Question

Higher values of ampere-conductors cannot be recommended for synchronous machines as it will cause :
A. Increase in copper loss leading to poor efficiency and temperature rise
B. Increase in synchronous reactance leading to poor inherent voltage regulation
C. Increase in stray load loss
D. Decrease in stray load loss
E. Decrease in synchronous reactance Choose the correct answer from the options given below :

• A. D and E only
• B. A, B and E only
• C. A, B and C only
• D. A, D and E only

Hint:

Excessive ampere-conductor loading in synchronous machines causes:
• higher copper loss,
• greater heating,
• increased synchronous reactance,
• poor voltage regulation,
• higher stray losses.

Answer 1

The Correct Option is C

Concept: Ampere-conductors in synchronous machines represent the total current-carrying capability of armature conductors. If ampere-conductors are excessively increased:
• copper loss increases,
• heating increases,
• synchronous reactance increases,
• voltage regulation deteriorates,
• stray losses rise. Hence practical design always limits ampere-conductor loading.

Step 1: Understanding statement \(A\). Statement \(A\): \[ \text{Increase in copper loss leading to poor efficiency and temperature rise} \] Copper loss is: \[ P_{cu}=I^2R \] Higher ampere-conductors imply higher armature current. Thus:
• copper loss increases,
• heating increases,
• efficiency decreases. Hence statement \(A\) is correct.

Step 2: Understanding statement \(B\). Statement \(B\): \[ \text{Increase in synchronous reactance leading to poor inherent voltage regulation} \] Large ampere-conductors increase armature reaction effects. This increases synchronous reactance: \[ X_s \] Higher synchronous reactance causes:
• larger voltage drop,
• poorer voltage regulation. Hence statement \(B\) is correct.

Step 3: Understanding statement \(C\). Statement \(C\): \[ \text{Increase in stray load loss} \] Higher current loading causes:
• leakage flux increase,
• eddy current effects,
• additional stray losses. Therefore stray load loss increases. Hence statement \(C\) is correct.

Step 4: Checking statement \(D\). Statement \(D\): \[ \text{Decrease in stray load loss} \] This is opposite to actual behavior. Higher current loading increases stray losses rather than decreasing them. Thus statement \(D\) is incorrect.

Step 5: Checking statement \(E\). Statement \(E\): \[ \text{Decrease in synchronous reactance} \] In practice synchronous reactance tends to increase with higher ampere-conductor loading. Hence statement \(E\) is incorrect.

Step 6: Selecting the correct option. Correct statements are: \[ A,\;B,\;C \] Hence the correct option is: \[ \boxed{(3)\; A,B,C\text{ only}} \]