Control Supply Selection

It all depends upon:

i) What is the total burden connected to the control supply?

ii) What is the maximum length of the control cable?

iii) What will be the voltage drop in the longest cable, both under steady-state conditions as well as during switching-in-rush conditions? Is it under permissible limits?

etc.

In addition to post #1,

(iv) What is your substation battery backup voltage?

(v) What do your substation electrical standards state (have you checked them)?

Also have a look on CR4 as I believe this question has been answered before (and the voltage does seem to depend on the country).

Hello,

Thanks for your reply. However, i am not talking about the existing Sub-sation. If it is the case of a green field project, probably i have to select my battery output also based on required control supply of various switchgears/panels,etc.,

Also, in Indian standards, there is no reccomendation for a specific voltage level. Users have to decide on thier own.

I am quite convinced with the ans from our fellow-user Mr. ElectricExpert65. I would still like to hear from you all if there is any other facts to consider for deciding the same.

Also a question in addtion to this reply, what is the reason for people to say dc control voltages are always more reliable than ac?

Regards,

Manimaran.V

Well it does depend a little on the equipment you want to power and the existing equipment supply voltage standardisation. You would likely want to use the voltage of the combined DC load(s) that draw the highest current as the standard voltage and then use additional step-up and step-down DC-DC converters for powering any other loads that require a different voltage. This generally results in the cheapest solution.

Also a question in addtion to this reply, what is the reason for people to say dc control voltages are always more reliable than ac?

The reason behind this comment is probably that DC power supplies can be equipped with a DC battery backup in the event that the AC supply is unstable or lost (hence DC can be a more reliable supply).

Manimarsan,

AS noted earlier check the specs to be sure your power authority has no specific standards, see what size and best availability of UPS/ battery backup power supply you can find/ but for non US where the standard is 50HZ 220 /380 country, use 220, as relays, control devices. etc are more readily available for emergency maintainance.

Best Regards

Soy Cowboy

What is the incoming power voltage?

Currently most Industrial controls systems use 480VAC 3PH with 24VDC control voltage.

What will be powered from the Sub Station? Heaters, Motors,etc...

What voltages will be needed to be supplied from the sub station?

Make a detailed list of all components included in the list all the voltages and current load that will be requied. Find the most common volt and start there. Most devices are available in different voltages. Some devices can run on voltage from 86 to 240VAC single phase. Safety is number one...using low voltage for controls can help limit arc flash in a failure.

Good luck, Sound like you may need to find someone who has done this before and ask/paid for help.