Monday, March 30, 2020

Coronavirus Cases in India Live on 30th March 2020 afternoon

India

Coronavirus Cases:

1,071

Deaths:

Recovered:

100

ACTIVE CASES

942

Currently Infected Patients

942 (100%)

in Mild Condition

0 (0%)

Serious or Critical

Show Graph

Show Statistics

CLOSED CASES

129

Cases which had an outcome:

100 (78%)

Recovered / Discharged

29 (22%)

Deaths

Show Graph

Show Statistics

Total Coronavirus Cases in India

Daily New Cases in India

Active Cases in India

Total Coronavirus Deaths in India

Daily New Deaths in India

Newly Infected vs. Newly Recovered in India

Outcome of Cases (Recovery or Death) in India

Latest Updates

March 30 (GMT)

47 new cases and 2 new deaths in India
March 29 (GMT)

37 new cases and 3 new deaths in India

March 28 (GMT)

100 new cases and 4 new deaths in India

March 27 (GMT)

160 new cases in India. According to reports from states cited by The Times of India, as of the end of Thursday, March 27 there were 727 total cases and 20 deaths in India. The discrepancy with the official numbers (which are lower for both counts) can be explained with a lag in reporting affecting the national aggregate. We are working on implementing a tracker by state so we can independently verify the data and report it at the state level with statistics and graphs

March 26 (GMT)

70 new cases and 8 new deaths in India

March 25 (GMT)

121 new cases and 2 new deaths in India

March 24 (GMT)

37 new cases in India. PM Modi announces 21-day complete national lockdown from midnight tonight

https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg RRB JE, SSC AE/JE UPSSSC JE, SSC JE, CIVIL ENGINEERING MCQs, ELECTICAL ENGINEERING MCQs, preavious year quesion papers, dmrc, lmrc, drdo,rrb ntpc, ntpc, pgcil, dsssb, states board, GATE IES EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA

COVID-19 CORONAVIRUS PANDEMIC Live Updates 30th March 2020

Coronavirus Cases:

723,732

Deaths:

34,000

Recovered:

151,833

ACTIVE CASES

537,899

Currently Infected Patients

511,180 (95%)

in Mild Condition

26,719 (5%)

Serious or Critical

CLOSED CASES

185,833

Cases which had an outcome:

151,833 (82%)

Recovered / Discharged

34,000 (18%)

Deaths

Confirmed Cases and Deaths by Country, Territory, or Conveyance

The coronavirus COVID-19 is affecting 199 countries and territories around the world and 2 international conveyances: the Diamond Princess cruise ship harbored in Yokohama, Japan, and the Holland America's MS Zaandam cruise ship. The day is reset after midnight GMT+0.

MCC Questions & Answers

MCC

1. What are the advantages of MCC?

a. Starters and contactors all will be a standard size.
b. Spares inventory will be less.
c. Cost of cables will be less because same size of cable is used for all capacity and
gland holes can be provided before hand.
d. Maintenance and trouble shooting is easier in MCC.

2. What type of motor starting adopted in MCC?

DOL (direct on line) starter.

3. What is the purpose of grounding secondary of the control transformer?

To protect the operating personnel from high induced voltage.

4. Based on what factors will you select rating of components for a starter cell?

Factors for selecting rating of components are,
a. Capacity of load.
b. Type of starting.
c. Duty (continuous or intermittent).
d. Type of protection.
e. Nature of starting (acceleration time is slow or fast).

5. What maintenance checks you will do for an MCC cells and MCC panel?

Maintenance checks on MCC cells
a. Ensure that the load is tripped from control room and switch is in off position.
Switch off the isolator at MCC cell.
b. Open the door and rack out the cell into isolation position.
c. Check the tightness of terminal of contactor, 3C, control transformer, control
fuses, wipe in contacts, power cables, etc.
d. Check the tightness of component mounted.
e. Look for any charred components or terminals.
f. Check the IR value of 3C, contactor, control transformer, isolator etc.
g. Check the isolator double switch feature.
h. Check the OLR and calibrate the OLR.
i. Check the pick and drop out value of contactor, 3C.
j. Check the fuses for healthiness and fuse carriers for proper contacts.
k. Clean the arc-chutes of the contactor and clean all the components of the MCC
cell properly.
l. Check the resistances of control transformer, contactor, 3C etc.
m. Check the tightness of control cable at main TB compartment.

Maintenance on MCC panel.
a. Ensure the permit and all isolations.
b. Open the bus bar chamber and discharge the bus bar.
c. Disconnect the cables connected to bus bar and take the IR value of bus bar and
cable individually. Connect it properly and tight it to proper torque.
d. Check the tightness of nut and bolts and cables connected to buses.
e. Open the main TB compartment and check the tightness of all cables and clean it.
f. See the tightness of power terminal compartment and clean it.
g. Check that cables are supported properly.
h. Do checks on CT, PT used for indication purposes.
i. Clean the entire MCC panel properly and take the IR value.
j. Carry the checks on relays, which are used in the MCC panel.
k. See for proper earthing connection and tightness of the earthing connections.
l. See for proper house keeping.

6. What is the difference between an auto reset and manual reset overload relay?
a. Auto reset relay closes its contacts when the bimetallic strip gets cooled. In
manual reset relay we have to manually reset the relay because even though
bimetallic strip cools its contacts are not closing without manual reset. L & T type
OLR have only manual reset and siemens type has both manual and auto facility.
b. Auto reset over load relay is reset by switching OFF the respective had switch
and again switching it ON.
c. Manual over load relay is reseted by pushing the reset button provided on the
MCC cell.

Switchgear Questions & Answers

Switchgear

1. Mention the commissioning tests on breaker and bus bars.

Breaker

a. Milli volt drops test between the interrupting contacts and between the isolator
contacts.
b. Closing and opening timing of the breaker for 5 times.
c. Checking whether the breaker trips or closes when the logics are fulfilled.
Bus bars

a. Milli volts drop test for the contact resistance value.
b. Tightness of the joints.
c. IR values between phase to phase and phase to ground.

2. Explain clearly the three positions in 415 V breaker.

a. Service position: Power connections and control connections are available to the
breaker.
b. Test position: Power connections are cut off but control connections are available
to the breaker and it can be tested.
c. Disconnect position or rack out position: This is for maintenance of the breaker
and in this positions both the control and power connections are not available.

3. What do mean by trip free system in breaker?

In trip free the breaker is free to trip at any time. If both close and trip signal is
present at same time (instant) the breaker will attempt to close and positively trip.
When the breaker trips it will not close again even if closing signal exists because of
anti pumping feature.

4. What is the purpose of spring charging in 415 V breaker?

If the breaker is to be closed and tripped manually the closing time and tripping time
would vary from person to person. Also it would not be very fast. So spring charging
is provided. It gives uniform timings irrespective of the operator and its action is fast
and closing and tripping time is very less.

5. What are the built in protections provided in 415 V breaker?

a. DINF (making current magnetic release)
This consists of a laminated magnetic circuit. This is placed under the lower
current terminal pole. This is provided for all the three poles. It has a core that
rotates in the air gap. It is held by spring. During protection the magnetic forces
developed overcome the spring tension and the core is attracted. The mechanical
force developed is used to trip the breaker. This protection acts during the closing
of breaker if any fault exists. The current is set to 5 times the rated current.
b. DIRS (short time magnetic release)
The construction is same as DINF, but it has a mechanical timer, which can be set
accordingly. This protection acts when any fault comes during breaker in service.
The current rating is set to 3 to 8 times the rated current.
c. DIT – S (thermal over load protection)
This consists of a three bimetallic strip, which gets heated up when over loaded
and trips the breaker by a lever. It is placed in front of the breaker. Setting range
is 60% to 100%.

Logics and circuits Questions & Answers

Logics and circuits

1. Give the definition of following.

27C Closing circuit supervisory relay
27T Tripping circuit supervisory relay
3C Interposing relay (closing coil)
3T Tripping coil
52 AC circuit breaker
88 Auxillary motor (spring charging motor)
52Y Anti-pumping relay
86.1 Lockout relay
42 Main contactor
50 Instantaneous over current relay
50N Earth fault relay
94 Trip or Trip free relay
49 Thermal overload relay
49S Stalling protection relay
27 Supervisory relay
64 Ground protection relay

2. What is the operating voltage of 3C?

48V DC.

3. DC relay coil or contactor coils must be connected to which side?

Negative side of the DC supply to avoid galvanic effect on the coil, which will corrode the coil.

4. How special current limiting resistance is connected with the seal in contact?

Special current limiting resistance is connected in series with the seal in contact.

5. How you will connect start and stop push button to control the motor from two different places?

Start push button should be connected in parallel and stop push button in series in the circuit.

6. What are the basic principles of ED?

Basic principles of ED are,

a) All the contacts of corresponding relays and contactors are shown in de-energised condition.
b) Control circuit gives us idea about ON / OFF selection of motor, fuse rating, forward reverse
control, seal in protections etc.
c) Power circuits are drawn in thick lines and control circuits are drawn in thin lines.
d) When relay or contactor energises normally open contact closes and normally closed contact
opens.
e) Auxillary contacts acts with main device such as contactors and relay.

7. What is anti pumping?

When a breaker is closed on fault condition there will be continuous tripping and closing of the
breaker because 3C is energized. Anti pumping in circuit avoids frequent tripping and closing of
circuit breaker when the breaker is closed in fault condition.

Protective relays and application Questions & Answers

Protective relays and application

1. What you mean by accuracy limit factor?

The ratio between the accuracy limited primary current to rated primary current is
called the accuracy limit factor.

2. What is the characteristic of inverse time over current relay?

If the fault current increases the time of the operation of the relay will be decreases.

3. What are the two errors in instrument transformer?

a. Ratio error.
b. Phase angle error.
4. Where core balance CT is used?
Core balance CT is used in earth fault protection.

5. Define knee point voltage of a CT.

When the primary of a CT is open circuited and supply (variable) of system
frequency is given to secondary, then a 10% increase in voltage constitutes 50%
increase in current. That voltage is the knee point voltage.
At this point the core is saturated and a little increase in voltage constitutes a great
increase in current. kpv decides the opening range of the CT. Above kpv the ratio of
transformer will not be applicable.
kpv = RCT + RLEADS + RRELAY

6. What do you mean by the term 5P10?

This indicates the type of relay, Its % error and accuracy limit factor.
5 – composite error (Phase angle error + ratio error) 5%.
P – Protection CT.
10 – Accuracy limit factor.

7. Mention the important properties of relay contacts.

a. Should be robust in construction.
b. Self-cleaning (oxides easily breakdown).
c. Corrosion resistant.
d. Bounces free and striction free (low contact resistance).
e. Able to carry rated continuous current and short time rated current.

8. What is a composite error and write down the formula for composite error?

Basically composite error = Ratio error + Phase angle error. It is the ratio error
integrated over one cycle at steady state of operation.
Composite error =100 * 1 oςT (kn * Is – Ip)2 dt
T Ip

9. Define pickup value and reset value.

Pickup value: It is the smallest value of actuating quantity when its value is increased
from zero to pickup value, the relay will energise.
Drop out value: It is the largest value of the actuating quantity when its value is
decreased from pickup value, the relay will reset or de-energize.

10. Draw the circuit diagram for finding out the knee point voltage and explain the
procedure.
0 – 5 A
A CT
V 0 – 300V Sec Primary
240 V AC
Variac V Saturation
kpv = RCT + RLEADS + RRELAY
Knee point
Ankle point A
Connect the circuit as shown. O/P of variac should be zero. Increase it to 5 Volts and
take down the value of current from the ammeter. Now increase the voltage by 10%
(5 + 10% = 5.5 V) and take the current reading. Now increase the voltage by 10%
(5.5 V +0.55 V =6.05 V) and note down the current. Now keep on increasing voltage
by 10% and note down current reading. At some value there will be 50% increase in
current for 10% increase in voltage.
Example 40 V􀃆 0.2 A
40.4 V􀃆 0.3 A (0.2 + 50% = 0.3 A).
That point is the knee point voltage of that particular CT. From this point onwards a
little increase in voltage will lead to a large increase in current, because the core is
saturated fully. When we plot all the values on a graph taking current as X-axis and
voltage as Y-axis, we will get the above graph. Protective relays operate between
ankle point and knee point. Above this they cannot detect the fault correctly.
Measuring CT operate in the ankle region.

11. Explain the procedure for finding out the polarity and ratio test in a CT with circuit
diagram.

Polarity test:
Connect the circuit as shown in figure with a battery, switch and
AVOmeter.
Now momentarily close the switch S and see the deflection in the
AVOmeter.
If it is in the direction as shown in the figure, then the polarity of the CT
is correct. If it is in opposite direction the polarity of CT is not correct. Polarity test is
very important because if polarity is not correct in differential protection the relay
will fail to act when fault occurs.
Ratio test: Connect circuit as shown in figure (2). Slowly increase the current. Take
down the readings of A1 and A2. Then see whether it confirms to reading of
nameplate. Ratio = A1/A2.
SECONDARY INJECTION KIT
+AVO - A A1
0 – 30 A
+ - 240 V AC
S1 S2
P1 P2
+ -
S B
POLARITY TEST (FIG 1) Fig – 2 Ratio test
Ratio – A1 : A2 A2
A 0 – 15A

12. Explain the principle of operation of attracted armature relay with equation and
characteristics curve.

Principle: It works on the principle that when a current is passed through a coil
magnetic lines of force develop and the coil behaves like a magnet. When we place a
magnetic material inside the coil it is attracted.
In attracted armature type of relays there is a spring that keeps the contact open, a
plunger that tends to close the contact and a coil through which current is passed.
The spring force and magnetic force oppose each other. When these both are equal
the relay will pickups.
At verge (time) of pickup Instantaneous select
k1 I2 = k2
f = k1 I2 = k2 Time Time delay select
I = k2 / k1
Where f – force.
k1 – magnetic force constant.
k2 – spring tension constant. current
I – current in the coil.

We can see the inverse characteristics from the above formulae. Usually attracted
armature relays are instantaneous. That is there is no intentional (fixed) time delay. If
we want a time delay we can add a slug in the armature core.

13. Mention the initial commissioning checks on CT’s, PT’s and relays.

Commissioning checks on
CT
a) Terminal marking correctness.
b) Polarity of terminals.
c) Insulation resistance between primary and secondary.
d) Insulation resistance between primary to earth and secondary to earth.
e) Magnetization characteristic and knee point voltage test.
f) Ratio test.
PT
a) Terminal markings.
b) Polarity checks of terminals.
c) Insulation resistance between primary and secondary.
d) Insulation resistance between primary to earth and secondary to earth.
e) Ratio test.
f) Whether PT can supply as per the burden of load check.
RELAYS
a) Pickup and dropout value check.
b) Insulation resistance of contacts and relay coil.
c) Time delay (if relay is not instantaneous), operating time value check of relay.
d) See that the correct circuit breaker trips on energisation of the particular relay.
e) Continuity checks of contacts after energisation of relay.
f) See if plug-shorting contacts are correct.
g) See if CT’s and PT’s are corrected in correct polarity.
h) Burden check of relay.
i) Primary injection test.
j) Secondary injection test.

14. Explain with simple diagram the core balance CT.

In core balance CT all the three phases go through the core and the resultant
magnetic flux is zero. Because the flux of three phases cancel each other. So the
secondary output of CT is zero and the relay will not energise.
When there is a earth fault in one of the phase the fluxes cannot balance each other
and there is a voltage induced in secondary of the CT and the relay is energised to
trip the circuit. Saturation is no problem because the core size is very big.
+R
Ground fault
R R Y
Relay dropped Relay pickup
B R
R Y B R Y B - R
Normal operation. During earth fault. Resultant diagram.

Power and control cables. Questions & Answers

Power and control cables.

1. Define conductor.

Conductor: A material of low resistance used to transmit electrical energy. Examle
wires, cables, bus bars etc.

2. Define unprotected insulated wire.

Unprotected insulated wire: Unprotected insulated wire is which the insulation of the
wire is not covered by a protective sheathing to prevent it from mechanical damage.

3. Define cable.

Cable: One or more insulated conductor enclosed in a protective mechanical
sheathing of either GI wire or GI strip or aluminium to protect the insulation from
mechanical damage.

4. Define insulated wire.

Insulated wire: A conductor or multi-stranded conductor which has a insulating
material on it is called a insulated wire.

5. Explain briefly about armouring for an under grounded cable.

Armouring is required to protect the cores from mechanical damage.

6. Explain briefly about grounding of cable trays.

Cable trays are grounded because to avoid any shocks to personnel incase of leakage.
A grounding wire runs at the side of tray through a parallel groove clamp through out
the length of the cable tray. If trays are one above another we can loop up the
grounding wire to the tray below. This saves extra ground wire.

7. What are the differences between the power and control cable?

Power cable: It is used for supplying current to load. It is of larger current carrying
capacity available in single core, 2 cores, 3 cores, 3 cores, and 4 cores. Single core
is available upto 1000 mm2. Usually power cables are of aluminium. These cables
are graded for higher voltages and possess more cross section area.
Control cable: Control cables are used for control purposes for logics, indication or
annunciation etc. These are of lower current carrying capacity and voltage grading is
also less. These are of less cross sectional area are available in pairs of 2,5,10,25,50
etc.

8. What is the purpose of using corrosion inhibiting compound?

It is used for aluminium conductors while crimping to a lug or ferrule. It prevents
corrosion of aluminium conductor due to oxidation and due to saline atmosphere.

9. Why aluminium armouring for single core 1000 mm2 is used?

Aluminium armouring for single core 1000 mm2 is used so that heating will not take
place due to the flux around the conductor, as the aluminium is a non-magnetic
material.

10. What is resistance of copper compare to the aluminium?

Copper is less resistive than aluminium.

11. What is applied over the steel tape armour of PILC cable as serving?

Bituminous covered jute.

12. What is used as insulation for PILC cable?

Impregnated paper.

13. A small quantity of impurity reduces how much of conductivity of copper?

35% of conductivity will be reduced due a small impurity in the conductor.

14. Why cast aluminium tri-foil clamp is used in single core cables laying?

When three conductors are clamped together the fluxes around the conductors are get
cancelled

15. What are the parts of a cable gland?

a. Check nut.
b. Nipple.
c. Metal washer.
d. Neoprene rubber.
e. Metal washer.
f. Compression nut.

16. What are the advantages of PVC insulated cable?

a. Plumbing is not required. Joints can be made easily.
b. As PVC is light the injury caused to it while laying is less.
c. It is corrosion resistant.
d. It has high fire retarding property.
e. It does not break down even if moisture enters.

Electrical equipment fundamental Questions & Answers

Electrical equipment fundamental

1. Why indoor switchyard is provided in MAPS?

The salt contamination in the switchyard is avoided by providing indoor switchyard
in MAPS. Because the plant is just 300 metres away from the seashore and the
atmosphere is saline. This salt will get deposited on the insulators and on the
conductors used in the switchyard. Due to this deposition insulators may fail to
unnecessary trip the system and conductor used must be copper for better
performance instead of low cost aluminum. So to avoid unnecessary trip and to have
low cost of installation and spare parts of aluminium indoor switchyard is used.

2. What do ABCB and ACB mean?

ABCB – Air blast circuit breaker.
ACB – Air circuit breaker.

3. What do you mean by frequency?

The number of cycles per second is called the frequency.

4. State the voltage and current relation in star and delta connection.

In star connection line current is equal to the phase current and line voltage is √3
times that of phase voltage.
In delta connection line voltage is equal to the phase voltage and line current is √3
times that of phase current.

5. In DC motor what is the relation between speed and field flux?

Speed of a DC motor is inversely proportional to the field flux.

6. What is the difference between self-excited and separately excited DC generator?

Self-excited generator: In a self-excited generator the field winding is excited by an
external DC source like a battery etc.
Separately excited generator: In a separately excited generator the field poles have
some residual magnetism. When the armature is rotated a small emf is induced in it.
This is fed to the field winding and if the current direction is such that it adds the
residual magnetic flux to the field winding and the field strength is increased. The
more emf in the armature, which is again fed to the field winding and goes on till the
generator builds up voltage.

Batteries and charger Questions & Answers

Batteries and charger

1. How you will prepare electrolyte for a lead acid battery?

While preparing electrolyte for lead acid battery sulphuric acid is added to distilled
water.

2. How battery capacity is expressed?

Always battery capacity is expressed in Ampere – hour.

3. What is the instrument used to measure the specific gravity?

The instrument used to measure the specific gravity is called Hydrometer.

4. What you mean by SCR?

SCR is meant for silicon controlled rectifier.

5. Define specific gravity and mention the specific gravity of a fully charged lead acid
battery?

Specific gravity of a substance is the comparison of density of the substance with the
density of pure water.
Specific gravity = Density of the substance / density of pure water.
= kg / cm2
kg / cm2
= (No unit)
Specific gravity is only number. It has no unit.
Specific gravity of pure water is one.
Specific gravity of fully charged lead acid battery is 1.215. Specific gravity should
always be corrected to 27°C.
Corrected specific gravity is equal to indicated specific gravity ± (t - 27°C)*0.0007.
Indicated specific gravity = 1.205 and ‘t’ means electrolyte temperature.

6. What are the parts of the battery?

Parts of the battery are
a. Battery container.
b. Battery cover.
c. Positive plate (Pb o2).
d. Negative plate (Pb).
e. Cell connector.
f. Grid.
g. Cell separator (porous material).
h. Sediment chamber.
i. Positive and negative terminals.
j. Vent plugs.
k. Dilutes sulphuric acid (electrolyte).

7. What are the indications of a fully charged cell?

a. The colour of the + ve plates will be dark brown. This can be seen only if the
battery has transparent cover.
b. Voltage per cell will be a 2.15 volts.
c. Gassing in the will electrolyte will indicate. But the current is splitting up water to
H2 and O2. Because the positive and negative plates are fully converted to their
original constituents.

8. What are the difference between primary cell and secondary cell?

Primary cell:
The electrolyte in primary cell is chemically irreversible. That is once
the cell is discharged it cannot be recharged. It should be replaced with a new cell.
The cells can supply only low currents and have low efficiency. They supply
intermittent current. Their internal resistance is more. These cells are comparatively
cheap.

Secondary cell:
These cells are chemically reversible. They can be discharged and
charged. They can supply large currents because their internal resistance is less.
These have high efficiency compare to primary cells. These can supply constant
current. These are comparatively costly.

9. What do you mean by sulphation? And what are the effects of sulphation?

Sulphation:
During normal discharge of battery Pb so4 is formed. This Pb so4 is
chemically reversible by passing current. These split up to their original constituents.
But under certain condition crystalline lead sulphate is formed (Example: under
charging after some time without trickle charging). This Pb so4 is chemically
irreversible. So if the sulphation occurs the battery life decreases. Efficiency
decreases and the active material starts falling of the grid.

10. Write down the equation for Nickel cadmium battery.

Equation for Nickel cadmium battery.
Ni (OH4) + Cd +2 kOH 􀃆Ni (OH2) + Cd OH2 + kOH (during charging)
(Nickel hydrate + cadmium + potassium hydroxide 􀃆 Nickel hydroxide + cadmium
hydroxide + potassium hydroxide.)
Ni (OH2) + Cd OH2 + kOH 􀃆 Ni (OH4) + Cd +2 kOH (during discharge)
We see that there is no change in electrolyte. It just acts as a catalyst. So there is no
need to change the electrolyte.

11. Write down the theory of lead acid battery.

A simple lead acid battery consists of positive and negative electrodes Immersed in
an electrolyte. The positive electrodes are Pbo2 (lead oxide) and the negative
electrodes are Pb (spongy lead). The electrolyte is dilute sulphuric acid.
On discharging the battery
Pbo2 + Pb +2 H2 so4 􀃆Pbso4 + Pbso4 + 2 H2o
Lead acid is converted into lead sulphate. Spongy lead is also converted into lead
sulphate and H2 so4 used up in the process. Only water is remain. So the specific
gravity of the cell comes down.
On charging the battery
Pbso4 + Pbso4 + 2 H2o 􀃆 Pbo2 + Pb +2 H2 so4
Here the products are converted to their original constituents and the acid is released.
So the specific gravity rises as the cell is charged. How much ever larger be the cell
the voltage of each cell will be approx. 2.15 V when fully charged.
The positive plate is made of a paste lead oxide, lead sulphate that is fitted in a mesh
like material and is connected to grid. All positive plates are made common and
connected to a grid.
The negative plate is made of spongy lead also it is in mesh and connected to grid.
These are also grouped together.
These plates are separated by a micro porous separator for the diffusion of
electrolyte.
The electrolyte is prepared by adding sulphuric acid to distilled water drops by drop
and stirring it until the reasoned specific gravity is attained.
Every thing is placed in a container of hard rubber. The cells of a battery are
connected by a cell connector. The container is leak proof.

12. What are the parts of a 48V DC charger?

Main transformer: This steps down the 3Φ 415V supply to the require value of
voltage.
Synchronizing transformer for phase sequence: This gives the synchronizing signal
to the firing card. That is, the pulses from this card if fed to the firing card. The firing
card gives pulses to the SCR of R or Y or B depending upon which phase is positive
maximum.
Half control module: This has a diode and a SCR for each phase. The firing card
controls the firing angle of SCR.
Firing card: This gives the firing pulses to SCR depending on phase sequence and
the feed back from output.
Controller card: This card monitors the output and gives signal to firing card to
conduct at certain angle to maintain constant output voltage.
Power supply card: This gives power supply for the controller card, firing card and
protection.

13. Explain the operation of 48 V battery charger.

The supply for the charger is from MCC. The supply is tapped for power supply to
control card, PF correction capacitor. LC filter is used for suppressing surge voltage.
The main supply is stepped down and given to the half control rectifier module. The
SCR conducts only when gate gets positive pulse. This pulse is given by pulse
transformer, which gets pulses from firing card. Firing card gives pulse to the
respective RYB SCR only when their phases are positive maximum. The freewheel
diode is incorporated to protect the SCR and diodes from back emf when supply to
coils is cut off due to collapsing magnetic field.
The filter is provided to smoothen the ripple output and the bleeder is used for
voltage regulation. It gives improved voltage regulation and acts as a minimum load.
Also it keeps the SCR in conducting state by drawing the minimum current which is
higher than the SCR holding current. Thus there is always output voltage irrespective
of load.
DC CT is used for limiting output current. It works on principle of magnetic
amplifier. There is also provision for smooth rising of output voltage.

14. What is purpose of freewheeling diode and DC filter circuit in the charger?

Freewheeling diode is used to protect the semiconductor components used in the
charger from the back emf, which is induced in the inductive coils of relays when the
supply to the relays is cut off. The magnetic field in the relays collapses and induces
high voltage in reverse direction. This emf is shunted by the freewheeling diode,
which is connected in reverse bios with the output.
DC filter is used to smoothen the output, which has ripple. Ripple frequency is same
as system frequency for half wave rectifier and 2 times of system frequency for full
wave rectifier. The filter, which is a capacitor, will oppose any change in voltage.
Thus the ripple will not be allowed to come to zero.

PKR ELECTRICAL ENGINEERING

Monday, March 30, 2020

Coronavirus Cases in India Live on 30th March 2020 afternoon

India

Coronavirus Cases:

Deaths:

Recovered:

Total Coronavirus Cases in India

Daily New Cases in India

Active Cases in India

Total Coronavirus Deaths in India

Daily New Deaths in India

Newly Infected vs. Newly Recovered in India

Outcome of Cases (Recovery or Death) in India

Latest Updates

March 30 (GMT)

March 28 (GMT)

March 27 (GMT)

March 26 (GMT)

March 25 (GMT)

March 24 (GMT)

COVID-19 CORONAVIRUS PANDEMIC Live Updates 30th March 2020

Coronavirus Cases:

Deaths:

Recovered:

Confirmed Cases and Deaths by Country, Territory, or Conveyance

MCC Questions & Answers

Switchgear Questions & Answers

Logics and circuits Questions & Answers

Protective relays and application Questions & Answers

Power and control cables. Questions & Answers

Electrical equipment fundamental Questions & Answers

Batteries and charger Questions & Answers

Featured Post

MAJOR 10 PANDEMICS (MAHAMARI) IN HISTORY

Popular Posts