Power System Protection Coordination
Bertha Simmons
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Electrical power systems are susceptible to electrical fault conditions. To ensure the power system is highly available and resilient, the adjustable settings of circuit breakers and relay circuits are determined.
For example, in a typical residential setting, the electrical technician determines the appropriate circuit breaker / fuses to install from applying a safety factor on the maximum load current expected on the circuit.
Short Circuit study is arguably the most important study of the three conducted on a power system. It deals with estimating the worst case(maximum) scenario of fault conditions expected at all nodes within a power system network. As a matter of fact, it plays a vital role when interconnecting new power sources such as wind farms, conventional thermal power plants and solar PV farms with the grid.
Arc flash hazard typically occurs when a qualified personnel is either performing work on an electrical equipment or within the vicinity the work is being performed. Arc flash hazard analysis honors IEEE - 1584 standards to estimate the bolted fault and arcing fault current, flash protection boundaries, and the incident thermal energy expected to be produced at each electrical node within the power system. These calculations help identify hazardous zones in the system with arc flash labels generated and posted on the equipment and points of interest.
Also, NFPA 70E and OSHA standards are considered when producing these labels to ensure compliance with observing a safe working distance and using the appropriate Personal Protective Equipment while working on an equipment or around those areas.
Protection Coordination determines the appropriate settings of protective relays, circuit breakers, fuses and other devices to safely break and make a circuit within an integrated power system in the advent of an overload, short circuit and other electrical unsafe conditions.
OEM's provide Time Current Characteristics (TCC) curves of protective devices and damage curves of conductors, transformers, motors, generators and other loads to be used for protection and coordination. They are comprehensively analyzed along with short circuit calculations to ensure the power system is effectively coordinated.
Nevertheless, if code (NEC, ANSI, OSHA) violations or operational issues are observed, they are resolved from changes to protective device settings. They may also require the replacement of protective devices and equipment within acceptable interrupting ratings (IR) and short-circuit current ratings (SCCR) respectively. However, depending on the selectivity and level of protection expected to be achieved, selective coordination may be required.
According to NEC Article 100, Selective Coordination is the localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the selection and installation of overcurrent protective devices and their ratings or settings for the full range of available overcurrents".
In plain words, selective coordination ensures that downstream breakers or fuses within the vicinity of an electrical fault reacts first to isolate the fault from tripping upstream devices. This results to optimal protection and coordination. Selective coordination is required in certain mission critical processes or cases where life safety is a concern such as in power systems found in healthcare, data centers, elevators, and fire pump systems.
Watch out for our next article where we share our experience working on protection coordination study for a transportation electrification (e-mobility) project we had the opportunity to be involved in.
The reliable operation of power systems is crucial to ensure the uninterrupted supply of electricity to consumers. Power systems are susceptible to various disturbances, such as faults, overloads, and equipment failures, which can lead to outages and disruptions. Protection coordination plays a vital role in mitigating the impact of these disturbances by isolating faulty components while minimizing the extent of the outage. This article explores the concept of protection coordination in power systems and its significance in maintaining a resilient and stable electrical grid.
Protection coordination involves designing and configuring protection devices, such as relays and circuit breakers, in a way that enables rapid and selective isolation of faulty components within the power system. The primary objective is to ensure that only the affected portion of the system is disconnected, allowing the rest of the grid to continue functioning normally. Protection coordination aims to strike a balance between sensitivity and selectivity, detecting faults accurately while minimizing the impact on unaffected sections.
Minimizing Downtime: Efficient protection coordination reduces downtime by isolating faults quickly. When a fault occurs, the protective devices closest to the fault should operate, isolating the faulted section without causing unnecessary outages in other parts of the grid.
Preventing Cascading Failures: In complex power systems, a fault in one area can lead to cascading failures that impact a broader region. Proper protection coordination prevents these cascading failures by isolating faults before they spread to other sections.
Equipment Protection: Protection coordination safeguards valuable and critical equipment from damage. For example, circuit breakers are designed to interrupt fault currents, preventing equipment overheating and other potential damage.
Improved Grid Resilience: In the face of unforeseen events such as extreme weather or equipment failures, protection coordination ensures that the grid can quickly recover from disturbances, minimizing the overall impact on consumers.
Sensitivity vs. Selectivity: Achieving the right balance between sensitivity (quickly detecting faults) and selectivity (isolating only the faulted component) is essential. Overly sensitive protection may lead to unnecessary tripping, while inadequate sensitivity might result in delayed fault isolation.
Communication and Coordination: Protection devices often need to communicate and coordinate with each other to make informed decisions. Establishing reliable communication networks and protocols is critical for effective protection coordination.
Numerical Relays: These digital devices offer advanced protection functions and flexibility in coordination settings. They can adapt to changing system conditions and allow for precise protection coordination adjustments.
Protection coordination is a cornerstone of power system reliability, ensuring that faults are detected, isolated, and resolved swiftly to maintain uninterrupted electricity supply. In a rapidly evolving energy landscape, where renewable energy integration and smart grid technologies are becoming more prevalent, efficient protection coordination becomes even more critical. By leveraging advanced protection devices, communication systems, and monitoring techniques, power system operators can achieve robust protection coordination and enhance the overall resilience and stability of the grid.
This 12-Hour live online Power System Protection Training course will provide a practical understanding of protective device applications and protective relay schemes for electrical power systems and equipment.
This 12-Hour ive Online Power System Protection and Coordination Training Course Will Provide A Practical Understanding of Short Circuit Currents and Protective Device Applications for Electrical Power Systems And Equipment.
The primary objective of a power system protection and coordination study is to protect the system in case of any abnormal operations, maintain continuity of service by restricting the extent and time of disruption and reducing damages to the system. It is impossible to avoid fault due to natural events, equipment failure, human errors etc.., however, a proper system study can help minimize the impact to the facility operations. A good maintenance practice also helps ensure that the system performs at its best and eliminates faults and outages associated with equipment failure
A severe short circuit fault in your power system can have catastrophic consequences. This makes short circuit study training fundamental. Fault levels vary from system to system, and location to location. Our training will help you to calculate the maximum available short circuit current at various points throughout the system. Calculated values are then used to evaluate the application of protective devices, and to develop circuit breaker trip settings, which is part of a Power System Coordination Study. A properly coordinated protection system isolates portions of the system affected by a fault or other disturbance as quickly as possible with less impact on the rest of the distribution.
The reliability and safety of electric power distribution systems depend on accurate and thorough knowledge of short-circuit fault currents that can be present, and on the ability of protective devices to satisfactorily interrupt these currents. Knowledge of the computational methods of power system analysis is essential to engineers responsible for planning, design, operation, and troubleshooting of distribution systems. Such knowledge is necessary to determine the interrupting requirements of circuit breakers and fuses, the mechanical and thermal requirements of devices exposed to fault currents, and to perform protection and coordination studies. A full and complete understanding of short-circuit fault currents is essential for the proper and safe coordination of power system coordination and arc flash mitigation.
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