Power System Studies
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Power System Studies
Few components of this study for electrical safety are:
- Load Flow Analysis
- Short Circuit Analysis
- Protection Coordination Analysis
- Arc Flash Analysis
Load Flow Analysis
Why Load Flow Analysis
- To optimize an existing system.
- Reduce system failure and downtime
- System Design conformance as per compliances.
- Reduce operating and Maintenance cost.
- Increase efficiency and reduce system energy losses.
- For development of new system.
- Helps in determination of power factor correction devices as per various load demands.
More importantly it should be performed during planning and development stage of a new system and before alteration to an existing system. It requires measurement of Active Power, Reactive Power, Power factor, Currents, Voltages, Harmonics and circuit loading. Load flow studies are used to determine how much reactive compensation should be applied at a bus, to bring its voltage up to an appropriate level.
These studies are performed with computer aided advanced software like NEPLAN and ETAP, and reports are generated
Short Circuit Analysis
Short circuit is a zero-impedance connection between two nodes. In short circuit analysis we perform both symmetrical and asymmetrical fault analysis. These excessive current potentially causes circuit damage, overheating, magnetic stress, arcing, fire and explosion. One of the major hazards due to short circuits are “Arc Flash” when currents start to pass through ionized air. Different types of faults are LLL, LL, LLG or LG faults. All these fault conditions are analysed in short circuit analysis technique.
Critical location where fault currents should be known in a system are service entrance, panel boards, motor control centres, transfer switches and load centres.
Potential Hazards of Short Circuit.
- Intense amount of heat release, heat densities up to 40 cal/cm2 temperature rise up to 20,000 0F
- System failure and equipment damage.
- Loss to assets and property.
- Disruption of industrial process.
- May cause huge economic loss.
- May cause second-degree burn, arc bright light may cause permanent vision damage.
Why Short Circuit Analysis is required?
- Provide necessary overcurrent protection devices.
- Prevent injuries to personnel and minimizes the risk to electrical technician.
- Prevent damage to system components and limit the duration of service interruption.
- Minimize equipment failure, overcurrent and short circuit conditions.
- Help in deciding fault interrupting device and their ratings.
Further short circuit analysis is a prerequisite for Protection coordination Analysis and Arc Flash Analysis. Short circuit analysis and its results will enhance the risk reduction and mitigation strategies for the system. It will also ensure the health and normal operation of the system.
Protection Coordination Analysis
Power coordination Analysis provide protection to isolate faulted region from a healthier network. Relay coordination guarantee fast, reliable and selective operation to isolate faulted section of a power system. Protection coordination is based on selectivity features of a protection device to differentiate between a fault and normal operating condition of a system. Relays are the most important component in the protection system for the proper identification of fault and operation of circuit breakers. The study includes determining fault clearing time and coordination of upstream electrical protective equipment. To ensure proper functioning of a relay, selectivity feature of relays is utilized. It is required for set these relays as per pickup current settings and time multiplier settings. It also provides features of application of time delay settings so three-layer protection of a power system can be achieved.
Why Protection Coordination Analysis to be performed?
- To ensure safety operation of the system are working properly.
- To avoid any unwanted tripping of a healthy section.
- To provide multiple levels of protection and safety of the system.
- To determine the characteristics, ratings, and settings of overcurrent protective devices.
- Utilization of time current characteristics to provide safe operation of system.
- Ensure to control the overlapping of TCC characteristics of protection devices.
Benefit of Protection Coordination
- Improved system protection and reliability.
- Improved equipment and worker protection.
- Increased efficiency of a system and exponential reduction in downtime.
- Less outage and disruption, leads to economic advantages.
- Identification of underrated and overloaded equipment in the system
Coordination study should be conducted in the tentative planning stage of a new system and selection of protection systems. In case of modification of an existing system or loading a new equipment in the system. It is also required when an existing equipment is replaced with higher rated equipment.
Arc Flash Analysis
An arc flash study is the engineered risk assessment of a workplace facility to determine hazards and risks in relation to electrical systems. It is required to establish safety protocol for qualified electrical personnel required to work on electrical equipment. Arc flash is important analysis for electrical technicians and other workers safety, working in proximity of an electrical apparatus. Flash Protection Boundary is the distance at which the incident energy equals 1.2 cal/cm2. It determines safe operating distance, grading and rating of PPE as per safety standards. Arc flash labelling is essential component of conformance to electrical safety compliances.
Why Arc Flash Analysis to be performed?
- To determine the arc flash incident energy
- To develop mitigation strategies to protect from arc flash incident energy
- Provide arc flash warning and labelling based on fault currents.
- Description of Incident energy boundary for electrical technician and other workers.
- Installation of fire detection and protection system for arc flash fire.
- Providing PPE clothing standards and rating when working on live systems.
As Per NFPA 70E section 130.1 provide provision for Arc flash Analysis. It should be performed for every 5 years interval and at time of system alterations.
How these studies are performed cumulatively
- Acquisition of Data like SLD, cable rating and equipment data sheets from manufacturer.
- Physical verification on field.
- Matching data provided with onsite installations.
- Performing Load flow analysis
- Short Circuit Analysis
- Protection Coordination Analysis
- Evaluate Arc Flash Analysis
- Evaluate the system.
- Documentation of the findings and Report Generation.
- Application of Mitigation Strategies.