Electric Mechanic

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

Stepper motor is the electrical machine which act upon input pulse applied to it. it is one type of synchronous motor which runs in steps in either direction instead of running in complete cycle.so, in automation parts it is used.

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.

In a System the output and inputs are interrelated in such a manner that the output quantity or variable is controlled by input quantity, then such a system is called Control System.

The output quantity is called controlled variable or response and the input quantity is called command signal or excitation.

During the triggering process of the thyristor from forward blocking state to forward conduction state through the gate signal, by applying the gate signal (voltage between gate and cathode) increases the minority carrier density in the p-layer and thereby facilitate the reverse break over of the junction J2 and thyristor starts conducting. Higher the magnitude of the gate current pulse, lesser is the time required to inject the charge and turning on the scr. By controlling the amount of charge we can control the turning on time of the scr.

At no load Synchronous Impedance of the alternator is responsible for creating angle difference. So it should be zero lagging like inductor.

Bus bars and isolators are rated for continuous power flow, that means they carry heavy currents which rises their temperature. so it is necessary to test this devices for temperature rise.

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.

The interviewer would like to know your motivation for leaving your current position. When discussing your current job be sure to stay in a positive mindset and keep the conversation light. There are many legitimate reasons for leaving a job. Be sure to be clear about your reasoning, and be honest. Stay away from any negative response! That is a complete interview killer.

Employers want to get a sense of what aspects of an electrician's job you might find to be challenging , as well as how you have responded in the past when facing such a situation. So, in addition to describing the situation, also provide details on how you handled the challenge and what you learned from it.

Working as an electronics technician means that one has to work around fumes and moving equipment parts, so one has to be careful. I make sure that I wear all assigned protective gear and follow safety instructions and protocols.

Be prepared to list the various types of electrical systems you have worked on in the past, giving specifics about the scope of each type of project and the role you played. If there are types of systems relevant to this job that you have not worked on before, explain how your past experience and training has prepared you to be ready to tackle these kinds of systems.

At the time of motor taking normal current (rated current)the speed of the motor is called rated speed. It is a speed at which any system take small current and give maximum efficiency.

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

TRANSFORMER LOSSES - Transformer losses have two sources-copper loss and magnetic loss. Copper losses are caused by the resistance of the wire (I2R). Magnetic losses are caused by eddy currents and hysteresis in the core. Copper loss is a constant after the coil has been wound and therefore a measurable loss. Hysteresis loss is constant for a particular voltage and current. Eddy-current loss, however, is different for each frequency passed through the transformer.

The different methods of starting an induction motor:

☛ a) DOL:direct online starter

☛ b) Star delta starter

☛ c) Auto transformer starter

☛ d) Resistance starter

☛ e) Series reactor starter

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.

Two major types of Control Systems are

1) Open loop Control System

2) Closed Loop Control Systems

☛ Open loop Control Systems:

The Open loop Control System is one in which the Output Quantity has no effect on the Input Quantity. No feedback is present from the output quantity to the input quantity for correction.

☛ Closed Loop Control System:

The Closed loop Control System is one in which the feedback is provided from the Output quantity to the input quantity for the correction so as to maintain the desired output of the system.

It reduces the harmonics and it also reduces sparking and arching across the mechanical switch so that it reduces the voltage spike seen in a inductive load.

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.