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IEC TR 62757-2015: Fire Prevention Measures on Converters for HVDC, SVC and FACTS and Their Valve Halls
This technical report provides comprehensive guidance on fire prevention, detection, and suppression for converter valves and valve halls in HVDC systems, static VAR compensators (SVC), and flexible AC transmission systems (FACTS). It consolidates industry experience from documented fire incidents across global HVDC projects, providing essential recommendations for utilities and consultants preparing technical specifications.
1. Fire Hazards in Valves and Valve Halls
IEC TR 62757-2015 identifies ten primary categories of fire hazards in converter valves and valve halls, based on systematic analysis of documented fire incidents from HVDC projects worldwide. The valve insulation failure category includes flashovers across valve structures due to pollution, moisture ingress, or voltage surges, which can initiate arc faults with energy sufficient to ignite adjacent materials. Loose connections or high resistance joints in the main power circuit represent a particularly insidious hazard, as they can develop gradually over years of thermal cycling and finally fail in a catastrophic manner.
Valve component failures include capacitor rupture, saturable reactor insulation breakdown, and bushing flashover. The report documents cases where capacitor failures in valve modules ejected hot dielectric material, igniting adjacent components. Semiconductor device level failures, though rare due to rigorous type testing, can occur when anti-parallel diodes fail short-circuit, causing explosion of the device casing and potential propagation to adjacent modules through the arc plasma.
| Hazard Category | Primary Cause | Potential Consequences | Risk Level |
|---|---|---|---|
| Insulation failure | Pollution, moisture, voltage surges | Flashover, arc propagation, fire | High |
| Loose connections | Thermal cycling, vibration | Overheating, molten metal ejection | High |
| Capacitor failure | Dielectric breakdown, overvoltage | Rupture, hot dielectric ejection | Medium |
| Semiconductor failure | Overcurrent, cosmic ray | Device explosion, arc flash | Medium |
| Coolant system | Leakage, pump failure | Reduced cooling, overheating | High |
| Valve hall bushing | Contamination, mechanical damage | Flashover, fire on bushing surface | Medium |
An important finding from the survey of fire incidents: coolant system problems are among the most frequent triggers of valve overheating and eventual fire. Reduced cooling flow due to pump failure, blocked filters, or air ingress into the coolant loop can cause rapid temperature rise in semiconductor devices. The report recommends redundant coolant pumps with automatic changeover and continuous flow monitoring with alarm thresholds set at 80 % of nominal flow rate.
2. Fire Detection and Suppression Systems
The technical report provides detailed guidance on fire detection technologies suitable for valve hall environments, where high electric fields, limited access, and the presence of sensitive electronic equipment impose unique constraints. Seven detection principles are evaluated:
- Air sampling systems (aspirating smoke detectors): Preferred for early warning, as they can detect pyrolysis products before visible smoke or flame develop. The report recommends Very Early Warning Smoke Detection Apparatus (VESDA) with sensitivity below 0.1 % obscuration per meter.
- Infrared beam smoke detectors: Effective for large volume valve halls but require careful alignment and can be affected by steam from coolant system vents.
- Arc detector systems: Detect the ultra-violet radiation from arc faults with microsecond response time, enabling rapid isolation of the faulted section before fire develops.
- Infrared flame detectors: Suitable for detecting hydrocarbon fires but may be triggered by hot work (welding, grinding) during maintenance.
For fire suppression, the report evaluates various extinguishing agents. Carbon dioxide (CO&sub2;) systems are effective but pose asphyxiation risks to personnel, requiring rigorous safety interlocks. Inert gases (IG-541, IG-55) offer a safer alternative but require larger storage volumes. Hydrofluorocarbon (HFC) agents provide effective suppression with lower space requirements but raise environmental concerns due to global warming potential.
| Extinguishing Agent | Advantages | Disadvantages | Typical Applications |
|---|---|---|---|
| CO&sub2; (Carbon dioxide) | Low cost, effective, no residue | Asphyxiation risk, requires sealed room | Small to medium valve halls |
| IG-541 (Inergen) | Breathable at design concentration | Large cylinder footprint, higher cost | Occupied valve halls |
| HFC-227ea (FM-200) | Compact, fast discharge | GWP concern, thermal decomposition byproducts | Retrofit, space-constrained halls |
| Water mist | No GWP, minimal damage, cooling effect | Requires high-pressure pumps, conductivity concern | Large valve halls, outdoor installations |
Engineering Insight: The report recommends a layered detection strategy combining aspiration smoke detection (for early warning) with arc detection (for rapid fault localization). The fire detection system should be integrated with the converter control system to enable automatic emergency shutdown sequences graded by alarm severity: alert (suspected pre-combustion), warning (confirmed smoke/fire), and emergency (immediate trip and suppression release). The converter control system must distinguish between fire alarms and electrical faults to avoid unnecessary shutdowns.
3. Valve Hall Layout, Access, and Ventilation Management
The standard provides specific recommendations for valve hall physical arrangement to minimize fire risk and facilitate firefighting. Key provisions include:
Physical segregation: Converter valves should be arranged in fire compartments separated by walls or barriers with minimum EI 120 (120-minute fire resistance). Cable penetrations between compartments must be sealed with firestop systems tested to IEC 61841.
Means of egress: The valve hall must have at least two exits located at opposite ends, with emergency lighting powered from a redundant source. Exit doors must open outward and be equipped with panic hardware. The report emphasizes that egress routes must remain usable during a fire event, considering the potential for smoke filling the hall.
Vent management: The ventilation system design must consider the fire scenario. Under normal operation, positive pressure is maintained with filtered air to prevent pollution ingress. In fire mode, the ventilation system should either be automatically shut down (for total flooding gas suppression systems) or switched to smoke extraction mode (for sprinkler or water mist systems). The transition between modes must be carefully sequenced to avoid creating pressure differentials that could damage the valve hall structure.
A critical lesson from documented incidents: Fire in valve halls can propagate rapidly through the coolant system. If deionized water coolant is used (common in high-power VSC valves), a coolant leak combined with an electrical fault can create a conductive path, leading to arc tracking along coolant hoses. The report recommends using flame-retardant hose materials (meeting IEC 60332-1), installing flow switches on each cooling branch, and implementing automatic valve isolation in the coolant system to limit the volume of coolant that can leak into a fire zone.
4. FAQs
Q: Is this standard applicable to both LCC and VSC HVDC systems?
A: Yes, the standard covers both line-commutated converter (LCC) and voltage-sourced converter (VSC) technologies. The fire hazards differ somewhat between the two — LCC valves use more oil-filled components, while VSC valves have more capacitor banks and coolant connections — but the overall fire prevention framework applies to both.
Q: What is the recommended fire detection coverage for valve halls?
A: The report recommends comprehensive coverage with aspirating smoke detection (sampling points every 50–100 m² of floor area and at each valve layer), arc detection on each valve structure quadrant, and infrared flame detection covering the entire valve hall volume. Overlapping coverage is essential to avoid blind spots behind valve structures.
Q: How should fire suppression systems coordinate with high-voltage equipment?
A: The suppression system must not compromise electrical safety. Before releasing any extinguishing agent, the converter must be blocked and all high-voltage connections grounded via the earthing switches. The hold-off time for CO&sub2; systems must account for the time required for personnel evacuation. Interlocks should prevent suppression release while personnel are detected inside the valve hall.
Q: Are there specific requirements for firefighting access in valve halls?
A: Yes, Clause 5.3 specifies that firefighting access routes must be provided with minimum 1.2 m clear width, and fire hydrants must be located outside the valve hall at a safe distance (minimum 15 m from valve hall walls) to allow firefighters to operate without exposure to electrical hazards. The valve hall design must include break-glass access panels at multiple locations for fire hose access.
