HEV Aux Power Grounding

[OnTarget]

I am working on a hybrid electric vehicle application. The electrical system will put out some auxiliary power (30kW) to use for various loads. Most of the power will be used when the vehicle is stopped (not during vehicle propulsion) but some will be used on-the-fly.

My question is ... Are there any best practices for grounding the HEV electrical system when the vehicle is parked and the power is being drawn for external use?

Vince Socci

http://www.ontargettechnology.com

 

[UKpete]

Do you mean to physically earth the vehicle body when it is stationary and feeding an external load? I don't see why you need to do this if the battery supply is properly isolated from the chassis (as it always is in HEV systems where the traction supply is typically 144 or 288V dc).

I have seen HEV systems where there is a potential divider system to the vehicle body (i.e. high value resistors are connected from each side of the battery to the vehicle body). The purpose of this is to detect when there is an earth fault on either side of the battery, because the voltages across the resistors no longer balance. In the case of a fault there is a contactor in the battery management system which opens to isolate the battery output.

 

[mc5w]

2005 National Electrical Code 625.26 does allow the use of an electric vehicle as an optional standby power source if it is listed for the purpose. For this use you do need an open sequence transfer switch.

You are also allowed to use a vehicle that is listed for the purpose as a parallel power production source but you have to have a listed cogeneration transfer switch with a control relay that disconnects from the utility when the utility power fails. Your hookup has to be approved by the utility for safety and power quality reasons.

Previous editions of NEC did not allow this.