Earthing System

[Xnikan]

Hello to everyone, this is my very first thread - I had a look on the forum but I didn't see anything relevant to my question.


Ok, so I design a battery storage system (800 DC Volts output) that will be connected though a 3-phase inverter to the local low-voltage grid.

My BESS has an IT-earthing system as you would imagine. Is there any restriction that I need to take into account, when connecting my BESS to the local grid which has (most likely) a TN-system?

Any opinion on that would be very helpful, thank you in advance!

 

[Mbrooke]

What is BESS?


Without knowing much more, my gut instinct is an isolation transformer.


BTW, welcome to the forum

 

[Hoxton]

Battery Energy Storage System (BESS) ?

Xnikan

Again welcome

It is convention when having a defined term, to capitalize it, if you want to abbreviate it, put the abbreviation in brackets after the first time you use the term, then the reader can skim back to find the meaning.

Have you asked your electrical utility if they have any requirements?

 

[protoslash]

I work in utility and we recently did connect a 500kW BESS on our system.

At this site, our customer were installing Tesla battery pack and they were following Tesla's recommendation on which grounding method is best for their battery's operation and protection. From our point of view, we don't care about customer's grounding very much. It's fine as long as you can demonstrate your protection can clear faults on your site. What we do look at is your short circuit contribution, generation capacity and islanding behavior.

 

[Xnikan]

Thanks everyone for the replies and apologies for not explaining the abbreviation BESS - Battery Energy Storage Sustem.

I design the system for a location in Germany and I have been searching through standards to confirm that there is no restriction for my system's grounding. So far I haven't managed to find anything relative to my question in the official regulations - My instict is (as protoslash already mentioned) that if the protection plan of my system is capable of clearing the faults that would't be any problem.

 

[Hoxton]

Germany!

One of the most regulated countries in Europe!

Try contacting VDMA

https://www.vdma.org/

They are a trade association who will be able to help you, but may decline, if you are not a member

or try this

http://www.electrical-installation.org/enwiki/Electrical_regulations_and_standards

 

[mc5w]

You should not leave the DC 100% ungrounded. My experience with 480 volts ungrounded that had no transformer + light bulb ground detector that ungrounded systems can build up EXPLOSIVE amnounts of static electricity. You should ultrahigh resistance ground your system by making up 2 series strings of 330,00 Ohm 3 watt metal film resistors with 6 resistors in series each string. Connect 1 string from the positive side to ground and the other from the negative side to ground. You should also use Merlin Gerin's Vigilohm subsonic automatic fault tracing system. This uses a 2.5 Hertz subsonic tracing tone and special ground fault relays to monitor for ground faults. This is the only subsonic tracing system that has permanently installed tracing transmitters and receivers for your voltage but I might be wrong - you should go to

http://www.benderinc.com

and check out their Isoscan system . You can also buy portable transmitters and receivers for deenergizerd or live troubleshooting for Vigilohm and Isoscan systems. Megger also makes a portable subsonic tracing system but it cannot be permanently installed. Merlin Gerin also makes a medical grade version of the Vigilohm system that uses the subsonic tone to monitor the insulation resistance of each portion of the system and soundfs an alarm if the insulation resistance falls below a threshold.

The Vigilohm system also has the ability on resistance grounded and IT systems to find ground faults that are close to or at the center of a source or load on a single phase or DC system or close to or at the neutral point of a wye source or load on a 3-phase system. Finding these kinds of faults on a solidly grounded system is extremely difficult. When you are using transformer + light bulb ground detectors on an ungrounded system the only method that works without the Merlin Gerin system is to unscrew 2 light bulbs at a time.

 

[Xnikan]

In accordance with the standard VDE-AR-E 2510-2 (Connection of stationary storage system to the low voltage grid) for an IT system (unearthed system) an earth fault relay that uses residual voltage as the evaluation criterion shall not be used. Instead, an Insulaltion Monitoring Device (IMD) should be used a part of the protection scheme.