MCQ Practice Test — Category 12
VFD & PLC MCQ
Variable Frequency Drive, PLC basics, automation — Gulf me modern electrical systems ka gyan. Agar ye aata hai to salary double hoti hai.
10 Questions (Page 1)
Medium-Hard Level
Hinglish Explanation
Attempted: 0/10
Correct: 0
Wrong: 0
Question 01Easy
VFD ka full form kya hai aur kya karta hai?
AVery Fast Drive
BVariable Frequency Drive — motor ki speed control karta hai frequency change karke
CVoltage Frequency Device
DVariable Force Drive
✓ Sahi Jawab: B
VFD = Variable Frequency Drive. Motor speed = (120 × f) / P. Frequency change karne se speed change hoti hai. VFD AC supply ko DC me convert karta hai, phir adjustable frequency AC generate karta hai. Gulf me pumps, fans, HVAC sab pe VFD lagti hai — energy saving + speed control dono milti hai.
Question 02Easy
VFD me motor speed kaise control hoti hai?
AVoltage kam karke
BResistance badha karke
COutput frequency change karke (Hz badho = speed badhti hai)
DPoles change karke
✓ Sahi Jawab: C
VFD output frequency change karta hai. 50Hz = full speed (1500 RPM 4-pole). 25Hz = half speed (750 RPM). 60Hz = 20% overspeed. V/f ratio maintain karta hai constant flux ke liye. Isse motor efficiently aur smoothly speed change karta hai bina overheating ke.
Question 03Medium
Affinity Law ke hisaab se pump motor 50% speed pe kitni energy consume karega?
A12.5% (1/8th of full power)
B50%
C25%
D75%
✓ Sahi Jawab: A — 12.5%
Affinity Law (Cube Law): Power ∝ Speed³. 50% speed pe: Power = (0.5)³ = 0.125 = 12.5%. Matlab 50% speed pe sirf 12.5% energy! Ye VFD ka sabse bada advantage hai pumps aur fans me. Gulf me HVAC VFDs se 30-60% energy saving hoti hai. Sidra Hospital HVAC me ye directly apply hota hai.
Question 04Medium
VFD ke basic sections kaunse hain?
ASirf inverter
BMotor aur capacitor
CTransformer aur switch
DRectifier (AC to DC) + DC Bus + Inverter (DC to AC)
✓ Sahi Jawab: D
VFD ke 3 sections: (1) Rectifier — AC to DC convert karta hai (diode bridge). (2) DC Bus — capacitors se DC smooth karta hai. (3) Inverter — IGBTs se PWM technique se adjustable frequency AC generate karta hai. Gulf interview me ye structure zaroor puchha jaata hai.
Question 05Medium
PLC ka full form kya hai?
APower Load Controller
BProgrammable Logic Controller
CParallel Logic Computer
DProcess Load Control
✓ Sahi Jawab: B — Programmable Logic Controller
PLC = Programmable Logic Controller. Industrial computer hai jo inputs (sensors, switches) read karta hai, program execute karta hai, aur outputs (motors, valves, lights) control karta hai. Gulf me pumping stations, HVAC systems, fire alarm panels me PLC common hai. Siemens, Allen-Bradley, Schneider — popular brands hain.
Question 06Medium
VFD lagane pe motor cable me kya change karna chahiye?
AKoi change nahi
BThinner cable use karo
CShielded cable use karo — VFD se EMI/harmonics hoti hain
DDC cable use karo
✓ Sahi Jawab: C — Shielded Cable
VFD PWM switching se EMI (Electromagnetic Interference) aur harmonics generate karta hai. Ye other equipment ko disturb karta hai. Solution: Shielded cable (screened cable) use karo VFD se motor tak. Shield grounded karo. Cable length short rakhna bhi important hai. Gulf me VFD installations me shielded cable specification mandatory hoti hai.
Question 07Hard
VFD pe motor trip ho raha hai — fault code “OC” (Over Current) aa raha hai. Kya karna chahiye?
AAcceleration time badhao, load check karo, motor check karo, VFD current limit setting check karo
BVFD replace karo
CSupply voltage badhao
DKuch mat karo
✓ Sahi Jawab: A
OC fault troubleshooting: 1. Acceleration time badhao — agar ramp up bahut fast hai to inrush current spike aati hai. 2. Load check — mechanical jam, bearing failure? 3. Motor insulation megger test — winding fault? 4. VFD current limit parameter check karo — motor FLC ke hisaab se set karo. Gulf interview me systematic VFD troubleshooting puchha jaata hai.
Question 08Hard
Bypass contactor VFD ke saath kyun lagata hai?
ACost save karne ke liye
BVFD fail hone pe motor DOL pe seedha chalane ke liye — emergency operation
CSpeed double karne ke liye
DEnergy save karne ke liye
✓ Sahi Jawab: B
Bypass contactor emergency backup hai. VFD fault pe ya maintenance pe motor seedha DOL pe chalaya ja sakta hai. Critical applications (fire pump, hospital HVAC) me bypass mandatory hota hai. Bypass ON karne pe VFD disconnected hota hai — dono ek saath ON karna forbidden (interlock lagao). Sidra Hospital me sab critical pumps me bypass tha.
Question 09Hard
PLC me DI, DO, AI, AO kya hote hain?
ADifferent Interface options
BDisplay Items
CDrive Interface
DDI=Digital Input, DO=Digital Output, AI=Analog Input, AO=Analog Output
✓ Sahi Jawab: D
DI (Digital Input) = ON/OFF signals (switches, sensors, limit switches). DO (Digital Output) = ON/OFF commands (contactors, solenoids, lights). AI (Analog Input) = variable signals 4-20mA ya 0-10V (pressure sensor, temperature, flow). AO (Analog Output) = variable command (VFD speed reference, valve position). Gulf me basic PLC understanding zyada demand me hai.
Question 10Hard
VFD se RCCB (30mA) false trip karta hai — kya karna chahiye?
ARCCB remove karo
BVFD replace karo
C300mA RCCB use karo ya EMC filter lagao — VFD capacitive leakage current hoti hai
DKuch mat karo
✓ Sahi Jawab: C
VFD ke internal capacitors se capacitive leakage current hoti hai — ye 30mA RCCB ko false trip kara sakti hai. Solutions: (1) 300mA RCCB use karo (30mA ki jagah). (2) Type B RCCB use karo (DC fault components bhi detect karta hai). (3) EMC input filter lagao VFD ke pehle. RCCB hataana mat — safety bypass nahi karna hai kabhi.
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