Ferroresonance
Encyclopedia
See also: ferroresonant transformer (also called the constant-voltage transformer or CVT).
Ferroresonance or nonlinear resonance is a complex electrical phenomenon. It can cause overvoltages and overcurrents in an electrical power system and can pose a risk to transmission
and distribution
equipment and to operational personnel.
It occurs when a circuit containing a nonlinear inductance
is fed from a source that has series capacitance
. One example of nonlinear inductance is the magnetic core of a wound type voltage transformer, but it may also arise due to the complex structure of a 3 or 5 limb three phase power transformer. The circuit series capacitance can be due to a number of elements, such as the circuit-to-circuit capacitance of parallel lines, conductor to earth capacitance, circuit breaker
grading capacitance, busbar
capacitance, or bushing
capacitance, etc.
Ferroresonance should not be confused with linear resonance that occurs when inductive and capacitive reactances of a circuit are equal. In linear resonance the current and voltage are linearly related in a manner which is frequency dependent. In the case of ferroresonance it is characterised by a sudden jump of voltage or current from one stable operating state to another one. The relationship between voltage and current is dependent not only on frequency but also on a number of other factors such as the system voltage magnitude, initial magnetic flux
condition of transformer iron core, the total loss in the ferroresonant circuit and the point on wave of initial switching.
In his paper "Examples of Ferroresonance in a High Voltage Power System", Jacobson claims that the term "ferroresonance" was coined by Bucherot in 1920 to describe the phenomenon of two stable fundamental frequency operating points coexisting in a series resistor, nonlinear inductor, capacitor circuit.
s (inductive component) and power cable
s (capacitive component). If such a network has little or no resistive load connected load
and one phase of the applied voltage is then interrupted, ferroresonance can occur. If the remaining phases are not quickly interrupted and the phenomenon continues, overvoltage can lead to the breakdown of insulation
in the connected components resulting in their failure.
The phenomenon can be avoided by connecting a minimal resistive load on the transformer secondaries or by interrupting the applied voltage by a 3-phase interrupting device such as a ganged (3 pole) circuit breaker
.
Ferroresonance or nonlinear resonance is a complex electrical phenomenon. It can cause overvoltages and overcurrents in an electrical power system and can pose a risk to transmission
Electric power transmission
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...
and distribution
Electricity distribution
File:Electricity grid simple- North America.svg|thumb|380px|right|Simplified diagram of AC electricity distribution from generation stations to consumers...
equipment and to operational personnel.
It occurs when a circuit containing a nonlinear inductance
Inductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...
is fed from a source that has series capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
. One example of nonlinear inductance is the magnetic core of a wound type voltage transformer, but it may also arise due to the complex structure of a 3 or 5 limb three phase power transformer. The circuit series capacitance can be due to a number of elements, such as the circuit-to-circuit capacitance of parallel lines, conductor to earth capacitance, circuit breaker
Circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
grading capacitance, busbar
Busbar
In electrical power distribution, a bus bar is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus....
capacitance, or bushing
Bushing (electrical)
A bushing is a hollow insulating liner through which a conductor may pass. Bushings appear on switchgear, transformers, circuit breakers and other high voltage equipment.- Description :...
capacitance, etc.
Ferroresonance should not be confused with linear resonance that occurs when inductive and capacitive reactances of a circuit are equal. In linear resonance the current and voltage are linearly related in a manner which is frequency dependent. In the case of ferroresonance it is characterised by a sudden jump of voltage or current from one stable operating state to another one. The relationship between voltage and current is dependent not only on frequency but also on a number of other factors such as the system voltage magnitude, initial magnetic flux
Magnetic flux
Magnetic flux , is a measure of the amount of magnetic B field passing through a given surface . The SI unit of magnetic flux is the weber...
condition of transformer iron core, the total loss in the ferroresonant circuit and the point on wave of initial switching.
In his paper "Examples of Ferroresonance in a High Voltage Power System", Jacobson claims that the term "ferroresonance" was coined by Bucherot in 1920 to describe the phenomenon of two stable fundamental frequency operating points coexisting in a series resistor, nonlinear inductor, capacitor circuit.
Conditions
Ferroresonance can occur when an unloaded 3-phase system consisting mainly of inductive and capacitive components is interrupted by single phase means. In the electrical distribution field this typically occurs on a medium voltage electrical distribution network of transformerTransformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s (inductive component) and power cable
Power cable
A power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power...
s (capacitive component). If such a network has little or no resistive load connected load
External electric load
If an electric circuit has a well-defined output terminal, the circuit connected to this terminal is the load....
and one phase of the applied voltage is then interrupted, ferroresonance can occur. If the remaining phases are not quickly interrupted and the phenomenon continues, overvoltage can lead to the breakdown of insulation
Electrical insulation
thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...
in the connected components resulting in their failure.
The phenomenon can be avoided by connecting a minimal resistive load on the transformer secondaries or by interrupting the applied voltage by a 3-phase interrupting device such as a ganged (3 pole) circuit breaker
Circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
.