Switchgear 400V vs 3.3kV

Try a cost comparison, for one.

Present a convincing argument. You know the circumstances of the installation, right? Why do you think it is better for the client?

Or, are you in marketing?

same kind of system is exisitng at site means 220kW from 3.3kV thats why i am finding difficulty in convincing. Budget is not a issue with client and i am not in marketing.

If budget is not an issue, provide the Client with what he is prepared to pay for. Redevelop the scheme with components at 3.3kV, and be done with it.

What if there is only one motor > 150kW? Does he then want to run a separate 3.3kV service for it, or a step-up transformer?

There are 4 motors of 220kW.

3.3kV is sounding better as the information in this thread continues to be uncovered.

What about the arc flash considerations? I would think the higher voltage would represent significantly higher damage potential in an arc flash.

This point of view might give you more credibility if safety is important. Just don't over emphasize the point.

I can only assume that YOU read the Client's specifications BEFORE you decided to take on this project.

As soon as you took on this program, YOU committed to provide THEM with what they wanted. IF you cannot meet this criteria, WHY DID YOU BID IT?

RULE #1 The Client is always right

If in doubt refer to RULE #1

The client is always right..... but there are times when you can point out how the client can be more right than he is now.

3.3kV will require extra certification for the client's maintenance personnel. If they are already working on 3.3kV no problem, if not "High Tension" trained electricians come at premium prices and are not easy to find. (Comment based on UK experience)

That's the Client's problem, not the Original Poster's.

Thanks for all the responses.........seems no escape from 3.3kV system.

Dear Spiki,

Surely your 4 nos. of 220kW motors are driving some applications....conveyors, pumps, blowers whatever. There may be a solution. Talk to your Mechanical Counterpart/Process designer.........tell him your your problem, your considerations and how the incorporation of a new 3.3kV Switchboard along with all associated equipments, protections etc. would affect your budget and the entire project as a whole (hopefully you are in EPC business). And finally request him to reduce the motor ratings by redisigning. This is very much possible and often done.

e.g I am assuming arbitrary figures. say a conveyor has a BKW (actual power requirment to drive the conveyor) of 200kW. There are 2 options with the designer. Either he can choose 1 no. 220kW motor (considering all margins and then standard rating); or; alternatively he can design his system with 2 nos. 150kW motors to drive his equipment. His outlook/matter of concern is not the motor rating or HT/LT volatge level. He is only concerned with the availability of the required BKW at his driving end to drive his equipment. However in the later case both the motors will have to run simultaneously to drive the conveyor. This principle can also be applied to achieve a desired flow rate (considering applications otherh than conveying)

Talk to your mechanical/proces designer. If you can take him in confidence, you are done. BEST OF LUCK.

We used to swap from 415 to 3.3kV at 90kW.

The impact of starting and loading 220kW drives onto an LV system is enormous and not desireable.

Long before you try and convince the client he wants to run his motors at 415V I think you need to do a load study. Find out what the fault currents are, find out what the implications are on the system of swapping voltages.

My guess is you have completely underestimated the impact these drives will have on your network.

If there is distance between the MCC and the motor consider the amount of copper you are going to have put into the ground.

If you haven't done a study doing a tool such as SKM power tools or similar its time to stop and hand this over to an electrical engineer. I'm not convinced you understand the potential problems.

Spikenet, I have 3 questions:

1- Is there 3.3KV switchgear running existing equipment at this site?

2- How big is the 400V transformer feeding the existing MCC you want to use and is there 880KW of extra capacity in the transformer and MCC?

3- Who designed these upgrades, is the design done?

I am wondering if you will really save any money by using 400V motors and If the client already has 3.3KV equipment you can't use the maintenance training argument.

As long as the lead time fits in your schedule the 3.3KV design will work better for the client. Just make sure to use the proper cable terminations. Some say the kits are not required below 6.9KV but for the price I think it is worth it.

Good planning = Good luck

Frankdolan yes 3.3kV is exisiting at site. As we have gone ahead in design with only 400V (involvement of vendor & all) ie why i was thinking to have a session with client to convince them to run 230kW from 400V. but seeing all the responses i have decided to include 3.3kV in design.

Thanks everyone for active contribution.

One reason for using 3.3KV equipment is to keep the motor physical size, motor supply cable/wiring physical size, and the switchgear physical size much smaller and thereby require less space for the equipment installation.

Another reason is to keep maintenance costs lower due to: less mobile equipment, smaller equipment, and fewer personnel being required to facilitate removal and/or movement of the motors when they fail. (And they will fail.)

While the initial installation costs are somewhat comparable, the long term maintenance costs are significantly higher for the lower voltage equipment in the higher horsepower/KW range.

I doubt you will be able to convince the client to change their mind but good luck.