Answer / vipul dhruv

basically vfd is a soft starter which is used for induction
machines. there are two methods of control on which a vfd
works... one is the vector control & the other is the scalar
control method. your question does not concern this so no
explanation is required i guess... now the function of the
vfd is to maintain a constant flux in the air gap of the
machine it is used for and that can be achieved only when
the V/HZ ratio of the machine is kept constant.so a ramp is
created in a vfd by the controller which gives a constant
v/hz ratio... and the flux is kept constant... by flux i
mean the magnetic flux.. so as the frequency varies the
voltage has to vary accordingly to keep the ratio constant
which is fed into the controller....the controller is the
heart of the vfd...

Answer / ashok

yes voltage is reduced (out put) when frequency is reduced..

50 hz = 415v
25 hz = 270 v
0 hz = 0 v

if u reduce the frequency voltage reduce vice versa

Answer / rahul waghmare

I think in VFD When frequency increases voltage also
increased & vice versa

Answer / lallan chodhu

simply v proportional to 4.44 phi f n
v n f variable phi n 4.44etc constant.to maintain constant flux whole ratio v/f is changed agar sirf v badhaoge f kam hoga n vice versa.toh vfd ek prakar se v/f contriol hai

Answer / amrinder

arvind please give reason why voltage will increase??

Answer / arvind

Dear Amrinder
we know through v/f ratio, if frequency will reduce that
means the voltage will increase.

Answer / amrinder

yes voltage is reduced when frequency is reduced..normally
for 1 hz, 7.42 volts is reduced.

Answer / arvind

In vfd when frequency is reduce the voltage will increase.
it is difficult to say that upto what level it will
increase or decrease, but speed can be find out by using
the formula.
Ns=120f/p
where f is frequency
p is poles

what is the diff. btwn. electronic regulator and ordinary rheostat regulator for fans?

3 Answers  

How to run 1ph motor(230 VOLTS its full load amps is 4.5 ampa))with 480 volts main(we didn hav neutral)Thn we go for step down transformer.Our load 10 amps,so we conisder this amps in primary are secondary side?

1 Answers  

As per IS why should the control be taken only from R phase, why not from B or Y phase??!!

2 Answers  

why lightning arrestor are made by 2 stack of insulator but why cvt are fully 1 stack of insulator.

1 Answers  

What is the role of link in neutral in a three phase ac system?

10 Answers  

what is cogging? how it can be controlled?

1 Answers   HCL,

what is the procedure for three phase motor differential relay testing can it do with single phase test kit?

1 Answers   ABB,

what is power factor? how can we correction the power factor if this is high or low? If anyone know please please send the answer on my email id ( kumarkirshan@in.com )

5 Answers  

how to calculate short circuit calculation of the transformer by usuing the percentage impedence? formula needed.

2 Answers   L&T,

what are factors to be consider to design a HT & LT motor?

1 Answers  

I want to know the 'Test voltage' for Tandelta testing of 3.3 / 6.6 / 11 KV Motors. Please explain

0 Answers  

why sielent pole is used only in hydro generators and not in turbo generators

1 Answers