Battery Storage inverter not earhted on AC side

[sivajith]

Hi,
I came across a design in which a grid tie inverter (110kVA at 415V) is connected to Battery system on DC side. On the AC side the inverter is connected via separate isolation transformer (delta -star). delta on inverter end and Star on utility end. Hence the inverter AC side is ungrounded. If there any minimum requirement stipulated by any standard if any type protection is required between inverter and the isolation transformer. The cable run between between the transformer and inverter is 10m.

 

[FreddyNurk]

Its quite difficult to advise on any relevant standards without knowing a location, however, I'd expect some sort of legislative requirement to be able to appropriately be able to detect and clear faults, which would include the ungrounded section of the installation. From where I am I know the utility took a very strong stance on not having appropriate protection on ungrounded schemes, but results may vary on location.

There are obviously varying ways to achieve this, its also usually a lot easier with a grounded system and some sort of current protection, but not impossible with an ungrounded scheme. An insulation monitoring scheme might be able to be used. Depending on the level of isolation on the DC bus to the AC stage, a DC ground fault system may also pick up inadvertent grounding on the AC side.

 

[waross]

(2) Wiring systems supplied by an ungrounded supply shall be equipped with a suitable ground fault detection
device to indicate the presence of a ground fault.
(3) Ground fault indication activated by the ground fault detection device required by Subrule (2) shall be
clearly
(a) labelled as to its purpose; and
(b) visible to persons monitoring the status of the system.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

I'm more used to seeing both inverter and transformer in a single, listed, package. Then it's all up to the testing lab to determine if everything is taken care of. I wouldn't be surprised to find that your inverter can do its own ground fault detection.