Electric Motor Repairer

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Its Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run.

DC Series motor has high starting torque. We can not start the Induction motor and Synchronous motors on load, but can not start the DC series motor without load.

Dc series is in the trains to get high starting torque while starting of the trains and operating voltage is 1500v dc.

When breaker is close at one time by close push button,the anti pumping contactor prevent re close the breaker by close push button after if it already close.

Armature reaction is the effect of magnetic field setup by armature current on the distribution of flux under main poles of a generator. The armature magnetic field has two effects

☛ It demagnetizes or weakens the main flux

☛ It cross-magnetizes or distorts it.

☛ The first effect leads to reduced generated voltage and second to the sparking at the brushes.

My work style matching exactlty what cashier job requires by: being reliable, responsible, and dependable, and fulfilling obligations, being careful about detail and thorough in completing work tasks, being pleasant with others on the job and displaying a good-natured, cooperative attitude, persistence in the face of obstacles, a willingness to take on responsibilities and challenges.

1. By using flux control method:in this method a rheostat is connected across the field winding to control the field current.so by changing the current the flux produced by the field winding can be changed, and since speed is inversely proportional to flux speed can be controlled

2.armature control method:in this method a rheostat is connected across armature winding by varying the resistance the value of resistive drop(IaRa) can be varied, and since speed is directly proportional to Eb-IaRa the speed can be controlled.

In thermal power plants dc motors are employed for certain control and critical emergency operations which are supplied by dedicated batteries. DC motors operate as backup drives for normal ac drive systems when ac power supply to the plant is lost.

In thermal power plant, the dc motors finds applications for performing control functions such as

☛ Turbine governor motor

☛ Governor limit setting

☛ Motor operated rheostats

☛ Emergency lubrication for the turbines (main, boiler feed pumps)

☛ Generator (H2 oil seal).

☛ DC motor operated valves

When scr is conducting current in forward conduction state, scr will return to forward blocking state when the anode current or forward current falls below a low level called Holding current

Note: Latching current and Holding current are not same. Latching current is associated with the turn on process of the scr whereas holding current is associated with the turn off process. In general holding current will be slightly lesser than the latching current.

DC Generators are classified into two types

1)separatly excited DC generator

2)self excited DC generator, which is further classified into;

☛ 1)series

☛ 2)shunt and

☛ 3)compound(which is further classified into cumulative and differential).

The shunt connection in four point starter is provided separately form the line where as in three point starter it is connected with line which is the drawback in three point starter.

What is the difference between synchronous generator & asynchronous generator?

In simple, synchronous generator supply's both active and reactive power but asynchronous generator(induction generator) supply's only active power and observe reactive power for magnetizing. This type of generators are used in windmills.

The change in terminal voltage of a generator between full and no load (at constant speed) is called the voltage regulation. It is usually expressed as a percentage of the voltage at full-load.

%Voltage Regulation= (VNL-VFL)/VFL*100

☛ VNL= Terminal voltage of generator at No load.

☛ VFL= Terminal voltage of generator at full load.

The different methods of starting an induction motor

☛ DOL:direct online starter

☛ Star delta starter

☛ Auto transformer starter

☛ Resistance starter

☛ Series reactor starter

Whenever a current carrying conductor is placed in an magnetic field it produce turning or twisting movement is called as torque.

The main advantage of using the star delta starter is reduction of current during the starting of the motor. Starting current is reduced to 3-4 times Of current of Direct online starting.

Hence the starting current is reduced , the voltage drops during the starting of motor in systems are reduced.

Gate signal is to be applied to the thyristor to trigger the thyristor ON in safe mode. When the thyristor starts conducting the forward current above the minimum value, called Latching current, the gate signal which is applied to trigger the device in no longer require to keep the scr in ON position.

It is used with generators for charging a number of capacitor in parallel and discharging them in series.It is used when voltage required for testing is higher than the available.

Dual ignitors are always used for in flight starts. FCOM 1 70.20.8

A two phase motor is a motor with the the starting winding and the running winding have a phase split. e.g;ac servo motor.where the auxiliary winding and the control winding have a phase split of 90 degree.