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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  gidarraga@gmail.com 

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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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