Conductor over current protection over 600 volts

[TmacK]

We have an existing outdoor 3,750 KVA transformer installation 12.4 KV to
2.4 KV
Currently 4 taps from the transformer 2.4 KV are in armored cable, in a cable tray, to metal clad switch gear. (Individual starters)

Loads are all Induction motors, the largest is 1000 hp.
The length of these taps from the transformer 2.4 KV secondary, to the starters is about 30 feet.

Transformer has primary fusing on the primary 12.4 KV and nothing at the secondary.
Co-ordination TCC plots indicate the primary is fused at about 400 amperes with an RBA-200.

We are an 18 MW user and It appears we meet guidelines of 70 E for supervised/qualified installations.

We would like to add 2 additional 350 hp motors onto this transformer secondary. One 350 motor will be the normal running conditions with 2 motors being intermitten during a switch from one pump to the other.

It appears as if only articles 240.100 and 240.101 apply.
Do we need overcurrent protection at the transformer for this new feeder?
Is there a tap rule that applies to installations over 600 Volts?
If 240.100 applies, do we have to upgrade the existing feeders if we touch it?

thanks

 

[wirenut1980]

I would say Table 450.3(A) applies. Depending on the transformer impedance, there are requirements for primary and secondary protection. If you have overcurrent protection at your starters, that meets the Table, then I think you are ok. For the 350 hp motors, I think you will need some type of secondary protection. I am not sure how the tap rules in Article 240 apply to over 600 V? I would think that the same principles apply as for under 600 Volt installations...