Brushless Alternator Working principle| Advantages, Disadvantages | Applications

This Article is all about What is Brushless Alternator ? Its Working Principle, Parts , Operations , Applications, Advantages and Disadvantages.

brushless alternator working principle

What is a Brushless Alternator ?

A Brushless Alternator is an alternator, which is used for generating the mechanical energy into electrical energy by using the two rotors fitted end to end on same shaft and transferring the induced electricity without Brushes and the slip rings.

or, we can defined as, it is an alternator which do not uses the brushes and the slip rings and consists of two alternator, main excitor and small exciter alternator which is fitted on the same shaft of main alternator with the help of the bridge rectifier.

Constructions of Brushless alternator

  1. .Stator Body
  2. Rotor assembly
  3. Bridge Rectifier

1. Stator Body :- The stator body housing includes main stator and the excitor stator at end of stator body.

2.Rotor body :- Rotor body consists of the main rotors and exciter rotor at end.

3.Bridge rectifier :- It is fitted at end of excitor rotor which is responsible for eliminating Brush and slip rings.

A brushless alternator mainly consists of two parts :-

  1. Main alternator and
  2. Excitor alternator

A Brushless alternator is made up of two alternators that are built end-to-end on a single shaft. Smaller brushless alternators may appear to be a single unit, but the two parts are easily distinguishable on larger models. The main alternator is the larger of the two sections, and the exciter is the smaller. The exciter contains stationary field coils as well as a rotating armature (power coils). The primary alternator employs the inverse configuration, with a rotating field and a stationary armature.

1.Main alternator

The main alternator which has a rotating field and a stationary armature (power generation windings). This is the part that can be confusing, so keep in mind that in this case, the armature is the stator, not the rotor.
The high current output does not have to pass through brushes and slip rings because the armature is in the stationary portion of the alternator. Although the electrical design is more complicated, it results in a very reliable alternator because the only parts subject to wear are the bearings.

2.Excitor alternator

The exciter field coils are located on the stator, while the armature is located on the rotor. The exciter armature’s alternating current output is fed through a series of diodes mounted on the rotor to produce a direct current voltage. This is fed directly to the main alternator’s field coils, which are also located on the rotor. Brushes and slip rings are not required to supply current to the rotating field coils in this configuration. In contrast, a simple automotive alternator uses brushes and slip rings to supply current to the rotating field.

Basic terminology of Alternator

stator – The stator is the stationary component of a motor or alternator, and

rotor :-the rotor is the rotating component.

Magnetic field :- The coils of wire used to generate a magnetic field are referred to as the field, and

Armature :- the coils that generate power are referred to as the armature.
This can be perplexing because most people associate the armature with the rotor. Traditionally, the armature was located on the rotor, but this is not always the case. The two terms are not interchangeable. In a typical automotive alternator, for example, the field is on the rotor and the armature is on the stator. The mechanical configuration consists of a rotor and a stator.

This is very confusing because most people associate the armature with the rotor. Traditionally, the armature was located on the rotor, but this is not always the case. The two terms are not interchangeable. In a typical automotive alternator, for example, the field is on the rotor and the armature is on the stator. The mechanical configuration consists of a rotor and a stator.

Basic working theory of alternator

A magnetic field is created when an electric current is passed through a wire coil (an electromagnet).
When a magnetic field is moved through a wire coil, a voltage is induced in the wire. When the electrons have somewhere to go, such as a battery or other load, the induced voltage becomes a current. Both of these processes occur in alternators, motors, generators, or dynamos.

When a wire coil is moved through a magnetic field, voltage or emf is produced. It makes no difference whether the coil or the magnetic field is moving. Depending on mechanical, electrical, and other objectives, either configuration works equally well and can be used separately or in combination. The old direct current (DC) generators (dynamos) had a stationary field and a rotating armature.
Alternators in automobiles use the opposite configuration, with a rotating field and a stationary armature. Both configurations are used in a brushless alternator in the same machine.

Working principle of Brushless alternator

Alternator works on the principle of faraday’s law of electromagnetic induction.

Brushless alternator Working

We understand the construction of working now let us know about working. There is a residual magnetism attach to the exciter stator. Now when main rotor starts rotating, excitor stator also rotates. Due to faradays law of electromagnetic induction ac current is produced in coils of rotor excitor ( excitor coil ).

Now this ac current is used for exciting. This AC current is passed through bridge rectifier converted into DC. This Dc supply is given to the main rotor. This Dc current produced magnetic field.

Due to rotation of main rotor, Flux of magnetic field cut and AC Current generated in the Coil of\ Stationary main stator. This DC output is used for different applications. Thus, we understand here that how brushless alternator work.

AVR

The another main components of brushless alternator is AVR, It is called automatic voltage regulator. It is used for maintaining constant voltage. In Many diagrams in parts and components and explanations will use the term “AVR” without explaining what it is. Automatic Voltage Regulator (AVR) is an abbreviation for Automatic Voltage Regulator. An AVR performs the same function as a car’s “voltage regulator” or a home power system’s “regulator” or “controller.”

Advantages of Brushless alternator

  1. Not use of Brushes and Slip rings
  2. less maintenance.
  3. The output power of this alternator is more than brushed alternator.

Disadvantages

  1. Initial cost is higher than brushed alternator.
  2. Required expert person to do maintenance.

Application Of brushless alternator

  1. It is used in the wind turbine.
  2. In the train
  3. It is used only in the Case of Alternating current.

Check Out Other Important Topics

( FAQ ) Frequently Asked Questions

Why it is called brushless alternator?

Because there is no use of Brush.

IC EngineImportant PDFsBoilersSynergy Maritime ExamNaval ArchMEO Class 4
Interview QuestionsDifference BetweenTypes of PumpsAuxiliary MachinesTypes of ValvesHome

Safety Devices of All marine Equipment

What is Safety Device ?

Electrical Safety Devices

Dead front type switchboard, Fuses, Relays, Circuit breakers, Earth fault indicators, Under voltage relay, Reverse power trip, Preferential trip, Over current trip, Short circuit trip, Arc chute, Ebonite Rod ( to remove static charge).

Main Engine Safety Devices


General Safety Devices :-


 Insulated  hand  gloves,  dry  boiler  suits,  shoes  without  metallic  part,  Rubber  pad  in  front  of  switchboard,  0.6m  gap  behind  switchboard,  Panel  doors  to  be  earthed,  interlocked  handles  for opening doors.
 No water, oil, or steam pipeline in its vicinity.


Overhead crane safeties

1)  The most important safety feature of the crane is the electromagnetic fail safe brakes which do notallow 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.


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.

Motor Safety Devices


Motor protection and safeties:

1.  Overcurrent and single phasing protection relays

2.  under voltage relay

3.  Short circuit relay (Trigger fuses for HV systems)

4.  Temperature sensor for motor insulation

Safety device on life boat


Mechanical brake (to prevent accident falling)

Centrifugal brake (to control life boat falling speed between 20 to 40 m/min)

Limit switch (to prevent over tightening of rope) (it is fitted arm of davit just before in limit)

Harbour safety pin (for davit)


Safety devices for steering system


@Hunting gear

@Buffer spring

@ Angle adjusting stop (Hand over position limit switch)

@ Double shock valve

@Relief valve

@ Tank level alarm (oil)

@ Over load alarm

STEERING GEAR SAFETIES
Hydraulic safeties:


  Level switch, low level, low low level alarm for hydraulic oil tank.·        

Relief valve.·        

Manual bypass valve.·       

Low pressure valve.·      

High lub oil temp. Cut out  

Low level cut out


Electrical safeties:


Electrical and mechanical stopper for rudder. 

Electrical motor overload alarm.·      

Power failure alarm.·      

High temp. Alarm.·   

Self starting after power failure.·    

Short-circuit trip.·      

Phase failure alarm.·       

 200% insulation in motor

Windless safety device·      

Cable stopper (chain stopper, bow stopper)·      

Overload trip·      

Overspeed trip·      

Hand brake·      

Slipping clutch for overload prevents any undesirable damage such hull damage due to anchor and rope broke out.


Scavenge Space Protection Devices
1)    Electrical temperature sensing device 

fitted within the trunking, which will automatically sound an alarm the event of an excessive rise in local temperature (above 200°C)
2)    Pressure relief valves

consisting of self-closing spring loaded valves are fitted and should be examined and tested periodically.


 3)  Fixed fire extinguishing system may be CO2, Dry Powder or Steam.


crankcase safety devices


1.     Breather pipe with flame trap

2.     Crankcase exhaust fan

3.     Oil mist detector

4.     Crankcase relief doors

5.     Bearing temperature sensor

6.     L.O return temperature sensor


Battery room safety arrangement


Safety is provided by

1)  Proper ventilation

2)  Prevention of heat source for ignition


Ventilation


 Independent exhaust fan provided·        

Inlet duct should be below battery level, and outlet at top of the compartment

Prevention of heat source for ignition
      

No naked light and no smoking·        

Uses of externally fitted light or flameproof light·        

Cables of adequate size and they are well connected·        

Never placed Emergency Switchboard in this room·        

Use insulated spanner and plastic jug for distilled water, to prevent short circuit·        

Room temperature, maintained at 15 ~ 25°C

Generator safety devices  ·      

Over speed trip·        

L.O low pressure trip

@ alarm·        

Low level sump trip·       

 F.O low pressure alarm·       

 Jacket water high temperature alarm·        

Thermometer·       

 Pressure gauge·       

 L.O high temperature alarm·        

Dip stick·        

Crankcase relief valve


ALTERNATOR  SAFETIES 


The three main type alternator protection are:

a. Over current protection.

b. Reverse power tripc.

c.Under voltage trip

Safety devices on starting air line

Î Spring loaded safety valve or bursting cap.(if bursting cap fitted, no need relief valve)

Î Flame trap.(At Joint where manifold to each cylinder startingline)

Î Starting air line drain valve (Inlet of automatic valve)

Π Turning gear interlock

Safety device on O.W.S

Pressure relief valve on discharge pipeO.D.M system with high ppm alarm and automatic pump stopping device.Test cock (level), drain valve


Incinerator Safety System

1)  The safety devices shut down the unit and give out alarms:a.  When the pilot and main burner fail to operateb.  When the flue gas temperature reaches above 400’Cc.  When the cooling fan fails to operate

2)  Emergency fuel shutdown valve

3)  Micro switch, fitted to hinged furnace door (Interlock)

AUTOMATIC MOISTURE DRAIN VALVE(Unloader)this reduced the starting torque for the machine and clear out any accumulated moisture and oil in the system


Safety devices on refrigeration system.

1)L. P cut-out on compressor suction side: Set at a pressure corresponding to 5°C below the lowest expected evaporating gauge reading

2)H.P cut-out on compressor discharge side:Set at a pressure corresponding to 5°C above thehighest expected evaporating gauge reading

3)  Lube oil low pressure cut-out: Oil pressure usually set at 2 bar above crankcase pressure

4)  Cooling water L .P cut-out in condenser side

5)  Safety spring loaded liquid shock valve on compressor cylinder head

6)  Bursting disc on cylinder head, between inlet and discharge manifold

7)  Bursting disc on Condenser, [if fitted]

8)  Relief valve on Condenser; air purging valve on condenser

9)  Master solenoid valve: to prevent liquid being entered into Compressor, when theplant is standstill, especially in Large Plant

COMPRESSOR

Relief valve:

Fitted after every stage to release excess pressure developed inside it. The setting of the lifting pressure increases after every ascending stage. Normally fitted between 1st stage and intercooler and 2nd stage – aftercooler.


Bursting disc:

A bursting disc is a copper disc provided at the air cooler of the compressor. It is a safety disc which bursts when the pressure exceeds over the pre-determined value due to leaky air tubes of the cooler (intercooler or aftercooler).

Fusible plug:

Generally located on the discharge side of the compressor, it fuses if the air temperature is higher than the operational temperature. The fusible plug is made up of material which melts at high temperature.

Lube Oil low pressure alarm and trip:

If the lube oil pressure goes lower than the normal, the alarm is sounded followed by a cut out trip signal to avoid damage to bearings and crank shaft.

Water high temperature trip:

If the intercoolers are choked or the flow of water is less, then the air compressor will get over heated. To avoid this situation high water temperature trip is activated which cut offs the compressor.

Water no-flow trip:

If the attached pump is not working or the flow of water inside the intercooler is not enough to cool the compressor then moving part inside the compressor will get seized due to overheating. A no flow trip is provided which continuously monitor the flow of water and trips the compressor when there is none.

Motor Overload trip:

If the current taken by motor during running or starting is very high then there is a possibility of damage to the motor. An overload trip is thus fitted to avoid such situation.

Boiler safety devices

1)  Safety valve

2)  Low / high water level alarm

3)  Too low water level alarm and shut down

4)  Water level indicators

5)  Pressure gauge

6)  Low fuel oil pressure alarm

7)  Low / high fuel oil temperature alarm

8)  Flame failure alarm

9)  Smoke density alarm

10)  Easy gear arrangement

11)  Air vent

12)  Force draught fan stop alarm

13)  Low / high steam pressure alarm

Follow on Twitter

Salvaging of motor

How to do Salvaging of motor ?

● First of all,take out the motor from the sea water by Isolating it from the connections and take it to the electrical workshop.

● Now,measure the insulation resistance which will be very low hoti 200 ohm so,the main problem is to restore the insulation resistance and this can be restored by three ways.

1.cleaning

2.Drying

3.Re-varnishing

●Dismantle it and wash the windings with fresh water and clean the grease or oil on the windings with the help of using a degreasant liquid such as Armaclean.

●Now, dry the stator windings with the help of heaters or cargo clusters with plenty of ventilation to allow the dampness to escape

●Same thing fir rotors and bearings cleaning can be done with high speed diesel oil.

● Now, Assemble the motor and turn the motor for some revolutions for checking tightness and all.

●Go for insulation resistance test (IR Test ) ,as if it remains high over a few hours .Apply a couple of coats of good quality air -drying Insulating varnish.

●Now load the motor with the pump by taking proper alignment.

Servicing a motor effected/washed by seawater

  1. Cut out power supply by circuit breaker & taking out fuse. Mark & disconnect supply wire. Took Megger reading & recorded.
  2. Take out the motor, open up & dismantle. (Make sure marking on both cover & body)
  3. Clean and wash with warm fresh water.( About 180′ F)
  4. Cover by canvas, dry with positive ventilation & 500 watt lamp
  5. Clean with Electro cleaner.
  6. Baking by 500 Watt lamp for few hours.
  7. Take Megger reading. (test stable or constant reading) Apply insulation varnish to the winding while warm.
  8. Baking & taking the Megger.
  9. Reassemble & put back into service.
  10. When test run check sound, ampere & temperature.