20+ Pon Pure Logistics Interview Questions and Answers

Composite error and ratio error are two types of errors in current transformers.

• Composite error is the combination of ratio error and phase angle error in a current transformer.

• Ratio error is the difference between the actual turns ratio and the specified turns ratio of a current transformer.

• Phase angle error is the angular difference between the primary and secondary currents of a current transformer.

• Composite error and ratio error affect the accuracy of current measurement ...read more

The chance of survival depends on various factors such as insulation, grounding, and the strength of the electrical surge.

• The chance of survival depends on the insulation of the car, as it acts as a barrier against electrical current.

• If the car is properly grounded, it can help dissipate the electrical surge and reduce the risk of injury.

• The strength of the electrical surge also plays a crucial role in determining the chance of survival.

• If the car has safety features like lig...read more

Power transformers are used in transmission systems to step up or down voltage, while distribution transformers are used in distribution systems to step down voltage.

• Power transformers are used in high voltage transmission systems to step up or down voltage for long distance transmission.

• Distribution transformers are used in low voltage distribution systems to step down voltage for local distribution.

• Power transformers have higher voltage ratings and power capacities than dis...read more

Buchholz relay is used to protect transformers from faults by detecting gas and oil flow abnormalities.

• Buchholz relay is installed in the pipe connecting the transformer tank and conservator tank.

• It operates based on the principle that faults in the transformer generate gases and cause oil flow disturbances.

• When gas or oil flow abnormalities occur, the relay trips and sends a signal to the control panel to isolate the transformer.

• It provides protection against faults such as ...read more

A single line diagram of a distribution system is required with proper specifications.

• The diagram should show the flow of power from the source to the load

• It should include all components such as transformers, switchgear, and cables

• The specifications should include voltage levels, power ratings, and protection devices

• The diagram should follow standard symbols and conventions

• Example: A 11 kV distribution system with a 500 kVA transformer and 630 A circuit breaker

Dewpoint test is done in transformer to check the moisture content in the insulation oil.

• Moisture in insulation oil can cause breakdown of transformer insulation

• Dewpoint test helps to determine the moisture content in the oil

• It is a preventive maintenance measure to avoid transformer failure

• The test involves cooling a mirror until dew forms on it, and measuring the temperature at which dew forms

The material used in transformers is typically iron or steel.

• Transformers use a magnetic core made of laminated iron or steel sheets to increase efficiency.

• The core material is chosen for its magnetic properties and ability to withstand high temperatures.

• Other materials such as ferrite or amorphous metal may also be used in certain types of transformers.

• The winding material for the coils is typically copper or aluminum wire.

Different types of communication cables used in the electrical engineering industry include coaxial cables, twisted pair cables, and fiber optic cables.

• Coaxial cables: used for high-frequency transmission and commonly used in cable television and computer networks.

• Twisted pair cables: consists of pairs of insulated copper wires twisted together to reduce electromagnetic interference, commonly used in Ethernet networks.

• Fiber optic cables: use light pulses to transmit data and ...read more

Minimum insulation resistance value for HT motor.

• HT motor insulation resistance should be at least 1 Mega Ohm

• Insulation resistance should be measured regularly to ensure safety

• Factors like temperature and humidity can affect insulation resistance

An AC drive circuit diagram controls the speed of an AC motor by varying the frequency and voltage of the power supplied to it.

• An AC drive consists of a rectifier, DC link, inverter, and control circuitry.

• The rectifier converts AC power to DC power, which is stored in the DC link.

• The inverter converts the DC power back to AC power with variable frequency and voltage.

• The control circuitry adjusts the frequency and voltage of the output to control the motor speed.

• Examples of AC...read more

The minimum insulation resistance value for a Lt Motor.

• The minimum insulation resistance value for a Lt Motor is typically 1 Megaohm.

• This value is important to ensure the motor is properly insulated and protected from electrical faults.

• Insulation resistance can be measured using a megohmmeter.

• Factors that can affect insulation resistance include temperature, humidity, and contamination.

• Regular testing of insulation resistance is important for preventative maintenance and safe...read more

Lenz's law states that the direction of an induced current in a conductor is always such that it opposes the change in magnetic field that produced it.

• Lenz's law is a fundamental law of electromagnetism.

• It is named after Heinrich Lenz, a Russian physicist.

• It is used to determine the direction of induced current in a conductor.

• The law is based on the principle of conservation of energy.

• It is used in many applications, including electric motors and generators.

Single mode fiber optic cable has a smaller core size and allows only one mode of light to propagate, while multimode fiber optic cable has a larger core size and allows multiple modes of light to propagate.

• Single mode fiber optic cable has a core size of 8-10 microns, while multimode fiber optic cable has a core size of 50-62.5 microns.

• Single mode fiber optic cable provides higher bandwidth and longer transmission distances compared to multimode fiber optic cable.

• Single mode...read more

Transformer parts include core, windings, insulation, tap changer, and cooling system.

• Core: magnetic material that provides a path for the magnetic flux

• Windings: conductors that carry the electrical current

• Insulation: material that separates the windings and core to prevent short circuits

• Tap changer: device that adjusts the number of turns in the windings to regulate voltage

• Cooling system: dissipates heat generated by the transformer

• Examples: bushings, conservator, breather, ...read more

PLC stands for Programmable Logic Controller, used in industrial automation to control machinery and processes.

• PLC is a digital computer used for automation of electromechanical processes.

• It uses a programmable memory to store instructions and specific functions.

• PLCs are commonly used in manufacturing plants, assembly lines, and other industrial settings.

• They can be programmed using ladder logic, function block diagrams, or structured text.

• PLCs help in controlling various pro...read more

Transformer nameplate details include manufacturer, model, kVA rating, voltage rating, frequency, and serial number.

• Manufacturer name

• Model number

• kVA rating

• Voltage rating

• Frequency

• Serial number

Protection system for transformers includes Buchholz relay, differential protection, overcurrent protection, and temperature monitoring.

• Buchholz relay detects internal faults like gas accumulation or oil leakage

• Differential protection compares currents entering and leaving the transformer to detect faults

• Overcurrent protection safeguards against excessive current flow

• Temperature monitoring ensures the transformer operates within safe limits

Regular maintenance of transformers and motors is crucial for ensuring optimal performance and preventing breakdowns.

• Regularly inspecting for signs of wear and tear

• Checking and replacing worn out parts such as brushes and bearings

• Testing insulation resistance

• Cleaning and lubricating moving parts

• Monitoring temperature and vibration levels

• Following manufacturer's maintenance guidelines

• Keeping records of maintenance activities for future reference

Differential protection of transformer ensures that any internal fault is quickly detected and isolated to prevent damage.

• Differential protection compares the current entering and leaving the transformer windings. If there is a difference, it indicates a fault.

• The relay used for differential protection operates when the difference in current exceeds a set threshold.

• This protection scheme is effective in detecting internal faults like short circuits or winding failures.

• Differe...read more

Ten delta test is a method used to determine the phase relationship between the primary and secondary windings of a transformer.

• Ten delta test involves injecting a low voltage signal into the primary winding and measuring the corresponding output in the secondary winding.

• The test helps in identifying any phase shift or angular displacement between the primary and secondary windings.

• It is important for ensuring the proper functioning and efficiency of the transformer.

• Results o...read more