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Questions and Answers
What has allowed for a reduction in alternator size without decreasing output power?
What has allowed for a reduction in alternator size without decreasing output power?
What is the term used for the three electrical subassemblies that make up the generator portion of the IDG?
What is the term used for the three electrical subassemblies that make up the generator portion of the IDG?
What is the normal operating temperature for the cooling oil in most constant-speed drives?
What is the normal operating temperature for the cooling oil in most constant-speed drives?
What mechanism is typically activated in most constant-speed drive units in case of an in-flight oil loss or an over temperature condition?
What mechanism is typically activated in most constant-speed drive units in case of an in-flight oil loss or an over temperature condition?
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What voltage and frequency does the IDG on the Boeing 747 produce for aircraft electrical systems?
What voltage and frequency does the IDG on the Boeing 747 produce for aircraft electrical systems?
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Why is the term 'generator' still used even though brushless alternators are in use?
Why is the term 'generator' still used even though brushless alternators are in use?
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What is the part of the relay attracted by the electromagnet to close the contact points called?
What is the part of the relay attracted by the electromagnet to close the contact points called?
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How does the movement of the armature affect the contact points in a relay?
How does the movement of the armature affect the contact points in a relay?
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What is the function of the main contacts in a Bus Tie Breaker (BTB)?
What is the function of the main contacts in a Bus Tie Breaker (BTB)?
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Which component in a Bus Tie Breaker (BTB) remains in a closed position even after power is removed from the close coil?
Which component in a Bus Tie Breaker (BTB) remains in a closed position even after power is removed from the close coil?
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What causes the main contacts in a Bus Tie Breaker (BTB) to open?
What causes the main contacts in a Bus Tie Breaker (BTB) to open?
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What happens to the auxiliary contacts in a Bus Tie Breaker (BTB) when the main contacts are mechanically locked in a closed position?
What happens to the auxiliary contacts in a Bus Tie Breaker (BTB) when the main contacts are mechanically locked in a closed position?
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What is the purpose of a freewheeling diode installed across the coil of a solenoid?
What is the purpose of a freewheeling diode installed across the coil of a solenoid?
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Why would voltage spikes be harmful in a system without a freewheeling diode?
Why would voltage spikes be harmful in a system without a freewheeling diode?
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How does a freewheeling diode prevent damage to electronic components when the master switch is opened?
How does a freewheeling diode prevent damage to electronic components when the master switch is opened?
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What is the function of a battery in an aircraft system?
What is the function of a battery in an aircraft system?
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Why do some aircraft isolate the battery when external DC power is applied?
Why do some aircraft isolate the battery when external DC power is applied?
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What feature do aircraft without battery isolation incorporate to prevent thermal runaway?
What feature do aircraft without battery isolation incorporate to prevent thermal runaway?
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Why are circuit breakers and fuses placed close to the power supply?
Why are circuit breakers and fuses placed close to the power supply?
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What does a tripped circuit breaker indicate?
What does a tripped circuit breaker indicate?
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What does a small white band show on a tripped circuit breaker?
What does a small white band show on a tripped circuit breaker?
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What is a trip-free circuit breaker characterized by?
What is a trip-free circuit breaker characterized by?
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When are non-trip-free circuit breakers typically used?
When are non-trip-free circuit breakers typically used?
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What distinguishes non-trip-free circuit breakers from trip-free ones?
What distinguishes non-trip-free circuit breakers from trip-free ones?
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What would happen if the cut-out relay or line contactor fails to open under reverse current conditions?
What would happen if the cut-out relay or line contactor fails to open under reverse current conditions?
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What is a potential consequence of overvoltage in an aircraft system?
What is a potential consequence of overvoltage in an aircraft system?
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How is overvoltage protection typically achieved in aircraft systems?
How is overvoltage protection typically achieved in aircraft systems?
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What effect does reverse current have on a generator under certain conditions?
What effect does reverse current have on a generator under certain conditions?
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Why is it important for a circuit breaker to release its contacts when reverse current reaches a certain value?
Why is it important for a circuit breaker to release its contacts when reverse current reaches a certain value?
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What is the purpose of a latching mechanism in an overvoltage relay?
What is the purpose of a latching mechanism in an overvoltage relay?
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Study Notes
Alternator and Generator Design
- Advances in materials and technology have facilitated a reduction in alternator size without sacrificing output power.
- The generator portion of the Integrated Drive Generator (IDG) consists of three electrical subassemblies: the main generator, the exciter, and the rotating rectifier.
Operating Conditions and Mechanisms
- Most constant-speed drives operate cooling oil at a standard temperature, typically around 80-100 degrees Celsius.
- In-flight oil loss or overtemperature conditions trigger an automatic deactivation mechanism in constant-speed drive units to protect the system.
IDG Specifications
- The IDG on the Boeing 747 produces 115V AC at a frequency of 400Hz for aircraft electrical systems.
- The term "generator" persists due to historical usage despite the prevalence of modern brushless alternators.
Relay Operation
- The part of the relay attracted by the electromagnet to close contact points is known as the armature.
- The armature's movement directly affects the contact points, allowing or interrupting electrical flow.
Bus Tie Breaker (BTB) Functionality
- The main contacts in a Bus Tie Breaker (BTB) provide a connection between busbars, facilitating power distribution.
- A mechanical latching mechanism ensures that certain components within a BTB remain closed even after power is removed from the closing coil.
- Main contacts open due to overload or fault conditions, ensuring safety and system integrity.
Auxiliary Contacts and Protection Features
- When the main contacts of a BTB are mechanically locked closed, the auxiliary contacts retain their function by reflecting the status of the main contacts.
- A freewheeling diode installed across a solenoid coil protects electronic components by absorbing voltage spikes that occur when the coil is deactivated.
Voltage Spike Protection
- Without a freewheeling diode, voltage spikes can cause detrimental effects, potentially damaging sensitive electronic components.
- When the master switch is opened, the freewheeling diode channels transient currents away, preventing harm to the circuit.
Battery System in Aircraft
- In aircraft systems, the battery serves as a critical electrical power source, especially during engine start-up phases.
- Some aircraft isolate the battery when external DC power is supplied to prevent potential overload or damage.
- Aircraft without battery isolation may include mechanisms to detect thermal runaway, ensuring battery integrity.
Circuit Protection
- Circuit breakers and fuses are strategically placed close to power supplies to enhance safety and minimize the risk of damage from faults.
- A tripped circuit breaker signifies a fault condition or overload occurred, disconnecting power to prevent further issues.
- A small white band indicates a tripped circuit breaker, serving as a visual alert for maintenance personnel.
Circuit Breaker Functionality
- Trip-free circuit breakers can be reset manually even if the circuit is still under fault, providing operational flexibility.
- Non-trip-free circuit breakers must remain tripped under fault conditions and cannot be reset until the fault is cleared.
- Should a cut-out relay or line contactor fail to open during reverse current conditions, it can lead to serious system failures or damage.
Overvoltage Considerations
- Overvoltage in aircraft systems can lead to equipment failure and safety hazards.
- Protection against overvoltage is achieved through dedicated circuit protection devices like overvoltage relays.
- Reverse current can create issues for generators; thus, circuit breakers must release contacts when excessive reverse current occurs for operational safety.
Latching Mechanisms
- The latching mechanism in an overvoltage relay ensures that once activated due to overvoltage detection, it prevents re-energization until manually reset, safeguarding the system.
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Description
Learn about the importance and function of a freewheeling diode in solenoids to prevent voltage spikes and damage to electronic components. Understand how the diode allows the induced EMF from a collapsing coil to feed back into itself effectively.
