EV Rule 2015 clarification

[Sharan]

Hello,
I'm Piyush from India. We are building our first Elecric Race car to participate in Formula Student 2015.
I have a doubt in the undermentioned 2015 rule.

EV3.3.3:
Maintenance plugs, additional contactors or similar measures have to be taken to allow electrical separation of the internal cell segments such that the separated cell segments contain a maximum static voltage of less than 120VDC and a maximum energy of 6MJ. The separation must affect both poles of the segment.

This separation method must be used whenever the accumulator containers are opened for maintenance and whenever accumulator segments are removed from the container.
Doubts:
1. What are maintenance plugs?
2. How to control auxilary contacts of additional contactors?
3. What does the line ' The separation must affect both poles of the segment' mean?


We are currently using a cell configuration of 24s4p.
https://www.dropbox.com/s/to9mc5nt9g...photo.JPG?dl=0 contains the top view schematic of the connections.
Each compartment contains 24 cells with 6s4p configuration.

[Adam Farabaugh]

1. A device which can be used to separate both poles of the described segments (smart alec response).

2. Not sure what you're asking here... are you thinking of using contactors as maintenance plugs?

3. Your maintenance plugs must separate both poles of each 6S4P segment from all the other 6S4P segments. You can't just separate the positive terminal, you have to separate the positive terminal AND the negative terminal of your segment from the other segments.

[Sharan]

Yes, I'm talking about using contactors as maintenance plugs.

[Adam Farabaugh]

If that's legal at all then you definitely will have to use normally-open contactors then.

Is there a particular reason why you want to use contactors? What are the benefits?

[sekl]

Sharan,

below some thoughts from me about your questions / rule EV3.3.3. As you are not very specific in your post, please do not automatically assume my thoughts are applicable to your system.

The rules are in my opinion very clear about all your questions and I can only advise to read them over and over again, discuss them as a team (document how you interpret the rules as a team!), and review your designs specifically for rules compliance throughout the design process.

However, here´s my thoughts.

1. What are maintenance plugs?
3. What does the line ' The separation must affect both poles of the segment' mean?

For reference, the complete rule EV3.3.3 in italic - my interpretation between the paragraphs:

Maintenance plugs, additional contactors or similar measures have to be taken to allow electrical
separation of the internal cell segments such that the separated cell segments contain a maximum
static voltage of less than 120VDC and a maximum energy of 6MJ. The separation must affect both
poles of the segment

"Maintenance Plugs" is a random name for a device used for separation of the cells into segments. It is written in the same sentence as "or similar measures", so you got some design freedom about how this device might look like.
Both poles have to be affected means, in case you have to separate parallel cells to maintain the energy limit, it is not acceptable to separate only one pole of parallel segments. As I do not know what capacity your pack has, I do not know if this is needed for your pack. With a max voltage of just 88.8 V, I recommend you have a look at it.

This separation method must be used whenever the accumulator containers are opened for
maintenance and whenever accumulator segments are removed from the container.

Whatever measure chosen, it must be possible to make use of it as first thing after opening the accumulator container. It is not acceptable to work on the accumulator by any means before the pack is separated into segments. If contactors are used, this can easily be realized by removing power form the contactors before opening the container already.

Maintenance plugs requiring tools to separate the segments will not be accepted.

"Maintenance Plugs" can (should) be replaced with "Separation methods", the rest is pretty clear I think.

Maintenance plugs must include a positive locking feature which prevents the plug from
unintentionally becoming loose.

"Maintenance Plugs" can (should) be replaced with "Separation methods other than contactors". In my interpretation, positive locking is to be understood as described in EV4.5.12 as the separation device is in any case part of the high current path.

Maintenance plugs must be non-conductive on surfaces that do not provide any electrical connection.

Seems clear to me.

2. How to control auxilary contacts of additional contactors?

There is no specific requirement by the rules about how to control contactors used as separation device. I suggest to keep them closed whenever the accumulator system is supplied with your GLV System Voltage. Depending on how your BMS is connected to the cells, you have to avoid opening any of these contactors while your main "accumulator insulation relais" are closed, as this can cause load current to flow through the BMS - which will likely damage it. Having the contactors between the segments always powered when your control system is on, can be considered an electrical positive lock to avoid said situation, another would be to ´design the BMS with respect to it but I will not go into further detail what the needed considerations for this are. Again, I recommend to not open the maintenance contactors in case the shutdown circuit opens but only if the GLV system is off.


My personal opinion is, contactors are not a good thing to use. A well done mechanical solution will be much smaller, lighter, cheaper and less complex to integrate into the accumulator system than contactors. A simple bayonet lock of the shelf connector with appropriate electrical ratings does the job and you can even design measures for positive locking (as mentioned, from my rules interpretation rule EV4.5.12 does apply) which gives you endless options to design something yourself.

Not to be forgotten, in my opinion a mechanical system is also safer, as it can easily be designed to allow visual inspection whereby a contactor looks always the same - failed or functional - causing high risk that a stuck contactor will not be detected.

I hope my thoughts help you a little.

Best Regards,
Sebastian

[Sharan]

Thank You Sebastian for your thoughts