Transformer Impedance

My power transformer capacity is 30/35MVA, 6.6KV.. the transformer impedance is 18%..
Is it advisible to have such value??

What will be the benefit and impact of having higher impedance for a power transformer?

Please suggest

Pragathees.

Generator Neutral Earthing

In my Site, our Contractor is running a DG Set of 250KVA, 415V. to feed power to our site office
The entire distribution is through a 100A ELCB of 30mA. and it is unbalance load.

One morning, the ELCB has tripped but unfortunately "R" phase is continuously available from ELCB since there is internal problem in ELCB. The voltage on particular phase has gone high upto 270V and some of the tube light chokes got burnt and a personal computer power supply unit failed.
On investigation it was noticed that alternator neutral is not connected to the earth system.
I insisted the contractor to earth the alternator neutral. When they are trying to ground the alterantor terminal, the ELCB in the distribution board is tripping always.

Please suggest me, whether we can earth the alternator neutral solidly through some cu. flat.
I hope the any alternator netural should be earthed to avoid this kind of over voltage problem due to unbalance loads..

I understand, if we are earthing the neutral on the load side of ELCB, it may trip because there is difference in the return current through the neutral.
I am earthing the netural in the alternator terminal itself (-ie- Line side of ELCB) but why the ELCB should trip?

Pragathees..

Neutral To Earth Voltage..

Dear Sirs,

Many of the electrical equipments manufacturers insisting for almost 0V between Supply neutral and earth in a single phase system.... In my installation the voltage between Neutral to Earth is around 4 Volts..

In what way this voltage will affect the performance of the equipments.. and will it cause any harm to equipments ??

The netrual is earthed at the transformer end. My distribution board in my building is connected to an earth..and I could not find any earth pit around the building area. Since it is a rental building we could not get the contractor to confirm this.

In this condition, to bring down the Neu-Earth voltage, shall I link both neutral and earth without having an additional earthpit..?
Will this cause any problem to my system at certain conditions ?? please suggest..

Or else, if I am introducing a UPS (without havng an earthpit), what will be the voltage between Neutral and earth..?

Experts opinion in this regard will be much helpful for me..

Pragathees...

800kw, 415volt Motor Through Vfd

This topic has already been discussed that starting a 800KW, 415V motor in DG power.
The DG set has to be well designed on higer side to handle the starting current of the motor taking the losses in consideration..

Instead of having higher size DG Sets exclusively to handle the starting current of this motor, why don't I can have a Variable frequency Drive for this application?? I hope my problem is only starting the 800KW motor..on DG power..

Whether 800KW, 415V motor (Water pump application) can be smoothly started and operated using Variable frequency drive ? What will be the starting current ?? In this case, it is no need to have a higher capacity DG sets and I can go with normal rating suitabel for handling the running load only.. Is it correct??

For example, my running load is say 1100 KW including the 800KW motor load, I can select the DG set capacity of approx. 1500KVA ?? Is it ok ??

Will be any problem on the performance of LV VFDs(415V) for 800KW capacity since higher rating ??

Please suggest..

Pragathees...

Max. Temp. Limit Over Ambient..

Dear All,

What could be the max. temperature rise limit over ambient temperature allowed for Cu busbar in a LV switchgear as per IEC or EN standards..

If any body having soft copies of IEC or EN Standards kindly forward it to :
pragatheeswar@mail.yahoo.co.in

Regards

Pragathees..