DC मशीनों में कम्यूटेशन के संबंध में निम्नलिखित कथनों पर विचार कीजिए:
1. कम्यूटेशन वह प्रक्रिया है जिसमें आर्मेचर चालकों का प्रत्यावर्ती करंट टर्मिनलों पर दिष्ट करंट में बदलता है।
2. खराब कम्यूटेशन से ब्रशों पर स्पार्किंग होती है और कम्यूटेटर सतह क्षतिग्रस्त हो सकती है।
3. ब्रश शिफ्टिंग और इंटरपोल का उपयोग कम्यूटेशन प्रदर्शन सुधारने में मदद करता है।
4. DC मशीनों के कुशल और स्पार्क-रहित संचालन के लिए उचित कम्यूटेशन आवश्यक है।
उपरोक्त में से कौन-सा/से कथन सही है/हैं?
उत्तर और चरणबद्ध हल
कम्यूटेशन अंतराल में कुंडली ब्रश द्वारा शॉर्ट होती है और उसका करंट +I से −I में उलटना चाहिए। इंटरपोल मुख्य पोलों के बीच लगाए जाते हैं ताकि उनका फ्लक्स आवश्यक ध्रुवता का कम्यूटेटिंग emf दे। मुख्य संबंध: करंट उलटने के दौरान रिएक्टेंस वोल्टेज L·di/dt से जुड़ा है।
परीक्षा फोकस: कम्यूटेशन = करंट उलटना; इंटरपोल = स्पार्क-रहित कम्यूटेशन।
विस्तृत हल (मूल भाषा में)
Statement-wise Verification
- Statement 1 - Correct.
Commutation is the process by which alternating current in armature conductors is converted into direct current at the terminals.
The armature conductors generate/experience alternating current internally, while the commutator mechanically rectifies the terminal current/voltage to unidirectional form. - Statement 2 - Correct.
Poor commutation results in sparking at the brushes and can damage the commutator surface.
Delayed or incomplete current reversal creates brush sparking and damages brush/commutator surfaces. - Statement 3 - Correct.
Brush shifting and use of interpoles help in improving commutation performance.
Brush shifting can assist in older/basic arrangements and interpoles provide a commutating emf that counteracts reactance voltage. - Statement 4 - Correct.
Proper commutation is essential for efficient and sparkless operation of DC machines.
Good commutation is essential for efficient, low-maintenance and sparkless DC-machine operation.
Core Concept
During the short commutation interval, a coil is effectively short-circuited by the brush and its current must reverse from +I to −I. Coil inductance resists this reversal and creates reactance voltage. Interpoles are placed between main poles and connected so their flux produces a commutating emf of the required polarity.
Formula / Key Relationship
Reactance voltage is associated with L·di/dt during current reversal; ideal commutation completes the reversal within the brush short-circuit time.
Step-by-Step Check
Each statement matches the physical commutation process and standard corrective methods. Therefore “All of the above” is correct.
Why the Other Options Are Wrong
Option B is incorrect because it omits correct statement(s) 2, 4. Option C is incorrect because it omits correct statement(s) 1, 3. Option D is incorrect because it omits correct statement(s) 3, 4.
Answer-Key Verification Note
The uploaded provisional key marks C . After independent technical verification, the defensible answer is A . This discrepancy is stated explicitly rather than silently copying the provisional key.
Exam Shortcut / Approach
Keywords: commutation = current reversal; interpole = sparkless commutation.
Common Mistake
Confusing the commutator with a source of DC; it is a mechanical switching/rectifying element.
Quick Revision
Sparkless Commutation in DC Machines is linked with Commutation, DC Machines and Electrical Machines. Keywords: commutation = current reversal; interpole = sparkless commutation.
Consider the following statements regarding Commutation in DC Machines:
1. Commutation is the process by which alternating current in armature conductors is converted into direct current at the terminals.
2. Poor commutation results in sparking at the brushes and can damage the commutator surface.
3. Brush shifting and use of interpoles help in improving commutation performance.
4. Proper commutation is essential for efficient and sparkless operation of DC machines.
Which of the above statements is/are correct?
Answer & step-by-step solution
During the short commutation interval, a coil is effectively short-circuited by the brush and its current must reverse from +I to −I. Interpoles are placed between main poles and connected so their flux produces a commutating emf of the required polarity. Key relation: Reactance voltage is associated with L·di/dt during current reversal; ideal commutation completes the reversal within the brush short-circuit time.
Exam focus: Keywords: commutation = current reversal; interpole = sparkless commutation. Common trap: Confusing the commutator with a source of DC; it is a mechanical switching/rectifying element.
Statement-wise Verification
- Statement 1 - Correct.
Commutation is the process by which alternating current in armature conductors is converted into direct current at the terminals.
The armature conductors generate/experience alternating current internally, while the commutator mechanically rectifies the terminal current/voltage to unidirectional form. - Statement 2 - Correct.
Poor commutation results in sparking at the brushes and can damage the commutator surface.
Delayed or incomplete current reversal creates brush sparking and damages brush/commutator surfaces. - Statement 3 - Correct.
Brush shifting and use of interpoles help in improving commutation performance.
Brush shifting can assist in older/basic arrangements and interpoles provide a commutating emf that counteracts reactance voltage. - Statement 4 - Correct.
Proper commutation is essential for efficient and sparkless operation of DC machines.
Good commutation is essential for efficient, low-maintenance and sparkless DC-machine operation.
Core Concept
During the short commutation interval, a coil is effectively short-circuited by the brush and its current must reverse from +I to −I. Coil inductance resists this reversal and creates reactance voltage. Interpoles are placed between main poles and connected so their flux produces a commutating emf of the required polarity.
Formula / Key Relationship
Reactance voltage is associated with L·di/dt during current reversal; ideal commutation completes the reversal within the brush short-circuit time.
Step-by-Step Check
Each statement matches the physical commutation process and standard corrective methods. Therefore “All of the above” is correct.
Why the Other Options Are Wrong
Option B is incorrect because it omits correct statement(s) 2, 4. Option C is incorrect because it omits correct statement(s) 1, 3. Option D is incorrect because it omits correct statement(s) 3, 4.
Answer-Key Verification Note
The uploaded provisional key marks C . After independent technical verification, the defensible answer is A . This discrepancy is stated explicitly rather than silently copying the provisional key.
Exam Shortcut / Approach
Keywords: commutation = current reversal; interpole = sparkless commutation.
Common Mistake
Confusing the commutator with a source of DC; it is a mechanical switching/rectifying element.
Quick Revision
Sparkless Commutation in DC Machines is linked with Commutation, DC Machines and Electrical Machines. Keywords: commutation = current reversal; interpole = sparkless commutation.
DC મશીનોમાં કમ્યુટેશન સંબંધિત નીચેના વિધાનો ધ્યાનમાં લો:
1. કમ્યુટેશન એ પ્રક્રિયા છે જેમાં આર્મેચર વાહકોનો પ્રત્યાવર્તી કરંટ ટર્મિનલ પર દિષ્ટ કરંટમાં ફેરવાય છે.
2. ખરાબ કમ્યુટેશનથી બ્રશ પર સ્પાર્કિંગ થાય છે અને કમ્યુટેટરની સપાટીને નુકસાન થઈ શકે છે.
3. બ્રશ શિફ્ટિંગ અને ઇન્ટરપોલનો ઉપયોગ કમ્યુટેશનની કામગીરી સુધારવામાં મદદ કરે છે.
4. DC મશીનોની કાર્યક્ષમ અને સ્પાર્ક-રહિત કામગીરી માટે યોગ્ય કમ્યુટેશન જરૂરી છે.
ઉપરોક્તમાંથી કયું/કયા વિધાન સાચું/સાચા છે?
જવાબ અને પગલાવાર ઉકેલ
કમ્યુટેશન સમયગાળામાં ગૂંચળું બ્રશ દ્વારા શોર્ટ થાય છે અને તેનો કરંટ +I થી −I માં ઉલટાવો જોઈએ. ઇન્ટરપોલ મુખ્ય પોલ વચ્ચે મૂકાય છે જેથી તેમનું ફ્લક્સ જરૂરી ધ્રુવતાનું કમ્યુટેટિંગ emf આપે. મુખ્ય સંબંધ: કરંટ ઉલટાવા દરમિયાન રિએક્ટન્સ વોલ્ટેજ L·di/dt સાથે જોડાયેલ છે.
પરીક્ષા મુદ્દો: કમ્યુટેશન = કરંટ ઉલટાવવો; ઇન્ટરપોલ = સ્પાર્ક-રહિત કમ્યુટેશન.
વિગતવાર ઉકેલ (મૂળ ભાષામાં)
Statement-wise Verification
- Statement 1 - Correct.
Commutation is the process by which alternating current in armature conductors is converted into direct current at the terminals.
The armature conductors generate/experience alternating current internally, while the commutator mechanically rectifies the terminal current/voltage to unidirectional form. - Statement 2 - Correct.
Poor commutation results in sparking at the brushes and can damage the commutator surface.
Delayed or incomplete current reversal creates brush sparking and damages brush/commutator surfaces. - Statement 3 - Correct.
Brush shifting and use of interpoles help in improving commutation performance.
Brush shifting can assist in older/basic arrangements and interpoles provide a commutating emf that counteracts reactance voltage. - Statement 4 - Correct.
Proper commutation is essential for efficient and sparkless operation of DC machines.
Good commutation is essential for efficient, low-maintenance and sparkless DC-machine operation.
Core Concept
During the short commutation interval, a coil is effectively short-circuited by the brush and its current must reverse from +I to −I. Coil inductance resists this reversal and creates reactance voltage. Interpoles are placed between main poles and connected so their flux produces a commutating emf of the required polarity.
Formula / Key Relationship
Reactance voltage is associated with L·di/dt during current reversal; ideal commutation completes the reversal within the brush short-circuit time.
Step-by-Step Check
Each statement matches the physical commutation process and standard corrective methods. Therefore “All of the above” is correct.
Why the Other Options Are Wrong
Option B is incorrect because it omits correct statement(s) 2, 4. Option C is incorrect because it omits correct statement(s) 1, 3. Option D is incorrect because it omits correct statement(s) 3, 4.
Answer-Key Verification Note
The uploaded provisional key marks C . After independent technical verification, the defensible answer is A . This discrepancy is stated explicitly rather than silently copying the provisional key.
Exam Shortcut / Approach
Keywords: commutation = current reversal; interpole = sparkless commutation.
Common Mistake
Confusing the commutator with a source of DC; it is a mechanical switching/rectifying element.
Quick Revision
Sparkless Commutation in DC Machines is linked with Commutation, DC Machines and Electrical Machines. Keywords: commutation = current reversal; interpole = sparkless commutation.
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