Question { 5810 }

Difference between ups and invertor

Answer

Inverter:
The proper meaning of inverter is a device which
converts dc into ac.
The inverter also contains a battery unit and an dc to to ac
conversion unit. when the power fails the inveter will
deliver power from switching from main source to battery
source. The switching time here is normally greater than 20
ms.

UPS:
The proper meaning of this is a device, which delivers
power, even if the source power fails(Uninterrupted power
supply).
This is also contains the same thing as a inverter except
here the switching time from main source to backup source is
less than 10ms, so that the computer hard drives or an
sensitive power products should not be affected from this.

Depending on the switching time there is a online ups and
offline ups. off line ups is same as a inverter.

Question { 8990 }

What happens if the secondary of the transformer is shorted?

Answer

If the secondary of the transformer is shorted
Only the leakage inductance limits the current
during a short. It seems that the current through the
primary is limited by winding resistance and leakage
resistance when the secondary is shorted.

For more details log on to:-

http://www.epanorama.net/documents/components/transformers.h
tml

Question { APC, 16727 }

ups and invertor battery selection chart and full formula

Answer

UPS Battery Cacl:-


BATTERY RATING CALCULATION:-

The formula employed rating calculation is as stipulated
below :-

FORMULA EMPLOYED :

DC Current X Duration in Hrs
Capacity of Battery ( AH )=%age capacity utilization

UPS(KVA) x 1000 x Load Power Factor (=1)

Where , DC Current=Inverter efficiency x End Voltage

Hence , VAH = AH x Nominal Voltage

For e.g. : for 3 KVA UPS , 1 hour Backup :
3 x 1000 x 1
DC Current= 17.0 A
0.93 x 10.5 x 18
17.0 x 1.0
Battery ”AH “ = 27.4 AH
0.62
Hence , 18 nos of 12V/28AH batteries will suffice .

TOTAL VAH = 18 x 12 x 28 = 6048 VAH

The following assumptions have been made in the above
calculations :-

1. DC Voltage – 216 for 3 KVA
2. End cell voltage / battery of 10.5 V
3. Load Power Factor = 1.0
4. Inverter efficiency = 93%

% Capacity utilization is :

Duration % Capacity utilization

½ hr (30 mins) 52%
1hrs 62%
2hrs 74%
3hrs 83%
4hr 85%

For ups and invertor battery selection chart lOG On to:-

http://www.sharanapower.com/selection2.htm

Question { 3580 }

What is the Ideal Earth to Neutral Rating for Techonology
Equipment like Routers, Switched, PABX, Computers etc etc?

Answer

Hi,

Earth-to-neutral voltage will vary with the current
drawn in the neutral conductor. There is no 'specification'
to it as such. It is not uncommon for it to be around 10V
in some areas. The procedure to measure it is to place a
voltmeter actoss the neutral and earth terminals.

But for Communication devices it should be around <1.8 V

Question { 16401 }

short notes on npn & pnp transisitor..........

Answer

NPN Transistor :-

Just as in the case of the PN junction diode, the N
material comprising the two end sections of the NP N
transistor contains a number of free electrons, while the
center P section contains an excess number of holes. The
action at each junction between these sections is the same
as that previously described for the diode; that is,
depletion regions develop and the junction barrier appears.
To use the transistor as an amplifier, each of these
junctions must be modified by some external bias voltage.

PNP Transisitor:-The PNP transistor works essentially the
same as the NPN transistor. However, since the emitter,
base, and collector in the PNP transistor are made of
materials that are different from those used in the NPN
transistor, different current carriers flow in the PNP
unit. The majority current carriers in the PNP transistor
are holes. This is in contrast to the NPN transistor where
the majority current carriers are electrons. To support
this different type of current (hole flow), the bias
batteries are reversed for the PNP transistor.

Question { 7986 }

What is the formula to calculate capacitor bank rating for
a certain load.

Answer

Hi Pls find the following link:-


http://www.nepsi.com/kvars_required_calculation.htm

Question { BARC, 8228 }

what is inrush curent.

Answer

Inrush current or input surge current:-

It refers to the maximum, instantaneous input current drawn
by an electrical device when first turned on. For example,
incandescent light bulbs have high inrush currents until
their filaments warm up and their resistance increases.
Alternating current electric motors and transformers may
draw several times their normal full-load current when
first energized, for a few cycles of the input waveform.
Power converters also feature high inrush currents relative
to their steady state currents. This is typically the
charging current of the input capacitance. The selection of
overcurrent protection devices such as fuses and circuit
breakers is made more complicated when high inrush currents
must be tolerated. The overcurrent protection must react
quickly to overload or short circuit but must not interrupt
the circuit when the (usually harmless) inrush current flows

Question { NTPC, 12455 }

diff between grounding & earthing

Answer

Upto my knwldge Two different names for the same thing.
Earthing is used in European standards and Grounding is
used in North American standards.

Question { Synergy, 18984 }

what is impedance of transformer?

Answer

The percentage impedance of a transformer is the volt drop
on full load due to the winding resistance and leakage
reactance expressed as a percentage of the rated voltage.

Question { 24029 }

what is the difference between a feeder and a cable?

Answer

Feeder:-
A circuit, such as conductors in conduit or a
busway run, which carries a large block of power from the
service equipment to a sub-feeder panel or a branch circuit
panel or to some point at which the block power is broken
into smaller circuits.

Cable:-A cable is two or more wires or ropes running side
by side and bonded, twisted or braided together to form a
single assembly

Question { 16240 }

If you see the HRC fuse name plate. Its shown ampere rating
shown which is in many KA (like 80KA and so on). any body
explain what is meaning of this value?

Answer

Hi,

That is the short-circuit breaking capacity of that HRC
Fuse.

Question { 5191 }

how brushless dc motor is operating ?

Answer

Hi,

Log on to
http://en.wikipedia.org/wiki/Brushless_DC_electric_motor

Question { 6629 }

What is ac and dc drive.

Answer

DC Drives:-
Commonly a DC drive is a device that uses AC as
poer source to power and control a DC motor. The cheap
definition... The drive has two parts the power components
and a controler. The power components convert AC power to
DC by a Rectifier. The controller (among other things) is
basicly a high speed timer that fires a solid state device
(BPT, IGBT or some other gate) very rapidly (Pulse width
modulation on and off). The controller gets a setpoint from
a potentiometer or some other means perhaps a digital
number via some protocol and uses a means of maintaing this
setpoint by calculating the difference between the setpoint
and the actual speed with a tach or some other means and
adjust the output accordingly.

AC Drive:-

AC drives are also known as adjustable-
frequency drives (AFD), variable-speed drives (VSD),
Variable-frequency drives, microdrives or inverter drives.
Since the voltage is varied along with frequency, these are
sometimes also called VVVF (variable voltage variable
frequency) drives.


A AC drive is a system for controlling the rotational speed
of an alternating current (AC) electric motor by
controlling the frequency of the electrical power supplied
to the motor A variable frequency drive is a specific type
of adjustable-speed drive.

Question { 4243 }

What is plc.

Answer

A programmable logic controller (PLC) or programmable
controller is a digital computer used for automation of
electromechanical processes, such as control of machinery
on factory assembly lines, amusement rides, or lighting
fixtures. PLCs are used in many industries and machines,
such as packaging and semiconductor machines. Unlike
general-purpose computers, the PLC is designed for multiple
inputs and output arrangements, extended temperature
ranges, immunity to electrical noise, and resistance to
vibration and impact. Programs to control machine operation
are typically stored in battery-backed or non-volatile
memory. A PLC is an example of a real time system since
output results must be produced in response to input
conditions within a bounded time, otherwise unintended
operation will result.

For Details log on to:-
http://en.wikipedia.org/wiki/Programmable_logic_controller

Question { 3819 }

1.what type of wave is produced from i.online ups ii.offline
ups iii.inverter.why don't we use inverter instant of
offline ups for computer,what's the reason?

Answer

1.Online ups - Sinusoidal Wave from.
2.Offline ups - Quasi Sine Wave from.
3.Inverter - Sine Wave from.