Alternator

Principle
Faradays law of electromagnetic induction
When an alternating current is passed thru the primary coil, an alternating flux is generated in the core. This flux travels thru the core and links with the secondary coil. This alternating flux cuts the secondary coil and an emf is induced in it depending on the no. of turns.
The amount of emf produced depends on the amount of flux linked with the sec winding. Air has high reluctance due to which the mag flux doesn’t link properly in full amount with the sec winding. To increase the amount of flux linkages, a (common) soft iron core of low reluctance used so that max amount of flux pass thru the core and links with the sec winding.
LOSSES
Copper loss which is usually heat loss due to the resistance offered to the load current. I2Rt.
CORE/IRON Loss – depends on mag prop of the material used in the core.
HYSTERISIS LOSS
The alternating mag flux in the core, the magnetic elements called as domains in the core tend to align themselves with the magnetic field. But it is alternating and the domains are not able to respond so fast and friction occurs…. This loss is called as hysteresis loss.
Sometimes core retains magnetization and becomes magnetized by the external field. This causes power loss and is called hysteresis.
Soft magnetic materials like silicon steel having low hysteresis are used.
Hysteresis loss increases with increase in temp and frequency.           
       EDDY CURRENT LOSS
Induction of eddy current within the core causes a resistive loss. Higher the resistance, lower the loss.
Laminations are used to reduce eddy current losses. Area decreases and resistance increases.
Why HUMMING NOISE
Magnetic flux in a ferro magnetic material causes it to physically expand and contract in each frequency cycle. This phenomenon known as magnetostriction causes the humming sound
The stray magnetic field causes the enclosure and eq to vibrate.
Factors affecting hysteresis leakage
High Permeability and low reluctance properties of the material
Hysteresis loss increases with increase in frequency and temp.
How to reduce flux leakage
Flux prop to NI   and (A/L)
N-no of turns; I-current; A=area of the core and L- length of the flux path.
Prop of core material- high permeability relative to air (causes the mag field to be concentrated in the core) and magnetic properties.
Geometry of the core and Using shell type construction
Amount of air gap
Operating temp of core
Making transformer window long and narrow
Using soft core of lower reluctance and laminated

Purpose of Instrument Transformers
Used to supply proportional current/voltage from a high power network for instruments and protection relays.
VT supplies voltmeter, protection relays and volt operated coils
CT supplies for ammeter, protection relays and current operated coils
CURRENT TRANSFORMER
348 mitra
Primary winding connected in series with the line carrying current and has only 1 winding or few turns. The secondary winding has more no of turns depending on how much primary winding has to be reduced to say 5A or 1A(by more winding) in the sec. The ammeter or wattmeter is connected across the secondary.
The sec terminals shud never be left open with the primary carrying current. If ther is no back emf in the sec, the mmf in the primary becomes high, an abnormal high flux in the core which will produce excessive core loss with heating and da,age to insulation and a high voltage across the sec terminals.
One of the terminals of sec is always earthed to protect the equipment and the personnel in the vicinity  in the event of insulation breakdown
If the insulation btw the primary and secondary winding breakdown, the secondary circuit will be raised to full primary voltagewith a serious risk to person and also equipment. Hence one end of the CT is always earthed
Difference btw welding transformer and lighting transformer
WT is also a step down transformer to 15-45V with secondry winding has several taps to adjust the voltage. It has more cross section and less no of turns to ensure less voltage and more current(200-600A).
Impedance of WT is higher than normal which helps in establishing arc and controlling current
DC Welding transformer has a rectifier and smoothing choke filter and are highly reactive. Otherwise a separate reactor is used in series with the winding – Tapped reactor, Moving coil reactor, Moving shunt reactor, Continuously variable reactor.
VT,PT,CT comparision
PT are used in high power transmission lines above 33kv
Why 3 single phase transformers used instead of one single 3phase transformers
3phase 440/220V lighting transformers are usually composed of 3 separate single phase tranformers instead of one 3phase.
Enables easy replacement of a single phase unit if any fault.
Transformers for use on 3phase insulated systems are generally interconnected in delta-delta configuration using copper links between phase windings. If a fault occurs in one phase, the faulty unit can be disconnected using links, creating an open delta or V-configuration and a 3phase supply is still available.

Permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. Thus it is the degree of magnetization a material obtains in response of the applied magnetic field.

Alternators

Why alternator not building up voltage
Loss of residual magnetism cos it was idle for long time or it was motored before;
Field excitation ckt is open or very high resistance
wire broken
voltmeter faulty,
too many rotary diode shorted or fuse of diode blown
rectifier,transformer…..
ALTERNATOR HEATING
Is due to friction and windage loss, core loss, tooth loss, stator and rotor copper loss, stray loss
Friction and windage loss is due to the overhang portion of the windings which cause heat generation due to air friction.
Core loss is due to hysteresis loss and eddy current loss
Tooth loss is due to cross armature reaction depending on the load
Copper loss are due to its internal resistance
Stray losses is caused by alternating stray fluxes that appear, in loaded condition, in the pole faces, teeth,core,over hang.
Due to heating on load, voltage drop increases inside the alternator and terminal voltage drops. This voltage drop is due to winding resistance, leakage reactance and armature reaction. Due to the reduced terminal voltage, the load equipment is compelled to draw more current to derive same power.
To reduce – well ventilated, duct pointing to the alternator, air filter mesh for circulating air, end brgs are lubricated sufficiently to avoid heat generation due to friction
What is AMP
It is ALTENATE MARITIME POWER. Shore supply. Port of L.A was first to adopt it and is done basically for clean air to the port
Interpoles and its function
Small poles fixed to the yoke in btw the main poles. They are wound with few heavy Copper wire turns and are connected in series with the main winding.
Neutralizes the cross-magnetising effect of the armature reaction
Makes commutation sparkless
SARKAR ALTERNATOR
Advantages of brushless over conventional alternator?
No brushes hence no downtime maintainence and also no sparks.
It makes use of field boosting so that recovery time of any voltage dip is recovered in abt 0.6sec compared to 1.8sec taken by conventional alternators using carbon pile AVR
Brushless alternator and advantages?
A brushless alternator is composed of two alternators built end-to-end on one shaft. The larger of the two sections is the main alternator and the smaller one is the exciter. The exciter has stationary field coils and a rotating armature (power coils). The main alternator uses the opposite configuration with a rotating field and stationary armature.
Exciter
The exciter field coils are on the stator and its armature is on the rotor. The AC output from the exciter armature is fed through a set of diodes that are also mounted on the  rotor to produce a DC voltage. This is fed directly to the field coils of the main alternator, which are also located on the rotor. With this arrangement, brushes and slip rings are not required to feed current to the rotating field coils. This can be contrasted with a simple automotive alternator where brushes and slip rings are used to supply current to the rotating field.
Main Alternator
The main alternator has a rotating field as described above and a stationary armature (power generation windings).

Avr with full diagram?
Draw and explain voltage dip and transitional time period ?
Types of excitation system. Which one you have in last ship – 65DT hall
Rotary exciters and static exciters
What is motoring? (Reverse power)
Safeties in alternator?
Instantaneous overload relay – 2-10times the rated FLC with  0.1-3sec
Sustained overcurrent of IDMT type with preferential trip- 110% of rated FLC; 0.7-2times FLC with 1-10sec
Reverse power trip for alt (turbine- 2-3% & diesel 5-15% with a time delay of 0.5-3sec)and rev current trip for DC Generator
Under voltage protection delay with time delay(80% of rated voltage)
Over voltage (120% of rated voltage)
Under Freq(58) and Over Freq (62)
Differential protection for short circuit inside the alternator at 0.1 times the rated current
Negative Phase sequence relay determines the amount of unbalance in the stator currents which is a measure of rotor and stator temp. 0.2 times rated current
HRC fuse for short circuit prot
Earth leakage relay or sometimes called zero phase sequence detects earth fault current returning back to earthed neutral connection.
Master lock out  is a protection relay which trips the prime mover and also suppresses the generator field

ALTERNATOR MAINTENANCE
All wirings for damage and terminal conn tightness
Cleaning and drying of air filter and ventilation passages are free of dust
Blowing out dirt on windings using a vacuum cleaner or dry lint-free cloth
Removing if any oil deposits on windings
Minor windind damage repaired by dry varnish
Checking the air gap (usu 2-3mm in the middle)
Insulation resistance of windings( min 1Mohm usu 1Kohm/1volt is the rule) and remember to isolate nay electronic components which can get damaged---- check polarization index test if insulation reduced after using heating….. ratio of insulation res after cranking for 10min to IR value of cranking for one min…..
If it is increasing more than 1, then heating is effective…. Otherwise, sth is broken and rewinding is reqd)

In brushless alternator, rotating diode and fuses checked for continuity; transformer, avr, zener…. Free of dust and oil and dampness
In conventional alternator, slip rings checked for uniform wear and brushes for movement. Brushes spring press checked pull type spring balance of 1-1.4kg.
The brushes length is also important as shorter(below 2cm) brushes create spark. New ones of correct size to be chosen and have to check if it is of same shape as the slip ring.

MSB protection
Sectioning thru bus tie bar
Dead front panel -  live wire behind and covered with insulating plates
Hinged doors are earthed and cannot be opened unless the breaker is put off
Fused isolators are isolating switches which incorporate fuses
CB are of draw out type and can be easily drawn only if they r properly isolated
Drip proof protection
No pipelines above
Sufficient space around of atleast 0.6m
Ebonite rods
Insulating mat of atleast 3mm front and back
MSB on raised platform

MSB SAFETIES AND TESTING
Fuse isolators
CB with Overcurrent tested by current injection method- primary injection and secondary injection
Under voltage – will close the stdby generator breaker
Reverse power- reducing the load gradually down….
MSB Maintenance (unknown)

Nut bolt Conn and checks shud be checked for tightness
Vacuum cleaner for dust
Remove if any dead lizards
Check insulators on which bar r held are in place and not damaged
Check for signs of overheating

Incoming cables for soundness and glands
Aux winding for soundness
Earth bonding of panel doors to b checked
Operation of bus tie to be checked
Switches and indication lamps checked
Safety devices
Why reverse current and over current trip provided?
Reverse current is provided for DC generator for protecting mc from motoring
Current injection? (over current test)
If ship p.f is less, how it will affect marpol and ship owner
Disadv of low P.F
Cost of generating station and distribution eq is more for a given load
Makes voltage regualtions poor
For transmission of same power, low pf means more conductor and hence more energy for the same size of conductor
For the same KW load, lower power factor requires more magnetizing current which means more current passing and requires large cable size – means more capital cost and more cu loss and more
As the reactivecomponent is more, wasting energy in not doing useful work

Causes of low power factor
Transformer run at low load drawing more magnetizing current
Large use of IM at low loads
Arc lamps

How to increase PF on ship. Basics of power factor     -    57 of mitra
Is defined as the cosine of the phase angle btw V and current in ac circuits
In an ac circuit, V & I are vector quantites having magnitude and direction at any instant.
In a resistive circuit, V & I are in phase, so The active power consumption is Vrms * Irms.
In an purely inductor, the electrical energy is stored in the form of magnetic energy. The current lags voltage by 90.
In a purely capacitor, electrical energy in the form of electrostatic energy. The current lags voltage by 90.
In a combination circuit, p.f. will be lagging if XL>XC and pf is leading is XC>XL
Power factor= true power/apparent power=(VIcos@) / VI     [kW/kVA]

It is the percentage of power available to do useful work.

METHODS OF IMPROVING POWER FACTOR
Not Running IM in low loads and using high speed IM
Static Capacitor providing leading current when capacitor bank is connected in parallel to load
Synchronous condenser is nothing but synchronous motor with over excitation and no load current. It gives leading current and works like a capacitor. When synchronous condenser is connected across the supply voltage in parallel, then it provides reactive component reqd for the inductive load.
Phase Advancer is a particular type of AC exciter which is connected to the rotor circuit of an IM. It is connected on the shaft of the motor. By providing more ampere-turns than reqd, IM can be made to operate on leading PF like an over excited SM. Current is injected thru the slip rings of the motor, which is leading with regard to the rotor voltage. This current relieves the stator current from providing the magnetizing current, thus improving pf.
Types of earthing?
EARTHED NEUTRAL SYSTEM
Is used where any single fault current is passes thru the hull and has potential to pass thru the hull into another equipment and damage
We can get 2 system voltages
Easier to locate the earth fault by earth fault relay placed in neutral earth line,
In the event of inductive or capacitive faults, the voltage surge can rise to 3.5-4 times the system voltage to earth. Since it is only VL/3, it is small compared to neutral earthed system
In ships with more than one generator neutral earthed, circulating harmonic current will be there and cause stator loss and extra heating.
Thus for 3.3kv, a NER is provided to limit the the earth fault current. This reduces the fire risk and over voltage problem.
INSULATED NEUTRAL SYSTEM
Used wher it is required for an uninterrupted supply to essential services for navigation and propulsion
One single earth fault doesn’t interrupt the supply but gives an alarm
In the event of inductive or capacitive faults, the voltage surge can rise to 3.5-4 times the system voltage which is VL.
Low values of the earth fault current reduces the risk of fire
Earth fault is difficult to find as the earth fault is indicated in which only phase fault is found and then done in trial and error method
Sometimes, the alternator has its third harmonic currents and have no return path for them to flow btw generator windings, in neutral earthed system.
Emergency power supply?
Emergency generator solas?

MITRA ALTLERNATOR
Generators not sharing KW load? You took AE on load after some time you saw one taking more load, why? Droop and how to adjust
Droop of governor is not set properly. For two generators to run in parallel, it must have same droop characteristics within a tolerance of =/- 0.5%
A governor with 2% droop means a 2% variation of speed will raise the load from 0to 100.
Too low droop- high sensitivity and instability
Too high droop – gov late response
Droop is set by compensation arrangement in which needle has to be adjusted manually by trial and error method and then has to be locked.
2 alternators are running in parallel and supplying unequal currents. What should be the reason for this? how would their power factors and kvar load shared be related
If droop of the AVR is not same, then the KVAR loading will be different and unequal current distribution. There is a voltage trimmer inside the MSB, by varying the potentiometer, we change the resistance and thus change the KVAR sharing.
Two AE in parallel showing same voltage but different current and power factor, why?
KW loading is based on the droop of governor.
KVAR load sharing is dependent on droop of the AVR.
How to improve PF other than capacitor
Alternator stator – star or delta. Y delta not used
For the same no of turns, star generates more voltage
For the same line voltage gen, amount of insulation reqd is also less
Star provides a neutral which can be earthed or insilated and also helps in gving another sys voltage thru neutral
By using star connection, we have Vph= 1/3 of VL
That means the conductors used per phase is less
What is the value of AVR voltage and current in alternator
110V and 80 amps
Value of air gap in alternator and significance of it?
2-3mm.
If more, the reluctance of the air gap increases which reduces the flux density passing and hence less alternating flux will cut and less emf is induced.
If less, voltage will be more due to increased flux density but we will have a non uniform voltage waveform and overheating problems

Ship operates on 60Hz, what will happen if operates on 50Hz?
Speed of the motors is prop to freq
And delivered output and head is prop to speed
Power consumption is also prop to cube of speed
Since freq reduced by 16.7%, moor stator winding current will be higher by abt 16.7% as their impedance is dependant on the freq.
The higher current if unnoticed, can cause damage to insulation in the long run and burn out
SOLUTION- I is prop to V/Z i.e. V/f…………     hence by maintain v/f ratio same, the prob can be solved. So the voltage has to be dropped by same 16.7%. this can be changed by changing the tap end transformer
What checks made on an alternator after it is been tripped on over speed.
Mechanical checks – rotating components…. Any two units opened up for inspection of cracks, deformations. Ring grooves, rings, gudgeon pin and its bushes, con rod trueness and length, crank pin and bearing, c/shaft deflection. Any two main bearings opened and checked.crankcase, gear case,camshaft,cams,rollers. Crankcase l.o also checked as it might got overheated and oxidised   All con rod bolts changed compulsorily.
Electrical – diodes, avr excitation windings, check if conductors got displaced, main alternator windings for damage, insulation testing, air gap,
What is D in the ME electronic governor? IPAD
Motor on top of governor, how it is rotating
Is called synchronizing motor or speed setting motor and runs only on DC.
Purpose is to provide a means of remote speed adjustments. It enables the remote switchboard operator to match the freq of the alternator with that of the other alternator…… so that load is distributed evenly when running parallel in droop.
PID controller, how integral and derivative actions are achieved in electronic governor on AE
in HV system, what protection alternator provided.
VCB or SF6 CB
High impedance NER to limit earthing current

Overcurrent trip, how is it tested, where to inject current?
Reverse power trip how to try out, what will happen if trip not activated?
Diff between earthing and bonding?
Variable voltage variable frequency controller

BHOUMIK alternator
Why pf is lagging and not leading?301
Significance of PF? 301
Why do we prefer AC than DC?
No maintenance- no slip rings and brushes
Power transmission is easy by using transf
Plant cost for AC transmission is much lower than equivalent DC transmission
When a large fault current occurs, it is easy to interrupt ac as sine wave tend to become zero at some point.
AE governor droop significance
Emergency generator and its working? Interlocks and time etc
Synchroscope operation and detail? Written notes
Tolerance -       -10to+10% of phase angle and freq slip of +/-0.067Hz if synchro rotating at 4rpm.
Different types of single phase protection?        Negative phase relay
Reverse power trip arrangement and purpose?
How generator connected to bus bar exactly?
Single phasing and short circuit prevention equipment?   Pg62
How to order new DG without having any information from old DG(name plate marking gone) he was asking for some manual which we have on ship to find how much capacity is required
Checks to be made before opening backside of MSB?
Fluctuation on load while two generators are running in parallel. Reason
Earthing system in tankers and advantages? 295

BHATTA ALTERNATOR
Reverse power trip principle and diagram. Reverse power trip and method of testing? 209

189
Function of bus bar. How bus bar fitted and why in that way? 185

Shore connection box? Specification
Sys volt, sys amp, terminal size, earthing cable.
Alternator maintenance? 117
Two alternators has arrived onboard, same rating. One for DG and other for steam turbine. Just by looking how will you decide which one for what? 118
Maintenance of running alternator? 117
Why air gap in alternator?119
Stator winding connection how and why. Advantage? 120
Advantage of each test of alternator
Salient pole alternator used in? 101
What is residual magnetism, significance in generator, how to restore?
How fault find in insulated system.
Insulated neutral system advantage?
Diff between bonding and earthing?
Insulation and resistance difference?
Diff btw distribution board, section board, feeder board and MSB? I books
Difference between MSB and section boards. safeties in section board
ACB safeties. Short circuit trip test (over current trip)?
Diff between earthing and bonding?
Variable voltage variable frequency control

BHATTA ALTERNATORS
Shaft generator advantage? 268
HV system advantage and range. Safety?
Advantage
High voltage means less current- means the size of the conductor can be reduced
Less current means less copper losses, hence transmission losses are less
Less current also measn less voltage drop, hence better voltage regulation

Why we earth in HV system? Prot in steering motor for single earth fault
Supplied via transformers, whose sec winding is not earthed.

Harmonic filter?
Skin effect and proximity effect?

Battery

UNKNOWN
Difference btw lead acid and Alkaline battery
Lead acid

+Ve plate lead peroxide PbO2
-ve terminal lead
Electrolyte dilute sulphuric acid
During discharge,
the electrolyte dissociate and hydrogen ions reacts with oxygen dissociated from lead peroxide and forms water.
PbO2 + H2 + H2SO4 -->PbSO4 + 2H2O
At negative plate,
Pb + SO4- --> PbSO4
After DISCHARGED
Voltage – 1.75V
Sp gr – 1.110

During Charging
At negative plate
PbSo4+H2 --> Pb+H2So4      AND accumulated sulphate So4 returns to the solution.
The H2O breaksdown to return H+ to the solution and  the oxygen recombine with pb and form PbO2
PbSo4 + 2So4+ 2H2O --> PbO2 + 2H2So4
Provided with a vent and releases gases only when nearing the top of the charging
Fully charged
Voltage 2v
Sp gravity – 1.285 @ 15degrees

Produces 2v per cell
Takes time for charging
Less life 5yrs
Preferred for regular recycling
Life considerably reduce above 25degrees

Nickel Cadmium
+ve plate Nickel hydrate with small % of graphite to increase conductivity
-ve terminal – mixture of Cadmium and iron
Electrolyte strong alkaline KOH with an addition of lithium hydroxide(1-2%) to minimize the coagulation of nickel hydrate electrode on cycling and increase the electrolyte resistance.

During discharge,
Nickel hydrate releases hydroxyl ions n becomes nickel hydroxide
Ni(OH)4+2K --> Ni(OH)2+2KOH
Cd+2(OH) --> Cd(OH)2
Hydroxyl ions combine with the Cd and form cadmium hydroxide
Since the hydroxyl are passed from one plate to another, no change in sp gravity of the electrolyte….. hence state of charge is not known by electrolyte sp gravity.
Continuously evolve gases, oxygen at the positiveplate and hydrogen at negative plate.
Provided with a non retun vent so that the electrolyte doesn’t come in contact with Carbon dioxide in air and form potassium carbonate.
Discharged
Voltage   1.09V

DURING CHARGING
Ni(OH)2+2(OH) --> Ni(OH)4
Cd(OH)2 + 2K --> Cd+ 2KOH
1.2V
Renewal reqd wen sp gravity drops to 1.170

Produces only 1.2v per cell. So more wt for same rating
Quick charging due to less resistance
More life 10-15yrs
Can be used for keeping it idle for long time
Can operate continuously at 45degrees
SEALED Ni-Cd batteries donot have vent caps and are sealed and maintenance free n donot require topup. Negative plate is made with surpus Cd(OH)2 so that it is only partially charged when the positive plate is fully charged. Since the active material is still available while charging, no production of hydrogen gas
Oxygen is produced in positive plate
4OH- -->2H2O+2O2+4e-
This reaction reverses at the negative plate replacing hydroxyl ions.

SARKAR BATTERIES
Criteria for renewal of batteries
Lead acid
Relative density/ sp gravity is 1.285   normal      reduces to 1.110
Normal 2v &  @ disch volt – 1.75V
End charge is indicated when the terminal voltage is 2.6V
Ni-Cd battery
Voltage 1.2v/cell discharge – 1.09
Rel density of a new cell– 1.190-1.210 at 15degrees
Replaced or electrolyte replaced at 1.145/1.170
End charge is indicated when the terminal voltage is 1.7V

Lead acid battery maintenance and about hydrometer?
Terminals Clean and dry. Use petroleum jel on the terminals to prevent corrosion
Terminal connection tight.
Secured in a wooden tray
Electrolyte proper level of atleast 1/8” higher than the top end of plates
Vents clean of deposits
Check container for deformation
Donot charge @ high rate – cos voltage of fully charged is a variable qty which varies  with rate of charging, the temp and sp gravity. Hence only hydrometer is used to check the state of charge of the battery
Donot keep the battery in a discharged condition for a long time. – lead sulfate formation on the plates and cannot be connected to active material.
Atleast once in a month fully discharge and charge again
HYDROMETER
Checking sp gravity with hydrometer for lead acid battery. Hydrometer is used to check the state of charge/relative density/sp gravity. The low readings of the hydrometer are at the top of the float and the high readings at the bottom.For every temp increase above 15degrees, then add 0.007 to the reading

Battery room safety with Exd? 25,30 and 243
Non sparking type Exh fan with its motor outside the ventilation passage and independent of other ventillation system, ventilation outlet on the top.
Ventilation duct of corrosion resistance paint
Flameproof lighting fitting
Voltage drop test of battery?
The condition of the battery is tested by discharging the battery at its rate for 10hrs (means 25A for a 250AH rating), the voltage drop shud not exceed 12.5% of the nominal system voltage after the test.
Voltage variationshud be within the limit of +10% to -12.5%
Unit of battery capacity?
Ampere-hours
A ship's battery capacity is usually rated in terms of its discharge at the 10-hour rate
How to check output voltage of emergency battery?
Battery what all checks.
trickle charging.
Float charging will charge the battery drains/loss due to load and has a circuitary to prevent overcharging
Trickle charging is set to constant current supply when the battery is in stdby to supply enough which compensates the leakage current
How to connect battery from 220V to battery charging connection?
How batteries are connected together, draw diagram, how much volt of one battery?
Battery ratings on ship voltage?

BHATTA BATTERY
Sulphanation in battery?
In a lead acid battery while discharging, at the negative terminal, pb reacts with SO4 to form amorphous lead sulphate.
During use, small crystals of lead sulphate is common and not harmful. During prolong charge deprivation, however, amorphous lead sulphate converts to a stable crystalline that deposits on negative plates. Sulphation lowers charge acceptance
Battery room ventilation and blade material?

Advantages and disadvantages of lead acid and alkaline batteries, where used onboard?

Few numbers of batteries are given to you, what factors you will consider for connecting them? 29 (voltage and amp-hr. for voltage in series and amp-hr in parallel)
Battery type of connection?
Polarization in battery?
Battery ordering, meaning of amp-hr, can a battery of 350amps, be used for 70amps and 5 hours?
Life boat battery charging system from where u will get the connection. What is the input and output value?

BATTERY CAPACITY TEST PROCEDURE
Battery capacity is expressed in Amp Hr .
It is measured how much AH it can deliver before its voltage drops down to end of discharge. The disch current must be constant during the entire process.
The test time tables gives the disch current and terminal voltage for the selected time period of testing.
Normally the test is carried out for 5/8 hrs. time is inversely prop to current.
At the end of discharge, the terminal voltage drops to 1.75-1.8V

If the battery reaches its terminal voltage before the mentioned time, then the battery capacity reduced and has to be discarded if the capacity reduced below 80%(As per IEEE- Inst of Electrical and Electronic Engineers)
If the battery capacity is sufficient but not within the time limit, theen also discarded

BEFORRE TESTING
Remove the charging connection. Check the battery and cell terminal voltage. Check sp gravity of the lead acid battery.

INDUCTION MOTOR

Uses

Single phase IM- vacuum cleaner, hand drill, hand blower,mixer and grinder

3phase squirrel cage IM – Main sw pump, l.o pump,jcw pump

Double cage IM- Turning gear motor for high starting torque

Construction​

FRAME closely grained alloy CI
Stator core made up of thin laminations of silicon steel to reduce hysterisis and Eddy current loss. Insulated 3phase windings are placed in the evenly spaced slots provided in the core which are spaced 120degrees apart. Insulated 3phase windings usually has 3 sets of could with a 30% overlap.

Rotor core is built of silicon steel stampings individually insulated to eliminate Eddy currents.  Has skewed slots to give smooth start. Copper or aluminum bar is placed in each slot. Conductor bars may be insulated to cut stray losses.
AIR GAP abt 2-3mm. smaller the air gap, smaller thestarting surge current, higher the starting torque and higher the power factor.

Principle

When a 3phase supply is given to the 3phase stator winding, a rotating mag field s set up at synchronous speed due to the switching sequence of RYB.

The rotating field passes thru the air gap and cuts the rotor conductors. Due to the relative speed between the rotating field and stationary rotor, emf is induced in rotor conductors. Since the rotor circuit is short circuited, current starts flowing in the rotor conductors.

This induced current inturn produces a magnetic field which interacts with the stator rotating magnetic field and thus a rotor torque is produced in the conductor bars.

(A/c to lenz law, the direction of the rotor current will tend to oppose the cause producing them, which is the relative speed btw the rotating field and stationary rotor conductors. Hence the rotor rotates in the same direction as that of stator field to reduce this relative speed.)

  Note that when the load on the induction motor is increased the slip increases slightly which results in Greater relative speed between the rotating flux and the rotor conductors. consequently rotor current is increased producing a higher torque to meet the increased load. Thus the IM are termed constant speed motors.

Slip

Slip s the difference in rotor speed and synchronous speed.

The rotor never catches up the synchronous speed. If it does, there will be no relative speed btw rotating field and rotor conductors, no induced water currents and therefore no torque to drive the Rotor. The friction and windage would immediately cause the rotor to slow down. In IM, the change in slip in Induction Motors from no load to full load is 0.1-3%.

Power factor

Power factor depends on the active component of the total current that is Icos¢. At no load, an induction motor draws a large magnetizing current and a small active component to meet the no load losses. Therefore the induction motor takes a high no load current lagging the applied voltage by a large angle. Hence the power factor of an induction motor on no load is low.

Where an IM is loaded, the active component increases while the magnetizing current remain same . Consequently the power factor of the motor is increased. Due to the larger magnetizing current regardless of load, the power factor rarely exceeds 0.9 lagging.

Types of rotors

1. squirrel cage rotor... Cu bar in each slot of laminated cylindrical core. Then bars are shorted by end rings.

 Disadvantage cannot add external resistance as rotor is shorted permanently. Low starting torque.

The resistance cannot be varied in squirrel cage rotor as it is possible in slip ring induction motor. The fixed resistance of the rotor of the squirrel cage induction motor is very low. At the starting moment, the induced voltage in the rotor has same frequency as the frequency of the supply. Hence the starting inductive reactance gets higher value at stand still condition. The frequency of the rotor current gets same frequency as the supply frequency at standstill. Now the case is that the rotor induced current in spite of having higher value lags the induced voltage at a large angle. So this causes poor starting torque at the stand still condition. This torque is only 1.5 times of the full load torque though the induced current is 5 to 7 times of the full load current. Hence, this squirrel cage single bar single cage rotor is not being able to apply against high load. We should go for deep bar double cage induction motor to get higher starting torque.

2. wound rotor has laminated core and provided with 3phase, double layer, distributed winding in the rotor slots and are wound for the same no of poles as that of stator, i.e, the 3windings are starred internally and the other are brought to connect to the 3 insulated phosphor bronzeslip rings and brushes. the brushes are externally connected to a 3phase star connected variable rheostat.

At starting resistance is given to increase the torque and as motor picks up speed resistance is reduced, slip rings are shorted. And wound rotor runs like a squirrel cage rotor with rotor winding end shorted on both ends.

Starting torque

The rotor circuit has low resistance and high high inductance. At the starting, rotor frequency is equal to the stator frequency, the rotor reactance is large compared with the rotor resistance therefore a rotor current lags the Rotor e.m.f by larger angle which means power factor is low and consequently starting Torque is also low. (T prop to cos¢)

Therefore by adding resistance, rotor power factor improves which results in improved starting torque. (cos¢=R/Z)

This of course also increases the rotor impedance due to which rotor current is decreased.     (I=V/Z)

Methods of starting squirrel cage motors

1. DOL closing coil activates the main switch. Main disadvantages are high starting current and low starting torque and single speed operation.This torque is only 1.5 times of the full load torque though the induced current is 5 to 7 times of the full load current when motor is connected in delta. When connected in star, at the beginning, the starting current is reduced to 3 times the FLC.

2. Star delta... End connections are brought to a starter box where changeover contacts in starter enable star delta switching.

Starting current and torque are only third of DOL. Can only be used with low starting loads. Built in interlocks or double throw switches prevent closing together.

3. Stator resistance starting By using deep bar double cage IM

4. Auto transformer starting

Consists of switches and 3phase transformer of single winding type in btw main supply and motor. During starting, motor recieves voltage through the tapped transformer giving reduced voltage to the stator. Reduced voltage gives reduced starting current and also reduced torque.

5. Soft starting method which uses thyristors. These solid state controlled switches controls the current flow upto 1000amps. Each AC half sine wave, from the mains, can be passed thru thyristor in full or in part dictated by the early or late triggering.

Methods of starting Wound rotor motors

Dol starting

Rotor resistance

Stator resistance

Auto transformer

Methods of improving starting torque

1. Wound rotor motor

the star connected rotor winding end connections are brought out to slip rings and brushes by which external 3phase star rheostat is connected. By increasing the resistance, the starting torque will be increased.

2. Double cage rotor

 The inner bars or deep bars are of large cross section, low resistance cu bars. also inductive reactance is high due to the high rate of cutting of magnetic field with the stationary rotor.

The outer bars have high resistance and low inductance with small cross section.

Due to the high inductive reactances of the inner bar during starting, the current flows in the outer cage. Thus more torque due to more resistance offered by it.

As speed increases and slip reduced, the rate of cutting drops due to which frequency of the rotor current and induced emf get gradually decreased consequently​ the rotor reactances decreases. Hence inductive reactances in the deep bar decreases. Thus the current faces less reactances and less resistance as a whole.

The advantages of squirrel-cage motors compared with the wound rotor type are that they:
(i) are cheaper and more robust
(ii) have slightly higher efficiency and power factor
(iii) are explosion-proof, since the risk of sparking is eliminated by the absence of slip rings and brushes.
Less starting torque as external resistance cannot be added.
The advantages of the wound rotor motor compared with the cage type are that they:
(i) have a much higher starting torque
(ii) have a much lower starting current
(iii) have a means of varying speed by use of external rotor resistance.

Comparison between single cage and double cage motors:

1.    A double cage rotor has low starting current and high starting torque. Therefore, it is more suitable for direct on line starting.

2.    Since effective rotor resistance of double cage motor is higher, there is larger rotor heating at the time of starting as compared to that of single cage rotor.

3.    The high resistance of the outer cage increases the resistance of double cage motor. So full load copper losses are increased & efficiency is decreased.

4.    The pull out torque of double cage motor is smaller than single cage motor.

5.    The cost of double cage motor is about 20-30 % more than that of single cage motor og same rating.

Speed variation

1. frequency,
2. cascade system

In this two number 3phase IM – main motor and auxiliary motor are connected to a common shaft and thus called cascadecontrol. 3phase supply is given to stator of main motor  while the aux motor is derived at a slip frequeny from the slip rings of main motor. 4 speeds are obtained – main alone (120F/P1), aux alone(120F/P2), cumulative cascading (120F/P1+P2)and differential cascading(120F/P1-P2)

3. adding resistance in rotor winding

4. Pole change arrangement

i)             MULTIPLE STATOR winding where stator is provided with two seperate windings which are wound for two different poles equal to the poles of stator winding. One winding is energized at a time

ii)            Consequent Pole CHANGING

In the slow speed version, the stator poles are in series but delta connected. For high speed, poles r in parallel and star connected.

In practice, stator winding is divided into only two coils to get two different speeds.

iii)                 POLE AMPLITUDE MODULATION if speed other than 2:1 is reqd.

MOTOR PROTECTION

1. under voltage protection 
2. Overload Relay
3. Dual element fuse or HRC fuse for short Circuit Protection
4. Resistance heaters inside the motor- space heaters
5. For large motors, Thermistors or bimetallic strips are provided to sense overload and give alarm and trip with a time delay.

UNKNOWN MOTOR

SINGLE PHASE IM

Stator is provided with a single phase winding which creates only alternating flux and not synchronously revolving. This cannot produce rotation. That is why it is not self starting

To make it self starting, it is temporarily connected into a two phase by providing a starting winding inaddition to main winding. The two windings are spaced 90degrees electrically apart and connected in parallel across the single phase supply. Phase difference btw the two windings is made large abt 90… these two currents produce revolving flux which makes the motor self starting.

Starting torque is prop to sin@, so larger the angle higher the starring torque.

HOT SPOT IN I.M.

When centre of the coil or winding is higher in temp than at the surface

What is Single Phasing

Loss of current thru one phase. Causes – broken fuse, loose contact in contactor, broken wire.

Will draw huge current and if not tripped… it keeps running till it burn the motor. Stopped one doesn’t start.

AIR GAP

If air gap more, high reluctance for magnetic path, flux strength reduces which inturn reduces induced emf and torque produced by the rotor. Cos of the reduced torque, starting surge current is higher. Power factor of the rotor current is low, which also hampers the running torque.

EFFECT

Uneven air gap can cause unbalanced magnetic pull which may result in vibration. Pulsation loss also reduces effective motor torque. 

Protection motor

INGRESS PROTECTION by two or three digit code

First digit says the protection against solid bodies and the second digit designates for protection against liquids

DRIP PROOF-IP22 ;   TOTALLY ENCLOSED IP54; DECK WATER TIGHT IP56

FIRST DIGIT

FIRST DIGIT

SECOND DIGIT

1 large sized foreign bodies

1 drops of condensed water

2 protection against solid bodies larger than 12mm

2 protection against fallings drops and not exceeding 15degrees angle 

3   small sized solid impurities, wires and tools of thickness greater than 2.5mm

3 ingress of rain

4   small sized solid impurities, wires and tools of thickness greater than 1mm

4 protection against water falling from all directions.

5 against dust of all sizes

5    jets of water

6   

6 protection against jet of water equivalent to heavy seas

Purpose of motor Varnish

Secondary layer of insulation to protect the coils and windings. To immobilize the insulated windings. It also increases dielectric strength of the windings which is more important in transformer than motor.

Steering gear protection

Each electro hydraulic s/g with two independent power supply shall be fed from two circuits from MSB and ESB

Short circuit protection and overload alarm 

Protection against excess current shall not be less than twice the FLC.

Main & aux s/g power units shall be arranged to restart once power restores

In the event of power failure, audio-visual alarm sounds 

Negative phase sequence for single phasing

Motor provided with 200% insulation

Overload and also short circuit trip

Power failure alarm

No voltage trip

Hydraulic oil low alarm

Windlass safeties

Overload relay

Short circuit protection

Electro magnetic brake

Delayed restart timer 

     

SARKAR            MOTOR

E/R crane motor construction

Principle of IM?

Slip? Why?

Material of winding in stator? 

Types of rotors. Construction of squirrel cage rotor? 

Terminal connections of IM with diagrams? – star delta connection

How to change the direction of rotation in 3 phase motor?  - change any two phase terminals

Starting of AC motor? – DOL, Star-Delta, Auto Transformer,  Soft starting.

Types of starting, DOL starter draw

Pole change motor?

Various method of AC motor speed change? 

Freq, cascade system, multiple stator, pole changing arrangement, rotor resistance.

Why SM is not self starting? 

Diff btw IM and SM?

SM construction is complicated and IM is simple

Economical below 300rpm for SM; economical above 600rpm for IM

SM is Not self starting torque.

S.M requires dc excitation

S.M - speed remains constant while for IM decreases with increase in load

Power factor can b unity, leading or lagging for S.M, and lagging for I.M 

Why IM cannot run as SM?

If IM runs at synchronous speed, then there will be no relative speed btw the rotating magnetic flux and the rotor, n thus no magnetic field will be induced and no current and no interation…. So rotor will stall

In an induction motor, the field winding in the rotor are shorted by end rings, so it cannot act as SM.

Dual core rotor advantages? Comparison between single cage and double cage motors:  high torque and low starting current

Which type of starter you prefer onboard and then cross questions?

New motor for sewage pump is installed what kind of connection to be done?          Delta

Cogging of motor? 

Crawling of a squirrel cage motor means motor running slower, 1/7th of the Synchronous speed. due to the fact that harmonics fluxes produced in the gap of the stator winding of odd harmonics like 3rd, 5th, 7th etc. These harmonics create additional torque fields in addition to the synchronous torque. The torque produced by these harmonics rotates in the forward or backward direction at Ns/3, Ns/5, Ns/7 speed respectively. Here we consider only 5th and 7th harmonics and rest are neglected. The torque produced by the 5th harmonic rotates in the backward direction. This torque produced by fifth harmonic which works as a braking action is small in quantity, so it can be neglected. Now the seventh harmonic produces a forward rotating torque at synchronous speed Ns/7.

Hence, the net forward torque is equal to the sum of the torque produced by 7th harmonic and fundamental torque. The torque produced by 7th harmonic reaches its maximum positive value just below 1/7 of Ns and at this point slip is high. At this stage motor does not reach up to its normal speed and continue to rotate at a speed which is much lower than its normal speed. This causes crawling of the motor at just below 1/7 synchronous speed and creates the racket. The other speed at which motor crawls is 1/13 of synchronous speed.

COGGING of the motor refusing to start at all because of low supply voltage, the slots of the stator get locked up with the rotor slots. When the slots of the rotor are equal in number with slots in the stator, they align themselves in such way that both face to each other and at this stage the reluctance of the magnetic path is minimum and motor refuse to start. Apart from this, there is one more reason for cogging. If the harmonic frequencies coincide with the slot frequency due to the harmonics present in the supply voltage then it causes torque modulation. As a result, of it cogging occurs. This characteristic is also known as magnetic teeth locking of the induction motor.

This problem can be easily solved by adopting several measures. These solutions are as follows: The number of slots in rotor should not be equal to the number of slots in stator & Skewing of the rotor slots,

Deck motor immersed in SW, action?   Pg71

Machine is disconnected from power sources and dismantled

Terminal  box removed and earthed toavoid shock due to accumulated voltage.

All salt deposits washed out with freshwater

If deposited with oily bilge water, wash out with Electro Cleaner.

Check polarization index test, R10minutes Cranking/R1min Cranking >1.5, then it indicates insulation low is due to moisture and can be improved by external lamp heating or low voltage “heat run” drying of the winding. Moisture should be escaped, by lifting the cover continuously or periodically

Hottest part of the machine shall not exceed 90°C, while heating

IR readings and temperatures taken regularly, until constant value reach about 1 mega ohms. 

Then spray the machine with insulation vanish

Assemble and out in service with low load, if possible

Main SW pumps maintenance, tell electrical safeties?

Safeties starter with overload current safety trip

Dual element fuse or HRC fuse for short circuit protection

Resistance heaters to avoid moisture

Short circuit winding how to find?

Continuity by multimeter – 0 and beeps gud; if 1/OL, then broke

Short circuit by checking the resistance in btw phases and also btw phase and earth. Best method is to use a megger. And to test resistance wen motor is hot as it has more leaking current wen it is hot. Insulation resistance is inversely proportional to the rise in temp

Current has to be measured in series with the circuit

Voltage measured across the load circuit

Insulation test and improvement?

Check resistance by megger. 

If more, then visual check for any damage in windings, use vacuum for dirt and heating for moisture (current injection method or lamp method)

MITRA MOTOR

SM used onboard, working principle? 

SM torque zero, why? 154

Methods of starting SM? PONY MOTOR and DAMPER WINDING

Cogging of IM, what effect of lengthy conductor due to skewing?

Rotor slots are lightly skewed to reduce the magnetic hum and help in reducing the locking tendency btw the rotor and stator teeth, therferoe giving a smooth start.

Principle diff btw soft starter and star delta starter

What are criteria for using star delta motors? Which pumps not to be star delta connected?     

motors larger than 7.5kw (10hp) rated at 220V are required to use reduced voltage starters like the Wye-delta starter. Motors less than 7.5kw are usually started direct-on-line, or the motor already connected in Delta permanently.

Synchronous motor donot use star delta. Double cage sq cage motor is best suitable for star delta. 

Which motor has the highest IR in ER and why? (SG motor)

Electric motor used in electric propulsion with reason – SYNCHRONOUS MOTOR

IP protection of deck motor and testing? 

IP 56. All screws have sealing washers and a labyrinth sealing gland at the shaft exit from end casing

Star delta starter change over time delay how much from star to delta?

In star Delta usually we consider that the load and motor torque are equal when the motor reach 75-85% of the speed. At this time you stop the star connection to go with delta connection, the time is around 30 to 50 milliseconds, to avoid short-circuit. But when the motor is connected in delta, at start you've got a temporary current peak due to back electromotive force. So to avoid this you have different option, by these, you can delay of 1 or 2 seconds the time between star and delta, but it depend on inertia of the load, another solution is to put a resistor in series with the delta connection for 3 seconds to limit the current peak, another is to put the resistor directly in series with the motor at star disconnection.

By seeing a motor , how can u tell which type of connection without opening the terminal box

When the three-phase motor is connected to the mains, the data on the rating plate must correspond with the main voltage and mains frequency. The connection is implemented via six screw terminals (standard version) in the terminal box of the motor and  distinguishes between two types of circuit, the star connection and the delta connection. 

Example : Let the mains supply voltage of 3 AC 400 V, 50 Hz.

And we have 2 Specifications for 2 different motor –

For Star connection:

•With its voltage specification of 230/400 V, this motor must

be connected to the three-phase supply (LN = 400 V) in a

star configuration.

•The voltage in a motor winding is designed for a maximum

of 230 V here.

•The three winding phases (W2-U2-V2) are configured in the

terminal box to the so-called star point. The voltage for the

individual phases to the star point is 230 V.

For Delta connection:

•With its voltage specification of 400/690 V, this motor must

be connected to the three-phase supply (LN = 400 V) in a

delta configuration.

•Every motor winding is configured for a maximum phase

voltage of 400 V and can be directly connected.

•For direct-on-line starting, the ends of the phase windings

are connected in the terminal box (U1-W2, V1-U2, W1-V2)

to the individual phases.

Below shows terminal box connection how it should be made.

HV motor and normal motor both having same voltage rating give constructional difference

Which machinery in ER takes maximum current?

High starting torque motor?

What types of motor used on decks?

SG telemotor, electric type. How getting reversed

What is the type and rating of motor used in LNG cargo tank

If one SG motor running in 3 phase, taking over current? Reasons – short circuit, single phasing, 

High winding temp alarm comes what ll be ur action and what are the reasons?

Stator purpose?

Name plate details of IM?       

Freq,power in kw, cos@, rpm, protection, voltage for star/delta.

BHOUMIK MOTOR

Starting system for SM and IM?

Can SM can be made IM, how?

IM details? 

SM details?

Where DOL and star delta used onboard and why? 

What are the common features btw transformers and IM?

BHATTA MOTOR

IM why starting current is high? 178

Cogging of IM? 134

Hysteresis losses everything?

SW entered DC motor, how to bring back to service condition?

What is no volt coil and why you need it?