transitorios clase i
TRANSCRIPT
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Electromagnetic
Transients
UNIVERSIDAD AUTÓNOMA DE NUEVO LEÓNFacultad de Ingeniería Mecánica y Eléctrica
Posgrado en Ingeniería Eléctrica
www.uanl-die.net
Monterrey, N.L., México Enero-Junio, 2009
Dra. Gina Idárraga Ospina [email protected]
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Contents
• Fundamental notions
• Basic of transients
• Energy concepts
• Circuit Modeling
• Homework
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Fundamental Notions
Transients events electrical manifestation of a sudden change incircuit conditions
• switch opens
• switch closes • network fault
transient period is very short relative to the timespent in steady state operation, but is extremely
important• greatest stresses on circuit components • excessive currents and voltages • circuit damage
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• The analysis of this type of events and aclassification of them are necessary in the
transmission systems.Design protection schemes appropriately,
Select the suitable isolation level,
Calculate the coordination of isolation, andInsure accurately operation of the system.
Fundamental Notions
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Power system transient studies
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Transient Classification
• Temporary Overvoltages
• Switching Overvoltages
• Lightning Overvoltages
Group Frequency range
for representation
Shape
designation
Representation mainly for
I 0.1 Hz – 3 KHz Low
frequency
oscillations
Temporary overvoltages
II 50 Hz – 20 kHz Slow frontsurges
Switching overvoltages
III 10 kHz – 3 MHz Fast front
surges
Lightning overvoltages
IV 100 kHz – 50 MHz Very fast
front surges
Restrike overvoltages
Overvoltage classification according to the CIGRE
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• Low frequency transients
• Medium frequency transients
• High frequency transients
Transient Classification
Classifications of frequency range
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Energy concepts
• Electric field energy storage:
• Magnetic field energy storage:
• Energy dissipation:
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Energy Balance
• Under steady-state conditions – dc circuit – the energy stored is constant.. – ac circuit – the energy is being transferred cyclically between
the L’s and C’s of the circuit.
• Sudden changes in a circuit causes a redistribution of energy – energy redistribution cannot take place instantaneously.
– change in the magnetic field requires a change in current, but isopposed by the induced emf:
– change in the electric field requires a change in the charge or thevoltage, but is opposed by the flow of current:
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Circuit Modeling
• set down the differential or algebraic equations
– use Kirchhoff’s voltage and current laws
• example:
– switch closing
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Circuit Modeling
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Circuit Modeling
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Circuit Modeling
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• Circuit parameters: R, L, and C all components and devices have all three parameters these attribute differ to a greater or lesser degree under steady-state conditions, one will dominate
in transient conditions the conditions are very different
• lumped vs. distributed parameters in reality, parameters are distributed in nature
in circuit analysis, we frequently lump the parameters for ease of analysis under many conditions, good analysis requires usingdistributed parameters
Relevant aspects
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Lumped Parameter Modeling
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Lump Circuit Characteristics
• Three basic circuit types
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Lump Circuit Characteristics
• the only kind of response that is evoked when a linear electric circuit comprising lumped elements is
disturbed takes the form of exponential functions or combinations of exponential functions with real or imaginary components (sine or cosine functions)
• for circuits with more elements, the responses may be more complicated but they are no more complex
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