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Questions and Answers
What is the main reason shunts should be replaced as soon as possible?
What is the main reason shunts should be replaced as soon as possible?
What happens to copper strands in a shunt when the terminals overheat?
What happens to copper strands in a shunt when the terminals overheat?
What are contact tips primarily made of?
What are contact tips primarily made of?
What condition do normally open interlocks indicate when the main contacts are closed?
What condition do normally open interlocks indicate when the main contacts are closed?
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What type of contactor is preferred for heavy current traction circuits?
What type of contactor is preferred for heavy current traction circuits?
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In what situation is an electromagnetic contactor NOT typically used?
In what situation is an electromagnetic contactor NOT typically used?
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What material is commonly used for the piston packing in air operated contactors?
What material is commonly used for the piston packing in air operated contactors?
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What happens in the unsaturated region of the magnetisation curve?
What happens in the unsaturated region of the magnetisation curve?
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Which of the following correctly describes the coercive force?
Which of the following correctly describes the coercive force?
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What characterizes the saturation region of the magnetisation curve?
What characterizes the saturation region of the magnetisation curve?
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What does the area within the hysteresis loop represent?
What does the area within the hysteresis loop represent?
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How does heat treatment affect the magnetisation curve?
How does heat treatment affect the magnetisation curve?
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What is one of the primary functions of the lubricant used in air operated contactors?
What is one of the primary functions of the lubricant used in air operated contactors?
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What happens to the operation of contactors if the cylinder walls become sticky?
What happens to the operation of contactors if the cylinder walls become sticky?
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Which pressure is typically required for the normal operation of air operated contactors?
Which pressure is typically required for the normal operation of air operated contactors?
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How does the magnet valve affect the flow of air to the piston?
How does the magnet valve affect the flow of air to the piston?
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What is a common issue that can occur with the ground valve seat of a magnet valve?
What is a common issue that can occur with the ground valve seat of a magnet valve?
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What component is used to minimize the arc created when the contactor opens a circuit?
What component is used to minimize the arc created when the contactor opens a circuit?
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What role does the return spring play in the operation of a contactor?
What role does the return spring play in the operation of a contactor?
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What effect does cutting off the current through the operating coil have on the magnet valve?
What effect does cutting off the current through the operating coil have on the magnet valve?
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What characteristic do contactor tips possess to aid in their operation?
What characteristic do contactor tips possess to aid in their operation?
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What primarily influences the capacitance of a capacitor?
What primarily influences the capacitance of a capacitor?
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Which of the following is a type of fixed capacitor?
Which of the following is a type of fixed capacitor?
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Which type of capacitor is commonly used to prevent burning flash in relay contacts?
Which type of capacitor is commonly used to prevent burning flash in relay contacts?
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What does the breakdown voltage of a dielectric refer to?
What does the breakdown voltage of a dielectric refer to?
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What happens to a capacitor when connected to a DC voltage?
What happens to a capacitor when connected to a DC voltage?
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In the context of magnetism, what is true about electron spin within an atom?
In the context of magnetism, what is true about electron spin within an atom?
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Which type of capacitor allows for variable capacitance based on construction material?
Which type of capacitor allows for variable capacitance based on construction material?
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What is the commonly used smaller unit of capacitance in practical applications?
What is the commonly used smaller unit of capacitance in practical applications?
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Which of the following materials is not listed as a dielectric type for fixed capacitors?
Which of the following materials is not listed as a dielectric type for fixed capacitors?
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What effect does increasing the thickness of the dielectric have on a capacitor rated for higher voltage?
What effect does increasing the thickness of the dielectric have on a capacitor rated for higher voltage?
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What is the product of the number of turns of a coil and the current flowing through the coil called?
What is the product of the number of turns of a coil and the current flowing through the coil called?
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What does the symbol mmf stand for?
What does the symbol mmf stand for?
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How is permeability (μ) defined?
How is permeability (μ) defined?
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If a coil produces 1000 lines of flux in air and 6000 lines with another material, what is the permeability of that material?
If a coil produces 1000 lines of flux in air and 6000 lines with another material, what is the permeability of that material?
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What is reluctance in magnetic circuits analogous to in electric circuits?
What is reluctance in magnetic circuits analogous to in electric circuits?
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What happens to the flux density at very low magnetizing forces according to the B-H curve?
What happens to the flux density at very low magnetizing forces according to the B-H curve?
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What occurs beyond 5 ampere turns per inch on the B-H curve?
What occurs beyond 5 ampere turns per inch on the B-H curve?
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What does the term 'saturated' refer to in the context of magnetic materials?
What does the term 'saturated' refer to in the context of magnetic materials?
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What is the relationship between flux density (B) and magnetic force (H)?
What is the relationship between flux density (B) and magnetic force (H)?
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What indicates that a material has high permeability?
What indicates that a material has high permeability?
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What primarily defines the function of a relay in an electrical circuit?
What primarily defines the function of a relay in an electrical circuit?
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Which component is directly responsible for closing the contact tips in an electromagnetic contactor?
Which component is directly responsible for closing the contact tips in an electromagnetic contactor?
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What is a significant risk associated with the wear of the knife edge on the armature of a contactor?
What is a significant risk associated with the wear of the knife edge on the armature of a contactor?
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What is the consequence of an arc striking the shunt in a contactor?
What is the consequence of an arc striking the shunt in a contactor?
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In what manner do relays typically indicate their de-energized position in circuit diagrams?
In what manner do relays typically indicate their de-energized position in circuit diagrams?
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What is a common characteristic of contactors as compared to relays?
What is a common characteristic of contactors as compared to relays?
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What factor influences the operational lifespan of an electromagnetic contactor's shunt?
What factor influences the operational lifespan of an electromagnetic contactor's shunt?
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How does the presence of DC current in the control winding affect the operation of the magnetic amplifier?
How does the presence of DC current in the control winding affect the operation of the magnetic amplifier?
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What is the mathematical expression for impedance in an AC circuit involving resistance and inductive reactance?
What is the mathematical expression for impedance in an AC circuit involving resistance and inductive reactance?
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What happens to inductive reactance as the core saturates due to the control current?
What happens to inductive reactance as the core saturates due to the control current?
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According to Faraday's Law, what is induced in a circuit when there is a change in flux?
According to Faraday's Law, what is induced in a circuit when there is a change in flux?
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What is a direct consequence of the alternating current varying from maximum to minimum in a load winding?
What is a direct consequence of the alternating current varying from maximum to minimum in a load winding?
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Which function of the lubricant in air operated contactors is essential for ensuring an airtight seal?
Which function of the lubricant in air operated contactors is essential for ensuring an airtight seal?
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What happens to the contact tips when the current is cut off from the magnet valve?
What happens to the contact tips when the current is cut off from the magnet valve?
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What is a potential consequence of having a bent or sticky valve stem in a magnet valve?
What is a potential consequence of having a bent or sticky valve stem in a magnet valve?
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How does the blow out coil function to protect the contact tips?
How does the blow out coil function to protect the contact tips?
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What is indicated by a hissing sound coming from a magnet valve?
What is indicated by a hissing sound coming from a magnet valve?
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Which factor can lead to sluggish operation of air operated contactors?
Which factor can lead to sluggish operation of air operated contactors?
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What role does the current flowing through the operating coil of a magnet valve serve?
What role does the current flowing through the operating coil of a magnet valve serve?
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What is a critical factor that the blow out coil helps to manage when a contactor opens?
What is a critical factor that the blow out coil helps to manage when a contactor opens?
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How does air pressure assist in the normal operating function of air operated contactors?
How does air pressure assist in the normal operating function of air operated contactors?
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What determines whether a material is considered magnetic or non-magnetic?
What determines whether a material is considered magnetic or non-magnetic?
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What occurs when an external force aligns the domains of magnetic materials?
What occurs when an external force aligns the domains of magnetic materials?
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Which of the following statements correctly describes a 'domain' in magnetic materials?
Which of the following statements correctly describes a 'domain' in magnetic materials?
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How is flux density (B) defined mathematically?
How is flux density (B) defined mathematically?
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What does it mean for a magnetic material to be 'saturated'?
What does it mean for a magnetic material to be 'saturated'?
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Which term describes the force required to create a flow of magnetic flux in a material?
Which term describes the force required to create a flow of magnetic flux in a material?
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What effect does the alignment of electron spins have on the magnetic properties of a material?
What effect does the alignment of electron spins have on the magnetic properties of a material?
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Which of the following best describes the internal arrangement of domains in a non-magnetic material?
Which of the following best describes the internal arrangement of domains in a non-magnetic material?
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What is the significance of 'lines of flux' within a magnetic field?
What is the significance of 'lines of flux' within a magnetic field?
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What role does the magnetic flux unit 'Maxwell' play in magnetism?
What role does the magnetic flux unit 'Maxwell' play in magnetism?
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What is represented by the symbol mmf in the context of magnetism?
What is represented by the symbol mmf in the context of magnetism?
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How is the permeability of a substance mathematically defined?
How is the permeability of a substance mathematically defined?
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In the magnetic circuit analogy, what does reluctance correspond to in electrical circuits?
In the magnetic circuit analogy, what does reluctance correspond to in electrical circuits?
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What does the B-H curve indicate at very low values of magnetizing force?
What does the B-H curve indicate at very low values of magnetizing force?
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What characterizes the linear region of the B-H curve between 2 and 4 ampere turns per inch?
What characterizes the linear region of the B-H curve between 2 and 4 ampere turns per inch?
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If a material shows increased flux density when subjected to a magnetizing current, what may this suggest about its permeability?
If a material shows increased flux density when subjected to a magnetizing current, what may this suggest about its permeability?
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When a material reaches saturation, what does this signify regarding its magnetic domains?
When a material reaches saturation, what does this signify regarding its magnetic domains?
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What does the term 'ferromagnetic' materials refer to in terms of permeability?
What does the term 'ferromagnetic' materials refer to in terms of permeability?
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What effect does an increase in magnetizing force have on an ideal magnetic material's saturation point?
What effect does an increase in magnetizing force have on an ideal magnetic material's saturation point?
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In what scenario does the flux density stop increasing, despite increases in magnetizing force?
In what scenario does the flux density stop increasing, despite increases in magnetizing force?
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Study Notes
Relays
- A relay is a switch operated by an electromagnet, not manually.
- It can open or close one or more circuits when energized.
- Used when the operation of one circuit depends on another.
- Can be calibrated to operate at specific current values.
- A relay is represented in a circuit diagram as a coil and a set of contacts.
- When the operating coil is energized, a normally open contact closes, and a normally closed contact opens.
- Circuit diagrams show relays in their de-energized state.
Contactors
- Contactors are heavy-duty switches operated by relays or other switches.
- They fall into two main categories: electromagnetic (EM) and electro-pneumatic (EP).
- Electromagnetic contactors are operated by electricity.
- When energized, the current flows through the operating coil; the coil becomes a magnet, and the armature is pulled toward the core, closing the contacts.
- The armature spring returns the armature to its original position when the current is stopped, opening the contacts.
- The knife-edge on the armature may wear out, causing faulty operation.
- A shunt, made of very thin copper wire, is a flexible lead that improves operation but can be easily damaged through misdirected arcs.
Contact Tips
- Contact tips are the parts that make contact to complete the circuit.
- They can wear out mechanically or due to electrical burning.
- They are usually made of copper and bolted into place.
Interlocks
- Small contact fingers that operate simultaneously with the main contacts.
- Typically connected to a low-voltage or battery circuit.
- Used for signaling when the main contacts operate.
- Normally open or normally closed types.
- Usually have silver contacts to reduce electrical resistance, common in low voltage circuits.
Air Operated Contactors
- Commonly used in heavy current traction circuits.
- Contain a piston, piston rod, spring, and cylinder.
- Flexible piston packing (often rubber or leather).
- Piston rod moves a contact tip, "movable tip."
- The cylinder is smooth for easy piston movement.
- Lubrication is crucial to reduce wear and create an airtight seal.
- Operated by compressed air at 70 psi (5 kg/cm²).
- Air enters the cylinder, the spring forces the piston back when the compressed air stops flowing, opening the contact tips.
Magnetic Valves
- Used to control air flow to the piston in air-operated contactors.
- Position determined electrically, operated by a remotely controlled coil.
- One position admits air to the cylinder, the other cuts off the air supply for exhaust.
- Require minimal maintenance but should be checked for leaks or bent/sticky stems.
Switches
- Devices used to make or break electrical current.
- Exist in varying sizes depending on the application.
- A common example is turning on/off a light, switching low-current circuits.
- Can also carry heavy currents.
- Switch design includes a hinged blade attached to terminals of a switch, connected to one terminal portion, and a switch base to the other.
Capacitors
- Components that oppose changes in voltage.
- Made of two conductors separated by an insulator, often thin plates separated by an insulator (dielectric).
- Measured in farads (F), microfarads (µF), or picofarads (pF).
- Capacitance depends on the plate area, dielectric constant, and dielectric thickness.
Magnetic Amplifiers
- Devices that use magnetism to regulate or control the flow of current to the load.
- Their operation is based on the magnetic properties of materials (especially iron)
- The domains in magnetic materials can be controlled/affected by external magnetic forces causing an increase or decrease of the flux density in the material.
- This can alter the inductive reactance of the material, influencing current flow.
Additional Notes
- The text includes figures and diagrams in describing some component parts.
- Additional details and specifications vary depending on the application, but the core components involved are similar.
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Description
This quiz covers the fundamentals of relays and contactors, including their operation and applications in electrical circuits. Learn about how relays are controlled by electromagnets and how contactors function as heavy-duty switches. Test your knowledge on their circuit representations and energizing mechanisms.