Question { Siemens, 10628 }

Any one Give me formula for to increse the power factor,
0.8 to 0.95, How much the KVAr Required

Answer

Hi Pls Provide me the following Details:-

Input Load in KW....

Question { Siemens, 10628 }

Any one Give me formula for to increse the power factor,
0.8 to 0.95, How much the KVAr Required

Answer

Calculation of Required Kvar:-

Initial P.f-PFi , Desired P.f-PFd and Real Power of Load in
KW...


KVAR=KW(tanAi-tanAd)

where,

Ai=Cosinverse(PFi) = Initial Power Factor Angle.

Ad=Cosinverse(PFd) = Final Power Factor Angle.

For Example:-

PFi=.85 & PFd=0.9 & Real Load=50 KW

For this required KVAR is 6.7 KVAR....

Question { TCS, 11116 }

how regenerative breaking is done in electrical traction

Answer

Basics of Regenerative breaking:-

A regenerative brake is a mechanism that
reduces vehicle speed by converting some of its kinetic
energy into a storeable form of energy instead of
dissipating it as heat as with a conventional brake. The
captured energy is stored for future use or fed back into a
power system for use by other vehicles.

Electrical regenerative brakes in electric railway vehicles
feed the generated electricity back into the supply system.
In battery electric and hybrid electric vehicles the energy
is stored in a battery or bank of capacitors for later use.
Energy may also be stored by compressing air or by a
rotating flywheel.

Regenerative braking is not the same as dynamic braking,
which dissipates the electrical energy as heat and does not
maintain energy in a usable form.



Regenerative breaking in Electrical Traction:-

During braking, the traction motor connections are
altered to turn them into electrical generators. The motor
fields are connected across the main traction generator
(MG) and the motor armatures are connected across the load.
The MG now excites the motor fields. The rolling locomotive
or multiple unit wheels turn the motor armatures, and the
motors act as generators, either sending the generated
current through onboard resistors (dynamic braking) or back
into the supply (regenerative braking).

For a given direction of travel, current flow through the
motor armatures during braking will be opposite to that
during motoring. Therefore, the motor exerts torque in a
direction that is opposite from the rolling direction.

Question { 16961 }

What is industrial automation ??????

Answer

Industrial Automation & Applications:-

Industrial automation is the use of robotic
devices to complete manufacturing tasks. In this day and
age of computers, industrial automation is becoming
increasingly important in the manufacturing process because
computerized or robotic machines are capable of handling
repetitive tasks quickly and efficiently. Machines used in
industrial automation are also capable of completing
mundane tasks that are not desirable to workers. In
addition, the company can save money because it does not
need to pay for expensive benefits for this specialized
machinery. There are both pros and cons for a company when
it comes to industrial automation.

On the plus side, with soaring healthcare costs, paid days
off, vacation time, and other costly employee benefits,
companies can save money with industrial automation. While
robotic machinery can initially be extremely expensive, the
loss of monthly wages for production workers leads to
incredible savings for the company. While machinery used
for industrial automation can break down, it does not
happen often. If it does, only a handful of maintenance or
computer engineers are needed to handle repairs and get
lines running smoothly again.

In addition, many plants hire dozens of production workers
for a variety of shifts and need to close on certain days.
Industrial automation, however, allows a company to run the
plant twenty-four hours a day, 365 days a year, without
paying overtime. This fact alone can add up to significant
savings.

A company that employs forty-eight factory workers on three
different shifts and closes on weekends, for example, can
save thousands of dollars with industrial automation. This
is particularly true if weekend work is necessary, which
means overtime pay of time and a half must be paid for
Saturday work and double-time for Sunday. This equates to
an additional twelve hours of pay per employee. Of course,
life insurance, 401K benefits, dental insurance, health
insurance, pension coverage, and disability also contribute
to the expense.

Industrial automation can eliminate the need for all forty-
eight jobs. The robotic machinery used for industrial
automation may only involve a monthly payment until the
machinery is paid for, a couple technicians to keep the
robotic machinery running, and electricity costs.
Unfortunately for workers, industrial automation can
eliminate thousands of jobs. As the workforce decreases and
the cost of living increases, many families struggle to
make ends meet as their jobs are replaced by high-tech
machines.

Question { TATA, 8402 }

how we can improove power factor?????????

Answer

APFC Panels:-
An automatic power factor correction unit is
used to improve power factor. A power factor correction
unit usually consists of a number of capacitors that are
switched by means of contactors. These contactors are
controlled by a regulator that measures power factor in an
electrical network. To be able to measure power factor, the
regulator uses a current transformer to measure the current
in one phase.

Depending on the load and power factor of the network, the
power factor controller will switch the necessary blocks of
capacitors in steps to make sure the power factor stays
above a selected value (usually demanded by the energy
supplier), say 0.9.

Syncronous Condenser:-

Instead of using a set of switched
capacitors, an unloaded synchronous motor can supply
reactive power. The reactive power drawn by the synchronous
motor is a function of its field excitation. This is
referred to as a synchronous condenser. It is started and
connected to the electrical network. It operates at full
leading power factor and puts vars onto the network as
required to support a system’s voltage or to maintain the
system power factor at a specified level.

Question { 34837 }

what is wave trap? please explain the working and principle

Answer

Wave trap is a parallel tuned inductor - capacitor 'tank'
circuit made to be resonant at the desired communication
frequency.
It is the effort to utilize the same transmission line
between two substation for the purpose of communications.
At this communication frequencies the tank ckt provides
high impedance and does not allow to pass through them &
onto the substation bus & into transformers.

Question { 4977 }

Dear friends , I am going attend interview for WARTSILA
INDIA LIMITED , power plant .Could any 1 pls send me few
questions. the area i have to concentrate? please send it
to mikalraj@gmail.com. pls help me out

Answer

Hi Mikalraj,

Pls go through d following link:

http://www.allinterview.com/company/Wartsila/interview-
questions.html

Question { SISL, 7066 }

What is protection for single phasing ?

Answer

For Which Electrical M/C????

Question { 3725 }

how can we test the vector group of transformer

Answer

Assumed the transformer vector group As DYn11;

1.1U1V1W-which is primary -Delta Connection
2.2U2V2W- Which is secondary-Star connection
3.join 1U& 2U terminals
4.Supply 1U-1V-1W 440v Measured
a.1U-1V
b.1V-1w
c.1W-1U
d.1W-2W
e.1V-2W
f.1V-2V
g.1W-2V
h.1U-2N
i.1V-2N
TO CHECK
1.1V-2W=1V-2V
2.1W-2V>1W-2W
3.1U-1V=1V-2N+1U-2N
From above check(1,2,3) the vector group of transformer is
tested.....

Question { GMR, 13804 }

what is the similarity and difference between ups and
inverter?

Answer

A UPS consist of 3 parts ,inverter ,charger,and AVR
(voltage regulator).when mains is present a UPS provides
supply to computer in regulated mode using inbuilt AVR ,and
simultaneously charges the batteries.
when mains fails it changes over to inverter mode using an
electromechanical relay (The changeover time is as fast as
4 milli secs in offline UPS).The charging current of ups is
normally 1amps to max 6 amps

in case of inverter when mains is present it bypasses what
ever comes in betweeen 100-280 volt(a typical setting in
all reputed brands)
when mains fails it changes over to inverter mode and
change over time as high as 200 mill secs.
The charging current is high minimum 8 amps and can go upto
20 amps

there are some companies which make special kind of
inverter under the name of home ups.These are ordinary
inverter with two difference ,one----the change over is
made very fast upto 10 millisecs,
second input mains range is reduced to 190-250 v A/C,so
that if it goes below 190 volts it goes to batt mode and
same is te case when input exceeds 250.These kind of home
UPS are succes ful only upto one PC ,with higher number of
PCs the complaint of rebooting whem mains fails increases
drastically,hence never recommended.

Question { L&T, 5887 }

What is stray current in DC Traction?

Answer

Stray Current:-

Current flowing in the soil or water environment in the
vicinity of the rail
lines and arising mainly from cathodic protection, electric
power or
traction installations, and which can pass from the
environment into the
structure, pipelines or other metallic services and vice
versa.

Question { 5581 }

what is meant by armature reaction & where its happen ?

Answer

We know that all current-carrying conductors produce
magnetic fields. The magnetic field produced by current in
the armature of a dc generator affects the flux pattern and
distorts the main field. This distortion causes a shift in
the neutral plane, which affects commutation. This change
in the neutral plane and the reaction of the magnetic field
is called ARMATURE REACTION.

We know that for proper commutation, the coil short-
circuited by the brushes must be in the neutral plane.
Consider the operation of a simple two-pole dc generator,
shown in figure 1-8. View A of the figure shows the field
poles and the main magnetic field. The armature is shown in
a simplified view in views B and C with the cross section
of its coil represented as little circles. The symbols
within the circles represent arrows. The dot represents the
point of the arrow coming toward you, and the cross
represents the tail, or feathered end, going away from you.
When the armature rotates clockwise, the sides of the coil
to the left will have current flowing toward you, as
indicated by the dot. The side of the coil to the right
will have current flowing away from you, as indicated by
the cross. The field generated around each side of the coil
is shown in view B of figure 1-8. This field increases in
strength for each wire in the armature coil, and sets up a
magnetic field almost perpendicular to the main field.

Question { 3949 }

how DC motor operating in detail .pls any one guide me .iam
not clear idea about that .thank u

Answer

Hi Dear :)

Pls find the bellow links:-

For DC Machines:-
http://www.reliance.com/mtr/mtrthrmn.htm

For DC Motors:-
http://ecmweb.com/ops/electric_direct_current_motor/

Question { NTPC, 82454 }

what is the difference between squirrel cage & slip ring
induction motor?

Answer

Igonre the second answer that is for Armature Reaction...

Question { NTPC, 82454 }

what is the difference between squirrel cage & slip ring
induction motor?

Answer

The windings on the rotor of a squirrel cage motor is
comprised of aluminum (or sometimes copper) bars embedded
in the steel laminations of the rotor. The ends of the
rotor bars are shorted together by rings at each end of the
rotor. There is no external electrical connection to the
rotor. The bar and ring structure looks like an exercise
wheel for a pet squirrel.

The rotor of a slip-ring motor is wound with wire coils.
The ends of the windings are connected to slip rings so
that resistors or other circuitry can be inserted in series
with the rotor coils through carbon brushes that slide on
the slip-rings allowing an electrical connection with the
rotating coils.