MCQ Practice Test — Category 03
Electric Motor MCQ
Electric Motor MCQ : Induction Motor, DC Motor, Star-Delta — motor types, working aur troubleshooting. Gulf me motor knowledge must hai.
10 Questions (Page 1)
Easy-Hard Level
Hinglish Explanation
Attempted: 0/10
Correct: 0
Wrong: 0
Question 01Easy
3-Phase Induction Motor kaise start hota hai?
ABattery se
B3-phase supply se rotating magnetic field banta hai jo rotor ko ghumaata hai
CMechanical push se
DSingle phase se
✓ Sahi Jawab: B
3-phase supply stator me Rotating Magnetic Field (RMF) create karta hai. Ye RMF rotor me EMF induce karta hai, current flow hoti hai, aur rotor ghumne lagta hai. Ye Faraday’s law of electromagnetic induction hai. Gulf me mostly 3-phase induction motors use hote hain.
Question 02Medium
Motor ka Slip kya hota hai?
AMotor girna
BSynchronous speed se zyada speed
CSynchronous speed aur rotor speed ka fark
DMotor band hona
✓ Sahi Jawab: C
Slip = (Ns – Nr) / Ns × 100%. Ns = Synchronous speed, Nr = Rotor speed. Normal slip 2-5% hota hai. Zyada slip matlab motor overloaded hai ya problem hai. Full load pe slip badh jaata hai.
Question 03Easy
DOL Starter ka full form kya hai?
ADirect On Line
BDelayed On Load
CDirect Over Load
DDual On Line
✓ Sahi Jawab: A — Direct On Line
DOL = Direct On Line — motor directly full voltage pe start hota hai. 5.5kW tak ke motors ke liye use karte hain. Isse starting current 6-8 times FLC hoti hai. Gulf me KAHRAMAA rule: 5.5kW se upar DOL nahi — Star-Delta ya VFD mandatory. Star Delta guide padho.
Question 04Medium
Motor ki nameplate pe 15kW/20HP likha hai. Kaunsa value use karein cable sizing ke liye?
A20HP use karo
B15kW (shaft output) use karo, input power alag calculate karo
CDono same hain
DKoi bhi use karo
✓ Sahi Jawab: B
Nameplate pe 15kW = shaft output power hai. Input power = Output / efficiency. Agar efficiency 90% hai to input = 15/0.9 = 16.67kW. Cable sizing ke liye input current use karo. Motor Nameplate Calculator se sab ek saath nikalo.
Question 05Medium
Motor vibration ka sabse common karan kya hai?
AZyada voltage
BLow current
CWrong color cable
DBearing failure, misalignment, ya unbalanced load
✓ Sahi Jawab: D
Motor vibration ke common causes: Bearing failure (most common), misalignment (coupling ya belt), unbalanced load/rotor, loose foundation bolts, single phasing. Gulf me pumps aur fans pe ye zyada hota hai. Vibration meter se measure karo — 2.8 mm/s se zyada hone pe maintenance karo.
Question 06Medium
Single Phasing motor me kya hota hai?
AMotor overheats aur burn ho sakta hai
BMotor faster chalega
CKoi problem nahi
DMotor reverse chalega
✓ Sahi Jawab: A
Single phasing me ek phase missing hoti hai. Baaki 2 phases pe motor zyada current draw karta hai — overheating aur winding burn ho sakta hai. Overload relay single phasing detect karta hai. Gulf me bade motors pe phase failure relay mandatory hai. Overload relay properly set karo — 1.0x FLC.
Question 07Hard
4-pole motor 50Hz supply pe synchronous speed kya hogi?
A3000 RPM
B1000 RPM
C1500 RPM
D750 RPM
✓ Sahi Jawab: C — 1500 RPM
Ns = 120 × f / P = 120 × 50 / 4 = 1500 RPM. 2-pole = 3000 RPM, 4-pole = 1500 RPM, 6-pole = 1000 RPM, 8-pole = 750 RPM. Gulf me 50Hz frequency hai. Actual rotor speed thodi kam hogi slip ki wajah se — typically 1440-1480 RPM.
Question 08Medium
Overload relay kaise set karte hain?
AMaximum possible current pe
BMotor ke Full Load Current (FLC) pe
CMCB rating pe
DKoi bhi value pe
✓ Sahi Jawab: B — Motor FLC pe
Overload relay motor ke nameplate FLC pe set karte hain. FLC se 5-10% upar set karo for tolerance. Zyada set karne pe motor burn hoga, kam set karne pe nuisance tripping hogi. Motor Calculator se FLC nikal ke set karo.
Question 09Hard
Star-Delta starter me starting current DOL se kitna percent kam hota hai?
A50% kam
B25% kam
C75% kam
D66.7% kam (1/3 hota hai)
✓ Sahi Jawab: D — 66.7% kam
Star-Delta me starting current = DOL starting current / 3. Agar DOL pe 60A starting current hai to Star-Delta pe 20A (1/3) hogi. Torque bhi 1/3 ho jaata hai. Isliye Star-Delta unloaded ya light load motors pe use hota hai. Gulf projects me 5.5kW+ motors pe ye mandatory hai.
Question 10Hard
VFD ka main advantage kya hai Star-Delta ke muqable me?
AVariable speed control + smooth starting + energy saving
BSasta hota hai
CZyada current deta hai
DKoi advantage nahi
✓ Sahi Jawab: A
VFD ke main advantages: Variable speed control (pumps/fans me energy 50% tak save), smooth start (zero to full speed gradually), no current spike, fault protection built-in. Sidra Hospital aur Qatar University HVAC systems pe VFDs lage hain. Initial cost zyada hai lekin long-term energy saving huge hai.
VoltGuru.in — Electric Motor MCQ — Free for Gulf Electricians
Q1. मोटर की रेटिंग HP में क्यों होती है?
Ans: HP (Horse Power) मोटर की मैकेनिकल ताकत को दर्शाता है। 1 HP में 746 वॉट होते हैं।
Q2. मोटर ओवरहीट (Overheat) क्यों होती है?
Ans: ओवरलोड, खराब बेयरिंग, या लो वोल्टेज की वजह से मोटर ज्यादा करंट लेती है और गर्म होने लगती है।
Q3. स्टार-डेल्टा स्टार्टर का मुख्य काम क्या है?
Ans: यह मोटर को शुरू होते समय कम वोल्टेज देकर ‘स्टार्टिंग करंट’ को कंट्रोल करता है।
Q4. इंडक्शन मोटर में ‘रोटर’ और ‘स्टेटर’ क्या हैं?
Ans: स्टेटर मोटर का स्थिर (Fixed) हिस्सा है और रोटर वह हिस्सा है जो अंदर घूमता है।
Q5. थ्री-फेज मोटर ‘सिंगल फेजिंग’ होने पर क्यों जल जाती है?
Ans: अगर एक फेज कट जाए, तो बाकी दो फेज पर लोड बढ़ जाता है, जिससे वाइंडिंग जल सकती है।
