السؤال الاول
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1- State the functions of circuit breaker..؟
Answer:
1- Protect cables against overloads and short circuits
2-Let the nominal current flow without problems.
3-Open and close a circuit under rated current.
4-Protect against insulation faults (with an integrated earth leakage device).
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السؤال الثاني
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2- What is more danger on the human body AC current or DC current & why? What is the effect of AC current on the human body?
Answer:
2-Let the nominal current flow without problems.
3-Open and close a circuit under rated current.
4-Protect against insulation faults (with an integrated earth leakage device).
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السؤال الثاني
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2- What is more danger on the human body AC current or DC current & why? What is the effect of AC current on the human body?
Answer:
* AC current is more danger than AC current because the human heart is affected more by fluctuation in
frequency (i.e sine wave of AC current) rather than DC current which is constant (frequency is zero).
frequency (i.e sine wave of AC current) rather than DC current which is constant (frequency is zero).
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السؤال الثالث
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3- In order to select the right circuit breaker. What are the Criteria’s of choice that should be followed?
Answer:
"Basic" Criteria:
Rating I, U, F, ...
Breaking capacity
Number of poles (grounding system).
Standards (IEC, UL, JIS, ...)
Type of loads to be protected (cable, bus-bar, generator, motor, direct current devices).
"Dependability" Criteria:
Earth leakage protection
Isolating function
Positive break indication
Front face double insulation
Locking
Interlocking
Limiting technology
"Continuity of Service" Criteria:
Selectivity
Draw-out possibility
Maintainability
"Performing" Criteria:
Cascading
Reverse feeding without de-rating
Field installable auxiliaries
"Comfort" Criteria:
Simple to install, easy to work with
Evolutive network (modular system)
Network monitoring, communication
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السؤال الرابع
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السؤال الخامس
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السؤال الثالث
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3- In order to select the right circuit breaker. What are the Criteria’s of choice that should be followed?
Answer:
"Basic" Criteria:
Rating I, U, F, ...
Breaking capacity
Number of poles (grounding system).
Standards (IEC, UL, JIS, ...)
Type of loads to be protected (cable, bus-bar, generator, motor, direct current devices).
"Dependability" Criteria:
Earth leakage protection
Isolating function
Positive break indication
Front face double insulation
Locking
Interlocking
Limiting technology
"Continuity of Service" Criteria:
Selectivity
Draw-out possibility
Maintainability
"Performing" Criteria:
Cascading
Reverse feeding without de-rating
Field installable auxiliaries
"Comfort" Criteria:
Simple to install, easy to work with
Evolutive network (modular system)
Network monitoring, communication
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السؤال الرابع
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4- What are the Benefits of improving Power Factor?
Answer:
- Reduce Utility Cost.
- Optimize Equipment Utilization.
- Improve Reliability:
- Avoids the overload of the network.
- Decreases Voltage Drops.
- Masters polluted networks level of harmonics and avoids resonance cases.
- Reduce Utility Cost.
- Optimize Equipment Utilization.
- Improve Reliability:
- Avoids the overload of the network.
- Decreases Voltage Drops.
- Masters polluted networks level of harmonics and avoids resonance cases.
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5- How the penalty on power factor is calculated?
Answer:
- For 0.9 <cos (φ) < 0.92 ------- No penalty No Bonus.
- For cos (φ)> 0.92 ------- Bonus. (For a maximum of 0.95).
- For cos (φ) < 0.9 ------- Penalty (The company will be charged for reactive power.).
- For 0.9 <cos (φ) < 0.92 ------- No penalty No Bonus.
- For cos (φ)> 0.92 ------- Bonus. (For a maximum of 0.95).
- For cos (φ) < 0.9 ------- Penalty (The company will be charged for reactive power.).
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السؤال السادس
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6- What’s the difference between SWA & STA, which is more expensive, which one can withstand more
mechanical load, is the 2 types are accepted by BS & IEC?
mechanical load, is the 2 types are accepted by BS & IEC?
excuse me could u tell me the reference of these answers specially Q no. 2 ...
ردحذفand thank you for your effort
can you tell us more about q#3????
ردحذف