A standby UPS or "offline UPS" draws current from the AC
outlet and switches to battery within a few milliseconds
after detecting a power failure.
The line interactive UPS "interacts" with the AC power line
to smooth out the waveforms and correct the rise and fall of
The "Online UPS" is the most advanced and most costly UPS.
The inverter is continuously providing clean power from the
battery, and the computer equipment is never receiving power
directly from the AC outlet. However, online units contain
cooling fans, which do make noise and may require some
location planning for the home user or small office.
Online UPS, it is getting power AC is converting to DC, then
the DC source stored to Battery at power supply on mode when
power fail, the DC sorce is changed to AC by inverter so
output power is having without noise.
OFFline UPS is having automatic voltage regulator, it
getting power from supply, it is regulated by AVR, then
power stored to battery so the change over time approx 2ms
to 5ms so change over noise comes.
Online UPS is unterrupted power suppy to the load,
Offline UPS can't ensure uninterrupted power supply, it
depends on the tolerance of the load. For any sophisticated
equipment (medical equipment), Online UPS is recommended.
online ups is a double conversion(dual) ups which firstly
converts AC power to D.c ,then D.c to A.C .the stored D.c
form of electricity remains within the batteries. in online
ups systems load is always connected to inverter. in online
ups system the power supply goes to the end user through
the battery,if there is A.c power cut ,then no harm or
interruptibility occurs .
APPLICABLE IN CRITICAL INSTRUMENTS LIKE C.T SCAN,X-
by SAMEER HUSSAIN
SNA POWER ENG. PVT LTD LUDHIANA
while in case of offline ups sytems the raw A.c supply is
connected by a realy type of mechanism,then the battery and
inverter is bound tothe msin supply. so when there is A.c
Power cut ,the really needs a time gap of 3-5 ms to shift
it to battery mode.
This is about the recent problem that we have faced in our
We have 6/7.5 MVA. 66/11kV three phase star - star power
transformer. The neutral was solidly connected to the
earthing mat. But because of high resistance of earthing
mat (130 ohm on LV and 180 ohm on HV), one day LV side
neutral earthing conductor melted and we had a huge damage.
Can any one plz tell me what might happen when we connect
power transformer neutral to the earthing mat which has
high resistance (>100 ohm ) ?????
my company total load is 1000kw, 415volt, all load are
inductive load. incoming powerfactor is .8. we want to
have0.95 pf connecting capacitors. so now how much rating of
capacitors we have to connect? show how?