Answer / suneetha

this is due to form factor
rms value of induced emf= form factor * average value

form factor is calculated as 1.11
so the ratings are usually expressed in multiples of 11

Answer / chandru_williams

1. When an alternator generates voltage, its rms value is
given by 4.4*f*$*t, where $ is value of total flux per
pole. So we can see all the voltages are made inevitably
multiple of this value (1.1, which is the form factor of
ac wave). Also it provides us the best economic
construction of step up and step down transformers.



2. We always use a multiple of 1.11 bcoz for a pure sine
wave the FORM FACTOR is the ratio of rms value of voltage
or

current with the avg. value of voltage or current and for
pure sine wave rms value of current is Imax/root '2' and

avg. value is 2Imax/pie. and which comes out to be 1.11 so
we cant have a combination of other then a multiple of 1.11.

Answer / shankar rao

Transformer rating depending up on Emf induced on Trafo.
Emf. induced Eqs. is depending up on Farm factor : 1.11

Answer / manolito aguilar

bcoz for a pure sine wave to form factor is the ratio of
rms value of voltage.

Answer / shakir hussain

They aren't always - here are a few examples - 13.8, 34.5, 69, 115, 230, 345. In reality, voltage is a range, perhaps .96 - 1.04 times this value, so equipment is sized according to this range (e.g. 69kV may have equipment rated for 72.5kV).

The reason is probably because someone started using that voltage, and everyone else joined in so systems fit together nicely - you can have a backup source from your neighbor if you're using similar stuff.

Insulation coordination can also a factor for this standard.

In order that work may be done:(a) Two wires are necessary(b) The circuit must have a switch(c) Coal must be burnt(d) A supply of energy is required

1 Answers  

In Which vector group power transformers are mostly manufactured?

1 Answers   MRF,

what is wave trap? please explain the working and principle

4 Answers  

I HAVE A INCOMING 100A MCCB TPN 25KA, CABLE LENGHT OF 80M 70MM CABLE SIZE FROM MAIN SUBBOARD TO NEW DB.BASE ON THE FAULT LEVEL SETTING OF 45KA.I WOULD LIKE TO FIND OUT 25KA ENOUGH KA. APPRECIATE IF SOMEBODY CAN ASSIST ME WITH FORMULA FOR THIS. FRM: JEFF

0 Answers  

HI FRIENDS,MYSELF & MY GROUP OF FINAL YEAR ELECT ENGG. ARE MAKING A 50/3HZ,5HP,1000RPM,440V SALIENT POLE SYNCHRONOUS GENERATOR.COULD ANYONE OF U TELL ME WHAT COULD BE THE ADV. & DISADVANTAGES OF MAKING SUCH A LOW FREQN.GENERATOR/

2 Answers  

how to select the surge suppresor for the 33 KV supply and what will be the rating, selection guide

1 Answers  

IN TWO WATTMETER METHOD WE GOT W1,W2,WE KNOW V.HOW TO FIND Q????????????

7 Answers   APTransco,

What is neutral and how to produced

1 Answers   L&T,

1.what is the difference between MPCB and MCB ? 2.what is the difference between MPCB and MCCB ?

6 Answers  

please forward me the type of questions which would rise while me attending to 33KV Electrical License to my mail ID:vadrevu_raghava@yahoo.co.in

0 Answers  

Why we apply 100ADC for contact resistance measurement?.If we apply AC what will happen

4 Answers  

How can we measure the residual voltage in dc machines?

0 Answers   GPREC,