Switchgear Guidance

can u upload one line

any way for 1MVA xfrm the current is 1519A so you may need a 1600 CB .

also keep the factors of cable , lenght , voltage drop , inrush and how much SC power is available at the point ..

Hello,

I am assumimg the primary voltage is 11kV, single phase (as you noted two wires) and your transformer rated at 1mVA will result in the primary current at 90.91 A. You did not indicate the secondary voltage of your new transformer so I am not sure how the 1519A was calculated.

Cheers,

Fred

HI

Fred 'm not sure how do come to 90.91A. Because my calculation come to 0.0909A WHICH IS 90.91mA ( PRIMARY CURRENT)

Dan Segami

RSA

You will have to contact with a qualified consultant regarding this,then you have to find a well organized switchgear industry to build all switchgear for you.However for three sources of supply from your utility depends on your utilization and you current need/situation,your can buy a synchronization switchgear plant or inlocked between 3 sources type of switchgear.

Regards

Aseer

I am going to do what I almost never do and make an assumption. The assumption is that the two cables that you are talking about are three phase cables meaning that you have three electrical conductors and a neurtral conductor that make up each cable. If that is not the case then I would really like to see a drawing of a 315 or 500 KVA fed with a two phase feed.

I suggest that you take a look on the S&C switchgear website and see what they have to offer. You should be able to get a four (4) compartment switchgear from them with a gang operated switch in the compartment that your cable feeding from the utility terminates in and the other three (3) compartments equipped with fused switches to handle the cable terminations for each of the three (3) transformers. The switchgear will be approximately four feet in height and form a rectangular box measuring about 8X4 feet. It should be mounted on a cement pad that is slightly bigger than the switchgear. It should have four doors on it, one for each compartment. The gang switch for the incoming cable should have an operating handle that is accessible from the outside of the switchgear. The 3M company makes a great flexible terminator kit for the cable terminations. You will have one large cable running from the switchgear to the Tanzania Power Company pole. The power company should, although I am not positive, provide three fused switches on the riser pole for your cables. Be sure you keep a supply of fuses on hand for your switchgear and also at least three on hand to "loan" to the power company in case of an emergency.

Please be sure that you don't cut corners and direct bury the cable like most of the contractors in this part of the world try to do. Even if you are using armored cable you will be much smarter if you use a schedule 40 or better PVC conduit for your installation. Use galvanized pipe with the correct radius bends for your corners as the friction from the cable and the pulling ropes will melt through the PVC at the corners. Also, you can probably buy a cheaper switchgear from China. If you do that be sure and get two of them. The S&C Company makes their switchgears with insulated boards inside them to shield the metal sides thus preventing an accidental phase to ground flash. They have the same boards installed between the individual fused switches to prevent a phase to phase flash. The cheap stuff does not have these little extras so when you get an accidental flash you wind up with a hunk of junk on your hands. I'll leave it to the engineers to discuss cable and fuse size with you as I just build and operate the systems. Good luck.

hi

it is very difficult to calculate the secondary current because you did'nt state your secondary voltage of your transformer 3. and the H.T SIDE do u mean one 11k pole(overhead line) with 2 cables that supply 2 transformers. please specify so that we can help

Dan Segami

RSA

Yes H.T. side mean 11K pole.

Thanks Mohamed

I think Tanzania is using voltage system of 11KV / 415V,50Hz, Dyn11. If this is the case, the following possible methods depending on approval from the supply authority can be used:-

(1). The simpler/cheaper method. Use one outdoor 3-phase,11kv pole mounted switch with 3 HRC (50A to 60A) fuses (drop out type) to take in power from the same main supply line.As the authority already know your additional KVA need,there should be enough power from that line.Max normal current for outdoor 1000KVA at 11kv is 52A.However you should use 3 core cables that is also having sufficient KA rating.For e.g. 150sq mm copper conductor or 185 sq mm aluminium XLPE/SWA/pvc cables to withstand any possible short circuit current.This way you do not need to build a substation building.Your 415V MSB needs to be indoor type.Metering of consumtion is on LV MSB,incomer.

(2).A much better way ( more expensive ) is to have a indoor 11kv,630A,20ka,VCB switchboard comprising of one incomer VCB with metering and one feeder VCB panel with protection.Buy one 2000KVA oil transformer and one 415V MSB that has at least 3 ACB/MCB feeders to 2 existing and 1 new areas.Keep or sell the old transformers.

There are always other combination such as using Ring main units,load break switch etc.

Regards,

Khor

This is not something you can learn over the internet.... Get an Electrical Engineer to do the design ... DON`T take risks...