101 Electrical interview questions with answer | Marine

What is the different position of the needle synchronoscope? What is the difference between 6 and 12?
06.00 means that at synchronization. We can not parallelize the incoming generator. Means 24:00 perfectly synchronized state (voltage, frequency, and phase sequence identity).

Why do we close switch 11 and not 12?
When the synchroscope is about 12 hours, the "slip" between the sine waves is near the minimum (the slip equals zero when the synchroscope 12) and the difference voltage between the phases minimum synchroscope is 12 hours) . Because of the time it takes to close the switch synchronous, usually it has in 11 hours. Due to the low delay to close, 11, are nearly 12 hours approach.

Why is a Megger used for insulation testing and not for a multimeter?
With a Megger, a voltage of not less than 500 volts DC is used to test the insulation resistance of the windings. Using a multimeter, the voltage does not use more than 3 volts DC. Megger test uses a high impedance and is more accurate than a multimeter

What are the MSB guarantees?
Circuit breakers, fuses and overcurrent relays. The panels are dead front panel, for example, can not open the control panel for maintenance, until we turn off the power to the plate by the circuit breaker.

When the reverse current is flowing?
The situation of a generator is supplied by a system switching device has a multiplicity of generators that are parallel to the generator. The current flow, when the system is operating normally, is between the generators of the distribution boxes. If you have problems and generator connection voltage under the system voltage, the generator can act as a motor, as a motor as a generator, and the current flows in the generator area. This is the inversion force. The effects can end from low range in the event of a complete mechanical failure generator failure.

What is the damage when the backflow flows?
Suppose the generator usually generates an amount of power equal to P, and during motor operation will absorb a similar amount. Therefore, P., the net effect on the grid will be the same after an increase in load experience step equal to 2P. Depending on the size of the gate and the resistance of the remaining generation, an increase in the 2P step could result in a significant change in the network frequency.
In some cases, damage to the engine (especially steam turbines) may occur.

How does he enjoy protection from return?
The protection of the reverse power is used for anti-motor. This function is not the first motor generator to protect. You can stop the fuel supply and stop the main engine.

How to test performance releases?

When two generators operate in parallel and a generator can carry the load, the return path of energy can be tested by changing the load by means of the inductor. When the load is moved enough to discharge and load generator off a small percentage of the charge of its ignition and the fuel supply to the drive motor is turned off. That is, the reverse relays are being operated. The relay can be tested by simulation (use the test key on the relay) to see when a trigger signal is started.

What is the complete form of CLA?

Circuit breaker. In general they are in power applications and 400 V (generator switch).

ACB By pressing the close button in an inactive generator, what will happen?
Normally, the circuit breaker is not closed until it is synchronized even if the press does not close the stop switch. The switch has protection from voltage do not let it close.

What is low-voltage protection?
Prevents the switch from accidentally closing or the generator load for parallel operation. It also provides protection against the loss of voltage while the machine is connected to the control unit.

What is the importance of preferential travel? Why is it planned?

The preferred type of pickup is an electrical device on the ship which is designed on the main track in the event of partial failure or non-essential current main circuit overload, that is to separate uncritical load.

What is the rms value?
The root mean square root is the maximum value divided by the square root of two.

What is the importance of the power factor?
The power factor is the cosine of the angle between the waveform of voltage and current.

What is the typical value you see on board?
Usually 0.8.

What is the best value?
1 is the best value. This is possible with a purely resistive load.

What is the benefit of improving the performance factor?
Near 1 means that power factor for a given lower effective power in kW, the charging current becomes lower and consequently the losses are I2R. System efficiency is higher, the losses are lower. Improved tension control.

How can it be improved?
The capacitor banks improve power factor, when the charges are mainly resistive.

What is the meaning that I and V are in phase?
The angle between the waveforms I and V is equal to zero, which means that the load is purely ohmic.

Why ratings KW motor and generator and transformer KVA given?
KW mechanical power from a motor and is expressed in kW.
KVA is the entry of the net power (apparent) of the transformer. The power input is the initial loss +.
KW = kVA x power factor system

Where is the reactive power?
Reactive power is not lost. Motor it lasts electric field, which the engine will convert the effective (power) of the mechanical torque.

What is a semiconductor?
Germanium or silicon, their electrical conductivity between a metal and an insulator; Its conductivity increases with the temperature and in the presence of impurities

What is Doping?
The deliberate introduction of impurities in a high-purity semiconductor (also known as intrinsic name) doping their electrical properties. Impurities are dependent on the semiconductor type. Light semiconductor doped moderately called extrinsic. A semiconductor is doped at so high levels that it acts degenerate more like a conductor of a semiconductor.

What is insulation when temperature rises?
For insulation, a temperature increase causes its resistance to decrease, causing too high temperature the main reason, why is often the insulation

What happens to the resistance when the temperature rises?
For drivers, an increase in temperature causes its resistance increases.

What is an induction motor?
An induction motor is an alternating current motor in which the primary winding of a member (usually the stator) is connected to the power supply, and a secondary winding or a cage secondary winding on the other side element (usually the rotor) current.

What "slip"?
An AC induction motor (current amplitude) consists of two assemblies: a stator and a rotor. The interaction of the currents in the rotor bars and the rotating magnetic field of the stator flows, generates a torque. In actual operation, the rotor speed is lagged, nor is the speed of the magnetic field that intersects the rotor rods, allowing the lines of the magnetic force to produce a useful torque. This speed difference is referred to as slip.

What is a synchronous motor?
A constant speed motor, depending on the frequency of the alternating current and the number of poles for which it is designed.

Where is it used?
Synchronous motors have applications in all industrial applications where constant speed is required. Improved power factor and synchronous capacitors. Power plants almost always use synchronous generators because it is important to maintain a constant frequency at which the generator is connected. Low-power applications are positioning machines where you have high precision, and the robot drives.

How a multimeter is used?

What is an AVO Meter?

The avometer was one meter of the British brand, owned by Megger. It is often simply called AVO and has its name from the first letter of words ampere, volts, ohms

How continuity is tested?
Set the multimeter resistance mode and the resistance of the probes between the points of the circuit or under control. If the resistance is low or equal to zero, this means continuity. If it is high or infinite, it means idling.

This limits the electrical charge?
The available power is fixed and the voltage is adjusted so that the setting of the switch or fuse is the normal load current. If the load exceeds the rated current, the circuit breaker or fuse function and load limit.

What is the voltage used in a meggar?
500V DC.

How does the current flow during welding?

Current flows in the electrode and in the terminal. Here, as the river of MIG, stick, ground flow. In Tig, current flows through the electrode, Only now the only same function, the rod held in the hand and the other electrode.

What is welding on ships? AC or DC?

What is the tension?

What is the voltage to ignite, the boiler / waste incinerator used, etc.?

Typically, 000 V 10 (10 kV).
Why is it different from welding?
It is higher than the power away occurs from breaking the park. Air decomposes at this high voltage 10 kV. Therefore, it is higher than the normal tension of welding.

Is it current through the shell during welding?
Yes I believe.

If so, why not shock you?
. Since the whole city is on the same potential, so no potential difference for a shock.

What is to prevent the safe voltage collision?
Normally 50V. It depends on the resistance of the body and how the way to perform is (the use of these chargers or matt separators can allow a slightly safer voltage)

What is the only phase?
The only phase is a state in motors and transformers phase in which the current is switched off to one of the phases.

How can it happen?
The only phase adjustment is caused by the use of single-phase protective devices such as fuses. The three-phase loads must be protected by devices that cause a power failure in all three phases at the same time when an error occurs. Defective contacts or loose connections in three-phase circuit breaker can also cause a single phase.

What is caused by the damage?
The only phasing makes the highest rated currents in the healthy phase loads such as motors that cause engine overheating and thus damage the engine.
A single-phase drive can sometimes cause engine noise and vibrations.
What is the protection against that?
Individual phases can be identified by special protective relays to identify the loads and isolate them. The smaller motors are based on current relay and negative phase sequence. The motor protection relays for large motors are easily equipped with one-phase protection.

Why is it necessary that the frequency of the incoming alternator is more than the busbar?
Before parallel together Alternators Monday, the frequency of the incoming alternator is slightly higher. Is to ensure that the incoming generator part in the bus load take. When the incoming generator is slow, it will be motorized and add loads to the bus. When this happens, it is possible that even other generators are out of line.

What is the dark lamp and luminous method to synchronize? How to connect?
So far, three light bulbs are connected between the terminals of the generator and the connection system. As a modification of the rotational speed of the generator is turned on, and the intensity is proportional to the difference between the frequency generator and the frequency of the system speed. When the voltage on the voltage of the generator removed from the system (either forward or backward in phase), the lamps light up. If the voltage at the generator voltage corresponds to the system, the lights are dark. At this time, the switch of the generator connected to the system can be closed and the generator will then remain in sync with the system.

In addition to the renovation of the bearings there is no reason to open the engine for maintenance?
Test insulation and renewal (for example using insulation aerosol of the stator winding insulation).

Why use this reverse power instead of reversing alternators?
It is extremely difficult to detect reverse current with an alternative system, energy can be detected and inverted can be provided by a reverse relay.

What is the sense of excitement in a generator?
An electric generator or electric motor consists of a spinning rotor in a magnetic field. The magnetic field can be generated by permanent magnets or field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, since otherwise no force is transmitted to or from the rotor. A method for generating a magnetic field using an electric current is called excitation.
The field current in the alternator AC or DC?
DIRECT CURRENT. Dennis T Hall Check to confirm.

What is residual magnetism? Where is it important?
The residual magnetism is a property in which a certain amount of excitation remains in the drivers even after removal of the magnets.
It is necessary because we must start magnetism before the field winding is able to generate the entire field.

Sometimes the direction of travel of an E / R fan (supply the exhaust) when the change is triggered. Why?
If the ventilation flaps are not properly defined or open or filter clogged, the air supply is impaired and the fan causing cooking to be overloaded. Set / O for more information.

What is the function of the friction clutch mechanism used in cleaners?
It is a mechanical problem.

What is regular maintenance of the batteries?

The cell voltage is checked every week. The specific density was monitored using the densitometer of the battery. The clamps are greased to prevent corrosion. Sometimes tests load carried on the batteries.
What precautions should be taken when using the battery?
The space must be vented to prevent explosions caused by the battery generated gas. You should wear protective clothing, gloves and eyes to help prevent acid spatter. There should be no flames or sparks near batteries. Never short terminals both positive as well as negative as this will cause a short circuit and high energy surplus. When disconnecting the battery, always disconnect the first and reconnect the negative connections.

Why special lighting is used in the bedrooms of the battery?
The spark-proof lighting is used as explosive gases can be generated during charging the battery, and therefore there should be sparks in the room.
What is the voltage of each cell in a lead-acid battery?

What is the full voltage of the battery?

24 V DC.

How is this tension achieved?
12 Serial connection cells. 12 x 2 V = 24 V is the total voltage of the battery.

What is the meaning of a NO contact?
The contact is open in the normal state (idle state).

How does a salinometer work?
Detects the salinity in parts per million (ppm) and provides an alarm signal and triggers a command to the bypass valve with a fresh water generator. Set / O and watch your boat freshwater heater manual.

How to automatically start and stop the air compressor?
The air reservoir includes a pressure switch which is cut and cut accordingly to the desired pressure. When the pressure falls below the cut setting, the switch turns the contactor coil on and the compressor is started. When the pressure reaches the threshold, the switch opens the closed circuit in series with the circuit breaker and cuts the contactor's power contacts.

How to maintain the temperature of the refrigeration chamber?

The cooling chamber includes a temperature switch (thermostat) having a temperature setting of cutting and cutting. Depending on the setting, the compressor is turned off when the temperature rises, and is turned off when the temperature is cooled to the desired value.

What is a self-monitoring alarm circuit?
Auto monitors the state of the alarm circuit. That is, it detects when the power of the alarm circuit is healthy and all the relays and contacts are working normally. Check with I / O for details.

On the sea when there is a force cut during the show, the action you take?

The emergency power generator is activated after a power failure; To reset the main power supply, we close the main switches of the generator without regard to the synchronization. How is that possible?
There is a connection between the main generator and the emergency power unit. The switch is triggered during the failure. The emergency generator starts and closes the switch and feeds the emergency loads. When the main recovery restore is restarted and the switch is closed. Since the switching bridge is still open, there is no parallel between the main generator and an emergency.
How the emergency power unit starts automatically?
It is activated by a low voltage relay. When a power failure, low voltage relays detects a loss of voltage from the generator. Similarly, when the power is restored, the relay stops the backup generator.

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