690V Drives vs 6.6KV Drives

If 6.6 kv is available, you would not need a transformer so large as to power this motor.

Favoring higher voltage: smaller conductor sizes and ampacities of switchgear.

Favoring lower voltage: lesser requirements for operating personnel, maybe better availability of motor starter/drive, fewer safety issues.

Have you done any comparison pricing yet?

dear sir,

i have done the comparision cost only for drive,motor & cables.in that mv drive is 40% higher than LV drive.

so my doubt is we have to look losses of the cables also.kindly suggest me the back up calcualtion for the same.

ther is any harmonic issues in 690V drive when compared to 6.6KV drive.

As Tornado said it's mainly down to what supplies you have available, I think it would be highly unlikely you have 1.5MW spare capacity on your 690V system. So I would assume you're going to have to install a dedicated transformer. Then it comes down to cable sizes, @ 690V they are going to be hefty (expensive) cables. As for switchgear again it comes down to pricing.

You've just got to add up the costs of the transformer, cable and switchgear for each.

As standard practice in India, and as one of associate from india informed rightly, I would also like to suggest to operate this motor on 6.6 kV and not on 690V. I have good understanding of cost estimates, hence commercially cost of connecting this motor on 6.6 kV is less than on 690V. Maintenance wise also, there is not a big problem, as in India, if you do purchase in Lot from BHEL, SIEMENS, CGL, MARATHON you are going to get good service and spares and maintenance is not at all a problem. Go for 6.6kV system.

dear sir,

i am worring about HT drive cost.it is 40% greater than 690V drive.

kindly advise me

How much is the cable and switchgear?

i have calcualted the number of cable runs.that is 6.6KV 1 no of 3*240sq.mm cable.690V 5 No's of 3*240Sq.mm cables. cost also i did.

but how shall i calculate the switchgear cost?

kindly advise me.

voltage cast

dear Sir,

in that siemens also offered 690V drive upto 1500KW. my clarification is i need the technical details like cable losses is higher in 690V . then only we compare the 690V & 6.6KV other than costing.Kindly advise me in this regard.

I.e. Cable losses results in cable voltage drop. For which we have to select proper sized cable to restrict voltage drop. We have to make sizing calculations then. But, it's not the criteria for selection of voltage level. If siemens is ready to offer this system in 690v then you can take suitable decision.

dear sir,

thaks for ur reply.

in cable we have considered 250Mtrs.socable i^2 R loss also present. In the 690V motor they considered two terminal box to accomodate more cables.then another one is ABB considered two 3.3KV drives with external converter duty transformer & it cascaded for 6.6KV motor.why they not considered direct 6.6KV drive. or any advantages is there in that system.

kindly advise me.

sorry for inconvenience

Yes it is fact that Cable termination is a problem for such big rated motors. Cascading is also possible. It's no problem as long as vendor do take undertaking of satisfactory operation it's warranty. If your management had decided for 690V system then we should probably go along with it OR else I still emphasise on 6.6kv HT motor with variable speed fluid coupling. You can ask as many "technical" questions as you can. But non-technical replies are not expected from participants. It said that keeping mum is also better option!! U may also contact by personal msg for more details.

Do it your own way!

I'm sorry but to be asking the questions you have on an open forum makes me wonder if you're capable of satisfactorily placing the order.

We won't give you indemnity if you get it wrong.

This depends on the input voltage of the mains. If your mains input voltage is 6.6KV then it is advisable to goin for a MVD (Medium voltage drive) of 6.6KV input & 6.6KV output. If you use 690V drive if your mains input voltage is 6.6KV then you have to use a stepdown transformer. This will add to cost.

To use 6.6KV MVD the motor rating also should be 6.6KV. Though the cost of motor seems to be high, use of transformer is eliminated.

The over all cost actually will be less than using 690V drive system. And the performance of the entire system will be very good with less current harmonics and better life of motor and drive.

dEAR ganeshhakce-electrical

6.6 KV is to be opted than 690 volts. If possible go for 11 KV

Technical Merits:

1. Less Current and hence less I^2 x R Loss in the proportion of (690/6600)^2 or (690/11000)^2 to that of the Losses at 690 Volts. In the long run - this most economical.

2. Motor Size will be Less and hence cost will be less.

DHAYANANDHAN.S