Tuesday 30 June 2015

BASIC FORMULAS IN ELECTRICAL.

                                       
                   

                                     FORMULA DIAGRAMS








Saturday 27 June 2015

IBPS RRBs CWE-IV AND IBPS CWE-V SCHEDULE AND TENTATIVE EXAM SCHEDULE.

   

                                           IBPS CALENDER



IBPS was established during the year 1984 and comes in working full fledge medium from 1984. Many Public sector Banks are associated with this organization; the IBPS organize the exam for these Nineteen Public Sector Banks. All recruitment process has done by the IBPS.

All IBPS Online Application Form will be filled up through official website as per requirement.

Here aspirants can get the full information regarding to the IBPS 2015 – 16, also candidates find the updated IBPS Exam schedule included IBPS PO exam, IBPS Clerk Exam, IBPS SO exam.

Once aspirants clear the exam of IBPS then IBPS release the score card for those candidates who have been selected in the written exam. The score card is valid for the interview in nineteen public banks. Mostly all big public sector banks included in the IBPS CWE but only one big brand Bank SBI not cover in the IBPS entrance exam and conduct our own recruitment process separately.

Eligibility

Aspirants need to know firstly what are the eligibility criteria, like educational qualification, age limit, and other information which are related to the IBPS eligibility, here we will update you about all anything which you want regarding the IBPS eligibility.

Age Limitation
Candidate who wants to appear in IBPS exam they should be in age between 20 years to 28 years. The age relaxation as applicable according to Govt Reservation Policy for SC, ST and OBC.

Educational Qualification
Aspirants who are going for apply the IBPS clerk exam must have a Graduation degree in any stream from a recognized Institution. And for the IBPS SO exam candidate should have specific degree for the specific post. Candidates should also have analytic skill, knowledge in the basic computer.

Recruitment Process of IBPS
The Recruitment process of the IBPS as following manner:
  • Common Written Exam (CWE).
  • Score card release by IBPS those who clear the written exam
  • Based on score card candidates called for interview.
  • After the final interview concern bank called for Documents Verification.
  • After the document verification Appointment letter issued by the concern Bank.

IBPS STUDY PLAN

Friends as IBPS is approaching here is the link to download the study plan for it.

http://www.mediafire.com/download/17bcco1iqlp6ji7/IBPS+PO+V+Study+Plan+%28Updated%29.xlsx

Frequently Asked Electrical Engineering Interview Questions and Answers

                                 ELECTRICAL ENGINEERING QUESTIONS


1) What is meant by regenerative braking?
When the supply is cut off for a running motor, it still continue running due to inertia. In
order to stop it quickly we place a load (resistor) across the armature winding and the motor
should have maintained continuous field supply. so that back e.m.f voltage is made to
apply across the resistor and due to load the motor stops quickly. This type of breaking is
called as "Regenerative Breaking".

2) Why is the starting current high in a DC motor?
In DC motors, Voltage equation is V=Eb-Ia Ra(V = Terminal voltage.
Eb= Back emf in Motor,Ia = Armature current,Ra = Armature resistance).At starting, Eb is zero.
Therefore, V=Ia Ra,Ia = V/Ra , where Ra is very less like 0.01 ohm i.e, Ia will become
enormously increased.

3) What are the advantages of star-delta starter with induction motor?
(1). the main advantage of using the star delta starter is reduction of current during the
starting of the motor.Starting current is reduced to 3-4 times Of current of Direct online
starting.
(2). Hence the starting current is reduced; the voltage drops during the starting of motor in
systems are reduced.

4) Why star transformers are used for lighting loads?
For lighting loads, neutral conductor is must and hence the secondary must be star
winding.And this lighting load is always unbalanced in all three phases. To minimise the
current unbalance in the primary we use delta winding in the primary. So delta / star
transformer is used for lighting loads.

5) Why in a three pin plug the earth pin is thicker and longer than the other pins?
Answer: It depends upon R=rho l/a where area(a) is inversely proportional to resistance (R),
so if (a) increases, R decreases & if R is less the leakage current will take low resistance path
so the earth pin should be thicker. It is longer

Because the First to make the connection and last to disconnect should be earth Pin. This
assures Safety for the person who uses the electrical instrument.

6) Why series motor cannot be started on no-load?
Series motor cannot be started without load because of high starting torque. Series motor is
used in Trains, Crane etc.

7) Why ELCB can't work if N input of ELCB do not connect to ground?
ELCB is used to detect earth leakage fault. Once the phase and neutral are connected in an
ELCB, the current will flow through phase and that much current will have to return neutral
so resultant current is zero. Once there is a ground fault in the load side, current from phase
will directly pass through earth and it will not return through neutral through ELCB.
That means once side current is going and not returning and hence because of this
difference in current ELCB will trip and it will safe guard the other circuits from faulty loads.
If the neutral is not grounded, fault current will definitely high and that full fault current will
come back through ELCB, and there will be no difference in current.


8) What is the difference between MCB & MCCB, Where it can be used?
MCB is miniature circuit breaker which is thermal operated and use for short circuit protection
in small current rating circuit. MCCB moulded case circuit breaker and is thermal operated for
over load current and magnetic operation for instant trip in short circuit condition. under
voltage and under frequency may be inbuilt. Normally it is used where normal current is
more than 100A.

9) Where should the lighting arrestor be placed in distribution lines?
Near distribution transformers and outgoing feeders of 11kv and incoming feeder of 33kv and
near power transformers in sub-stations.

10) Define IDMT relay?
It is an inverse definite minimum time relay. In IDMT relay its operating is inversely
proportional and also a characteristic of minimum time after which this relay operates. It is
inverse in the sense ,the tripping time will decrease as the magnitude of fault current increase.

11) What are the transformer losses?
TRANSFORMER LOSSES - Transformer losses have two sources- copper loss and magnetic
loss.Copper losses are caused by the resistance of the wire (I2R). Magnetic losses are caused
by eddy currents and hysteresis in the core. Copper loss is a constant after the coil has been
wound and therefore a measurable loss. Hysteresis loss is constant for a particular
voltage and current. Eddy-current loss, however, is different for each frequency passed
through the transformer

12) What is the difference between Isolator and Circuit Breaker?
Isolator is a off load device which is used for isolating the downstream circuits from
upstream circuits for the reason of any maintenance on downstream circuits. It is manually
operated and does not contain any solenoid unlike circuit breaker. it should not be operated
while it is having load. first the load on it must be made zero and then it can safely
operated.Its specification only rated current is given. But circuit breaker is on load automatic
device used for breaking the circuit in case of abnormal conditions like short-circuit,
overload etc., it is having three specification 1 is rated current
                                                                        2 is short circuit breaking capacity
                                                                        3 is instantaneous tripping current.

13) What are bucholz relay and the significance of it in to the transformer?
Bucholz relay is a device which is used for the protection of transformer from its
internal faults; it is a gas based relay. whenever any internal fault occurs in a transformer, the
boucholz relay at once gives a horn for some time, if the transformer is isolated from the
circuit then it stop its sound itself otherwise it trips the circuit by its own tripping mechanism.

14) What is SF6 Circuit Breaker?
SF6 is Sulphur hexa Fluoride gas.. if this gas is used as arc quenching medium in a
Circuit breaker means SF6 CB.

15) What is ferranti effect?
Output voltage is greater than the input voltage or receiving end voltage is greater than the
sending end voltage.

16) What is meant by insulation voltage in cables?
It is the property of a cable by virtue of it can withstand the applied voltage without rupturing
it is known as insulation level of the cable.

17) There are a Transformer and an induction machine. Those two have the same supply. For
which device the load current will be maximum? And why?
The motor has maximum load current compare to that of transformer because the motor consumes real power.. and the transformer is only producing the working flux and it’s not consuming..
hence the load current in the transformer is because of core loss so it is minimum.

18) What is power factor? Whether it should be high or low? Why?
Power factor should be high in order to get smooth operation of the system. Low power
factor means losses will be more. it is the ratio of true power to apparent power. it has to be
ideally 1. if it is too low then cable over heating & equipment overloading will occur. if it is
greater than 1 then load will act as capacitor and starts feeding the source and will cause
tripping.
(if pf is poor ex:0.17 to meet actual power load has to draw more current(V constant),result in more losses if pf is good ex: 0.95 to meet actual power load has to draw less current(V constant),result in
less losses).

19) What happens if I connect a capacitor to a generator load?
Connecting a capacitor across a generator always improves power factor, but it will help
depends up on the engine capacity of the alternator, otherwise the alternator will be over
loaded due to the extra watts consumed due to the improvement on pf. Secondly, don't
connect a capacitor across an alternator while it is picking up or without any other load.

20) Why the capacitors work on ac only?
Generally capacitor gives infinite resistance to dc components (i.e., block the dc
components). it allows the ac components to pass through.

21) Explain the working principal of the circuit breaker?
Circuit Breaker is one which makes or breaks the circuit. It has two contacts namely fixed
contact & moving contact. Under normal condition the moving contact comes in contact with
fixed contact thereby forming the closed contact for the flow of current. During abnormal &
faulty conditions (when current exceeds the rated value) an arc is produced between
the fixed & moving contacts & thereby it forms the open circuit.
Arc is extinguished by the Arc Quenching media like air, oil, vacuum etc.

22) How many types of cooling system it transformers?
1. ONAN (oil natural, air natural)
2. ONAF (oil natural, air forced)
3. OFAF (oil forced,air forced)
4. ODWF (oil direct, water forced)
5. OFAN (oil forced,air forced)

23) What is the function of anti-pumping in circuit breaker?
when breaker is close at one time by close push button the anti pumping contractor preventre
close the breaker by close push button after if it already close.

24) What is stepper motor? What are its uses?
Stepper motor is the electrical machine which acts upon input pulse applied to it. it is one
type of synchronous motor which runs in steps in either direction instead of running in
complete cycle. So, in automation parts it is used.

25) What is Automatic Voltage regulator (AVR)?
AVR is an abbreviation for Automatic Voltage Regulator. It is important part in Synchronous
Generators; it controls the output voltage of the generator by controlling its excitation current.
Thus it can control the output Reactive Power of the Generator.

26) What is an exciter and how does it work?
There are two types of exciters, static exciter and rotary exciter. Purpose of exciter is to
supply the excitation dc voltage to the fixed poles of generator. Rotary exciter is an additional
small generator mounted on the shaft of main generator. if it is dc generator, it will supply dc
to the rotor poles through slip ring and brushes( conventional alternator). if it is an ac exciter,
output of ac exciter is rectified by rotating diodes and supply dc to main fixed poles. ac exciter
is the ac generator whose field winding are stationary and armature rotates. Initial voltage is
built up by residual magnetism. It gives the starting torque to the generator.

27) Difference between a four point starter and three point starters?
The shunt connection in four point starter is provided separately from the
line where as in three point state it is connected with line which is the drawback in
three point starter

28) Why use the VCB at High Transmission System? Why can't use ACB?
Actually the thing is vacuum has high arc quenching property compare to air because in VCB,
the die electric strength is equal to 8 times of air . That y always vacuum used as in HT
breaker and air used as in LT.

29) What is the difference between surge arrestor and lightning arrestor?
LA is installed outside and the effect of lightning is grounded, whereas surge arrestor
installed inside panels comprising of resistors which consumes the energy and nullify the
effect of surge.

30) Why synchronous generators are used for the production of electricity?
synchronous machines have capability to work on different power factor(or say different
imaginary power varying the field emf. Hence syn. generators r used for the production of
electricity.

31) What is the difference between synchronous generator & asynchronous generator?
In simple, synchronous generator supply's both active and reactive power but
asynchronous generator (induction generator) supply's only active power and observe reactive
power for magnetising. This type of generators is used in windmills.

32) 1 ton is equal to how many watts?
1 ton = 12000 BTU/hr and to convert BTU/hr to horsepower,
12,000 * 0.0003929 = 4.715 hp therefore 1 ton = 4.715*.746 = 3.5 KW.
33) Why syn. generators are used for the production of electricity?
synchronous machines have capability to work on different power factor(or say different
imaginary power varying the field emf. Hence synhronous. generators r used for the production of
electricity.

34) Enlist types of dc generator?
D.C.Generators are classified into two types
1)separately excited d.c.generator
2)self excited d.c.generator,
which is further classified into;
1)series
2)shunt and
3)compound(which is further classified into cumulative and differential).

35) Give two basic speed control scheme of DC shunt motor?
1. By using flux control method: in this method a rheostat is connected across the field winding
to control the field current.so by changing the current the flux produced by the field winding can
be changed, and since speed is inversely proportional to flux speed can be controlled
2.armature control method:in this method a rheostat is connected across armature winding by
varying the resistance the value of resistive drop(Ia Ra)can be varied,and since speed is
directly proportional to Eb- Ia Ra the speed can be controlled.

36) What is the principle of motor?
Whenever a current carrying conductor is placed in a magnetic field it produce turning or
twisting movement is called as torque.

37) What is meant by armature reaction?
The effect of armature flu to main flux is called armature reaction. The armature flux may
support main flux or opposes main flux.

38) What is the difference between synchronous generator & asynchronous generator?
In simple, synchronous generator supply's both active and reactive power
but asynchronous generator(induction generator) supply's only active power and
observe reactive power for magnetising. This type of generators are used in windmills.

39) What is the Polarisation index value ? (pi value)and simple definition of polarisation
index ?
Its ratio between insulation resistance(IR) i.e megger value
for 10min to insulation resistance for 1 min. It ranges from 5-7 for new motors &
normally for motor to be in good condition it should be Greater than 2.5 .

40) What is the one main difference between UPS &Inverter ? And electrical engineering & electronics engineering ?
Uninterrupted power supply is mainly use for short time means according to ups VA it
gives backup. ups is also two types : on line and offline . online ups having high volt and amp
for long time backup with with high dc voltage. but ups start with 12 volts dc with 7 amp. but
inverter is start with 12 volts,24 volts,dc to 36 volts dc and 120 amp to 180 amp battery with long time
backup.

This blog provides you with latest job openings and engineering materials.

HI,
      All the students who want to get job and notifications about latest job openings can go through this blog. You can also find many Engineering materials here. Wish you make this blog successful.