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This workshop has been designed to give plant operators, electricians, field technicians and engineers a better appreciation of the role played by power system protection systems. An understanding of power systems along with correct management will increase your plant efficiency and performance as well as increasing safety for all concerned. The workshop is designed to provide excellent understanding on both a theoretical and practical level. Starting at a basic level and then moving onto more detailed applications, it features an introduction covering the need for protection, fault types and their effects, simple calculations of short circuit currents and system earthing. This workshop includes some practical work, simple fault calculations, relay settings and the checking of a current transformer magnetisation curve. WHO SHOULD ATTEND? Design engineers Electrical engineers Electrical technicians Electricians Field technicians Instrumentation and design engineers Plant operators Project engineers MORE INFORMATION: http://www.idc-online.com/content/practical-power-system-protection-engineers-and-technicians-140?id=7086
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Practical Power System Protection for Engineers and Technicians
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Power system protection• Customers always demand power on a continuous basis without
interruptions.
• Hence it is necessary to foresee the likely interruptions that may occur
in the distribution system to detect failures and to isolate only the
faulty sections.
• Protective equipment or protective relay is used in a power network to
detect, discriminate and isolate the faulty equipment in the network to
ensure that the rest of the system is fed with continuous power and at the
same time, damage to faulty section is minimized.
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Power system protection basic requirements
1. To safeguard the entire system to ensure continuity of supply.
2. To minimize damage and repair costs.
3. To ensure safety of personnel.
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Power system protection basic qualities
1. Selectivity: To detect and isolate the faulty item only.
2. Stability: To leave all healthy circuits intact to ensure continuity or supply.
3. Sensitivity: To detect even the smallest values of fault current or system abnormalities and operate correctly at its setting before the fault causes irreparable damage.
4. Speed:To operate speedily when it is called upon to do so, thereby minimizing damage to the surroundings and ensuring safety to personnel.
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Electrical fault energy
Why is Speed Important?
Energy released into fault = I2 x R x t
Where: I = Fault Current
R = Resistance of Fault Arc
t = Time in seconds when fault is ON.
So, the faster the fault clearing time, the lesser is the energy released.
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The need for speed (Khutala Fault Throwing)
• Fault Current = 4000 Amps
• Clearance Time = 350 milliseconds
• Assume ARC Resistance of 1 Ohm
• Fault Energy = I2 x R x t = 4000 x 4000 x 1 x 0.35
= 5.6 MegaJoules
• If clearance time is reduced to 100 milliseconds
• Fault Energy = 4000 x 4000 x 1 x 0.1
= 1.6 MegaJoules
• HENCE, A 70% REDUCTION!
If steps could be taken to also reduce level of fault current then major strides would be made.
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Protection philosophy
• Selectivity - Stability - Speed - Sensitivity
• Emphasis on Speed for the following reasons:– To minimise damage and repair costs.
– To reduce production downtime.
– To prevent undue thermal and magnetic overstressing of healthy equipment on through fault.
– To keep voltage depressions as short as possible in the interests of plant stability. (SISHEN mine)
– Above all, to ensure the safety of personnel (Flashes).
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Power system protection qualities – facets of reliability
It MUST trip when required
It must NOT trip when not required
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Basic components of protection
1. Voltage Transformers and Current transformers: To measure the parameters of a system.
2. Relays: To convert the signals from the above devices and give instructions to open a circuit or to give alarms under faulty conditions.
3. Fuses: To protect the downstream equipment being protected by self destruction.
4. Circuit breakers: To make and break circuits carrying enormous currents.
5. DC Batteries: To give uninterrupted power to the relays and breakers independent of the main power source being protected.
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