Function 5 part-1
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WRITTEN NOTES:-
EKG: - JAN-19, FEB-19, MAR-19, APR-19, JUN-19, JUL-19, AUG-19, SEP-19, OCT-19, NOV-19, DEC-19, JAN-20
Question:- MSB Maintenance
Answer: 1. Checking contacts of circuit breaker for damage and dirt
2. Clean by electro-cleaner for contacts
3. Dirt and dust to be removed vacuum cleaner
4. Circuit breaker contact never to be filed and scrapped
5. Defective or burnt contact to be replaced.
Questions: - Safeties of MSB?
Answer: -1. Minimum 3 mm thick rubber mate on front and back
2. Insulated handgrip and rail ebonite handle
3. Dead front is required for switch board for AC
4. No pipeline to pass in vicinity
5. Earth fault indicator
6. If breaker is on top cover cannot be open
7. Ventilation grid
8. Manual tripping device
9. under voltage relay, 0.8 x normal voltage (3-5 seconds)
10. Reverse power trip (5 - 15 % below normal power)
11. over voltage trip- 1.3 X normal voltage.
12. Preferential trips- 110% full load current.
Question: How sound is transmitted through telephone from engine room to Bridge?
Answer: There is a diaphragm from where we speak due to sound wave diagram vibrates. A coil is there, due to vibration of diaphragm the coil rotates in a magnetic field, means sound wave is converted into electrical wave.
The diaphragm is vibrated by the sound wave and move the driving rod and armature rack out forth through the stationary magnetic field existing about the magnet and the armature.
The moving armature Alter the magnetic field making it to move and cut the conductor in the coil thereby inducing a small AC voltage produces a fluctuating magnetic field about the armature.
The armature is repelled and attracted by the field of the magnet and move back and forth.
The diagram of the receiver vibrated in and out by the driving rod, thus creating sound wave, which corresponding with the sound waves striking the transmitter diaphragm.
Question: As a second engineer how will you order a battery for emergency lightning?
Answer: voltage, ampere hour, make and model number, dimension and type of battery.
Question; what is ampere hour?
Answer; power rating for a given battery emperors that can be costly the battery completely discharged over a specific time.
Example of required amperage
Emergency load navigational equipment + lighting if the load Amps need minimum 8 hour so required capacity is 24 volt 800 ampere hour
Question; if your ship is design for 60 hearts at 440 volt show supply volt b is operating at 50 Hertz reasons
Answer; supply voltage should be 380 voltage. Has the frequency been reduced by 16.7% proportionally the voltage should be reduced by 16.7% ratio of voltage and frequency can be maintained speed of the motor is directly proportional to the frequency and torque current is directly proportional to the voltage so the increase in torque current is controlled by the proportional reduction in voltage
Question; difference between switch and circuit breaker centre
Answer; a circuit breaker is an automatically operated electrical switch designed to protect circuit from damage caused by circuit faults
Its basic function is to detect a fault condition while maintaining continuity and immediately disconnect the circuit upon the fault detection.
A Switch is manually operated by using contactor to open and close the circuit.
Question; current transformer secondary winding is earth why
Answer; the reason is to reduce the insulation costing add one second eternal you can insulate the current transformer I can see you f2 elite four line voltage might increase the cost as well as size of the current transformer by earthing one and of the current transformer in the circuit is anchored 20 volt age and any fault can be detected by Earth voltage monitor
Question; checks when taking short supply
Answer; connection box at entrance of accomodation for emergency generator room and action box must-haves You table cal to accept the Shore supply cable including toward the sorath action box must have circuit breaker isolator switch refuses to protect cable linking to connection box circuit board.
A voltmeter is fitted cricket polarity of DC shore connection foreign AC shor supply phase sequence indicator is used to indicate correct supply phase sequence
SOS apply switch on m s b is interlocked with circuit breaker so that it cannot be clear generator still connected
Reverse phase sequence will produce reverse phase rotation because the rotating magnetic field will be reversed with disastrous result
Phase sequence can be corrected by interchanging any two conductor Offshore supply
Higher power supply frequency will cause motor master be overloaded and overheated a higher voltage be generally cause equipments to take excessive current so overheated lower voltage is generally not so serious main cause water to run slower and overheat main cause motor to stall anta anta
Voltage frequency and phase sequence should be same metre reading should be tested earthing insulation of so supply cable and shore connection box to be tested
Question; what is slip?
Answer ; the difference between synchronous speed of the motor speed of the router sleep expressed as percentage by the synchronous speed.
Question; undervoltage trip?
Answer: It is intended to open the brakes are at loss of excitation for any reason time delay is wired across the main lead on the generator side of circuit breaker and man not energized leave the plunger in trip position and breaker cannot be closed. Normal voltage output with the machine running oil and flying Jatt ful town against loading spring to release the tric this allowed closer of breaker and means the device is set.
Question: Measurement of air gap in alternator
Answer: It is measured at 4 location 90 degree apart on both ends using feeler gauge rotate rotor by 90 degree and repeat the readings shall not be beyond 10% on average at each and values of air gap 1.5 mm maximum.
Question: What is SCR
Answer: A silicon controlled rectifier is a four layer pnpn semiconductor device that does not allow the current to flow until it is triggered. The flow of current is in one direction. It has three terminals gate - input terminal. Anode - output terminal. Cathode which is common to both the gate and anode application sCR is used in alarm circuit.
Question: Circuit breaker types?
Answer: Circuit breaker oil circuit breaker gas circuit breaker with sf6 Sulphur hexafluoride vacuum circuit breaker - the the high dielectric strength of a vacuum allow a very short contact separation and a rapid restrike free option of the arc is achieved.
Question: what is single phasing and method of protection against it?
Answer: single phasing is usually caused when one of the three backup fuse blows if one of the contactor contact is open circuited the effect of single phasing is to increase the current in the remaining two lines and cause the motor for become even torque produced in the Rotor.
The loss of current through 1 phase in 3 phase supply is single phasing ring prevents a motor from starting but running motor may continue to operate with fault.
Method of protection
Bi metal single phase production three bimetals old position three bimetals hot balanced. 2 bimetals hot and one cold differential.
Electromagnetic overload relay
Short circuit protection fuses
Question: Factors on which stresses losses depends on?
Answer: Applied voltage material of the core and frequency.
Eddy current losses is proportional to the square of the applied voltage and is independent of frequency.
Transformer losses is equal to iron losses + copper losses
Iron losses is equal to hysteresis losses and Eddy current losses.
Question : How to reduce flux leakage in the Transformer?
Answer: To reduce flux leakage primary and secondary on the same Core. page 496 BL theraja.
Question: What is zener diode? Uses?
Answer: It is a diode across which the voltage drop is control over the range of current.
It is used as a means of providing A stabilized voltage in same circuit. It acts as a electrical relief valve.
Uses: Voltage stabilizer and battery charging circuit.
Another definition of zener diode: A properly doped crystal diode which has a sharp breakdown voltage is known as zener diode.
Question: Function of Zener barrier and use and diagram?
Answer: Zener barrier prevents the transfer of unacceptably high energy from safe area to the hazardous area.
The Zener diodes in the real are connected in the reverse Biased direction. The breakdown voltage of the diode is not exceeded in normal condition.
If this voltage is exceeded due to fault in safe area, the diode start to conduct use to blow.
Application of Zener barrier:
Alarms, proximity sensors, fire and smoke detectors.
Question: Cable is wet how to bring back insulation resistance?
Answer: Cable drawing out by injecting heating current from: -
Current injection set
Welding transformer
The cable should be disconnected at both ends from equipment. The injection cable must have good connection at each end.
Current flow and cable temperature should be carefully monitored.
Criteria during heating:
The injected heating current must never exceed the rated current for the cable (connect and ameter).
The voltage should be in the region of 30 - 55 volts depending upon the current setting.
The temperature should not be allowed to exceed 30 degree Celsius.
Temperature and insulation resistance should be measured and recorded every hour.
Insulation resistance become study the heading should be carried out for a further 4 hours before switching off.
When satisfactory insulation resistance value have been restored A final check should be made with the cable at normal ambient temperature.
Insulation resistance final values reading.
Between Core and earth is approximately 20 mega ohms.
Between Core and core is approximately 100 Mega ohms.
Question: Cycloconverter, thyristor & transistor?
Answer: The cycloconverter method of controlling speed also relies on the ability of the converted to accept current from the switch board at constant frequency and voltage but to pass this current to the AC motor at a reduced frequency and with voltage adjusted.
The cycloconverter is different in that it operates without an intermediate stage of conversion.
Question: - Fuses
Answer: - tinned copper in rewirable fuse melts at 1080 degree Celsius.
Silver in Cartridge fuses at 90 degree Celsius.
Current rating gives the normal current that may be carried.
Minimum fusing current is the smallest current that will cause melting.
HRC fuses I have silver wire and lost ine quads powder filled ceramic tubes with metal end caps.
They have a great time/ current characteristic and reliability for discrimination.
Question: - semi enclosed fuses
Answer: - Re-wirable fuse has an insulated carrier force handling and containment of the wire in an asbestos lined tube.
Fault: - is that of premature failure of wire oxidation on contact with air or being stretched when fitted in.
Current characteristics are found by testing few of the same type of fuses and different current and plotting the result. The bottom current testing is not more than 1.05 % max fuse current. Top current is the one that will melt wire is not for more than 0.5 of a second. The other test current are equally spaced between these.
Question: - how you restore residual magnetism in an alternator?
Answer: - to restore residual magnetism connect a 12 volt battery to the exciter field generator is at rest.
Remove exciter field lead F+ & F- from the AVR.
Measure the exciter field resistance from the F+ and F- lead. You should be able to read some resistance as you are measuring the continuous winding. An infinite resistance reading good indicate and open in the exciter field. Also check to be sure is no path to ground.
connect F+ to positive pole of the battery.
Hold the F- led by the insulated portion on the lead wire, touch F- in the negative pole of the battery for 5 to 10 seconds, then remove.
Reconnect F+ and F- to the AVR regulator. Repeat the procedure if the generator fails to build voltage.
Question:- principle of a tachometer.
Answer:- types of tachometers are AC and DC.
It works on the principle of generation of EMF when a Rotary conductor cuts the magnetic flux. When magnetic flux is constant then EMF produced is directly proportional to the speed of armature that is coupled to the shaft of motor.
Question: - parts of MSB
Answer: - 1. Synchronoscope.
2. Air circuit breaker
3. Frequency meter.
4. Synchronising panel
5. Earth fault indicator.
6. Feeders
Question:- what is a diode and how it is tested?
Answer: - it is a semiconductor device that is formed by joining p-type and n-type materials and allow the current to flow only in one direction.
- Act as a non-return valve for the current.
- Use to convert AC to DC.
Testing: -
- Check the multi-meter for proper functioning. Short the probes and check resistance and/or continuity. Switch the instrument to diode test mode.
- Switch the power of circuit. Discharge the capacitors and remove the fuses.
- Connect the two probes of multi-meter across the diode.
- In forward biased measurement, a healthy should be showing 0.5-0.8volts
- If display is over range in both the directions, the diode has open circuit fault.
- If displays < 1volts in both the directions, the diode may be short circuit fault.
Question: - Alternator maintenance.
Answer: - before maintenance, safety should be taken.
1. Shut down and lock off generator prime mover.
2. Generator circuit breaker is locked off.
3. Electric heaters are switched off and isolated.
4. Put the tag. “MAN AT WORK”.
Checks: -
All wiring of the generator should be inspected for damage. Check oil and water contamination of cable insulation within terminal box. Check cooling air filter and exhaust opening are not blocked and free from dirt and dust. Remove dust and dirt from winding by vacuum cleaner. Welder position on insulation will reduce the insulation resistance the oil deposition can remove by washing with special detergent liquid. Winding insulation can be improved by suitable air drying and warnishing. Measure the insulation of stator and motor winding to earth and between stator phase minimum insulation resistance should be 1 Mega Ohm.
Check pedestal bearing lubrication.
The area between rotor and stator( 1.8- 3 mm). Check the space heater.
Question:- alternator safeties
Answer under voltage protection reverse power protection preferential tripping of non essential load overcurrent protection overload trip short circuit trip Prime mover over speed trip emergency stop.
Question:- an induction motor has been flooded with seawater insulation resistance is down to zero ohm. What is the procedure for putting back into the service?
Answer: - isolated electrically discharge all Static Current by earthing dismental rotor and stator clean all parts through fresh water allow stator and rotor for dry completely with low power electrical heater or lamp sufficient ventilation to allow the moisture to escape. Once droidjack insulation resistance if it is zero continue waiting till it get good value of insulation resistance is achieved.
If it is not improving then send motor ashore for rewinding. if insulation resistance improves then warnings can be applied. Varnish has to impregnate through the winding. Commutator separate. Commutator required to be cleaned by appropriate contact electro cleaner and soft brush. Resurface the commentator by sanding to remove pitting arcing marks and embedded dirt.
Check brush contact by pressing. Is the pressing not ok change the spring. Change both the bearing. Assemble and check insulation resistance again. Run on no load if everything is ok. After 2 hours is temperature rise and noise are normal then connect the motor to the load.
Question:- what kind of stator winding in generator? Why so is required? Hard reduces cable size? Why you wish to reduce cable size?
Answer:- in case of star connection phase and current are same. Four same number of turn in star connection voltage generation is more but insulation of winding is less it provide neutral for earthing. Size cost and maintenance are reduced.
In case of delta connection line current is equal to the √3 x phase current. For same voltage we need larger cross sectional area of cable.
Want to reduce label size following the cost of installation as well as maintenance
Question:- AVR
Answer:- it is a automatic voltage regulator which senses The generator output voltage and alters the field current to maintain the voltage at its set value.
Question: - ensure the fair current sharing man generator continues to run.
Answer: - ensure the overvoltage and undervoltage alarm & trips are operational.
Question:- how capacity of battery is decided?
Answer- by passing fixed amount of current and the voltage drop to set value that time for discharge is multiplied to current and amp-hr is found out.
Question:- what are motor protections?
Answer:- overload trip fuse thermistors bimetallic strips
Question:- difference between welding Transformer and normal transformer?
Answer:- welding transformer is a step down transformer that reduces the voltage from the source voltage that is suitable for welding usually between 15 to 45 volts. Secondary current is quite high 200 to 600 amps. The secondary mein hai use several steps to adjust the secondary voltage to control the welding current. For welding with DC a rectifier is connected to the secondary of the transformer.
Question:- purpose of motor varnish
Answer:- it refers to the secondary layer of insulation that is applied to the coils on the rotor and stator winding in a motor. It immobilizes windings so that coils do not move. If the coils are allowed to move coating of inner primary insulation would quickly wear out as the rotating magnetic field cause the winding to vibrate. Motor varnish also increases the dielectric strength of the winding which is more important for transformer winding then motor winding. Dielectric strength is the maximum voltage that can be applied to a material without causing it to break down.
Question:- purpose of interpole in DC machine?
Answer:- intercourse auxiliary poles place in between main poles. Their function is to assist commutation by producing auxiliary flux which thereafter helps in eliminating brush sparking. Interpole winding are connected in series with the armature windings.
Question: - MSB trips and method of testing?
Answer:- mSB trips
Overcurrent undervoltage reverse power
Testing
Reverse power can be tested by lowering the power of DG.
Question:- difference between induction and synchronous motor
Answer:- induction motor
They only required AC 3 phase supply
They run at speed less than synchronous speed which varies with load.
Power factor at full load is maximum. reduced to a very low 0.2 value at a load below 50%.
It is a robust motor applied in all type of duties in engine room.
Most economical.
Least maintenance.
They are self starting.
Synchronous motor:-
They require both DC to Rotor and three phase AC supply to stator.
Run at constant speed at all loads.
Synchronous motor can run at a constant power factor at all loads by varying the DC excitation voltage.
Selectively used to their constant speed is required at all loads.
They are costly.
Require regular maintenance of slip rings and brushes.
They are not self starting.
Question:- difference between acid and alkaline battery
Answer:- lead acid battery contain two plate emerged in an electrolyte the positive terminal is lead peroxide and negative terminal is lead the electrolyte used is dilute sulphuric acid during discharge the hydrogen ion from sulphuric acid react with oxygen dissolved from lead peroxide and forms water. The water formed dilute the electrolyte and its specific gravity decreases.
at negative plate the sulphate ion combines with the lead and form lead sulphate .the lead sulfate covers the active material of the plate the further reaction is stifled.
Fully charged cell is capable of producing two volt and relative density will be 1.285@ 15 degree Celsius
After a period of discharge the voltage on load drops to 1.75 volts and relative density to 1.110.
Flow of current supply source reverse discharge action of the cell the sulphate ion song lead sulphate goes into solution leaving the plate as pure lED electrolyte breaks down returning hydrogen ion into the solution and allowed oxygen to recombine with the lead of positive plate and form lead peroxide.
Differences acid battery the electrolyte is sulfuric acid during discharge specific gravity decreases lead acid battery voltage drops as it discharges take more time in charging and discharging
Electrolyte is potassium hydroxide no change in specific gravity during charging or discharge alkaline battery maintains voltage until discharge completely.alkline battery has low internal resistance that allow quick charging and discharging.
Maintenance of battery
should be placed in well ventilated rooms.
Ventilation fan should be Spark proof room should be kept dry and clean no smoking sign should be displayed in and out of the room no naked light is allowed only explosive proof light is allowed condition of battery should be checked regularly in Lead acid battery is the specific gravity is checked by hydrometer. fully charge battery has a specific gravity of 1.280 fully discharged battery as a specific gravity of 1.12.
In alkaline batteries the condition is checked by voltmeter.
Tightness of terminals is to be checked.
Terminals are to be applied with petroleum jelly to prevent corrosion.
Battery should be secured in a wooden tray.
All tools used in a battery room should be insulated.
Temperature of the electrolyte should not exceed 45 degree Celsius.
Vent hole should be kept clean.
Excessive Rapid charging should be avoided.
Always top up with distilled water.
When should always be open.
Battery plates Should always be submerged in electrolyte.
At least once in a month the battery should be completely discharge and recharge to increase performance.
Why there is salt deposition on battery terminals.
Answer during discharge negative side.
Question:- working of a brushless alternator
Answer:- in brushless alternator slip rings and brushes are eliminated and excitation is provided by small alternator.
DC exciter has three phase output winding on the rotor in magnetic field in the casing.
poles are supplied with with DC from an AVR.
3 phase current generated on the winding on the exciter Rotor through a rectifier assembly on the shaft & then to the main alternator poles
No slip rings are needed
There is no direct electrical connection between rotating and steel machinery winding of a generator Exide field is supplied from DC from a static AVR rectification fighter voltage is achieved by shaft mounted indian supply to the main alternator field.
Question: - principle of induction motor
Answer: - when a 3 phase supply is connected to the stator winding the current produce rotating magnetic field which rotates at a speed all a synchronous speed the value of synchronous speed depends on the number of magnetic poles on my status and the frequency of the supply connected to the stator a magnetic field produced by the circuit flowing 3 stator winding is cut by a rotor winding and does induced magnetic flux in them just relax is changing and EMF in is induced which call a circuit to flow in these winding the flow of current produced at talk in the rotor winding which causes them to rotate in the direction of RMS at a speed which is less than the synchronous speed.
Question: - Application of induction motors
Answer: - 3 phase squirrel cage induction motor used for mens water pump Motors men jacket cooling water pump Motors small single phase synchronous motor Radar motor gyro compass motor three phase synchronous motor of large size is used for main electric propulsion and bow thruster.
Synchronous motor act as synchronous condenser in shaft generator system.
Double cage induction motor turning gear motor for high starting torque.
Phase induction motor exhaust fan motor used in toilet hand drill hand blower mixer grinder.
Question:- what are intrinsic safe circuits.
Answer:- circuits there is no Spark thermal effect is produced under normal and faulty condition to cause ignition. The circuit condition is limited to 50 Milliamps and 30 volt.
This protection is used in low power instrumentation alarm and communication system
Question:- reduced voltage starters
Answer:- auto transformer starter star delta starter soft starter.
Question:- direct online starter?
Answer:- high starting current low starting torque.
Question:- what is the purpose of seath on cable?
The seat of cable protects the protects the insulation from damage or injury.
Material required to be heat oil and chemical and flame retardant.
polychloroprene or neoprene.
chlorosulphonated polythelene or bypalon.
Question: - types of fuses?
Answer: - HRC, kit Kat type, cartridge type, semi-closed type.
Fuse material:- silicon, Copper or Aluminium.
Question:- to ulta natives are in parallel have same kilowatt load rating but they are at different power factor what is the reason for this?
Answer:- load load sharing is done by droop of the Governor.
KVAr load sharing is done by droop of the AVR.
Reasons:- if there is fault in the droop of AVR.
Excitation of one of the alternator more than the other.
Question:- What is the reason for and alternator failing to build voltage?
answer:- the generator is remaining in stand still for a long time there is a loss of the schedule magnetism.
If the shunt field DC generator excitation field resistance is more than the critical resistance.
Wire may be broken
Voltmeter is faulty.
Question:- Relay
Answer:- it is an electrically operated switch main relays use an electromagnet to operate a switch mechanism.
Release are used where it is necessary to control circuit by low power signal in type of relay that can handle high power is required directly to derive an electric motor is called a contactor.
Types of relay: -
Magnetic,
thermal bimetallic strip,
electronic
Parts of relay: -
Electromagnet armature that can be attracted by electromagnet, spring set of electrical contacts.
Question: - Thyristors
Answer: - they are solid state switches which are turned on by the application of lower switch static voltage through the trigger connection known as Gate electrode.
Examples are SCR & triacs.
Are used to control current greater than thousand ampere and voltage in excess of thousand voltage.
Uses latching switches in an alarm circuit. Conversion of AC to DC.
Control of electric motor speed.
Electric propulsion.
Dimmer lights.
Question: - alternator generating low voltage there is a problem with the AVR, find out where the problem is?
Answer: - problem with diodes
Question: - what is the function of the eco-sounder and where it is placed?
Answer: - it sends sound waves to the seabed for measuring its depth it is fitted at the forward bottom portion of the ship.
Question: - what was the specification of electrical distribution system of your ship?
Answer: - 3 phase 440 volt AC 60 hz system
Question:- why is the speed of the motor 900 not 950?
If we use 950 rpm then the effective number of pole we get would be a decimal value.
Question:- What to do if the voltage produced by a generator is 438 volt instead of 440 volts.
Answer:- adjust the heavier adjust the trimming voltage of AVR.
Question:- is it correct to put a fuse of 5 ampere into a motor which is running at 4ampere current?
Answer: - fuse current rating will always be higher than that of the current rating off the motor also during starting the current is high but there is a time delay for the blowing of the fuse.
Question: - how is the RPM signal from a turbocharger measured?
Answer: - on the compressor shaft the compressor will tightening nut has a projection with a magnet mounted on it. This rotates with a shaft and the rotation is pick up the two magnetic pickup sensor which are just like a pair of tongs. The projection rotates between the pair of the tonks cutting the lacs bind using a current which is calibrated to give RPM. Magnetic pickup sensor send signal to the transducer. Output from the transducer is filtered, chopped and the signal is conditioned and finally converted to square waves.
Square waves pass through a face lock loop multiplier,
Question: - what is the difference between MCB and MCCB?
Answer:- mCB or miniature circuit breaker with optimum protection facility for current protection only.
These are manufactured for fault level up to 10 kilo ampere only. The operating current range of 0.5 to 63 ampere. Single double aur three pole versions. These are used for small loads electric circuit, domestic wiring extra.
TVS are molded case circuit breaker with the production facility of overcurrent earth fault. It has variable range of 50% to 100% overcurrent. Can be wire for remote as well as local operation. They are manufactured for fault current of.
They are used for application related to large current flow requirement.
Question:- what is proximity effect?
In a conductor carrying AC is current flowing through one or more nearby conductors. Search has been a closely wound coil of wire, the distribution of current within the first conductor will be constraint to a small regions. Resulting current around is termed as proximity effect. . This gives an increase in effective resistance of the circuit which increases with frequency
Explanation:- a changing magnetic field will influence the distribution of electric current flowing within an electric conductor by electromagnetic induction when an AC flows through an isolated conductor it creates an associated alternating magnetic field around it. Lighting magnetic uses Eddy current in the adjacent conductor, altering the overall distribution of the current flowing through them. The result is that the current is concentrated in the area of conduction furthest away from nearby conductor. Carrying current in the same direction.
Example:- If two wires carrying the same AC lines parallel to one another the magnetic field of one wire will induce longitudinal Eddy current in the adjacent wire which slow in the longitudinal loops along the wire facing away from other wire, and back in opposite direction on the side of the wire facing the other wire. Does the Eddy current will rain force the main current on the side facing away from the first wire and what was the main current in the side facing the first wire. The net effect is the redistribution of current in the cross section how the wire into a strip on the side facing away from the other wire. The current is concentrated in the smaller area of the wire the resistance will increase.
Question:- gas explosion metre
Answer:- the instrument is first charge from the atmosphere using a rubber aspirator bulb.
On off switch S2 is closed along with check switch S1 and compensatory element C detector element I route to reach a steady state temperature.
Question: - what are transistors and how do you test them?
Answer: - the transistor is basically a diode that share one and the shared and is for the base and other two and are called emitter and collector collector excess input current from the circuit that can send the current through the transistor wire only if the best allows the current to pass the best act like a great Venice Mall current is applied to the gate it opens and large current can flow from the connected to the editor types are PNP and NPN use is switch and implication
Testing: - insert probe into the multimeter black probe into common and red terminal read to comment mark for testing iOS.
And selector knob to the electrode test function replace the probe tips with alligator clamps game the black Pro with one of the blade of the transistor.
Touch the red crop to each of the other two lead.
Please show high resistance that each of the lead artist you have found the best and it's a good pNP transistor.
If the display shows two different readings for the two leaders cam the black crop to another lead and repeat the test.
After camping the black rope to each of the three leads if you don't get the same high resistance reading when touching the lead with the red bro you either have a bad transistor or PNP transistor.
Remove the black crow and claim the red one of the lead.
Touch the black to each of other to leads touch the black crow to each of the other two leads are touched. You have found the base and you have a good PNP transistor
The display shows two different reading from Dadar to leads from the red road to another lead and repeat the test after clamping the red prove to each of the two years if you don't get the same high rating of resistance then touching the Other lead with you have a bad PNP transistor.
Question:- cascade control system for jacket cooling water
Answer:- in the master controller if there is a division between mg of the jacket cooling water temperature and svz by the operator the master control signal which act as the SP of the same controller any relation between the SVN MB of the cooling water inlet temperature cause the slave controller to send email to operation the safety valve to increase or decrease cooling water from the floor there any change in the inlet cooling temperature initiate the slave and ruler to set in a self-contained control loop to adjust the three way wall to bring ine inlet cooling water temperature to the correct value does any change in the cooler outlet temperature engine cooling water temperature due to see water pressure or temperature is prevented from react in the engine and causing any temperature change in the engine system which would have taken a long time to sense and correct temperature deviation if the inlet temperature of the cooling water is loosely 1 Tola outputs signal passes through the range the diaphragm control valve for the stem in lead to open steam to the heater.
Question: - tank scope
It is a combustible gas indicator it works in any atmosphere used during cow and purging operation calculation gas is butane electrode are not catalytic heated to 300 degree celsius temperature are decreases
Question:- advancement in alkaline batteries.
Answer:- maintenance free Shield no evolution of gas cause Cathode is with a little part of cadmium Hydroxide so that if it is partially charged when anode is fully charged no vent plug nose village.
Question:- Star delta starter?
Answer:-
Question: - barrier potential and depletion layer?
Answer: - the potential buildup in PN junction by the diffusion of negative electron from and to be reason and appearance of the holes on the inside is called variable tension very few countries remaining in the tension area as a result of the diffusion and it is for this reason called depletion layer.
Question: - accelerometer
Answer: - accelerometer pleasingly called in vibrations studies between they are small and respond to a wide frequency range and other transducers the natural Metro consist of the viceroy o'clock material path from which it is held between some masses and the body of the instrument is there is the store and is Austin to some device off the vibration machinery and the insert ownership of The Mask all the purpose of electric material to be subjected to AC stress and electrical signal generated as force is equal to the sale of the mass and acceleration marketing on the solution of the name of the Electric Corporation of growth of the to the solution of the marketing on the size electric material used for the next audition signature of the machine like pump turbocharger extra.
Question: - what is the cause of Humming sound in a transformer
Answer: - the cause of God transformation of the material in the best Indian contract in the largest as a small amount of the frequency is the Transformer be known as manifestations of urbanization caused by the earring back and forth at the frequency closing sound in latest generation which is Humming sound Transformer without do not generate the sound other regions in solution is added tolerating lose terminals no rubber float insulation there reduction in coming sound use v and padding and oil very are use good design and material like stiffeners while constructing the wall of the transformer proper 16 and clamping of lamination and framing of the transformer.
Question: - purpose of seathing on cable?
Answer: - To protect insulation of the cable from damage and injury. It is not classed as insulation. Sheath materials are required to be heat, oil, fire and chemical resistant they should be tough and flexible.
Question: - purpose of armouring?
Answer: - they gives extra mechanical protection to the cable braided wire of galvanized steel or fined phosphor bronze Airtel also act as a screen to reduce interference caused by magnetic field in adjacent communication and instrumentation cables.
Question:- what determines the current carrying capacity of a cable?
Answer:- restriction imposed by the insulation limits the current carrying capacity of the cable the current flowing the table the higher will be the heat radiated. Heat radiated is equal to the square of current X resistance. So greater will be the rise in temperature. Rise in temperature can damage translation and damage insulation can not serve its purpose of confining current flow in the conductor.
Question:- properties of conductor?
Answer:- there is no electric field inside the conductor electric field does not penetrate into conductor. Charge exist only at the surface of the conductor.
All points of a conductor are at the same potential.
Resistance increases with increase in temperature.
Ductile, maliable, valence band and conduction band overlap.
Copper is used commonly as a conductor sometime Aluminium is also used which have less current capacity require greater diameter.
Question:- continuity check of very long cable?
Answer:- continuity is checked by measuring the resistance of wire in ohms. It should be very small for healthy cable. In case of breakage the resistance will be very high in Mega ohms.
In order to measure/ video of a very long Cable one end of the cable can be connected to the hull of the ship/earthed. At the other end register should be changed between the cable terminal and hull.
Question:- Cable insulation and its purpose
Answer:- main purpose of cable insulation is to keep the current in the conductor and to prevent contact with live wire.
Insulation is adversely affected by humidity temperature moisture oil chemical vibration stresses dirt and old age.
Traditional insulants - cotton Silk paper mica glass fibre
Modern insulants:- PVC, butyl rubber, EPR.
Question: - hotspot in the induction motor?
Answer: - centre of the coil winding where the temperature would be higher than at the surface.
Question: - battery capacity Test procedure?
Answer: - battery capacity is expressed in ampere hour city dash is measured how much ampere hour the battery can deliver before its terminal voltage drop down to end of discharge. Voltage X number of cells.
The discharge current should be maintained constant during the test the test time can be selected from the table which will also give the corresponding discharge current and also the terminal voltage at the end of discharge normal the test is carried out for five or eight hours as the discharge time is increased discharge current will have to be reduced that test can be conducted in 1 hour also but then the discharge current has to be increased at the end of discharge the voltage of a lead acid battery cell is 1.75 voltage or 1.80 voltage if the battery reaches the end of discharge voltage before the specific time the capacity has reduced before carrying out the test check and record specific gravity of electrolyte cell terminal voltage each and battery terminal voltage charging should be discontinued and check all the battery connections.
Question: - Clamp metre working?
Answer: - clamp metre basically act as a current transformer. The instruments tongs are clicked around a single conductor without any physical contact the conductor carrying AC current is a primary and magnetic flux due to the current flowing in the conductor is alternating flux attitude and direction is continuously changing there must be change ine flux linkage to the secondary of current transformer as per Faraday's law of electromagnetic induction the rate of change of flux will produce EMF. Circuit is closed current will flow is measured in display.
Question:- purpose of electrical motor on governor.
Answer:- promoter is called synchronising motor for speed setting motor the motor run on DC power only the purpose is to provide a mean of remote speed adjustment it enable the switch board operator to match the frequency of an alternator to that of other alternator. Change the load distribution when operating with other units in troop mode.
Change in Governor speed setting produce the same effect governor moment as to change in the load on the engine. The motor is coupled to governors speed setting mechanism through friction clutches.
Question:- material of fuse wire other than silver? why can't we use mild steel as fuse wire?
Answer:- other materials are tin lead alloy, aluminium, zinc, antimony etc.
Properties of fuse material:
Low resistivity: that is the less opposition to flow of current.
Low melting point: So that when the current is too large the temperature of the fuse wire will rise and it will melt and break the circuit.
Mild steel has comparatively higher melting point which is approximately 1400 degree Celsius which is quite high. Also its resistivity is higher. Silver has a melting point of 962 degree Celsius. Resistivity of mild steel is 15 yocto ohmmeter where as resistivity of silver is 1.59 yocto ohmmeter.
Question: - what is CE written mostly on electrical equipment?
Answer:- CE is the abbreviation for confirmite europieenne.
Sectors declaration that the product meet the requirements of applicable EU directive.
Question: - fuse markings
Answer: - ampere, voltage, time current characteristics, approvals, manufacturer part number serial number and breaking capacity.
T 3.15A H 250V
In the above first letter means FF = very fast acting, F= fast acting, M= medium acting, T= slow acting, TT= very slow acting.
Question:- basics of transformer
Answer:- it works on the principle of mutual inductance of two coils of Faraday's law of electromagnetic induction primary coil is carrying AC current it produces alternating magnetic flux this alternating magnetic flux cuts through the secondary and using and EMF in it.
Primary secondary are wrapped around a common soft iron core made of individual laminations to reduce Eddy current and hysteresis losses.
Role of change of flux linkages depends on the amount of heat flux with the secondary winding. So it's a desired that almost all the flux of primary winding be linked to the secondary winding.
But in open a very tiny portion of the flux of first winding will link with second. In order to overcome this Ellora elektrans part in the form is placed common to both the windings. Maximum number of eggs produced by primary winding is passed through and linked to the secondary through this low reluctance path.
Question:- losses in transformer
Answer:- copper losses depends on the load current.
Core losses or iron losses = the sum of hysteresis and Eddy current losses magnetic properties of material used to construct the core of transformer.
Question:- Magnetostriction
Answer:- flux in a ferromagnetic material such as the core, causes it to physically expand and contract slightly with each cycle of magnetic field magnetostriction buzzing sound in transformer.
Question:- methods to reduce Eddy current losses
Answer:- thin laminated cores prevent most of the Eddy current from flowing at all. area decreases and hence resistance increases eddy current losses are proportional to the square of thickness of lamination.
Thickness = 0.25 mm to 0.5 mm insulated from each other.
Increasing resistivity by using core material as Silicon Steel.
So content up to 3% results in dramatic increase in resistivity three to four times higher the increase in Silicon impaired the Steels Mechanical properties causing difficulty for rolling due to brittleness .
Question: - Factors affecting hysteresis loss?
Answer: - maximum flux density, frequency and core material.
Use high grade silicon Steel.
Question: - how to reduce flux leakage in transformer?
Answer: - carefully selecting core material having low reluctance.
Careful design of the core, geometry of the core effects leakage flux.
- Making Transformer window long and narrow.
- arranging primary and secondary winding concentrically.
- interleaving/ sandwiching the primary and secondary winding.
- using shell type construction in which both primary and secondary are founded on the centre leg and limbs which has enlarged the cross sectional area.
Question: - reluctance?
Answer: - it is an opposition to magnetic flux in a magnetic circuit analogous to resistance in electrical circuit.
Question: - leakage flux?
Answer: - amount of flags lines that do not follow the core and are lost to the surrounding air.
Transformer core design is of two type core type and shell type.
Question:- single phasing?
Answer:- loss of current through 1 phase in a 3 phase supply is single phasing. This can be due to blown fuses, cable break, loose contacts.
Running 3 phase motor after single phasing will continue to run at slightly reduced RPM. Stopped three phase motor will not start if single phasing has occurred because in the absence of 3 phase rotating magnetic field it will not available.
Question: - How to determine positive and negative terminals of battery when there is no marking on battery.
Answer: - battery polarity can be checked by using multimeter when the red probe is connected to positive terminal and black probe to negative terminal multimeter will show positive value of voltage and vice versa
At positive plate there is some sulphate accumulation.
Question: - white deposits on battery terminals?
Question: -
Question: - battery maintenance
Answer: -
1. Clean the battery top to keep dry and clean with baking powder and water solution.
2. Checking tightness terminal legs.
3. Applying petroleum jelly to legs and terminals to prevent corrosion
4. Check electrolyte level and topping up with distilled water to cover the plates.
5. Checking specific gravity with hydrometer.
6. Checking terminal voltage under load.
7. vents have to be clean and free of deposits.
8. Check container for any leak or deformation.
Question:- MSB safety and maintenance.
Answer:- safeties
1. sectionalization through bus tie.
2. Rubber matting of at least 3 mm thick front and back of the MSB.
3. Earthing of hundred doors.
4. Dad friend comments are enclosed and sheet steel compartment.
5. No pipelines in the vicinity of busbar.
6. Insulated handrails.
7. Cabinet doors cannot be open if circuit breaker is closed.
8. Circuit breaker and Switch Gears are of drone out pipe.
9. earth lamps.
10. UV, OV protection
11. UF, OF protection.
12. Short circuit protection.
13. Overcurrent trip.
14. Reverse power trip.
15. Co2 fire extinguisher nearby.
16.24 volt DC emergency lighting provided.
17. Fuse puller, Lamp holder and circuit breaker operating handles.
18. MSB on raised platform.
19. Drip proof protection.
Maintenance
1. Should be clean inside and outside dust removed by vacuum cleaner.
2. Connection fixing should be checked for tightness.
3. Busbar insulation should be checked for deterioration and tracking.
4. Operation of bustie should be checked.
5. All auxiliary wiring should be checked for soundness.
6. Incoming cable should be checked for soundness and their gland inspected.
7. earth bonding of panel doors to be checked.
8. Switches and indication lamps checked.
9. Operation of all safety devices should be checked.
Question:- sf6 circuit breaker
Answer:- low voltage circuit breaker use air, meaning contact separate in air. While High Voltage 6.6 KV and 11KV uses vacuum type circuit breaker or gas field type circuit breaker.
Sf6 circuit breaker is a gas filled circuit breaker, in which sf6 is under pressure of 5 bar at 20degree Celsius. Contact separate in this pressurized gas chamber. Insulation is quite high. Dielectric constant high. Quicker arc extinction.
Question: - power factor and its significance?
Answer: - residential areas are charged for electric power consumption on the basis of KW-hr, while industries are charged for KVA consumption.
So power factor has got no significance for residential areas.
While in industries same load if supplied with a lower power factor shall require to draw higher KVA and would result higher electric bill.
For example:- KW=2 with P.F=0.9, when compared with a supply of P.F 0.7 found that later will consume 2.85KVA and while former had 2.22KVA consumption. Also the current value is increased to 12.4Amps which was 9.66Amps initially.
So the higher power factor is economical.
Question: - methods for improving power factor?
Answer: - 1.Static capacitors when connected in parallel with the inductive loads provide leading current.
2. Synchronous condenser: - when a synchronous motor operates at No-Load and over excited, then it provides leading current and work like a capacitor.
When a synchronous condenser is connected across supply voltage (in parallel), then it draws leading current and partially eliminates the reactive component and this way power to improved.
Phase advancer: - it’s a particular type of A.C exciter which is connected to the rotor circuit of an induction motor to improve P.F. It’s mounted on the shaft of main motor.
It supplies exciting ampere turns to the rotor circuit at slip frequency. By providing more ampere-turns than required the I.M can be made to operate on leading P.F like an over-excited synchronous motor.
Current is injected through the slip rings of motor, which is leading with regards to the rotor voltage.
This current relieves the stator circuit of the duty of magnetisation thus improves power factor.
Question: - Cogging and crawling of induction motor?
Answer: - when the no. of rotor slots and stator slots have common factor, the rotor in a squirrel cage exhibits a tendency to remain in one place and not at all, when energized from mains. When the rotor teeth force, the reluctance of the magnetic path is minimum, that is why rotor tends to remain fixed. (Magnetic locking occurs). This phenomenon is called cogging or Magnetic locking of induction motor.
Crawling: - when an induction motor runs at very low speed (precisely 1/7th of synchronous speed). Even if full voltage is applied to it, then it is called at crawling. It’s caused by 7th harmonics, which may be present in power supply.
Question: - losses in induction motor? Core loss constituents? Hysteresis loss in detail? Methods incorporated to reduce both eddy and hysteresis losses.
Answer: - Losses:
1. Stator cu losses + stator core losses.
2. Rotor copper losses + Rotor core losses (depends, in f’=1/s, which is, very small so negligible).
3. Friction losses + winding losses.
Core loss: - Hysteresis loss- because of magnetisation and de-magnetisation
And eddy current loss.
Hysteresis: - it’s the time lag when the magnetic field is first generated and when the field is fully developed.
Addition of silicon makes the steel more efficient and faster in forms of building and maintaining magnetic field. Silicon reduces reluctance and hysteresis loss.
Eddy current loss: due to alternating flux linking the core which will induce an EMF in the core due to which a current called eddy current is being circulated in the core. As there is some resistance in the core, with this eddy current circulation concerts into heat called eddy current loss.
Question: - condition for maximum efficiency of transformer? How?
Answer: - for transformer.
Iron loss= copper loss
Proof: - Ƞ = = =1-
;
All day efficiency of transformer is the ratio of output in KW-hr to input in KW-hr for 24hrs. Which is less than ordinary efficiency of transformer.
Question: properties of transformer oil? Why it is not used on board?
Answer: - properties
1. Thermal stability.
2. Excellent insulating properties.
3. High flash point > 140 degree Celsius.
4. Low pour point < - 6 degree Celsius.
5. Viscosity should remain low at temperature.
The cooling oil used in transformer is flammable at high temperatures and present a considerable fire hazard due to large quantity used.
A defective or aged insulation of winding or a high electrical surge may cause overheating in the transformer and leads to ignition of oil. The situation is compounded by damage to the transformer tank or oil carrying lines resulting in spray fire.
Question: - you are given a Y- starter and a motor. How will you say that the given starter is compatible with the motor?
Answer: - for a motor to be compatible with a starter all six terminals of the 3-phase winding shall be brought out and available at the terminal box. So that the connection can be made.
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