3.3.2 Operation and Maintenance
When working on high-voltage systems, always ensure that the main switch is in the “off” position and tag it and/or lock it in that position so that no one else can turn the vehicle on.
Always assume that high-voltage electrical components are live, even when the vehicle main switch is in the off position. Use a volt meter to check before touching any electrical component.
Always use appropriate personal protective equipment, such as high-voltage gloves, when working on high-voltage systems. Follow the safety recommendations in the manufacturer’s service manual.
Never wear jewelry when working around high-voltage systems.
Always reinstall high-voltage covers and barriers. Reapply high-voltage labels if they are removed or damaged.
Do not ignore warnings from the ground fault monitoring system. Follow instructions in the service manual to isolate and repair the source of the fault. Unrepaired ground faults can cause shocks or electrocution to vehicle occupants or service technicians.
High-voltage electrical cables are designed with special shielding and insulation, and the exterior cover should be made from orange colored material. Always replace high-voltage wiring and harnesses with parts as specified by the manufacturer. Do not manufacture your own high-voltage harnesses or substitute non-approved parts.
Remember that high voltage will always be present inside a traction battery or ultracapacitor pack (if vehicle has a hybrid-electric drive system) even when the main switch is off or automatic shutdown has occurred. Special tools and procedures are required to work safely inside the battery/ultracapacitor pack. Do not open the battery/ultracapacitor pack cover unless you have been trained to work safely with live high voltage.
Monday, June 9, 2014
3.3.1 Design
All electrical cables that carry greater than 30 VAC or 60 VDC should be considered high-voltage cables and should be permanently identified with orange covering material, and be located to preclude casual contact by vehicle operators and maintenance personnel. No high voltage cables should be routed through the passenger compartment.
Any part or connector energized with high voltage during normal operations should be located behind a cover or in an enclosure labeled with the hazardous voltage symbol. See Figure 18. Removal of the cover should require removal of special fasteners and/or should trigger an interlock system that de-energizes the high-voltage components. If the cover or enclosure is made of conductive material, it should be grounded to the vehicle chassis.
The electrical system should include an automatic disconnect function that isolates both poles of any high-voltage source (fuel cell stack and/or high voltage battery pack) from other system components.
The connectors used should be “fail safe” so that they will open if the control signal is lost due to a system fault. This automatic disconnect function should be triggered by the following:
• Turning off the main switch
• By automatic system shutdown (due to a hydrogen sensor detecting a leak, or other system fault that shuts off the hydrogen fuel supply)
All high-voltage components should be designed with adequate electrical isolation to prevent “current leakage” between them and other electrical components or the chassis. The vehicle control system should include a ground fault monitoring system that can detect leakage current and set a warning light and/or take other action (up to automatic system shutdown) when a current above a set threshold is detected.
All electrical cables that carry greater than 30 VAC or 60 VDC should be considered high-voltage cables and should be permanently identified with orange covering material, and be located to preclude casual contact by vehicle operators and maintenance personnel. No high voltage cables should be routed through the passenger compartment.
Any part or connector energized with high voltage during normal operations should be located behind a cover or in an enclosure labeled with the hazardous voltage symbol. See Figure 18. Removal of the cover should require removal of special fasteners and/or should trigger an interlock system that de-energizes the high-voltage components. If the cover or enclosure is made of conductive material, it should be grounded to the vehicle chassis.
The electrical system should include an automatic disconnect function that isolates both poles of any high-voltage source (fuel cell stack and/or high voltage battery pack) from other system components.
The connectors used should be “fail safe” so that they will open if the control signal is lost due to a system fault. This automatic disconnect function should be triggered by the following:
• Turning off the main switch
• By automatic system shutdown (due to a hydrogen sensor detecting a leak, or other system fault that shuts off the hydrogen fuel supply)
All high-voltage components should be designed with adequate electrical isolation to prevent “current leakage” between them and other electrical components or the chassis. The vehicle control system should include a ground fault monitoring system that can detect leakage current and set a warning light and/or take other action (up to automatic system shutdown) when a current above a set threshold is detected.
3.3 HIGH VOLTAGE SYSTEMS
Any voltage greater than 30 VAC or 60 VDC can harm humans through electric shock and is considered “hazardous voltage” (SAE, 2002).
Hydrogen fuel cells produce electricity at nominal voltages of 300 to 600 VDC, which is used to power an electric drive system that operates at similar voltages (often after conversion to alternating current). The drive system may be designed with a hybrid-electric configuration. If so, there will also be a high-voltage battery pack installed on the vehicle.
Hydrogen fueled ICEs do not produce electricity directly, but hydrogen ICE vehicles may also be designed with a hybrid-electric drive configuration. If so, they will also include a high-voltage battery pack and other high-voltage electrical components.
Any voltage greater than 30 VAC or 60 VDC can harm humans through electric shock and is considered “hazardous voltage” (SAE, 2002).
Hydrogen fuel cells produce electricity at nominal voltages of 300 to 600 VDC, which is used to power an electric drive system that operates at similar voltages (often after conversion to alternating current). The drive system may be designed with a hybrid-electric configuration. If so, there will also be a high-voltage battery pack installed on the vehicle.
Hydrogen fueled ICEs do not produce electricity directly, but hydrogen ICE vehicles may also be designed with a hybrid-electric drive configuration. If so, they will also include a high-voltage battery pack and other high-voltage electrical components.
Tuesday, June 3, 2014
3.2.2 Operation and Maintenance
Anyone who will operate or maintain liquid hydrogen-fueled vehicles should receive hydrogen safety training. At a minimum, this training should cover the characteristics of hydrogen and liquid hydrogen, operation of onboard safety systems, liquid hydrogen fueling operations, and actions to take in an emergency.
During maintenance, never substitute fuel system replacement parts that have not been specifically tested and certified for use with liquid hydrogen. Lines that will carry liquid hydrogen must be well-insulated with the outer layer of insulation vapor sealed. O-rings or other seals used in connections between liquid hydrogen lines must be made of special materials that can withstand liquid hydrogen temperatures without breaking. Substituting seals made of different materials can result in liquid hydrogen leaks.
When working on the liquid hydrogen fuel system, always wear personal protective equipment, including safety glasses and a full face shield, loose fitting insulated or leather gloves, leather boots ankle height or higher, a long-sleeved shirt, and long pants without cuffs. Pant legs should be worn outside of the boots.
Never loosen any joint in the hydrogen fuel system while the connected components are under pressure (gaseous hydrogen lines) or contain liquid hydrogen. Never disturb the insulation on liquid hydrogen lines or cryotanks while they contain liquid hydrogen. Shut down the system, isolate and vent components as directed in the manufacturer’s service manual. Torque all joints to the levels specified in the manufacturer’s service manual. Do not over tighten. Overtorquing can cause leaks.
Air must never be allowed to enter the hydrogen fuel system. If exposed to the atmosphere, any component that will carry liquid hydrogen (including cryotanks and lines) must be purged with helium before being refilled with liquid hydrogen. Nitrogen must not be used because the residual nitrogen in the lines could liquefy and freeze when exposed to liquid hydrogen. This could potentially plug pressure relief valves and other system valves. Alternatively, components can be purged of air with nitrogen and the nitrogen can be purged with gaseous hydrogen before refilling with liquid hydrogen. See the manufacturer’s service manual for specific purging procedures.
Periodically check all connections in the hydrogen fuel system for leaks using procedures outlined in the manufacturer’s service manual. Tighten or repair all leaking joints, no matter how small the leak.
Leak checks should also be conducted after repair or replacement of any fuel system lines or valves.
Periodically check the exterior surface of liquid hydrogen cryotanks and fuel lines for cuts or damage to the exterior insulation layer. All damage that breeches the vapor barrier must be repaired.
Periodically check and calibrate hydrogen sensors in accordance with the schedule and procedures in the manufacturer’s service manual.
Periodically check operation of the fan in the hydrogen diffuser and any ventilation fans, in accordance with the schedule and procedures in the manufacturer’s service manual.
Do not ignore warning lights or alarms. Do not attempt to override automatic system shutdown unless absolutely necessary (e.g., to move vehicle off railroad tracks).
Always make sure that the main switch is off before servicing the vehicle. Before working on the fuel cell system or liquid hydrogen storage system also disconnect the vehicle’s 12/24-VDC battery.
Do not walk on liquid hydrogen cryotanks or expose them to damage from impact or abrasion.
Always electrically ground and bond the vehicle when fueling. Connect the ground strap or cable at the fuel station if one is provided.
Before fueling, check that the onboard fuel port is free of dirt and debris. Always replace the fuel port dust cover after fueling.
Do not smoke or use a cell phone when servicing or fueling the vehicle.
The manufacturer of the liquid hydrogen cryotank will specify a minimum ullage13 space required in each tank. During fueling, this ullage space must be maintained and tanks should not be overfilled.
Anyone who will operate or maintain liquid hydrogen-fueled vehicles should receive hydrogen safety training. At a minimum, this training should cover the characteristics of hydrogen and liquid hydrogen, operation of onboard safety systems, liquid hydrogen fueling operations, and actions to take in an emergency.
During maintenance, never substitute fuel system replacement parts that have not been specifically tested and certified for use with liquid hydrogen. Lines that will carry liquid hydrogen must be well-insulated with the outer layer of insulation vapor sealed. O-rings or other seals used in connections between liquid hydrogen lines must be made of special materials that can withstand liquid hydrogen temperatures without breaking. Substituting seals made of different materials can result in liquid hydrogen leaks.
When working on the liquid hydrogen fuel system, always wear personal protective equipment, including safety glasses and a full face shield, loose fitting insulated or leather gloves, leather boots ankle height or higher, a long-sleeved shirt, and long pants without cuffs. Pant legs should be worn outside of the boots.
Never loosen any joint in the hydrogen fuel system while the connected components are under pressure (gaseous hydrogen lines) or contain liquid hydrogen. Never disturb the insulation on liquid hydrogen lines or cryotanks while they contain liquid hydrogen. Shut down the system, isolate and vent components as directed in the manufacturer’s service manual. Torque all joints to the levels specified in the manufacturer’s service manual. Do not over tighten. Overtorquing can cause leaks.
Air must never be allowed to enter the hydrogen fuel system. If exposed to the atmosphere, any component that will carry liquid hydrogen (including cryotanks and lines) must be purged with helium before being refilled with liquid hydrogen. Nitrogen must not be used because the residual nitrogen in the lines could liquefy and freeze when exposed to liquid hydrogen. This could potentially plug pressure relief valves and other system valves. Alternatively, components can be purged of air with nitrogen and the nitrogen can be purged with gaseous hydrogen before refilling with liquid hydrogen. See the manufacturer’s service manual for specific purging procedures.
Periodically check all connections in the hydrogen fuel system for leaks using procedures outlined in the manufacturer’s service manual. Tighten or repair all leaking joints, no matter how small the leak.
Leak checks should also be conducted after repair or replacement of any fuel system lines or valves.
Periodically check the exterior surface of liquid hydrogen cryotanks and fuel lines for cuts or damage to the exterior insulation layer. All damage that breeches the vapor barrier must be repaired.
Periodically check and calibrate hydrogen sensors in accordance with the schedule and procedures in the manufacturer’s service manual.
Periodically check operation of the fan in the hydrogen diffuser and any ventilation fans, in accordance with the schedule and procedures in the manufacturer’s service manual.
Do not ignore warning lights or alarms. Do not attempt to override automatic system shutdown unless absolutely necessary (e.g., to move vehicle off railroad tracks).
Always make sure that the main switch is off before servicing the vehicle. Before working on the fuel cell system or liquid hydrogen storage system also disconnect the vehicle’s 12/24-VDC battery.
Do not walk on liquid hydrogen cryotanks or expose them to damage from impact or abrasion.
Always electrically ground and bond the vehicle when fueling. Connect the ground strap or cable at the fuel station if one is provided.
Before fueling, check that the onboard fuel port is free of dirt and debris. Always replace the fuel port dust cover after fueling.
Do not smoke or use a cell phone when servicing or fueling the vehicle.
The manufacturer of the liquid hydrogen cryotank will specify a minimum ullage13 space required in each tank. During fueling, this ullage space must be maintained and tanks should not be overfilled.
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