Question { Star Wire, 5273 }

When capacitor bank connect on line. It's draw some current
but it's current not increase of main line ammeter. Why?

Answer

It is true only in case of a Load which is running a poor
power factor because capacitor draws the Leading current
which cancel outs the lagging current of load and thus no
current drawn from line but if a load which already having a
good power factor capacitor will draw the leading current
from the line.
For checking this fact, just switch on a capacitor on the
panel when there is no load condition.

Question { 12387 }

how to set time from star to delta starter

Answer

It depends on the motor rating. Big motor requires more time
to achieve the rated rpm so the timer can be set to 10-15
sec while for small motors (upto 50HP) it can set to 8-10 sec.

Question { Heidelberge Cement, 7757 }

what is the avr

Answer

Automatic Voltage Regulator is known as AVR

Question { 8325 }

what is the diffrence between single phase and three phase

Answer

in single phase, voltage is measured between the Neutral &
Phase is 230 V while in 3-Phase voltage measured between two
phases is 415 V. 3-Phase having a 2-types of connection
,(1) Star and (2) Delta.

Question { 28644 }

what is mathematical relation between ac to dc current
how will convert Iac=50amp to Idc

Answer

Iac = (pi/2)x Idc
50 = (pi/2) x Idc
Idc = 31.84 A dc

Question { DLF, 15742 }

How much KVAr bank reqired for 630 KVA transformer on full
load for maintain power factor upto.99

Answer

Capacitor calculation is depends on load. if 630 KVA transformer is loaded fully with load p.f.=1 then no compansation is required but if the same is fully loaded with load p.f. = 0.8 then, kvar required is calculated as below:
KVAR = KW ( tanǾ1-tanǾ2); Ǿ1=old p.f.angle, Ǿ2=new pf angle

= 504 ( 0.75 - 0.14) [ here, KW=504 because, 630 X 0.8 = 504]
= 307.44 KVAR
say, 300 KVAR bank is required at load end for compansation

Question { AIIMS, 4901 }

what are effects of harmonics in the three phase a.c power
system ?

Answer

- Heating of neutral conductor
- Nuisance tripping of Circuit Breakers, relays
- Overheating of electrical distribution equipments like cables, transformers etc.,
- Bearing failure from shaft current of motors
- flickering of lights
- Excess neutral current
- Metering error
- Generator failure