Freewheeling Diode in Solenoids

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.