Aux 1 Unit 12 Q1

In electrical engineering, preferential tripping is a protection scheme implemented in electrical power distribution systems to selectively disconnect non-essential loads in the event of an overload or partial power failure. The primary goal is to prevent a complete system shutdown (blackout) by shedding less critical loads to maintain power to essential services.  

1. Preferential tripping in a marine electrical distribution system – DieselShip

How it works:

• Load Prioritization: Electrical loads are classified into essential and non-essential categories. Essential loads include those critical for safety and navigation, such as propulsion, steering, communication, and emergency lighting. Non-essential loads might include things like air conditioning, galley equipment, or certain lighting circuits.   1. Preferential tripping in a marine electrical distribution system – DieselShip dieselship.com
• Overload Detection: The system continuously monitors the load current. If the current exceeds a predefined threshold, indicating an overload, the preferential tripping system activates.   1. Preferential tripping in a marine electrical distribution system – DieselShip dieselship.com
• Non-Essential Load Disconnection: The system automatically trips circuit breakers connected to non-essential loads, disconnecting them from the power supply.   1. Preferential tripping in a marine electrical distribution system – DieselShip dieselship.com
• Essential Load Preservation: By shedding these non-essential loads, the system reduces the overall load on the power source, preventing the main breaker from tripping and ensuring that essential services remain powered.

Benefits of Preferential Tripping:

• Prevents Blackouts: Helps to avoid complete power loss in case of overload or partial power failure, maintaining essential services.   1. Preferential tripping in a marine electrical distribution system – DieselShip dieselship.com
• Enhances Safety: Ensures critical systems for navigation, communication, and safety remain operational during emergencies.
• Protects Equipment: Reduces the risk of damage to electrical equipment and generators by preventing overloads.
• Operational Flexibility: Allows for temporary disconnection of non-essential loads while maintaining essential operations.

Implementation:

• Circuit Breakers with Preferential Trip Units: Special circuit breakers with built-in preferential trip units are used for non-essential loads. These trip units have a time-delayed trip mechanism that allows a brief overload without tripping, giving the system a chance to shed other non-essential loads first.   1. Preferential tripping in a marine electrical distribution system – DieselShip dieselship.com
• Control System: A control system or programmable logic controller (PLC) might be used to coordinate the preferential tripping process, ensuring that loads are shed in a predetermined sequence based on their priority.
• Alarms and Indications: The system typically includes alarms and indicators to notify the crew of an overload condition and which loads have been disconnected.

Examples of Non-Essential Loads:

• Air Conditioning and Ventilation Systems: While important for comfort, they can be temporarily disconnected in an emergency.
• Galley Equipment: Ovens, refrigerators, and other galley appliances can be considered non-essential in critical situations.
• Non-Essential Lighting: Certain lighting circuits, especially those for decorative or non-critical areas, can be shed.

In Summary:

Preferential tripping is an important safety and operational feature in marine electrical systems. It helps prevent blackouts, protects equipment, and ensures the continued operation of essential services in the event of an overload or partial power failure. By selectively disconnecting non-essential loads, it allows the vessel to maintain critical functions and navigate safely even in challenging situations.Sources and related content

In the context of electrical engineering, sequential starting refers to the controlled and timed starting of multiple electrical motors or loads in a specific sequence, rather than starting them all simultaneously. This approach is commonly employed in systems with several large motors or loads to manage the inrush current and prevent excessive voltage drops or overloading of the power source.

Benefits of Sequential Starting:

• Reduced Inrush Current: Large electric motors draw a high inrush current during startup, which can be several times their normal operating current. Starting multiple motors simultaneously can lead to a massive inrush current that can trip circuit breakers, overload the generator or power supply, or cause voltage dips that affect other equipment.
• Voltage Stability: Sequential starting helps maintain voltage stability in the electrical system by limiting the total inrush current at any given time. This is crucial for ensuring the reliable operation of sensitive electronic equipment and preventing voltage-related issues.
• Equipment Protection: By controlling the starting sequence and limiting inrush current, sequential starting protects the motors, generators, and other electrical components from damage caused by excessive current or voltage fluctuations.
• Load Management: It allows for better management of the overall electrical load on the system, especially during peak demand periods, preventing overloads and ensuring adequate power is available for essential services.

Implementation:

• Time Delays: The starting of each motor or load is delayed by a specific time interval, ensuring that one motor is up and running at its normal operating current before the next one starts.
• Current Sensing: In some systems, current sensors might be used to monitor the inrush current of each motor. The next motor in the sequence is only started when the previous motor’s current has dropped to an acceptable level.
• Control System: A control system or programmable logic controller (PLC) is often used to manage the sequential starting process, controlling the timing and sequence of motor starts based on predefined parameters or operator commands.

Typical Applications:

• Marine Vessels: Used to start multiple large motors, such as those for propulsion, pumps, winches, and other heavy machinery, to prevent overloading the ship’s generators.
• Industrial Plants: Employed in factories and industrial facilities with multiple large motors to manage the electrical load and ensure smooth startup.
• Power Generation Plants: Used to start multiple generators in a controlled sequence to stabilize the power grid and prevent blackouts.

In Summary:

Sequential starting is an essential technique for managing the startup of multiple electrical motors or loads in a controlled and safe manner. It helps to reduce inrush current, maintain voltage stability, protect equipment, and optimize load management, ensuring the reliable and efficient operation of electrical power systems.

Fuse back-up protection is a safety mechanism in electrical systems where an upstream fuse or circuit breaker with a higher breaking capacity is used to protect a downstream circuit breaker that might not be able to interrupt a fault current exceeding its own breaking capacity.  

1. Cascading and backup: Why coordination should be compulsory – Schneider Electric Blog

Here’s how it works:

• Downstream Circuit Breaker: This is the primary protective device for a specific circuit or load. It’s designed to trip and interrupt the current in case of an overload or short circuit within that circuit.   1. Circuit Breaker Basics | ABB US electrification.us.abb.com
• Fault Current Exceeds Capacity: In some situations, the fault current (the excessive current flowing during a fault) might be higher than the downstream circuit breaker’s maximum breaking capacity. This can happen if the system’s available fault current is very high or if there are changes in the electrical network.
• Upstream Fuse/Breaker: The upstream fuse or circuit breaker, with a higher breaking capacity, acts as a backup. If the fault current exceeds the downstream breaker’s capacity, the upstream fuse/breaker will operate and interrupt the current, protecting both the downstream breaker and the connected equipment.   1. SHORT-CIRCUIT BACK-UP AND CABLE PROTECTION – BEAMA www.beama.org.uk

Key Points:

• Conditional Rating: The downstream circuit breaker’s ability to interrupt fault currents above its rated capacity is conditional on the presence and proper coordination with the upstream fuse/breaker.   1. SHORT-CIRCUIT BACK-UP AND CABLE PROTECTION – BEAMA www.beama.org.uk
• Coordination: It’s important to ensure that the upstream and downstream protective devices are coordinated correctly. This means the upstream device should operate only when the fault current exceeds the downstream device’s capacity, and it should operate quickly enough to prevent damage to the downstream device.
• Energy Let-Through: The combined energy let-through (I²t) of the upstream and downstream devices during a fault is an important consideration. It should be within safe limits to prevent damage to the connected equipment and wiring.

Benefits:

• Enhanced Protection: Provides additional protection to the downstream circuit breaker and the connected load in case of high fault currents.
• Cost-Effectiveness: Allows the use of smaller and less expensive circuit breakers for individual circuits while relying on the upstream device for backup protection.
• Flexibility: Provides flexibility in system design and allows for future expansion or changes without needing to replace all downstream circuit breakers.

Applications:

• Common in Residential and Commercial Electrical Systems: Used in distribution boards and consumer units to protect miniature circuit breakers (MCBs) from high fault currents.
• Industrial Settings: Can be employed in industrial installations with high available fault currents to protect motor control centers and other critical equipment.

In summary: Fuse back-up protection is a safety measure that ensures the protection of downstream circuit breakers and connected equipment from high fault currents that exceed their breaking capacity. It relies on the coordination between upstream and downstream protective devices to provide reliable and effective protection for the electrical system.Sources and related content

In electrical terms, discrimination (also called selectivity or coordination) refers to the ability of an electrical protection system to selectively isolate a fault at the closest point to its origin, without affecting healthy parts of the system. This is achieved by coordinating the operation of various protective devices, such as fuses and circuit breakers, installed at different levels of the electrical network.  

1. Selectively coordinated overcurrent protection for power systems | Consulting – Specifying Engineer

2. Discrimination prevents electrical failures – DCD – Data Center Dynamics

Key Points:

• Fault Isolation: When a fault (like a short circuit or overload) occurs, the protective device closest to the fault should operate first, disconnecting only the faulty section of the circuit.   1. Overcurrent Protection and Overcurrent Protection Devices – Mechanical Products www.mechprod.com
• Minimized Disruption: This selective isolation minimizes disruption to the overall electrical system, ensuring that only the affected area loses power while the rest of the system continues to function normally.   1. Discrimination prevents electrical failures – DCD – Data Center Dynamics www.datacenterdynamics.com
• Easy Fault Identification: Discrimination makes it easier to identify the location of the fault, facilitating quicker troubleshooting and repairs.   1. Discrimination prevents electrical failures – DCD – Data Center Dynamics www.datacenterdynamics.com

Types of Discrimination:

• Current Discrimination: Based on the magnitude of the fault current. Protective devices are set so that the one closest to the fault, experiencing the highest fault current, will trip first.   1. Discrimination prevents electrical failures – DCD – Data Center Dynamics www.datacenterdynamics.com
• Time Discrimination: Based on the time delay of protective devices. Upstream devices have a slight time delay, allowing downstream devices to trip first if the fault is within their zone of protection.   1. Circuit Breakers- Discrimination and Its Techniques – C&S Electric cselectric.co.in2. Coordination between circuit-breakers – Electrical Installation Guide www.electrical-installation.org
• Zone Selective Interlocking (ZSI): A communication-based scheme where protective devices exchange information to coordinate their tripping and achieve selective isolation.   1. Zone Selective Interlocking (ZSI) Basic Principles – TestGuy Electrical Testing Network wiki.testguy.net

Benefits of Discrimination:

• Improved Safety: Prevents cascading failures and minimizes the risk of widespread outages.
• Enhanced Reliability: Ensures essential services and equipment remain operational during a fault.
• Reduced Downtime: Enables faster fault identification and repair, minimizing downtime and production losses.
• Cost Savings: Prevents damage to healthy parts of the system and reduces the need for extensive repairs.

Example:

Consider a simple electrical system with a main switchboard, a sub-panel, and several branch circuits. If a short circuit occurs on one of the branch circuits, the fuse or breaker on that specific circuit should trip, isolating the fault. The protective devices in the sub-panel and main switchboard should remain unaffected, ensuring power continues to flow to other healthy circuits.

Challenges and Considerations:

• Coordination: Achieving proper discrimination requires careful coordination of protective devices’ settings, considering their time-current characteristics and the available fault current levels at different points in the system.
• Changing Conditions: Changes in the electrical network, such as adding new loads or modifying the system configuration, can affect the coordination and require adjustments to the protective device settings.
• Selective Coordination Studies: In complex electrical systems, detailed selective coordination studies are often conducted using software tools to ensure proper discrimination across all levels of the network.

In summary:

Discrimination is a fundamental concept in electrical protection systems. It aims to selectively isolate faults, minimizing disruption, improving safety, and enhancing the reliability of the electrical network. By coordinating the operation of protective devices, discrimination allows for a more resilient and efficient power distribution system.  

1. Why are discrimination studies among protections so important? – Trace Software

In electrical terms, a “non-essential consumer” refers to an electrical load or device that is not critical for the basic operation or safety of a system, especially during an emergency or power shortage. These loads can be temporarily disconnected or shed to prioritize power supply to essential services.

Characteristics of Non-Essential Consumers:

• Non-Critical Function: They serve functions that are not vital for the immediate safety or operation of the system.
• Temporary Disconnection: They can be safely disconnected without causing immediate harm or compromising essential operations.
• Lower Priority: In a power management or load shedding scheme, they are assigned a lower priority compared to essential loads.

Examples of Non-Essential Consumers on a Vessel:

• Comfort and Convenience Systems:
  • Air conditioning and ventilation systems
  • Galley equipment (ovens, refrigerators, dishwashers)
  • Entertainment systems (TVs, audio systems)
  • Non-essential lighting (decorative lighting, some cabin lights)
• Non-Critical Machinery:
  • Certain pumps or motors that are not directly related to propulsion, steering, or safety.
  • Workshop equipment or tools.
• Other Loads:
  • Battery chargers for non-essential batteries.
  • Certain communication or navigation equipment that is not critical for basic operation.

Importance of Identifying Non-Essential Consumers:

• Load Shedding: During an overload or power shortage, non-essential consumers can be selectively disconnected to reduce the load on the power source and prevent a complete system shutdown.
• Power Management: Identifying and prioritizing loads allows for efficient power management and ensures that critical systems have sufficient power, especially in situations with limited generating capacity.

Methods of Disconnection:

• Manual Switching: Non-essential loads might be connected to manual switches that can be turned off by the crew in case of an emergency.
• Preferential Tripping: Specialized circuit breakers with preferential trip settings can automatically disconnect non-essential loads in a predetermined sequence during an overload condition.   1. Preferential tripping in a marine electrical distribution system – DieselShip dieselship.com
• Load Shedding Systems: Advanced power management systems can automatically monitor and control the electrical load, shedding non-essential consumers based on predefined priorities and load conditions.

In Summary:

Non-essential consumers are those electrical loads that are not critical for the immediate safety or operation of a vessel. Identifying and prioritizing these loads is crucial for effective power management and emergency response. In situations of overload or power shortage, non-essential consumers can be temporarily disconnected to protect essential services and ensure the vessel’s continued operation.