Electrical Q&A

Question: What causes harmonics in electrical systems?
Answer: Non-linear loads like VFDs, UPS, and computers distort the waveform, introducing harmonics that affect system performance.

Question: What is the significance of vector group in transformers?
Answer: It indicates the phase difference and winding configuration, which affects parallel operation and system compatibility.

Question: What is the function of a synchronous condenser?
Answer: To regulate voltage and improve power factor by supplying reactive power to the grid.

Question: What is the function of a relay in an electrical circuit?
Answer: To detect abnormal conditions and initiate the operation of protective devices like circuit breakers.

Question: Why is neutral grounding used in power systems?
Answer: To stabilize system voltage during faults and ensure safety by controlling fault currents.

Question: What is the function of an isolator in electrical systems?
Answer: To disconnect a part of the circuit for maintenance, ensuring safety without carrying load current.

Question: What is the difference between active and reactive power?
Answer: Active power performs actual work, while reactive power sustains the magnetic and electric fields in AC systems.

Question: Why is power factor correction important in electrical systems?
Answer: To reduce reactive power, improve energy efficiency, and avoid penalties from utility companies.

Question: What is the function of a circuit breaker?
Answer: To automatically interrupt the flow of current in case of overload or short circuit, protecting the system.

Question: What is the difference between VCB and SF₆ circuit breakers?
Answer: VCB uses vacuum to extinguish arc, ideal for medium voltage; SF₆ uses sulfur hexafluoride gas, suitable for high voltage with better insulation.

Question: Why is a star-delta starter used for induction motors?
Answer: To reduce the starting current by initially connecting the motor in star and then switching to delta for normal operation.

Question: What is the purpose of a lightning arrestor?
Answer: To divert lightning strikes safely to the ground, protecting electrical equipment from damage.

Question: What are the types of losses in a transformer?
Answer: Transformer losses include core losses (hysteresis and eddy current) and copper losses due to winding resistance.

Question: Why are transformers rated in kVA and not in kW?
Answer: Because transformer losses depend on voltage and current, not on the power factor, which varies with load.

Question: What is the significance of earthing in electrical installations?
Answer: To ensure safety by providing a low-resistance path for fault current, preventing electric shock and equipment damage.

Question: What is the difference between MCCB and MCB?
Answer: MCCB handles higher current ratings and has adjustable trip settings, while MCB is used for lower currents with fixed trip settings.

Question: Why is a capacitor used in single-phase motors?
Answer: To create a phase shift and generate a rotating magnetic field for starting and running the motor efficiently.

Question: What is the role of a CT (Current Transformer) in power systems?
Answer: To step down high current to a measurable level for protection, metering, and monitoring purposes.

Question: Why are synchronous generators preferred in power plants?
Answer: Because they maintain constant speed and frequency, ensuring stable power generation.

Question: What is the purpose of a busbar in a substation?
Answer: To distribute power efficiently to multiple outgoing feeders and maintain system flexibility.

Question: What is the function of a surge arrester?

Answer: To protect electrical equipment from voltage spikes caused by lightning or switching surges.

Question: Why is double insulation used in portable electrical devices?
Answer: To enhance safety by providing two layers of protection against electric shock.

Question: What is the role of a ground fault relay?
Answer: To detect leakage currents to ground and trip the circuit to prevent hazards and equipment damage.

Question: What is the function of a tap changer in a transformer?
Answer: To regulate output voltage by adjusting the transformer winding ratio, either manually or automatically.

Question: What is the role of a PLC (Programmable Logic Controller) in industrial automation?
Answer: To control machinery and processes using programmable logic, enhancing flexibility and reliability.

Question: What is the function of a thermal overload relay?
Answer: To protect motors from overheating due to prolonged overload by sensing temperature rise and disconnecting the supply.

Question: Why is a generator excitation system important?
Answer: It controls the generator’s output voltage and reactive power by regulating the field current.

Question: Why is transformer oil testing important?
Answer: To assess insulation quality, detect contamination, and ensure reliable transformer operation.

Question: What is the purpose of a harmonic filter?
Answer: To reduce harmonic distortion caused by non-linear loads and improve power quality.

Question: What is the purpose of a load balancing system?
Answer: To distribute electrical load evenly across phases, improving efficiency and reducing overheating.

Question: What is the purpose of a cable tray system?
Answer: To support and organize electrical cables in industrial and commercial installations.

Question: Why is transformer oil used in power transformers?
Answer: To provide insulation and dissipate heat generated during operation.

Question: What is the purpose of a breather in a transformer?
Answer: To prevent moisture from entering the transformer oil by using silica gel to absorb humidity.

Question: What is the function of a conservator tank in a transformer?
Answer: To accommodate the expansion and contraction of transformer oil due to temperature changes.

Question: Why is a transformer not used for DC supply?
Answer: Because it requires changing magnetic fields to operate, which DC does not provide.

Question: What is the function of a Buchholz relay?
Answer: To detect internal faults by sensing gas accumulation and oil movement in the transformer.

Question: Why is a transformer core laminated?
Answer: To reduce eddy current losses and improve efficiency.

Question: What is the function of a temperature gauge (OTI & WTI) in a transformer?
Answer: To monitor oil or winding temperature and trigger alarms or trip circuits if overheating occurs.

Question: What is the function of a pressure relief device in a transformer?
Answer: To release excess pressure during internal faults, preventing explosion or oil leakage.

Question: What is the ideal power factor value?
Answer : The ideal power factor is 1.0 (unity), but practically, values above 0.95 are considered good.

Question: How does APFC detect power factor?
Answer: APFC uses CTs (Current Transformers) and PTs (Potential Transformers) to measure current and voltage, calculating the power factor.

Question: What happens if power factor is too low?
Answer: Low power factor leads to higher current flow, increased losses, and possible penalties from the utility company.

Question: What is an Automatic Power Factor Controller?
Answer: An APFC is a device that automatically switches capacitor banks to maintain the desired power factor in an electrical system.

Question: What are the components of an APFC panel?
Answer: Components include capacitor banks, contactors, relays, microcontroller or PLC, CTs, and protection devices.

Question: What is the role of detuned reactors in APFC panels?
Answer: Detuned reactors prevent harmonic resonance and protect capacitors from damage due to harmonics.

Question: How is capacitor bank sizing done in APFC panels?
Answer: Capacitor bank sizing is based on reactive power (KVAR) required to correct the power factor to the desired level.

Question- What is Multimeter ?

Answer- Multimeter is a measuring instrument which is use to measure various parameter like Voltage, current, resistance etc.

Question- How to measure voltage & Current by using Multimeter ?

Answer- By Selecting the multimeter knob on voltage & current ( appropriate range)

Question- How to check the motor winding ?

Answer- Continuity of coils short circuit between coils, coils to body and winding to earth.

Question- What is ammeter ?

Answer- To measure the current.

Question- What is voltmeter ?

Answer- To measure the voltage.

Question- What is multifunction meter ?

Answer- To measure the various electrical parameter, like- Voltage, resistance, capacitance etc.

Question: What is TOD metering in HT meters?
Answer: TOD (Time of Day) metering records energy usage during different time slots, helping in differential tariff billing.

Question- What is megger & it's purpose ?

Answer- To check the insulation between windings of motor /transformer & cable insulation.

Question- Please explain the formula for power ?

Answer- For single phase- V X I X Cos $ and for 3 phase power- 1.732 x V x I x Cos$

Question- What is MCB & reason of tripping ?

Answer- Miniature circuit breaker, due to short circuit /over current.

Question- What is ELCB/RCCB reason of tripping ?

Answer- Earth leakage circuit breaker , due to leakage current in the circuit.

Question- What is transformer ?

Answer- Transformer is a static device which transfer electrical energy from one circuit to another circuit without any change in frequency but change in voltage.

Question- What is CT & it's purpose ?

Answer- It is a instrumental transformer (Current transformer) to use measure the high current.

Question- What is PT & it's purpose ?

Answer It is a instrumental transformer (Potential transformer) to use measure the voltage.

Question- What is full form of ACB ?

Answer -Air circuit breaker

Question: What is the primary function of an ACB?
Answer: To protect electrical circuits from overload, short circuit and ground faults in low-voltage systems.

Question: What is the significance of the closing coil in a circuit breaker?
Answer: It energizes to close the breaker contacts and allow current flow.

Question: What is the role of the trip coil in a breaker?
Answer: It energizes to open the breaker contacts during fault conditions.

Question: What is the function of an undervoltage release in a breaker?
Answer: To trip the breaker when supply voltage drops below a preset level, protecting equipment.

Question: What is meant by “breaking capacity” of a breaker?
Answer: The maximum fault current the breaker can safely interrupt without damage.

Question: What is the difference between fixed and draw-out type ACBs?
Answer: Fixed ACBs are permanently installed, while draw-out ACBs can be removed for maintenance without disconnecting cables.

Question: What is the role of arc chutes in ACBs?
Answer: To cool and split the arc during interruption, aiding in arc extinction.

Question: Why is contact resistance measurement(CRM Test) important in breakers?
Answer: To detect wear or corrosion in contacts that may lead to overheating or failure.

Question: What is the function of a spring charging motor in breakers?
Answer: To charge the operating spring for automatic closing of the breaker.

Question: What is the role of a breaker interlock system?
Answer: To prevent unsafe operations like closing on fault or opening under load without proper sequence.

Question: Why is thermal imaging used on breakers/Panels?
Answer: To detect hotspots indicating loose connections, overloads, or deteriorating components.

Question- What is full form of VCB ?

Answer- Vacuum circuit breaker.

Question: Why is VCB preferred for medium-voltage applications?
Answer: Because vacuum interrupters provide excellent arc quenching and require minimal maintenance.

Question- Full form of LT Panel ?

Answer- Low tension Panel.

Question- Protection of LT Panel ?

Answer- Under voltage, Over voltage, short circuit, earth fault etc.

Question- Protection of HT Panel ?

Answer- Under voltage, Over voltage, short circuit, earth fault etc.

Question- Full form of HT Panel ?

Answer- High tension Panel

Question- What is the purpose of starter for electric motor ?

Answer- To protect the motor winding from high starting current & various faults.

Question- Basis types of Stator ?

Answer- DOL & Star Delta

Question- What is battery charger & purpose of use ?

Answer- Battery charger is used to charger the battery & provide DC supply to the panel.

Question- What UPS/Inverter ?

Answer- Uninterruptable power supply to use as backup power during power failure.

Question- Difference between AC & DC ?

Answer- Alternative current & Direct current.

Question- What Is frequency in India ?

Answer- 50HZ

Question- How much voltage in single phase ?

Answer- 220-240V

Question- How much voltage in three phase ?

Answer- 415-440V