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From fundamental principles of electricity to causation circumstances and principals of causationof electrical power surges, ‘spikes’ in electrical systems
Eur Ing Dr Robert Brown
BEng (Hons) PhD CEng MIET IntPE (UK)
Abstract
The intent of this paper is to aid the understanding of the origins and consequences of ‘electrical transients’, ‘power surges’ or ‘spikes’ in electrical systems. The paper is intentionally non-technical to allow an appreciation of the circumstances should electrical transients become prevalent for whatever reason.
The paper content first introduces the attributes of electrical transients and on goes on to present the fundamental physics of transients i.e. electromagnetic force, electromagnetic or magnetic induction, propagation of transients through an electrical system, protection measures to eliminate the effects of electrical transients, the likelihood of damage by transients and the expected quantum of damage incurred by an electrical transient.
In electrical engineering, ‘electrical transients’are fast, short duration electrical events, induced in the fundamental electrical charge components of voltage (voltage spikes), current (current spikes), or transferred energy (energy spikes) of an electrical circuit.
Causation circumstances
Fast, short duration electrical transients in the electric potential of a circuit are typically caused by
• Faulty, intermittent wiring connections,
• lightning strikes,
• restoration of power after a power outage or blackout.
• Normal use of ‘switches’ to turn electrical systems on or off.
Principals of Causation
Why do the circumstances such as electrical overloads, faulty wiring, lightning strikes etc., generate electrical transients?
The fundamental phenomena that provokes the manifestation of electrical transients is known as electromagnetic induction.
Electromagnetic induction comes about due to the fundamental force known as the electromagnetic force.
Electromagnetic force
Originally, electricity and magnetism were considered to be two separate forces. This view changed with the publication of the work of James Clerk Maxwell's in 1873 who confirmed that the interactions of positive and negative charges were mediated by one force the “electromagnetic force”. There are four main effects resulting from the interactions:
· Electric charges attractor repelone another with a force inversely proportional to the square of the distance between them: unlike charges attract, like ones repel.
· Magnetic poles (or states of polarization at individual points) attract or repel one another in a manner similar to positive and negative charges and always exist as pairs: every north pole is yoked to a south pole.
· An electric current inside a wire creates a corresponding circumferential magnetic field outside the wire. Its direction (clockwise or counter-clockwise) depends on the direction of the current in the wire.
· A current is induced in a loop of wire when it is moved toward or away from a magnetic field, or a magnet is moved towards or away from it; the direction of current depends on that of the movement.
Electromagnetic or magnetic induction
The latter two bullet points are important for the understanding of the generation of electrical transients.
In simple terms, the movement of electrical charge, i.e. the flow of electricity in a conductor, generates a magnetic field which radiates orthogonally (at 90O) away from the conductor.
If the flow of electricity changes in magnitude (strength) then the strength of the magnetic field will equally change.
If the radiating magnetic field of one electrical conductor passes over a second, separate electrical conductor, or a second electrical conductor physically moves into a magnetic field radiating from a separate electrical conductor, then in both cases an electrical current will be induced in the second conductor.
So succinctly, electromagneticor magnetic inductionis the production of an electromotive force across an electrical conductor in a changing magnetic field.
Examples of surge generators with physical analysis
Here following are examples of surge generator circumstances with physical analysis of why such circumstances provoke surge manifestation.
Lightning
Lightening is the manifestation of an electrical conductor in ‘air’ which during the period of existence conveys a high magnitude electrical current and radiates a ‘strong’ magnetic field.
Consequently, given the phenomena of electromagnetic induction, an electromotive force ‘electrical (voltage) transient’, will be induced in all electrical conductors which are enveloped by the changing magnetic field generated by the lightening.
Use of switches/ faulty wiring/ power isolation/restoration
Generally, when electrical current flows in an electrical circuit, the dynamics of the current is referred to as being in a ‘steady state’.
Given the operation of a switch inherent in the circuit with the intent to isolate or restore electrical current form/to the circuit, will have a significant effect on the dynamics of the current and the magnetic field radiated by the current. In other simple words the switching action generates a transient wave of current and magnetism, which percolates within the electrical system and in the locality. The circumstances are akin to a stone dropping into a pond of water and the ensuing generation of ripples,… waves.
Similarly, given the phenomena of electromagnetic induction, an electromotive force ‘electrical (voltage) transient’, will be induced in all electrical conductors which are enveloped by the changing magnetic field generated by the change of electrical current a consequence of the switching action.
Correlated physical phenomena
The three fundamental parameters, electrical voltage (v), electrical current (i) and electrical power (p). are interrelated within electrical systems.
Generally, an electromotive force (voltage potential) gives rise to a flow of electrical current and the product of voltage and current derives the power of an electrical system, i.e. v x i = p.
In the case of electromagnetic induction, a magnetic field passing over an electrical conductor gives rise to the generation of electrical current, which fundamentally is associated an electromotive ‘charge’ force (voltage).
Consequently, the effect of a voltage spike is to produce a corresponding increase in current (current spike) and voltage spikes may be created by current sources.
Power surges are but the product of voltage and current spikes/surges.
Propagation of spikes through an electrical system
Recalling the analogy of a stone dropping into a pond of water and the ensuing generation of ripples,… waves, similarly as electrical transients propagate through an electrical system the magnitude/strength of a transient decays. Also similar to a stone in a pond, a transient will propagate in all directions within the system
Protection
Protection measures to counter the effects of electrical transients are now commonly integrated within electrical/electronic equipment.
Protection devices function to either quell the dynamic of a transient, i.e. slow the rate of evolution of the transient and its proliferation in the parent electrical system, or to ‘divert’ the energy of the transient away from the parent electrical system.
Protection devices come in a range of designs, to provide a shield from all forms of transients of all magnitudes and time varying signatures.
Common transient protection components such as ‘ferrite beads’ are observed on power cables of computers and peripheral equipment, with the aim to moderate and smooth electrical current transients.
Small, economical voltage transient suppressors are integrated in everyday electronic circuits as a matter of accepted design practice.
It is important to note that transient protection devices are not ‘sacrificial’ in operation as in the case of an electrical fuse. Consequently, when the transient has been dealt with, the overall function of the protected parent electrical system should function as intended.
Likelihood of damage to parent electrical systems by electrical transients
Given the present wide spread use of surge protection devices, the likelihood of damage to a parent electrical system by electrical transients is now low.
Of course, there will always be circumstances, even with transient protection measures in place within an electrical system that a transient will provoke damage to the system.
Quantum of damage
In the circumstance where damage has been incurred by the impact of an electrical transient, the quantum of physical damage to an electrical system in most cases are considered to be small i.e. some component will have been irreparably damaged, and the replacement cost of the component will be small compared with the cost of replacing the electrical system.
However, the diagnostic cost to identify the damaged component could be significant, as could the measures required say in the circumstances of systems in constant use, to substitute the system with a spare whilst the diagnostic action is undertaken.
The author
Eur Ing Dr Robert Brown is the Executive Director of Fraser George and Associates Limited and is a Consultant Engineer in the fields Electrical Electronic and Control Engineering.
Robert is also an accomplished professional Expert Witness having prepared and presented many court compliant reports and presented oral evidence within the High Court, Crown Courts and County Courts.
For further information please contact Robert via;
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