Dear Readers, Welcome to Generator Operator Interview Questions and Answers have been designed specially to get you acquainted with the nature of questions you may encounter during your Job interview for the subject of Generator Operator. These Generator Operator Questions are very important for campus placement test and job interviews. As per my experience good interviewers hardly plan to ask any particular questions during your Job interview and these model questions are asked in the online technical test and interview of many IT & Non IT Industries.
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.
The function of commutator is to facilitate the collection of current from armature conductors. It converts the alternating current induce in the armature conductors into unidirectional current in the external load circuit.
ACSR means Aluminium conductor steel reinforced, this conductor is used in transmission & distribution.
Compensation windings are used to neutralize the cross magnetizing effect of armature reaction.
Whenever an engine is at or below idle with the fuel control switch in RUN. FCOM 1 70.20.8
Dual ignitors are always used for in flight starts. FCOM 1 70.20.8
The currents in the coils connected to a brush are either all towards the brush (positive brush) or all directed away from the brush (negative brush). Therefore, current in a coil will reverse as the coil passes a brush. The reversal of current in a coil as the coil passes the brush axis is called commutation.
It is a procedure that is used for the protection of the workers and the equipments during the maintenance or repair of the power plant.
The purpose of brushes is simply to lead current from the rotating loop or winding to the external stationary load.
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.
The Feedback in Control System in one in which the output is sampled and proportional signal is fed back to the input for automatic correction of the error ( any change in desired output) for futher processing to get back the desired output.
The autostart will make continuous start attemps until the engine either starts or the pilot aborts the start attempt. FCOM 1 70.20.7
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.
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.
EPR, N1 and EGT. FCOM 1 70.20.1
Forced draft installed to force the air inside the plant while the induced draft fetches and pulls the air inside the air.
Because if coal is not crushed the combustion will not take place and also lump coal is very dangerous for the boiler water walls.
In the absence of compensation windings the flux will be suddenly shifting backward and forward with every change in load inducing an e.m.f in the armature coils. The magnitude of this e.m.f may be so high as to strike an arc between the consecutive commutator segments. This may further develop into a flash-over around the whole commutator thereby short circuiting the whole armature.
It is an inverse definite minimum time relay.In IDMT relay its operating is inversely proportional and also a characteristic of minimum time after which this relay operates.It is inverse in the sense ,the tripping time will decrease as the magnitude of fault current increase.
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.
As soon as the fuel control switch is positioned to RUN. FCOM 1 70.20.7
A block of coal takes a lot of time to burn and give out the energy, but the powdered coal burns uniformly faster and since it is in its powdered form the entire coal burns and there is no waste of coal which leads in achieving greater calorific value.
CHP & stock yard, crushers, coal conveyors, LDO HFO oil elevations, ash slurry disposal units, ash pond, wet or dry ash disposal.
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.
A boiler feed pump takes away one third part of the energy generated by the power plant.
CHP & stock yard, crushers, coal conveyors, wet or dry ash disposal, ash slurry disposal units, ash pond, LDO HFO oil elevations.
Match up the generator with the 500 KV line voltage so you're not back back to the generator reverse power.
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.
Then fan after boiler with flue gas will have induced draft, and the fan that has duct connecting to boiler will be the forced draft.Forced draft will give positive pressure to boiler and induced will give negative draft to the boiler.
A. A d.c. generator whose field magnet winding is supplied from an independent external d.c. source (e.g., a battery etc.) is called a separately excited generator.
If the voltage between the two phase is equal to the lamp voltage then the lamp will glow. When the voltage difference is big it will damage the lamp and when the difference is smaller the lamp will glow depending on the type of lamp.
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.
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.
For lighting loads, neutral conductor is must and hence the secondary must be star winding. and this lighting load is always unbalanced in all three phases. To minimize the current unbalance in the primary we use delta winding in the primary. So delta / star transformer is used for lighting loads.
Heat plays a mojor role in turbine, incase of absence of heat the turbine blades may got damage due to formation of rust. If there is no heat in steam means it has a moisture. So we need the heat.
It depends on the type of plant and the application the tower has to deal with it.
ENG THRUST (L or R). FCOM 1 70.20.16
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
MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit. MCCB moulded case circuit breaker and is thermal operated for over load current and magnetic operation for instant trip in short circuit condition.under voltage and under frequency may be inbuilt. Normally it is used where normal current is more than 100A.
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.
They place it usually at top because the higher the altitude the more effecient the cooling tower will be because its colder at high altitude than ground.
If the airspeed is below that recommended for a windmilling start. FCOM 1 70.20.7
This happens generally on every other day in this profession, but the key is not to stay back but move on. I will take some preventive measures to avoid loss of resources.
Shunt field losses
This computer humming sound is coming due to ionization (breakdown of air into charged particles) of air around transmission conductor. This effect is called as Corona effect, and it is considered as power loss.
The role of Feedback in control system is to take the sampled output back to the input and compare output signal with input signal for error ( deviation from the desired result).
Negative Feedback results in the better stability of the system and rejects any disturbance signals and is less sensitive to the parameter variations. Hence in control systems negative feedback is considered.
Those transformers installed at the ending or receiving end of long high voltage transmission lines are the power transformers. The distribution transformers (generally pole mounted) are those installed in the location of the city to provide utilization voltage at the consumer terminals.
Power transformers are used in transmission network of higher voltages for step-up and step down application (400 kV, 200 kV, 110 kV, 66 kV, 33kV) and are generally rated above 200MVA.
Distribution transformers are used for lower voltage distribution networks as a means to end user connectivity. (11kV, 6.6 kV, 3.3 kV, 440V, 230V) and are generally rated less than 200 MVA.
A power transformer usually has one primary and one secondary, and one input and output. A distribution transformer may have one primary and one divided or "Tapped" secondary, or two or more secondaries.
Power transformers generally operate at nearly full – load. However, a distribution transformer operates at light loads during major parts of the day.
The performance of the power transformers is generally judged from commercial efficiency whereas the performance of a distribution transformer is judged from all – day – efficiency.
The rating of a high transformer is many times greater than that of distribution transformer.
In Power Transformer the flux density is higher than the distribution transformer.
Power transformer's primary winding always connected in star and secondary winding in delta while in distribution transformer primary winding connected in delta and secondary in star.
In The Sub station end of the transmission line, The Power Transformer Connection is Star-Delta.( For the purpose of Step down the Voltage Level)
In the star up of the Transmission line (H-T), The Connection of the power Transformer is Delta – Star (For the purpose of Step Up the Voltage Level) But in case of Distribution Transformer, But Generally it is used in there-phase Step down distribution transformer( Delta – Star).
The Shunt winding has a large number of turns so that it has appreciable inductance. When A.C is applied to a shunt motor, the large inductive reactance of shunt winding will reduce the field current too much. Consequently, Shunt motor will not usually run on A.C Supply.
At no load Synchronous Impedance of the alternator is responsible for creating angle difference. So it should be zero lagging like inductor.
Improving commutation means to make current reversal in the short-circuited coil as spark less as possible. This can be done using
A d.c. generator whose field magnet winding is supplied current from the output of the generator itself is called a self-excited generator. There are three types of self-excited generators depending upon the manner in which the field winding is connected to the armature,
Series generator - , the field winding is connected in series with armature winding so that whole armature current flows through the field winding as well as the load.
Shunt generator - , the field winding is connected in parallel with the armature winding so that terminal voltage of the generator is applied across it.
Compound generator - there are two sets of field windings on each pole-one is in series and the other in parallel with the armature. A compound wound generator may be:
Short Shunt in which only shunt field winding is in parallel with the armature winding
Long Shunt in which shunt field winding is in parallel with both series field and armature winding
N1. FCOM 1 70.2016
Steam should be heated to the temperature it is before making it to enter the turbine because superheated steam produces a lot of energy and also prevents the blades from rusting or damaging.
A power plant operator is a person who operates a power plant. He has got to be good at the technical skills of using the power plant and must be equally talented in distributing the work to the other workers who are working with the power plant.
To avoid the transmission losses.
If actual thrust is less than commanded thrust during takeoff with airspeed between 65kts and V1-6kts. FCOM 1 70.20.16
Steam a bowl of saturated temperature.
Generators are generally classified based on their methods of field excitation Separately excited d.c. generators
Self-excited d.c. generators
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.
Continuity of service
Maintenance and Repair
Increasing plant capacity
Non availability of single large unit
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.
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.
If their is high power factor, i.e if the power factor is close to one:
Losses in form of heat will be reduced,
Cable becomes less bulky and easy to carry, and very cheap to afford, &
It also reduces over heating of tranformers.
The losses in a d.c. machine (generator or motor) may be divided into three types:
Copper losses: These losses occur due to currents in the various windings of the machine.
Iron or core losses: These losses occur in the armature of a d.c. machine and are due to the rotation of armature in the magnetic field of the poles. They are of two types
Hysteresis loss: Hysteresis loss occurs in the armature of the d.c. machine since any given part of the armature is subjected to magnetic field reversals as it passes under successive poles.
Eddy current loss: The voltages induced in the armature conductors produce circulating currents in the armature core known as eddy currents and power loss due to their flow is called eddy current loss. The eddy current loss appears as heat which raises the temperature of the machine and lowers its efficiency.
Mechanical losses: These losses are due to friction and windage. These losses depend upon the speed of the machine. But for a given speed, they are practically constant.
An electric generator is a machine that converts mechanical energy into electrical energy. An electric generator is based on the principle that whenever flux is cut by a conductor, an e.m.f. is induced which will cause a current to flow if the conductor circuit is closed. The direction of induced e.m.f. (and hence current) is given by Fleming's right hand rule.
N2, N3, fuel flow, oil pressure, oil temperature, oil quantity and engine vibration. FCOM 1 70.20.1
The different methods of starting an induction motor:
DOL:direct online starter
Star delta starter
Auto transformer starter
Series reactor starter.