Marine electro technology

Marine Electro Technology

1.      What is the use of 'kvar' meter fitted on the MSB?

A)     Measures reactive power i.e.

P = V*I Sinφ

Watt meter measure active power

P = V*I Cosφ

2.      Where auto transformer starter is used on board ships and why?

A)     By the use of 3 phase auto transformer any fraction of the supply can be applied to motor without alteration to motor connection. Starting voltage can be varied by changing the winding type i.e. stator voltage and torque is reduced.

Use:- Large motors

3.      Explain star delta stator?

4.      Why starters are not used for land based installations?

5.      Any two applications of zener diode on board ships?

A)     Voltage regulation, voltage comparison in AVR.(p-n type semi-conductor

6.      How will you come to know whether a fuse is blown out or not, explain two methods?

A)     If it is an open fuse then just pull it out and see the inside and if you see the small thin wire connecting the two ends is broken then the fuse is blown. Similarly if it a small tubular bulb fuse also you can see if the filament inside is connected or broken and if it is broken then the fuse is blown.

7.      What is meant by intrinsically safe?

A)     The theory behind intrinsic safety is to ensure that the available electrical and thermal energy in the system is always low enough that ignition of the hazardous atmosphere cannot occur. This is achieved by ensuring that only low voltages and currents enter the hazardous area, and that all electric supply and signal wires are protected by Zener safety barriers. Sometimes an alternative type of barrier known as a galvanic isolation barrier may be used.

8.      Name any three intrinsically safe equipments on board other than a torch light and lamp?

A)     Wakitaky , Two Radio communication equipment.

9.      Explain the working principle of an explosimeter and reasons for false readings?

A)     An explosimeter is a device which is used to measure the amount of combustible gases present in a sample. The device, also called a combustible gas detector, operates on the principle of resistance proportional to heat—a wire is heated, and a sample of the gas is introduced to the hot wire. Combustible gases burn in the presence of the hot wire, thus increasing the resistance and disturbing a Wheatstone bridge, which gives the reading.

10.  How will you check reverse power and overload relay in the MSB?

A)     Lamp indicator is there. If the lamp is luminates means breaker is on.

11.  What are the routine maintenance in an alternator?

Ø  Check wire for damage

Ø  Check terminals for tightness

Ø  Cooling air intake and exhaust are not blocked and free of dust and dirt

Ø  Clean rotor and stator with low pressure compressed air

Ø  Oil deposits can be removed by clean with special degreasant

Ø   Minor insulation leak can be repaired by air drying varnish

Ø  Rotor slip ring to be checked for wear

Ø  Check correct brush pressure using pull-type spring balance.

12.  How will you confirm solenoid is working or not?

13.  What kind of starter could be used for force draught fan for the boiler?

A)     DOL

14.  How to check the insulation resistance of a DC motor?

A)     OHM meter

15.  How to use a voltmeter for synchronization in the absence of synchroscope and synchronizing lamps?

A)     Connect a 500v voltmeter across one phase of incoming machine circuit breaker

Adjust the generator speed until voltmeter slowly fluctuates from zero to maximum. Close the breaker when voltmeter passes through zero.

16.  How does earth fault detector work?

A)     RCDs (Residual current detection) operate by measuring the current balance between two conductors using a differential current transformer. This measures the difference between the current flowing through the live conductor and that returning through the neutral conductor. If these do not sum to zero, there is a leakage of current to somewhere else (to earth/ground, or to another circuit), and the device will open its contacts.

                    Residual current detection is complementary to over-current detection. Residual current detection cannot provide protection for overload or short-circuit currents, except for the special case of a short circuit from live to ground (not live to neutral).

      For a RCD used with three-phase power, all live conductors and the neutral must pass through the current transformer.

17.  Explain the conditions of paralleling alternators?

Ø  Frequency

Ø  Phase sequence

Ø  Voltage

Frequency:- The cycles per second of alternating current, measured in Hertz.

Phase:-

18.  Draw the synchronizing method?

19.  What is he difference between a megger and a multimeter?

A)     megger is used to test the dielectric coaxial cable  whereas miltimeter is used to measure current(ac&dc), voltage(ac&dc), resistance, npn&pnp diode's emitter, base &collector etc.

20.  Comment on air circuit breakers?

A)     A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.

21.  What are the safeties provided on Main Switch Board?

Ø  Ebonite Rod.

Ø  Rubber pad infront of switchboard.

Ø  Dead-front type switchboard.

Ø  0.6 meter gap behind the switchboard.

Ø  Fuse

Ø  Circuit Breakers.

Ø  Earth Fault indicators.

Ø  Panel doors are earthed.

Ø  No water, steam or oil pipelines to pass in its vicinity.

Ø  Undervoltage Relay

Ø  Reverse Power trip.

Ø  Preferential trip.

Ø  Overcurrent trip

Ø  Arc Chute

Ø  Short-circuit trip.

22.  Describe how a self-excited generator works?

A)        A kind of excitation of generators where the magnetic field of the main poles is excited by a current supplied to the windings of the main poles from the armature (rotor) winding. A self-excited generator is thus distinguished from a separately excited generator, in which the windings of the main poles receive current from an external source.                                                                                                                                                Self-excitation is made use of most often in DC generators. When a self-excited generator is started, the initial current in the field winding is produced by the electromotive force (emf) induced in the armature winding by the residual magnetic field of the main poles. To sustain self-excitation, the initial current must reinforce this field. The additional magnetic flux increases the emf in the armature and, consequently, the current in the windings of the main poles. Because, however, of magnetic saturation in the magnetic circuit, the increments in magnetic flux corresponding to equal increments in current become smaller as the current builds up. The process of self-excitation continues as long as the emf in the armature exceeds the voltage drop in the field winding. At a certain magnitude of the magnetic flux, electric equilibrium is reached, and there is no further increase in magnetic flux, armature emf, and excitation current. Self-excitation can be achieved when the value of the resistance of the field winding does not exceed a certain limit, which depends on the electric parameters of the generator.

       Shunt-wound, series-wound, and compound-wound self-excited generators are used. In shunt-wound machines, the armature winding and field winding are connected in parallel. In series-wound machines, the armature winding and field winding are connected in series. Compound machines have both a series field winding and a shunt field winding. If a self-excited generator for some reason loses the residual magnetization of its main poles, a residual magnetic flux can be created by letting a current from an external source flow through the field winding in the required direction.

23.  What is the function of AVR?

Ø  also known as the "Automatic Voltage Regulator"

Ø  It is designed to automatically maintain a constant voltage level.

Ø  It regulates the sudden flow of electric current from AC supply.

Ø  It may use an electromechanical mechanism, or passive or active electronic

components.

Ø  Depending on the design, it may be used to regulate one or more AC or DC voltages.

24.  How will you find out earth fault in the system?

The seriousness of the action to be taken on an Earth Fault depends on the part of the electrical system it affects. Conventional ships which operate on 3 Phase, 440V, have earth fault indicators installed on all three phases. Any earth fault on a 440V system is considered to be a serious trouble and immediate action is required to identify the faulty circuit. Any earth fault on 220V or any low voltage lighting circuit can be considered as important but need not require immediate attention. However, attention should be paid at the next earliest opportunity.

Whenever there is an earth fault alarm, immediately inform to electrical officer (if he is on board). First action is to check the trueness of the alarm. Usually there will be a test button which when pressed, resets the alarm and rechecks the condition of the earth fault.

If the ship is having IAS (Integrated Automation System), check on the computer in the list of events after which the alarm has activated. If IAS facility is not available, there is only one option of isolating each and every machinery in the 440 V circuit and check whether the earth fault indication returns back to normal.

Isolation of all machinery, which operates on 440V, is not always possible. Certain critical equipment like steering gear and lubricating oil pumps cannot be isolated for when the ship is underway. However changeover can be done from running machinery to the standby one and thus the earth fault can be found.

25.  What is reverse power protection for?

A)  Generator intended to operate in parallel must have reverse power protection.

   A reverse power relay monitors the direction of power flowing between the generator and the load. If the prime-mover failure occurs the generator would act as a motor. The reverse power relay would detect the fault and acts to trip the generator circuit-breaker.

26.  What is Wheatstone bridge?

A)     A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Its operation is similar to the original potentiometer.

27.  Draw the synchroscope system?

28.  What do you understand by preferential trip and when they operate?

A)     Preferential trip is provided to safe guard the machineries which are important for safety of ship & safety of personnel onboard.

Preferential trips are designed to disconnect the non-essential services i.e., Breakers controlling Air Conditioning, Galley power, blowers, refrigeration) in the event of partial overload or partial failure of the supply, with the aim of preventing operation of the main breaker trip & loss of power to essential services.

29.  Describe AC and DC? Where DC is used on board ships?

A)     The difference between AC and DC is that AC is an alternating current (the amount of electrons) that flows in both directions and DC is direct current that flows in only one direction;

The wires outside of our house are connected at two ends to AC generators. DC is found in batteries and solar cells.

alternating current varies with time, sinusoidally... where as DC remains steady.

DC use:- battery charging

30.  What is induction motor?

A)     An induction or asynchronous motor is a type of AC motor where power is supplied to the rotor by means of electromagnetic induction, rather than a commutator or slip rings as in other types of motor.

In both induction and synchronous motors, the stator is powered with alternating current (polyphase current in large machines) and designed to create a rotating magnetic field which rotates in time with the AC oscillations. In a synchronous motor, the rotor turns at the same rate as the stator field. By contrast, in an induction motor the rotor rotates at a slower speed than the stator field. Therefore the magnetic field through the rotor is changing (rotating). The rotor has windings in the form of closed loops of wire. The rotating magnetic flux induces currents in the windings of the rotor as in a transformer. These currents in turn create magnetic fields in the rotor, that interact with (push against) the stator field. Due to Lenz's law, the direction of the magnetic field created will be such as to oppose the change in current through the windings. The cause of induced current in the rotor is the rotating stator magnetic field, so to oppose this the rotor will start to rotate in the direction of the rotating stator magnetic field to make the relative speed between rotor and rotating stator magnetic field zero.

For these currents to be induced, the speed of the physical rotor must be lower than that of the stator's rotating magnetic field (n_s), or the magnetic field would not be moving relative to the rotor conductors and no currents would be induced. As the speed of the rotor drops below synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the windings and creating more torque. The ratio between the rotation rate of the magnetic field as seen by the rotor (slip speed) and the rotation rate of the stator's rotating field is called "slip". Under load, the speed drops and the slip increases enough to create sufficient torque to turn the load. For this reason, induction motors are sometimes referred to as asynchronous motors. An induction motor can be used as induction generator, or it can be unrolled to form the linear induction motor which can directly generate linear motion.

31.  What are star delta windings?

32.  What is a short circuit?

A)     Joining two points having different electrical potential without load or bypassing the load is called short circuit.

    Current has tendency to take a path of least resistance hence it will bypass load and will pass through passage created by short circuit.

33.  What is meant by earth fault?

A)     Earth fault means "the fault that occurs when the current carrying conductor or live part get connected or touched with earth"

Cause of earth fault

1.      insulation failure

2.      cable damaged by any excavation works

3.    overloads

4.    due to dust

5.  any animals are enter into  the panel

6.  any loose objects near the power system

34.  What is meant by overload?

A)     an electrical load that exceeds the available electrical power.

35.  What is single phasing and how it happens?

A)     The loss of power through one phase in a three phase supply is termed as short circuit.

Casuses

Ø  Line fuse blown off

Ø  Terminal contacts broken due to vibration

Ø  Terminal contact become lose

Ø  Line wore broken

Ø  In  relay on of the contractor not  making proper contact

Ø  Relay con tact spring may be damage or weak

Ø  Contact points are coated with oxidation hence not making contact

36.  What is fuse and how many types of fuses have seen before?

A)     type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit

Type

  In general, there are two categories of fuses viz.

Ø  Low voltage fuses

Ø  High voltage fuses

Low voltage fuses

      Semi-enclosed or Rewireable  type voltage fuses

      Totally enclosed or Cartridge type

                           Totally enclosed or Cartridge type          

   D- Type Cartridges Fuses

   Link type Cartridge or High Rupturing Capacity

  

Link type Cartridge or High Rupturing Capacity

   KNIFE BLAD TYPE HRC FUSE

   BOLTED TYPE HRC LINK FUSE

37.  Why an air compressor is started unloaded?

38.  What is the difference between ordinary diode and zener diode?

A)     Diode is the uncontrolled rectifier and Zener diode is a controlled rectifier. Diode has practically no limits of voltage range to work in, whereas zener diode works only in a voltage range(e.g.  -4V to +4V).So, Zener diode is known as voltage regulator.

    Both are the rectifier, diode is conducted in forward direction only,It opposes the reverse direction ,but Zenor diode will conduct only in reverse bise, It won’t conduct in forward bise, we can use for Voltage regulator

39.  What is the function of starter and choke in a tube light?

A)     It provides a boost in voltage required to start the fluorescent process.

40.  What is the regular maintenance done on batteries?

A) a. Connection to be checked for tightness.

b. Casing surface to be kept clean.

c. Terminals are protected with petroleum jelly or Vaseline.

d. Specific gravity to be check with hydrometer.

            1.21 Charged Condition

            1.18 Discharged Condition

e. Batteries to be topped up with distilled water.

f. Check & clear vents to ensure H2 gas produced is vented.S

  Safeties to be observed while operation & maintenance.

i. Use hand gloves & safety goggles while adding distilled water, shifting of battery, or checking sp. Gravity.           

ii. Use insulated spanners to tighten terminals (No Sparking, short-circuiting should take place)

iii. Use plastic bottle or jar to add distilled water.

iv. Should not be left in discharged condition for long period.

v. If adding acid, then first put little Acid, then add water & do the same process.

vi. No naked lights to be taken inside.

vii. No smoking inside battery room.

41.  How does salinometer work?

A)     A salinometer is a device designed to measure the salinity, or dissolved salt content, of a solution.

              Since the salinity affect both the electrical conductivity and the specific gravity of a solution, a salinometer often consist of an ec meter or hydrometer and some means of converting those readings to a salinity reading. A salinometer may be calibrated in either micromhos, a unit of electrical conductivity, (usually 0-22) or else directly calibrated for salt in 'grains per gallon' (0-0.5). A typical reading on-board ship would be 2 micromhos or 0.05 grains per gallon. A reading of twice this may trigger a warning light or alarm.

42.  What will be your action on a blackout a sea?

Ø  Never panic in such situation, be calm and composed. Emergency generator will restore the power in no time.

Ø  Inform Officer on bridge briefly about the condition.

Ø  Call for man power and inform the chief engineer.

Ø  If the main propulsion plant is running, bring the fuel lever to zero position.

Ø  Close the feed of the running purifier to avoid overflow and wastage of fuel.

Ø  If auxiliary boiler was running, shut the main steam stop valve to maintain the steam pressure.

Ø  Find out the problem and reason for blackout and rectify the same.

Ø  Before starting the generator set, start the pre- lubrication priming pump if the supply for the same is given from the emergency generator; if not, then use manual priming handle (provided in some generator).

Ø  Start the generator and take it on load. Then immediately start the main engine lube oil pump and main engine jacket water pump.

Ø  Reset breakers and start all the other required machinery and system. Reset breakers that are included in preferential tripping sequence. (Non-essential machinery).

43.  How emergency generator does starts on its own?

A)     Falling of the mains frequency or voltage causes the sart up relay to operate the engine equipment. The prime mover may be electrically crancked from its own 24v battery and starter motor or air started from it own reservoir fitted local to engine generator engine.

44.  What are the cut out provided on the OWS and checks to be done before putting it into operation?

45.  Draw star, delta 3 phase connections?

46.  What are the motor safeties, deck crane safeties, and engine room overhead safeties to be checked?

Overhead  safeties

1)      The most important safety feature of the crane is the electromagnetic fail safe brakes which do not allow the crane to fall with the load even when there is failure of power. For this:

-          Normally centrifugal brakes are used which are fitted inside the rotating drum.

-           The brake pads are always in applied state and pushed by magnetic springs when not in operation or when there is a power failure.

-          As the crane is operated or the power is supplied, the spring gets pulled inward or compressed due to the electromagnetic effect of the current. This allows the crane to be operated normally.

2)      Emergency stop is provided in the remote so that the operator can stop the crane at any time.

3)      The motor is fitted with distance limit switch in both transverse and longitudinal direction so that the travel of the trolley and hence crane should not overshoot the rack’s end.

4)      Mechanical stoppers are provided for both directions in case the electrical distance limit trips fail.

5)      The up and down travel of the hook is also attaches with automatic stopper to avoid overloading of the motor.

6)      The motor is fitted with thermal protection trip. When the motor windings get overheated, trip will activate saving the motor winding from burning.

7)      Load limit switch is also fitted which will trip the motor if the load to be lifted is above the crane capacity.

8)      It’s the responsibility of senior officers to operate the crane and to make sure all the personnel involve in any lifting operation are at a safe distance during operation of the crane.

9)      Additional tools like i-bolts, shackle, wire sling, belts etc. used for lifting must be checked before use.

10)  It should be noted that no one walks or stand below the crane when it is in the loaded condition.

Deck crane safeties

Moto safeties

Short Circuit trip.

o   Overload trip.         

o   Reverse power trip.

o   Reverse current trip

o   Fuse

47.  What is relay? How it is different from a magnetic contactor?

A)     An electrical relay is an electromechanical device operated by a small amount of electricity to control a larger amount of electricity. Relays are used for both control and safety

         A magnetic contactor is a relay-controlled switch used to turn a power control circuit on and off. It is electrically controlled and uses less power than other circuits. A magnetic contactor comes in different forms and capacities.

Difference between magnetic contactor and relay

The contactors is primarily used for switching larger power circuits (such as motors, for example), since the control logic components cannot meet the current & voltage duty of the power circuit.

Relays can be as simple as 12 V dc solenoids with 12 V, 0.5 A rated contacts. Or they can be as complicated as microprocessor-based devices used to detect disturbances (faults) on the power system and signal a local or remote switching device (breaker) to trip the circuit.

48.   What is ohm's law?

A)     Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two point

                               

49.   What is the expression for resistance in terms of length and area of conductor?

                           R=ϱ L                 ϱ – resistivity      A – cross sectional area 

                        A                        L – length of wire

50.  What is sequential starting?

Soft starting method, is used with a time delay

Each motor must have a separate:

Ø  main contactor

Ø  bypass contactor

Ø  overload protection

                  

51.  What is the function of circuit breaker?      

A)     An automatic device for stopping the flow of current in an electric circuit as a safety measure.

52.  What essentials are supplied from emergency switchboard?

Ø  or a period of 3 Hrs at Emergency lighting at every muster & embarkation station.

Ø  For a period of 18 hrs at:-

Ø  In all service & accommodation alleyways, stairways & exits, personal lift cars & personnel lift trunks.

Ø  In the machinery spaces & main generating stations including their control positions.

Ø  In all control stations, machinery control rooms, and at each main & emergency switchboard.

Ø  At all stowage positions.

Ø  At the steering gear.

Ø  At the fire pump & in all cargo pump rooms.

Ø  The navigational lights.

Ø  VHF & MF Radio installation.

Ø  The ship earth radio station.

Ø  At all internal communication equipment

Ø  The fire detection & fire alarm system.

Ø  Intermittent operation of the daylight signalling lamp & all integral signals that are required in an emergency.

53.  How will you confirm a minimum insulation resistance reading?

54.   Describe steering power supply regulations?

55.  What is Coulomb's law?

A)     A law stating that like charges repel and opposite charges attract, with a force proportional to the product of the charges and inversely proportional to the square of the distance between them

56.  Describe Fleming's left and right hand rule

A)     Fleming's left-hand rule

When an electric current flows in a wire, and an external magnetic field is applied across that flow, the wire experiences a force perpendicular both to that field and to the direction of the current flow. A left hand can be held, as shown in the illustration, so as to represent three mutually orthogonal axes on the thumb, first finger and middle finger. Each finger is then assigned to a quantity (electric current, magnetic field and mechanical force). The right and left hand are used for generators and motors respectively

                                 

Right-hand rule

For a current-carrying wire, the rule that if the fingers of the right hand are placed around the wire so that the thumb points in the direction of current flow, the fingers will be pointing in the direction of the magnetic field produced by the wire. Also known as hand rule. For a moving wire in a magnetic field, such as the wire on the armature of a generator, if the thumb, first, and second fingers of the right hand are extended at right angles to one another, with the first finger representing the direction of magnetic lines of force and the second finger representing the direction of current flow induced by the wire's motion, the thumb will be pointing in the direction of motion of the wire. Also known as Fleming's rule.

57.  Describe lenz's law?

A)     A law stating that the direction of an induced current is always such as to oppose the change in the circuit or the magnetic field that produces it

58.  What is the difference between electric and magnetic circuit?

Ø  In magnetic circuit flux establishes but not flow like as current in magnetic circuit.

Ø  In magnetic circuit energy needed only to establish the flux but no consistent energy need to maintain it whereas in electric circuit continuous energy needed to flow of current.

Ø   Resistance of an electric circuit is constant (for same temperature) and is independent of current but reluctance of magnetic circuit is not constant because it depends on μ (=B/H) which is not constant and depends on B/H.

59.  Describe and Draw battery charging method

60.  How many types of DC motors are there?

A)     There are three basic types of dc motors

(1)   Series motors,

(2)    shunt motors

(3)   compound motors

61.  How many types of AC motors are there?

(1)   Induction motor

(2)   synchronous motor

62.  What is magnetic hysteresis?

A)     Lagging of changes in the magnetization of a substance behind changes in the magnetic field as the magnetic field is varied

63.  What is eddy current and how to minimize it?

A)     Eddy currents (also called Foucault currents[1]) are electric currents induced in conductors when a conductor is exposed to a changing magnetic field; due to relative motion of the field source and conductor or due to variations of the field with time. This can cause a circulating flow of electrons, or current, within the body of the conductor. These circulating eddies of current have inductance and thus induce magnetic fields. These fields can cause repulsive, attractive, propulsion and drag effects. The stronger the applied magnetic field, or the greater the electrical conductivity of the conductor, or the faster the field changes, then the greater the currents that are developed and the greater the fields produced.

64.  How many types of electric circuits are there?

A)     Parallel and series circuit.

65.  Describe Kirchoff's laws.

A)     two laws governing electric networks in which steady currents flow: the sum of all the currents at a point is zero and the sum of the voltage gains and drops around any closed circuit is zero

66.  How many types of battery used on board ships?

A)     Usually, two main types of batteries are used on board:

Ø  Lead- Acid Battery

Ø  Alkaline battery

67.  What is the constructional difference between AC and DC generators?

A)     AC generator, the brushes run on slip rings which maintain a constant connection between the rotating coil and the external circuit. This means that as the induced emf changes polarity with every half-turn of the coil, the voltage in the external circuit varies like a sine wave and the current alternates direction. DC generator, the brushes run on a split-ring commutator which reverses the connection between the coil and the external circuit for every half-turn of the coil. This means that as the induced emf changes polarity with every half-turn of the coil, the voltage in the external circuit fluctuates between zero and a maximum while the current flows in one constant direction.

68.  How to calculate number of poles of a generator?

N speed = 60 x f x 2 / poles     (f - frequency)

69.  What are the causes of zero voltage in a running generator?

70.  What is the difference between an induction motor and synchronous motor?

Synchronous machines:

Ø      Wound-rotor or permanent magnet to generate the rotor magnetic field.

Ø      Rotor magnetic field is stationary with respect to the rotor.

Ø      Always turn at synchronous speed.

Ø      Require some form of control to operate.

Ø      More expensive to produce than squirrel cage induction machines.

Ø      Not self-starting.

Ø      More efficient than induction machines.

Induction Machines:

Ø      Wound-rotor or squirrel cage to generate the rotor magnetic field.

Ø      Rotor magnetic field rotates with respect to the rotor.

Ø      Always turn at less than synchronous speed.

Ø      Do not require control.

Ø      Much cheaper to produce (true for squirrel cage machines).

Ø      Self-starting.

Ø      Less efficient than synchronous machines.

Ø      More suitable for explosive environments.

Ø      No maintenance (for squirrel cage machines).

71.  What is the reading of hydrometer reading in full charge and discharge?

72.  What is meant by transformer and rectifier?

Transformer

A)     A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils.

Rectifier

An electrical device that converts an alternating current into a direct one by allowing a current to flow through it in one direction only

73.  What is he units for voltage, current, power and resistance?

74.  Comment on the starting current while using a direct online starter for an induction motor?

75.  What is reluctance?

A)     The property of a magnetic circuit of opposing the passage of magnetic flux lines, equal to the ratio of the magnetomotive force to the magnetic flux

76.  Measurement of air gap of induction motor

         A) For induction motors, the typical procedure is measure at 5 locations 90 degrees apart, on both ends, using long feeler gages. Then rotate rotor by 90 degrees and repeat.