[SystemSafety] Recharging Electric Road Vehicles

[Peter Bernard Ladkin]

Folks,

Happy Halloween!

I just wrote a blog post asking for your comments on eight memes which we have encountered in our 
work on risk-analysing the recharging of electric road vehicles. Because I understand that many 
people now read e-mails on tiny devices such as smartphones, and because the post is about 3 A4 
pages long, I'll just provide the link: 
http://www.abnormaldistribution.org/2012/10/31/recharging-electric-road-vehicles/

Here are the first few paragraphs. As the post says, I would be very grateful for any comments, if 
possible with your name and affiliation for appropriate credit. I intend sharing comments with my 
colleagues in committee.

[begin excerpt]

Recharging Electric Road Vehicles

I chair a group of specialists (electrical engineers, safety analysts, others) mandated by the 
German electrical-engineering standardisation organisation DKE to undertake a risk analysis of the 
process of recharging electric road vehicles.

We have been working now for close on one and a half years, on conductive charging, and have a 
document under internal review purporting to offer a high-level risk analysis of recharging using 
so-called “Mode 3”, in which a charging station permanently attached to the ground or to a structure 
is used. This mode offers charging-service providers and equipment providers the widest scope to 
ensure safety of the charging process, because anything considered necessary to assure an 
appropriate degree of safety (“safety functions” in the lingo of IEC 61508) can be built in to the box.

Other modes are Mode 2, in which a “box” with appropriate circuitry and safety mechanisms is built 
into the cable used for charging a vehicle, while the cable itself plugs straight in to building 
circuitry; and Mode 1, in which a charging cable is attached at one end to the vehicle and at the 
other to building circuitry, without any intermediating electrics or electronics.

The Renault Twizy car has a cable in front allowing Mode 1 charging (also Mode 3) through a normal 
“SchuKo” plug (“SchuKo” is short for “Schutz-Kontakt”, which means “contact-protected”, the usual 
kind of household plug through which current cannot flow until the person handling the plug is 
physically separated from live parts).

Inductive charging is somewhat further in the future.

The method we are using is a mix of OHA and HazOp. The OHA part is to consider the entire connected 
chain as a system, consisting of objects (subsystems)
* grid supply
* fixed charging column with connection to grid
* charging column/charging cable interface (plugset)
* charging cable
* charging cable/ vehicle interface
* vehicle
and to define the properties of and relations between these objects which we consider relevant to 
safety properties. We use the HazOp guideword process to extend the set of properties to consider 
and to guide us to possible hazard situations. We associated each hazard specifically with one of 
the subsystems involved in it.

We then used event trees to estimate the severity (worst-possible outcome) of each hazard. We were 
concerned with outcomes “electric shock” (to a person) and “fire”. We consider electric shock to a 
person to be at worst immediately deadly, and fire less so because a person has a certain 
possibility in general to extricate himherself from a fire situation. We evaluated each hazard as to 
whether it was unforeseeable, theoretically possible, or plausible.

There are a number of memes concerning this task which I think would like to introduce into 
discussion amongst safety specialists. I would like to ask for any of your thoughts on the following 
memes. I would like to share some thoughts transparently with colleagues, and wish to give 
appropriate credit for contributions, so I would be grateful if you would indicate whether your 
name, with or without your affiliation, may be associated with your view or whether you wish your 
comment to be anonymous. My email address is ladkin”AT”rvs.uni-bielefeld.de.

[end excerpt]

PBL

-- 
Prof. Peter Bernard Ladkin, Faculty of Technology, University of Bielefeld, 33594 Bielefeld, Germany
Tel+msg +49 (0)521 880 7319  www.rvs.uni-bielefeld.de