangements and interconnections of an integrated fire detection
and control system . 32
Table 1 – Fire extinguishing agents . 26
Table A.1 – HVDC converters owners/suppliers reference list (May 2012) . 41
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIRE PREVENTION MEASURES ON CONVERTERS FOR
HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS, STATIC
VAR COMPENSATORS (SVC) AND FLEXIBLE AC TRANSMISSION
SYSTEMS (FACTS) AND THEIR VALVE HALLS
FOREWORD
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The main task of IEC technical committees is to prepare International Standards. However, a
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data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 62757, which is a technical report, has been prepared by subcommittee 22F: Power
electronics for electrical transmission and distribution systems, of IEC technical committee 22:
Power electronic systems and equipment.
– 6 – IEC TR 62757:2015 © IEC 2015
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
22F/347/DTR 22F/353A/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this 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.
FIRE PREVENTION MEASURES ON CONVERTERS FOR
HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS, STATIC
VAR COMPENSATORS (SVC) AND FLEXIBLE AC TRANSMISSION
SYSTEMS (FACTS) AND THEIR VALVE HALLS
1 Scope
IEC TR 62757, which is a technical report, deals with fire prevention measures on converters
and their valve halls for high voltage direct current (HVDC) systems, static VAR compensators
(SVC) and flexible AC transmission systems (FACTS). It is intended to be primarily for the use
of the utilities and consultants who are responsible for issuing technical specifications for new
converter valves and valve halls. It concerns fire incidents in HVDC projects using line
commutated converters (LCC) or voltage sourced converter (VSC) technology and it is from
these projects that most examples of fires and fire incidents are taken. This technical report
also addresses converter valves and valve halls for SVC and FACTS.
This technical report provides general recommendations to be considered while preparing
specifications for these systems. Specific requirements for a particular project need to be
clearly specified and mutually agreed upon between the supplier and the purchaser.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
Void.
3 Terms and definitions
For the purpose of this document the following terms and definitions apply.
3.1
alarm system
installation for initiating a fire alarm
3.2
automatic fire detector
device that detects abnormally high temperature, rate of temperature rise, visible or invisible
particles, infra-red or visible radiation, or gases produced by a fire
3.3
automatic fire extinguishing system
any system designed and installed to detect a fire and subsequently discharge an
extinguishing agent without the necessity of human intervention
3.4
burn, intransitive verb
undergo combustion
[SOURCE: ISO 13943:2008, 4.28]
– 8 – IEC TR 62757:2015 © IEC 2015
3.5
burn, transitive verb
cause combustion
[SOURCE: ISO 13943:2008, 4.29]
3.6
ignite, intransitive verb
catch fire with or without the application of an external heat source
[SOURCE: ISO 13943:2008, 4.184]
3.7
ignite, transitive verb
initiate combustion
[SOURCE: ISO 13943:2008, 4.185]
3.8
char, noun
carbonaceous residue resulting from pyrolysis or incomplete combustion
[SOURCE: ISO 13943:2008, 4.38]
3.9
char, verb
form char
[SOURCE: ISO 13943:2008, 4.39]
3.10
combustion
exothermic reaction of a substance with an oxidizing agent
Note 1 to entry: Combustion generally emits fire effluent (4.105) accompanied by flames (4.133) and/or glowing
(4.168).
[SOURCE: ISO 13943:2008, 4.46]
3.11
exit
designated point of departure from a building
[SOURCE: ISO 13943:2008, 4.86]
3.12
explosion
abrupt expansion of gas that can result from a rapid oxidation (see 4.245 of ISO 13943:2008),
decomposition reaction or other means, with or without an increase in temperature
[SOURCE: ISO 13943:2008, 4.87]
3.13
extinguishing medium¨
extinguishing agent
solid, liquid or gaseous substance especially suited to the extinction of fires
3.14
fire
process of combustion characterized by the emission of heat accompanied by smoke and/or
flame
3.15
fire alarm
alarm
alarm signal for alerting the fire service or people endangered by fire
3.16
fire alarm box
call box
pull station
part of a fire alarm system from which a fire call is made, either by hand or automatically
3.17
fire barrier
fire separation
separating element which provides, for a stated period of time, simultaneous integrity and
thermal insulation under specified test conditions
[SOURCE: ISO 13943:2008, 4.99]
3.18
fire control system
system which provides integrated control of fire detection, fire alarm, fire suppression, smoke
management and other services as part of a total fire protection scheme
3.19
fire damper
smoke damper
mechanical plate or shutter which is closed to restrict the passage of fire/smoke in a flue or
duct
3.20
fire department connection
connection through which the fire department can pump supplemental water into the sprinkler
system, standpipe, or other system furnishing water for fire extinguishment to supplement
existing water supplies
3.21
fire door
door of at least 30 min fire resistance which is prescribed for fire safety reasons and which
has to be kept closed in accordance with the authorities instructions
3.22
fire hazard
physical object or condition with a potential for an undesirable consequence from fire
[SOURCE: ISO 13943:2008, 4.112]
3.23
fire load
quantity of heat which can be released by the complete combustion of all the combustible
materials in a volume, including the facings of all bounding surfaces
[SOURCE: ISO 13943:2008, 4.114, modified – The notes have been deleted.]
– 10 – IEC TR 62757:2015 © IEC 2015
3.24
fire suppression system
any system provided for the extinguishing of a fire
3.25
fire wall
partition wall of specified fire resistance rating
3.26
fire-fighting
all measures involved in the combat against fire
3.27
flame, noun
rapid, self-sustaining, sub-sonic propagation of combustion in a gaseous medium, usually with
emission of light
[SOURCE: ISO 13943:2008, 4.133]
3.28
flame, verb
produce flame
[SOURCE: ISO 13943:2008, 4.134]
3.29
flammable
capable of flaming combustion (see 4.148 of ISO 13943:2008) under specified conditions
[SOURCE: ISO 13943:2008, 4.153]
3.30
foam
emulsive extinguishing agent, consisting of water, bubbles of gas or air, and a foam stabilizer
(foam compound which is used to extinguish burning liquids)
3.31
heat release rate
burning rate (deprecated)
rate of burning (deprecated)
rate of thermal energy production generated by combustion
Note 1 to entry: The typical units are watts (W).
[SOURCE: ISO 13943:2008, 4.177]
3.32
ignite, intransitive verb
catch fire with or without the application of an external heat source
[SOURCE: ISO 13943:2008, 4.184]
3.33
ignite, transitive verb
initiate combustion, light
[SOURCE: ISO 13943:2008, 4.185]
3.34
ignition
sustained ignition (deprecated)
general: initiation of combustion
[SOURCE: ISO 13943:2008, 4.187]
3.35
ignitability, ease of ignition
measure of the ease with which a test specimen can be ignited, under specified conditions;
ignition time, conditions; ignition time
[SOURCE: ISO 13943:2008, 4.182]
3.36
ignition source
source of energy that initiates combustion
[SOURCE: ISO 13943:2008, 4.189]
3.37
incipient fire
initial fire
3.38
means of egress
continuous and unobstructed way of exit travel from any point in a building or structure to a
public way and consists of three separate and distinct parts: a) the exit access, b) the exit and
c) the exit discharge
Note 1 to entry: A means of egress comprises the vertical and horizontal travel and should include intervening
room spaces, doorways, hallways, corridors, passageways, balconies, ramps, stairs, enclosures, lobbies,
escalators, horizontal exits, courts, and yards.
3.39
non-combustible
not capable of undergoing combustion (under specified conditions)
Note 1 to entry: In some regulations a material is classified as being non-combustible even if it is capable of
combustion, provided that its heat of combustion (4.174) is less than defined amount.
[SOURCE: ISO 13943:2008, 4.239]
3.40
non-flammable
not capable of burning with a flame (3.27 and 3.28) under specified conditions
[SOURCE: ISO 13943:2008, 4.240]
3.41
overheating
excessive rise in temperature of a material or body
3.42
quick response sprinkler
type of sprinkler that is both a fast response and a spray sprinkler
– 12 – IEC TR 62757:2015 © IEC 2015
3.43
flame spread
propagation of a flame front
[SOURCE: ISO 13943:2008, 4.142]
3.44
self-extinguish, verb
auto-extinguish, verb
cease combustion without being affected by any external agent
[SOURCE: ISO 13943:2008, 4.284]
3.45
self-extinguishing
the characteristic of a material ceasing to burn, under specified test conditions, after the
igniting source has been removed
Note 1 to entry: Although in common usage (including this report), this term is deprecated in international
standards because it may convey a false sense of security and lead to misunderstanding. The properties of
materials after removal of an ignition source are better described by the afterflame time, the afterglow time, the
extent of combustion and the damaged area (length) under specified test conditions (compiled from various
sources).
3.46
semiconductor device
one of the series connected devices used in valves such as thyristors, diodes or insulated
gate bipolar transistors (IGBTs)
3.47
smoke
visible part of fire effluent
[SOURCE: ISO 13943:2008, 4.293]
3.48
smoke detector
fire detector which initiates an alarm on the presence of a certain quantity of smoke
3.49
smoke development rating
smoke development rating means an index or classification indicating the smoke development
characteristics of a material or an assembly of a material as determined in a standard fire test
3.50
smoke management system
any system designed and installed to control the accumulation and spread of smoke in a
building
3.51
water spray deluge system
special fixed pipe system connected to a reliable source of fire protection water supply and
equipped with water spray nozzles for specific water discharge and distribution over the
surface or area to be protected
Note 1 to entry: The piping system is connected to the water supply through an automatically or manually
actuated valve that initiates the flow of water. An automatic valve is actuated by operation of automatic detection
equipment installed in the same areas as the water spray nozzles. (in special cases the automatic detection
equipment may also be located in another area).
4 Fire hazards in valves and valve halls
4.1 General
Converter valve halls house the converter valves, wall bushings or converter transformer
bushings, valve and group arresters as well as, in certain designs, other high voltage
components such as high voltage capacitors or voltage dividers.
The valve equipment is subjected to various mechanical and electrical stresses during
operation. They are designed and constructed from many series and parallel connected
components such as thyristors, diodes, IGBTs (and similar packages), capacitors, resistors
and saturable reactors.
To minimize the space requirement in the valve hall, the valves are often vertically stacked to
take advantage of the graded insulation level. The necessary creepage and electrical
clearances between and within the valves are achieved by the use of porcelain insulators
and/or composite insulators. Extensive use of composite materials is made in the structural
components of the valves.
Several years ago, following the spate of fires that culminated in the generation of CIGRÉ
Technical Brochure 136, several purchasers demanded that no oil-filled components be in the
valve hall and that valve components be generally fire retardant. Today also, the valve
structure comprises various materials such as plastics, composites, and rubbers, the non-
metallic materials being fire retardant, self-extinguishing, generally to UL94V-0 or equivalent.
There is essentially minimal combustible material in the converter valve equipment, however,
materials will burn if there is sufficient heat input from the ignition source. The possible
sources of fire in a valve hall are discussed in detail in the following clauses, and cover HVDC
and FACTS equipment (thyristor valves, SVCs, STATCOMs, VSC, etc.).
4.2 Possible causes
4.2.1 Valve insulation failure
Breakdown of electrical insulation within or between parts of the valve which are common to
more than one semiconductor device level can lead to arcing which could ignite flammable
materials.
Insulation failure could be internal, for example due to partial discharges in a dielectric
material, or external due to corona or contamination of insulating surfaces (e.g. as a result of
a coolant leak). Smoke or other ionised by-products arising from, for example, an overheated
electrical component can reduce the withstand voltage of the air insulation within the valve.
The consequences of insulation failure will strongly depend on the location, materials and
energy associated with the event. It should be noted that it is not necessary for total
breakdown of an insulation system to occur before hazardous conditions can arise. High
surface leakage currents, for example on a contaminated insulating surface can, depending
on the materials, present a direct risk of combustion.
4.2.2 Loose connections or high resistance joints in the power circuit
An overheated connection or series arc can arise from improper connection of bus bars used
for carrying the load current. These could be connections between different sections of the
valve, with the series reactor, with the semiconductor device or any other connector which
forms the path of the load current. Any loose connection or high resistance joint will overheat.
In the case of an open circuited connection, a series arc will develop. In either case the heat
generated will depend on the level of the current and may cause damage to adjacent
components, especially insulating material. If the temperatures reached are high enough then
it may lead to a fire.
– 14 – IEC TR 62757:2015 © IEC 2015
4.2.3 Valve component failures
4.2.3.1 General
Breakdown of electrical insulation within or between parts of the valve which are common to
more than one thyristor level can lead to arcing which could cause charring of components or
ignition in certain circumstances if the source is sufficiently intense.
4.2.3.2 Thyristors and diodes
When overstressed, thyristors and diodes fail to an approximate short circuit. Provided that
they remain properly clamped and cooled, short circuited thyristors can safely conduct normal
load current and overcurrents. By providing series redundant levels, a valve can be kept in
service for long periods in the presence of a small number of short circuited thyristors.
4.2.3.3 IGBT and similar semiconductor devices
These devices are, at the time of writing, manufactured mainly as single-side cooled
encapsulated assemblies, although press-pack assemblies are available. The press-pack
assemblies should fail to short-circuit but the encapsulated assemblies can fail to either short
circuit or open circuit. The mode of failure is not fully controlled. The mode of failure can
lead to rupture, or even a more explosive effect. To protect against this uncertainty, a
component such as a fast-acting switch in parallel with the semiconductor device needs to be
included.
The thyristors and diodes themselves are non-flammable and, because failure relieves other
components from significant voltage stress, it is often arranged that other component faults
lead directly or indirectly to thyristor short circuit, thereby avoiding a hazardous condition
elsewhere.
4.2.3.4 Capacitors
To obtain long life and high reliability at the operating voltage of one semiconductor device
level, capacitors which experience this voltage should employ an impregnated dielectric
construction.
Non-flammable impregnating fluids based on polychlorinated bi-phenyls (PCB) exist, but are
prohibited on environmental grounds.
Today, many capacitors contain (usually small) quantities of an impregnating medium in the
form of a resin which, if exposed to air and an ignition source can burn. Capacitors may also
be impregnated with special dielectric fluids, all of which are flammable material. Virtually all
high voltage capacitors today use polypropylene as the dielectric which also may burn if
exposed to air and ignition. The failure modes of these capacitors are therefore of particular
interest.
In all cases, rupture of the capacitor can is an essential pre-requisite for exposing the
dielectric material and impregnating medium to air. This could arise from mechanical damage
caused by abuse or resulting from a production defect, or from an electrical fault inside the
capacitor. Internal faults for example short circuit of one or more capacitor elements, sparking
at a broken internal connection, etc. can cause decomposition of the dielectric material and/or
of the impregnating medium, leading to a build-up of pressure inside the capacitor. Unless the
process can be arrested (e.g. the capacitor is rendered open circuit by operation of an over-
pressure protection device) or the pressure is relieved in a controlled and safe manner, then
the over-pressure may lead to rupture of the can. Electrical arcing/overheating of the now
disrupted capacitor provides a likely source of ignition. Recent experiences demonstrate that
the risk for fire of contained polypropylene capacitors is low.
Capacitors that are dry type, normally contain polyurethane or silicone gel, as filling material
does not burn itself even though it is exposed to air.
4.2.3.5 Reactors
The reactors within a valve equipment may be liquid cooled. A mode of failure of valve
reactors is overheating due to total or partial blockage of the cooling pipes within the reactors.
If such a condition goes undetected, failure of the reactor is possible and this may cause a
fire within the valve equipment.
Other modes of failure could be turn-to-turn or turn-to-core insulation failure or for example
failure of the banding straps used to secure the reactor cores.
The consequences of such failures will depend on the particular valve design.
4.2.3.6 Resistors
The resistors used in damping circuits are generally wire wound, although thick-film devices
are frequently used. The failure of resistors could be due to overheating of the element
caused by inadequate cooling or corrosion of resistor elements which are in direct contact
with the coolant. If the resistors are indirectly cooled, i.e. heatsink mounted, the breakdown of
the resistor to the heatsink could result in localised arcing. This may result in open circuit,
insulation or housing failure. If the insulation provided is flammable, then it may ignite.
Another scenario would be that the arcing inside the resistor persists and the resistor may fail
explosively, damaging other adjacent components. This can lead to arcing and flashover.
4.2.3.7 Electronic circuits
The electronic circuits for the control, protection and monitoring of the thyristors are normally
of low power. The failure of individual components may, however, pose a fire hazard. Two
situations could be:
a) The semiconductor device firing electronics provides gate trigger pulses to more than one
series-connected semiconductor device via insulated output pulse transformers. Failure of
the insulation of a pulse transformer could result in load current flowing in low current
wiring.
b) The electronic circuits require a source of power which, for HVDC valves, is normally
extracted from one of the voltage grading networks at the respective semiconductor
device level. The power supply must provide sufficient energy to meet performance
requirements under the worst operating conditions, therefore, under other conditions,
more energy than is needed is available. The technique adopted to control this surplus
energy could influence the consequences of a component failure in this part of the circuit.
4.2.3.8 Light guides
Light guides, either individually or in bundles involve a risk of fire ignition, if exposed to
conductive surface contamination. Certain types of light guide jacket material may sustain
combustion and transfer fire within the valve structure.
4.2.4 Semiconductor device level connections
When the semiconductor devices are electrically connected to damping circuits, grading
resistors and/or other circuitry, this requires auxiliary wiring of low current carrying capacity.
The semiconductor device control and protection circuitry, including network grading and
detection components, involves a large number of low current connections. If a connection
inadvertently becomes open-circuited, arcing can result which could ignite flammable
material.
– 16 – IEC TR 62757:2015 © IEC 2015
4.2.5 Coolant system problems
4.2.5.1 Water based systems
In liquid cooled valves the heat is removed from the semiconductor device, resistors and
reactors by deionized water or a mixture of deionized water and glycol. The flow, temperature
and conductivity of the coolant delivered to the valve are continously monitored externally to
the valve. Internally to the valve, the cooling water and plastic pipes are required to withstand
voltage stresses.
The failure modes of components of the valve cooling circuit are corrosion, leakage and
clogging. Failures can be caused by electrical, chemical or mechanical phenomena either
acting alone or in combination.
Unless the materials in contact with the coolant are carefully selected and applied, electro-
chemical processes within the cooling circuit may cause corrosion of metallic couplings and
other components of the coolant system. In the presence of leakage currents there is the
possibility of erosion and deposition of material in some parts of cooling water circuit. This
process, if c
...
IEC TR 62757 ®
Edition 1.1 2019-07
CONSOLIDATED VERSION
TECHNICAL
REPORT
colour
inside
Fire prevention measures on converters for high-voltage direct current (HVDC)
systems, static var compensators (SVC) and flexible ac transmission systems
(FACTS) and their valve halls
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IEC TR 62757 ®
Edition 1.1 2019-07
CONSOLIDATED VERSION
TECHNICAL
REPORT
colour
inside
Fire prevention measures on converters for high-voltage direct current (HVDC)
systems, static var compensators (SVC) and flexible ac transmission systems
(FACTS) and their valve halls
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 13.220.20 ISBN 978-2-8322-7142-1
IEC TR 62757 ®
Edition 1.1 2019-07
CONSOLIDATED VERSION
REDLINE VERSION
colour
inside
Fire prevention measures on converters for high-voltage direct current (HVDC)
systems, static var compensators (SVC) and flexible ac transmission systems
(FACTS) and their valve halls
– 2 – IEC TR 62757:2015+AMD1:2019 CSV
© IEC 2019
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Fire hazards in valves and valve halls . 13
4.1 General . 13
4.2 Possible causes . 13
4.2.1 Valve insulation failure . 13
4.2.2 Loose connections or high resistance joints in the power circuit. 13
4.2.3 Valve component failures . 14
4.2.4 Semiconductor device level connections . 16
4.2.5 Coolant system problems. 16
4.2.6 Failure of valve hall bushings . 17
4.2.7 Failure of surge arresters . 17
4.2.8 False operation of deluge system . 17
4.2.9 Other valve hall equipment . 17
4.2.10 Work in and around valve hall . 18
4.3 Assessment of possible consequences . 18
5 Valve hall layout and access. 18
5.1 Physical arrangements . 18
5.1.1 General . 18
5.1.2 Present practices . 19
5.1.3 Specific provisions . 19
5.2 HVDC valve hall construction . 19
5.2.1 General . 19
5.2.2 Valve hall construction . 20
5.3 Means of egress . 20
6 Supervision of valve components and other valve hall equipment . 21
6.1 General . 21
6.2 Supervision of valve components . 21
6.2.1 General . 21
6.2.2 On-line monitoring . 21
6.2.3 Off-line checks and inspection . 22
6.3 Supervision of other valve hall equipment . 22
7 Fire detection systems . 23
7.1 General . 23
7.2 Detection and operating principles . 23
7.2.1 General . 23
7.2.2 Air sampling systems . 23
7.2.3 Infra-red beam smoke detectors . 24
7.2.4 Arc detector systems . 24
7.2.5 Infra-red flame detectors. 24
7.2.6 Ultraviolet (UV) flame detectors . 24
7.2.7 Imaging video camera systems . 24
7.3 Guidelines for valve hall fire detection. 24
8 Fire suppression systems . 25
© IEC 2019
8.1 General . 25
8.2 Design considerations for an installed fire suppression system . 25
8.3 Types of fire extinguishing agents . 26
8.3.1 List of agents . 26
8.3.2 Carbon dioxide . 27
8.3.3 Inert gases . 28
8.3.4 Hydro fluorocarbons . 28
8.3.5 Other gases . 28
8.4 Installation requirements . 28
8.5 Guidelines for fire extinguishing agents . 29
9 Vent management . 29
9.1 General . 29
9.2 Design considerations . 30
9.2.1 General . 30
9.2.2 Natural ventilation . 30
9.2.3 Forced ventilation . 31
9.2.4 Design . 31
10 Control and integration of fire detection, fire protection and converter control
systems . 32
10.1 General . 32
10.2 Fire alarm classification . 32
10.2.1 General . 32
10.2.2 Classification by detection principle . 33
10.2.3 Classification by detection objective . 33
10.2.4 Detection system reliability . 34
10.3 Fire control system . 34
10.3.1 General . 34
10.3.2 Basic system functions . 34
10.3.3 Other system components . 35
10.3.4 Outline of system design . 35
10.4 Guidelines for integrated fire control systems . 36
11 Fire fighting and maintenance . 36
11.1 General . 36
11.2 Role of station and fire fighting personnel . 36
11.2.1 General . 36
11.2.2 Actions in case of a fire . 36
11.2.3 Fire fighting . 37
12 Guidance for purchaser specifications . 37
12.1 General . 37
12.2 Purchaser specification . 37
12.2.1 General . 37
12.2.2 Semiconductor valves . 38
12.2.3 Other valve hall equipment . 39
12.2.4 Valve hall construction . 39
12.2.5 Fire detection systems . 39
12.2.6 Fire suppression systems . 40
12.2.7 Vent management system . 40
12.2.8 Fire alarm and control systems . 40
Annexe A (informative) Valve hall fire hazards and survey of fire incidents . 41
– 4 – IEC TR 62757:2015+AMD1:2019 CSV
© IEC 2019
A.1 General . 41
A.2 Hazard categories . 41
A.3 Reports from HVDC users . 42
A.4 Reported incidents . 43
A.4.1 Overheating of valve components due to reduced cooling . 43
A.4.2 Valve component failures . 45
A.4.3 Loose or high resistance connections in the load current carrying circuit . 58
A.4.4 Failure of auxiliary circuit electrical connections . 59
A.4.5 Insulation failures . 59
A.4.6 Failures of equipment associated with the valve hall . 62
A.4.7 False alarms . 63
A.4.8 Unknown causes . 64
A.5 Conclusion and recommendations . 65
Bibliography . 66
Figure 1 – Types of ventilation . 30
Figure 2 – Possible arrangements and interconnections of an integrated fire detection
and control system . 33
Table 1 – Fire extinguishing agents . 27
Table A.1 – HVDC converters owners/suppliers reference list (May 2012) . 42
© IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIRE PREVENTION MEASURES ON CONVERTERS FOR
HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS, STATIC
VAR COMPENSATORS (SVC) AND FLEXIBLE AC TRANSMISSION
SYSTEMS (FACTS) AND THEIR VALVE HALLS
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
This consolidated version of the official IEC Standard and its amendment has been
prepared for user convenience.
IEC TR 62757 edition 1.1 contains the first edition (2015-07) [documents 22F/347/DTR
and 22F/353A/RVC] and its amendment 1 (2019-07) [documents 22F/520/DTR and
22F/526/RVDTR].
In this Redline version, a vertical line in the margin shows where the technical content
is modified by amendment 1. Additions are in green text, deletions are in strikethrough
red text. A separate Final version with all changes accepted is available in this
publication.
– 6 – IEC TR 62757:2015+AMD1:2019 CSV
© IEC 2019
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 62757, which is a technical report, has been prepared by subcommittee 22F: Power
electronics for electrical transmission and distribution systems, of IEC technical committee 22:
Power electronic systems and equipment.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of the base publication and its amendment will
remain unchanged until the stability date indicated on the IEC web site 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.
A bilingual version of this publication may be issued at a later date.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
© IEC 2019
FIRE PREVENTION MEASURES ON CONVERTERS FOR
HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS, STATIC
VAR COMPENSATORS (SVC) AND FLEXIBLE AC TRANSMISSION
SYSTEMS (FACTS) AND THEIR VALVE HALLS
1 Scope
IEC TR 62757, which is a technical report, deals with fire prevention measures on converters
and their valve halls for high voltage direct current (HVDC) systems, static VAR compensators
(SVC) and flexible AC transmission systems (FACTS). It is intended to be primarily for the use
of the utilities and consultants who are responsible for issuing technical specifications for new
converter valves and valve halls. It concerns fire incidents in HVDC projects using line
commutated converters (LCC) or voltage sourced converter (VSC) technology and it is from
these projects that most examples of fires and fire incidents are taken. This technical report
also addresses converter valves and valve halls for SVC and FACTS.
This technical report provides general recommendations to be considered while preparing
specifications for these systems. Specific requirements for a particular project need to be
clearly specified and mutually agreed upon between the supplier and the purchaser.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
Void.
3 Terms and definitions
For the purpose of this document the following terms and definitions apply.
3.1
alarm system
installation for initiating a fire alarm
3.2
automatic fire detector
device that detects abnormally high temperature, rate of temperature rise, visible or invisible
particles, infra-red or visible radiation, or gases produced by a fire
3.3
automatic fire extinguishing system
any system designed and installed to detect a fire and subsequently discharge an
extinguishing agent without the necessity of human intervention
3.4
burn, intransitive verb
undergo combustion
[SOURCE: ISO 13943:2008, 4.28]
– 8 – IEC TR 62757:2015+AMD1:2019 CSV
© IEC 2019
3.5
burn, transitive verb
cause combustion
[SOURCE: ISO 13943:2008, 4.29]
3.6
ignite, intransitive verb
catch fire with or without the application of an external heat source
[SOURCE: ISO 13943:2008, 4.184]
3.7
ignite, transitive verb
initiate combustion
[SOURCE: ISO 13943:2008, 4.185]
3.8
char, noun
carbonaceous residue resulting from pyrolysis or incomplete combustion
[SOURCE: ISO 13943:2008, 4.38]
3.9
char, verb
form char
[SOURCE: ISO 13943:2008, 4.39]
3.10
combustion
exothermic reaction of a substance with an oxidizing agent
Note 1 to entry: Combustion generally emits fire effluent (4.105) accompanied by flames (4.133) and/or glowing
(4.168).
[SOURCE: ISO 13943:2008, 4.46]
3.11
exit
designated point of departure from a building
[SOURCE: ISO 13943:2008, 4.86]
3.12
explosion
abrupt expansion of gas that can result from a rapid oxidation (see 4.245 of ISO 13943:2008),
decomposition reaction or other means, with or without an increase in temperature
[SOURCE: ISO 13943:2008, 4.87]
3.13
extinguishing medium¨
extinguishing agent
solid, liquid or gaseous substance especially suited to the extinction of fires
© IEC 2019
3.14
fire
process of combustion characterized by the emission of heat accompanied by smoke and/or
flame
3.15
fire alarm
alarm
alarm signal for alerting the fire service or people endangered by fire
3.16
fire alarm box
call box
pull station
part of a fire alarm system from which a fire call is made, either by hand or automatically
3.17
fire barrier
fire separation
separating element which provides, for a stated period of time, simultaneous integrity and
thermal insulation under specified test conditions
[SOURCE: ISO 13943:2008, 4.99]
3.18
fire control system
system which provides integrated control of fire detection, fire alarm, fire suppression, smoke
management and other services as part of a total fire protection scheme
3.19
fire damper
smoke damper
mechanical plate or shutter which is closed to restrict the passage of fire/smoke in a flue or
duct
3.20
fire department connection
connection through which the fire department can pump supplemental water into the sprinkler
system, standpipe, or other system furnishing water for fire extinguishment to supplement
existing water supplies
3.21
fire door
door of at least 30 min fire resistance which is prescribed for fire safety reasons and which
has to be kept closed in accordance with the authorities instructions
3.22
fire hazard
physical object or condition with a potential for an undesirable consequence from fire
[SOURCE: ISO 13943:2008, 4.112]
3.23
fire load
quantity of heat which can be released by the complete combustion of all the combustible
materials in a volume, including the facings of all bounding surfaces
[SOURCE: ISO 13943:2008, 4.114, modified – The notes have been deleted.]
– 10 – IEC TR 62757:2015+AMD1:2019 CSV
© IEC 2019
3.24
fire suppression system
any system provided for the extinguishing of a fire
3.25
fire wall
partition wall of specified fire resistance rating
3.26
fire-fighting
all measures involved in the combat against fire
3.27
flame, noun
rapid, self-sustaining, sub-sonic propagation of combustion in a gaseous medium, usually with
emission of light
[SOURCE: ISO 13943:2008, 4.133]
3.28
flame, verb
produce flame
[SOURCE: ISO 13943:2008, 4.134]
3.29
flammable
capable of flaming combustion (see 4.148 of ISO 13943:2008) under specified conditions
[SOURCE: ISO 13943:2008, 4.153]
3.30
foam
emulsive extinguishing agent, consisting of water, bubbles of gas or air, and a foam stabilizer
(foam compound which is used to extinguish burning liquids)
3.31
heat release rate
burning rate (deprecated)
rate of burning (deprecated)
rate of thermal energy production generated by combustion
Note 1 to entry: The typical units are watts (W).
[SOURCE: ISO 13943:2008, 4.177]
3.32
ignite, intransitive verb
catch fire with or without the application of an external heat source
[SOURCE: ISO 13943:2008, 4.184]
3.33
ignite, transitive verb
initiate combustion, light
[SOURCE: ISO 13943:2008, 4.185]
© IEC 2019
3.34
ignition
sustained ignition (deprecated)
general: initiation of combustion
[SOURCE: ISO 13943:2008, 4.187]
3.35
ignitability, ease of ignition
measure of the ease with which a test specimen can be ignited, under specified conditions;
ignition time, conditions; ignition time
[SOURCE: ISO 13943:2008, 4.182]
3.36
ignition source
source of energy that initiates combustion
[SOURCE: ISO 13943:2008, 4.189]
3.37
incipient fire
initial fire
3.38
means of egress
continuous and unobstructed way of exit travel from any point in a building or structure to a
public way and consists of three separate and distinct parts: a) the exit access, b) the exit and
c) the exit discharge
Note 1 to entry: A means of egress comprises the vertical and horizontal travel and should include intervening
room spaces, doorways, hallways, corridors, passageways, balconies, ramps, stairs, enclosures, lobbies,
escalators, horizontal exits, courts, and yards.
3.39
non-combustible
not capable of undergoing combustion (under specified conditions)
Note 1 to entry: In some regulations a material is classified as being non-combustible even if it is capable of
combustion, provided that its heat of combustion (4.174) is less than defined amount.
[SOURCE: ISO 13943:2008, 4.239]
3.40
non-flammable
not capable of burning with a flame (3.27 and 3.28) under specified conditions
[SOURCE: ISO 13943:2008, 4.240]
3.41
overheating
excessive rise in temperature of a material or body
3.42
quick response sprinkler
type of sprinkler that is both a fast response and a spray sprinkler
– 12 – IEC TR 62757:2015+AMD1:2019 CSV
© IEC 2019
3.43
flame spread
propagation of a flame front
[SOURCE: ISO 13943:2008, 4.142]
3.44
self-extinguish, verb
auto-extinguish, verb
cease combustion without being affected by any external agent
[SOURCE: ISO 13943:2008, 4.284]
3.45
self-extinguishing
the characteristic of a material ceasing to burn, under specified test conditions, after the
igniting source has been removed
Note 1 to entry: Although in common usage (including this report), this term is deprecated in international
standards because it may convey a false sense of security and lead to misunderstanding. The properties of
materials after removal of an ignition source are better described by the afterflame time, the afterglow time, the
extent of combustion and the damaged area (length) under specified test conditions (compiled from various
sources).
3.46
semiconductor device
one of the series connected devices used in valves such as thyristors, diodes or insulated
gate bipolar transistors (IGBTs)
3.47
smoke
visible part of fire effluent
[SOURCE: ISO 13943:2008, 4.293]
3.48
smoke detector
fire detector which initiates an alarm on the presence of a certain quantity of smoke
3.49
smoke development rating
smoke development rating means an index or classification indicating the smoke development
characteristics of a material or an assembly of a material as determined in a standard fire test
3.50
smoke management system
any system designed and installed to control the accumulation and spread of smoke in a
building
3.51
water spray deluge system
special fixed pipe system connected to a reliable source of fire protection water supply and
equipped with water spray nozzles for specific water discharge and distribution over the
surface or area to be protected
Note 1 to entry: The piping system is connected to the water supply through an automatically or manually
actuated valve that initiates the flow of water. An automatic valve is actuated by operation of automatic detection
equipment installed in the same areas as the water spray nozzles. (in special cases the automatic detection
equipment may also be located in another area).
© IEC 2019
4 Fire hazards in valves and valve halls
4.1 General
Converter valve halls house the converter valves, wall bushings or converter transformer
bushings, valve and group arresters as well as, in certain designs, other high voltage
components such as high voltage capacitors or voltage dividers and current transducers.
The valve equipment is subjected to various mechanical and electrical stresses during
operation. They are designed and constructed from many series and parallel connected
components such as thyristors, diodes, IGBTs (and similar packages), capacitors, resistors
and saturable reactors.
To minimize the space requirement in the valve hall, the valves are often vertically stacked to
take advantage of the graded insulation level. The necessary creepage and electrical
clearances between and within the valves are achieved by the use of porcelain insulators
and/or composite insulators. Extensive use of composite materials is made in the structural
components of the valves.
Several years ago, following the spate of fires that culminated in the generation of CIGRÉ
Technical Brochure 136, several purchasers demanded that no oil-filled components be in the
valve hall and that valve components be generally fire retardant. Today also, the valve
structure comprises various materials such as plastics, composites, and rubbers, the non-
metallic materials being fire retardant, self-extinguishing, generally to UL94V-0 or equivalent.
There is essentially minimal combustible material in the converter valve equipment, however,
materials will burn if there is sufficient heat input from the ignition source. The possible
sources of fire in a valve hall are discussed in detail in the following clauses, and cover HVDC
and FACTS equipment (thyristor valves, SVCs, STATCOMs, VSC, etc.).
4.2 Possible causes
4.2.1 Valve insulation failure
Breakdown of electrical insulation within or between parts of the valve which are common to
more than one semiconductor device level can lead to arcing which could ignite flammable
materials.
Insulation failure could be internal, for example due to partial discharges in a dielectric
material, or external due to corona or contamination of insulating surfaces (e.g. as a result of
a coolant leak). Smoke or other ionised by-products arising from, for example, an overheated
electrical component can reduce the withstand voltage of the air insulation within the valve.
The consequences of insulation failure will strongly depend on the location, materials and
energy associated with the event. It should be noted that it is not necessary for total
breakdown of an insulation system to occur before hazardous conditions can arise. High
surface leakage currents, for example on a contaminated insulating surface can, depending
on the materials, present a direct risk of combustion.
4.2.2 Loose connections or high resistance joints in the power circuit
An overheated connection or series arc can arise from improper connection of bus bars used
for carrying the load current. These could be connections between different sections of the
valve, with the series reactor, with the semiconductor device or any other connector which
forms the path of the load current. Any loose connection or high resistance joint will overheat.
In the case of an open circuited connection, a series arc will develop. In either case the heat
generated will depend on the level of the current and may cause damage to adjacent
components, especially insulating material. If the temperatures reached are high enough then
it may lead to a fire.
– 14 – IEC TR 62757:2015+AMD1:2019 CSV
© IEC 2019
4.2.3 Valve component failures
4.2.3.1 General
Breakdown of electrical insulation within or between parts of the valve which are common to
more than one thyristor level can lead to arcing which could cause charring of components or
ignition in certain circumstances if the source is sufficiently intense.
4.2.3.2 Thyristors and diodes
When overstressed, thyristors and diodes fail to an approximate short circuit. Provided that
they remain properly clamped and cooled, short circuited thyristors can safely conduct normal
load current and overcurrents. By providing series redundant levels, a valve can be kept in
service for long periods in the presence of a small number of short circuited thyristors.
The thyristors and diodes themselves are non-flammable and, because failure relieves other
components from significant voltage stress, it is often arranged that other component faults
lead directly or indirectly to thyristor short circuit, thereby avoiding a hazardous condition
elsewhere.
4.2.3.3 IGBT and similar semiconductor devices - diode pairs
These devices are, at the time of writing, manufactured mainly as single-side cooled
encapsulated assemblies, although press-pack assemblies are available. The press-pack
assemblies should fail to short-circuit but the encapsulated assemblies can fail to either short
circuit or open circuit. The mode of failure is not fully controlled. The mode of failure can
lead to rupture, or even a more explosive effect. To protect against this uncertainty, a
component such as a fast-acting switch in parallel with the semiconductor device needs to be
included.
The thyristors and diodes themselves are non-flammable and, because failure relieves other
components from significant voltage stress, it is often arranged that other component faults
lead directly or indirectly to thyristor short circuit, thereby avoiding a hazardous condition
elsewhere.
4.2.3.4 Capacitors
To obtain long life and high reliability at the operating voltage of one semiconductor device
level, capacitors which experience this voltage should employ an impregnated dielectric
construction.
Non-flammable impregnating fluids based on polychlorinated bi-phenyls (PCB) exist, but are
prohibited on environmental grounds.
Today, many capacitors contain (usually small) quantities of an impregnating medium in the
form of a resin which, if exposed to air and an ignition source can burn. Capacitors may also
be impregnated with special dielectric fluids, all of which are flammable material. Virtually all
high voltage capacitors today use polypropylene as the dielectric which also may burn if
exposed to air and ignition. The failure modes of these capacitors are therefore of particular
interest.
In all cases, rupture of the capacitor can is an essential pre-requisite for exposing the
dielectric material and impregnating medium to air. This could arise from mechanical damage
caused by abuse or resulting from a production defect, or from an electrical fault inside the
capacitor. Internal faults for example short circuit of one or more capacitor elements, sparking
at a broken internal connection, etc. can cause decomposition of the dielectric material and/or
of the impregnating medium, leading to a build-up of pressure inside the capacitor. Unless the
process can be arrested (e.g. the capacitor is rendered open circuit by operation of an over-
pressure protection device) or the pressure is relieved in a controlled and safe manner, then
the over-pressure may lead to rupture of the can. Electrical arcing/overheating of the now
© IEC 2019
disrupted capacitor provides a likely source of ignition. Recent experiences demonstrate that
the risk for fire of contained polypropylene capacitors is low.
Capacitors that are dry type, normally contain polyurethane or silicone gel, as filling material
does not burn itself even though it is exposed to air.
Capacitors that are dry type, normally containing polyurethane, silicone gel or N2 and SF6
gas, have no flammable fluids that can leak out of the housing.
4.2.3.5 Reactors
The reactors within a valve equipment may be liquid cooled. A mode of failure of valve
reactors is overheating due to total or partial blockage of the cooling pipes or the leakage of a
joint within the reactors. If such a condition goes undetected, failure of the reactor is possible
and this may cause a fire within the valve equipment.
Other modes of failure could be turn-to-turn or turn-to-core insulation failure or for example
failure of the banding straps used to secure the reactor cores.
The consequences of such failures will depend on the particular valve design.
4.2.3.6 Resistors
The resistors used in damping circuits are generally wire wound, although thick-film devices
are frequently used. The failure of resistors could be due to overheating of the element
caused by inadequate cooling or corrosion of resistor elements which are in direct contact
with the coolant. If the resistors are indirectly cooled, i.e. heatsink mounted, the breakdown of
the resistor to the heatsink could result in localised arcing. This may result in open circuit,
insulation or housing failure. If the insulation provided is flammable, then it may ignite.
Another scenario would be that the arcing inside the resistor persists and the resistor may fail
explosively, damaging other adjacent components. This can lead to arcing and flashover.
4.2.3.7 Electronic circuits
The electronic circuits for the control, protection and monitoring of the thyristors are normally
of low power. The failure of individual components may, however, pose a fire hazard. Two
situations could be:
a) The semiconductor device firing electronics provides gate trigger pulses to more than one
series-connected semiconductor device via insulated output pulse transformers. Failure of
the insulation of a pulse transformer could result in load current flowing in low current
wiring.
b) The electronic circuits require a source of power which, for HVDC valves, is normally
extracted from one of the voltage grading networks at the respective semiconductor
device level. The power supply must provide sufficient energy to meet performance
requirements under the worst operating conditions, therefore, under other conditions,
more energy than is needed is available. The technique adopted to control this surplus
energy could influence the consequences of a component failure in this part of the circuit.
4.2.3.8 Light guides Fibre optics
Light guides Fibre optics, either individually or in bundles, involve a risk of fire ignition, if
exposed to conductive surface contamination or uncontrolled voltage distribution along the
fibre optics. Certain types of light guide fibre optics jacket material may sustain combustion
and transfer fire within the valve structure.
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