Breakdown voltage

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High voltage breakdown of an insulator string Lfa.JPG
High voltage breakdown of an insulator string

The breakdown voltage of an insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive.

Contents

For diodes, the breakdown voltage is the minimum reverse voltage that makes the diode conduct appreciably in reverse. Some devices (such as TRIACs) also have a forward breakdown voltage.

Diode abstract electronic component with two terminals that allows current to flow in one direction

A diode is a two-terminal electronic component that conducts current primarily in one direction ; it has low resistance in one direction, and high resistance in the other. A diode vacuum tube or thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from cathode to plate. A semiconductor diode, the most commonly used type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. Semiconductor diodes were the first semiconductor electronic devices. The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Today, most diodes are made of silicon, but other materials such as gallium arsenide and germanium are used.

TRIAC generic trademark for a three-terminal thyristor that conducts current in either direction when triggered

TRIAC, from triode for alternating current, is a generic trademark for a three terminal electronic component that conducts current in either direction when triggered. Its formal name is bidirectional triode thyristor or bilateral triode thyristor. A thyristor is analogous to a relay in that a small voltage induced current can control a much larger voltage and current. The illustration on the right shows the circuit symbol for a TRIAC where A1 is Anode 1, A2 is Anode 2, and G is Gate. Anode 1 and Anode 2 are normally termed Main Terminal 1 (MT1) and Main Terminal 2 (MT2) respectively.

Solids

Breakdown voltage is a characteristic of an insulator that defines the maximum voltage difference that can be applied across the material before the insulator conducts. In solid insulating materials, this usually[ citation needed ] creates a weakened path within the material by creating permanent molecular or physical changes by the sudden current. Within rarefied gases found in certain types of lamps, breakdown voltage is also sometimes called the striking voltage. [1]

Electric current flow of electric charge

An electric current is the rate of flow of electric charge past a point or region. An electric current is said to exist when there is a net flow of electric charge through a region. In electric circuits this charge is often carried by electrons moving through a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionized gas (plasma).

The breakdown voltage of a material is not a definite value because it is a form of failure and there is a statistical probability whether the material will fail at a given voltage. When a value is given it is usually the mean breakdown voltage of a large sample. Another term is also withstand voltage, where the probability of failure at a given voltage is so low it is considered, when designing insulation, that the material will not fail at this voltage.

Dielectric withstand test

A dielectric withstand test or high potential or hipot test is an electrical test performed on a component or product to determine the effectiveness of its insulation. The test may be between mutually insulated sections of a part or energized parts and electrical ground. The test is a means to qualify a device's ability to operate safely during rated electrical conditions. If the current through a device under test is less than a specified limit at the required test potential and time duration, the device meets the dielectric withstand requirement. A dielectric withstand test may be done as a factory test on new equipment, or may be done on apparatus already in service as a routine maintenance test.

Two different breakdown voltage measurements of a material are the AC and impulse breakdown voltages. The AC voltage is the line frequency of the mains. The impulse breakdown voltage is simulating lightning strikes, and usually uses a 1.2 microsecond rise for the wave to reach 90% amplitude, then drops back down to 50% amplitude after 50 microseconds. [2]

Utility frequency Frequency used on standard electricity grid in a given area

The utility frequency, (power) line frequency or mains frequency is the nominal frequency of the oscillations of alternating current (AC) in an electric power grid transmitted from a power station to the end-user. In large parts of the world this is 50 Hz, although in the Americas and parts of Asia it is typically 60 Hz. Current usage by country or region is given in the list of mains power around the world.

Two technical standards governing performing these tests are ASTM D1816 and ASTM D3300 published by ASTM. [3]

Gases and vacuum

In standard conditions at atmospheric pressure, air serves as an excellent insulator, requiring the application of a significant voltage of 3.0 kV/mm before breaking down (e.g., lightning, or sparking across plates of a capacitor, or the electrodes of a spark plug). In partial vacuum, this breakdown potential may decrease to an extent that two uninsulated surfaces with different potentials might induce the electrical breakdown of the surrounding gas. This may damage an apparatus, as breakdown is analogous to a short circuit.

In a gas, the breakdown voltage can be determined by Paschen's law.

The breakdown voltage in a partial vacuum is represented as [4] [5] [6]

where is the breakdown potential in volts DC, and are constants that depend on the surrounding gas, represents the pressure of the surrounding gas, represents the distance in centimetres between the electrodes,[ clarification needed ] and represents the Secondary Electron Emission Coefficient.

A detailed derivation, and some background information, is given in the article about Paschen's law.

Diodes and other semiconductors

Diode I-V diagram Diode-IV-Curve.svg
Diode I-V diagram

Breakdown voltage is a parameter of a diode that defines the largest reverse voltage that can be applied without causing an exponential increase in the leakage current in the diode. Exceeding the breakdown voltage of a diode, per se, is not destructive; although, exceeding its current capacity will be. In fact, Zener diodes are essentially just heavily doped normal diodes that exploit the breakdown voltage of a diode to provide regulation of voltage levels.

Rectifier diodes (semiconductor or tube/valve) may have several voltage ratings, such as the peak inverse voltage (PIV) across the diode, and the maximum RMS input voltage to the rectifier circuit (which will be much less).

Many small-signal transistors need to have any breakdown currents limited to much lower values to avoid excessive heating. To avoid damage to the device, and to limit the effects excessive leakage current may have on the surrounding circuit, the following bipolar transistor maximum ratings are often specified:

VCEO (sometimes written BVCEO or V(BR)CEO
The maximum voltage between collector and emitter that can be safely applied (and with no more than some specified leakage current, often) when no circuit at the base of the transistor is there to remove collector-base leakage. Typical values: 20 volts to as high as 700 volts; very early Germanium point-contact transistors such as the OC10 had values around 5 volts or less.
VCBO
The maximum collector-to-base voltage, with emitter open-circuit. Typical values 25 to 1200 volts.
VCER
The maximum voltage rating between collector and emitter with some specified resistance (or less) between base and emitter. A more realistic rating for real-world circuits than the open-base or open-emitter scenarios above.
VEBO
The maximum reverse voltage on the base with respect to the emitter.
VCES
Collector to emitter rating when base is shorted to emitter; equivalent to VCER when R = 0;

Field-effect transistors have similar maximum ratings, the most important one for junction FETs is the gate-drain rating.

Some devices may also have a maximum rate of change of voltage specified.

Electrical apparatus

Power transformers, circuit breakers, switchgear and other electrical apparatus connected to overhead transmission lines are exposed to transient lightning surge voltages induced on the power circuit. Electrical apparatus will have a basic lightning impulse level (BIL) specified. This is the crest value of an impulse waveform with a standardized wave shape, intended to simulate the electrical stress of a lightning surge or a surge induced by circuit switching. The BIL is coordinated with the typical operating voltage of the apparatus. For high-voltage transmission lines, the impulse level is related to the clearance to ground of energized components. As an example, a transmission line rated 138 kV would be designed for a BIL of 650 kV. A higher BIL may be specified than the minimum, where the exposure to lightning is severe. [7]

See also

Related Research Articles

Insulator (electricity) material whose internal electric charges do not flow freely, and which therefore does not conduct an electric current

An electrical insulator is a material whose internal electric charges do not flow freely; very little electric current will flow through it under the influence of an electric field. This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors.

Multivibrator

A multivibrator is an electronic circuit used to implement a variety of simple two-state devices such as relaxation oscillators, timers and flip-flops. It consists of two amplifying devices cross-coupled by resistors or capacitors. The first multivibrator circuit, the astable multivibrator oscillator, was invented by Henri Abraham and Eugene Bloch during World War I. They called their circuit a "multivibrator" because its output waveform was rich in harmonics.

Bipolar junction transistor transistor that uses both electron and hole charge carriers.In contrast,unipolar transistors such as field-effect transistors,only use one kind of charge carrier.For their operation,BJTs use 2 junctions between 2 semiconductor types,n-type and p-type

A bipolar junction transistor is a type of transistor that uses both electrons and holes as charge carriers.

Rectifier AC-DC conversion device; electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction

A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction.

Zener diode diode that allows current to flow in the reverse direction at a specific voltage

A Zener diode is a type of diode that allows current to flow not only from its anode to its cathode, but also in the reverse direction, when the Zener voltage is reached.

Darlington transistor compound structure consisting of two bipolar transistors

In electronics, a multi-transistor configuration called darlington pair, or the Darlington configuration is a compound structure of a particular design made by two bipolar transistors connected in such a way that the current amplified by the first transistor is amplified further by the second one. This configuration gives a much higher current gain than each transistor taken separately.

In electronics, a linear regulator is a system used to maintain a steady voltage. The resistance of the regulator varies in accordance with the load resulting in a constant voltage output. The regulating device is made to act like a variable resistor, continuously adjusting a voltage divider network to maintain a constant output voltage and continually dissipating the difference between the input and regulated voltages as waste heat. By contrast, a switching regulator uses an active device that switches on and off to maintain an average value of output. Because the regulated voltage of a linear regulator must always be lower than input voltage, efficiency is limited and the input voltage must be high enough to always allow the active device to drop some voltage.

Silicon bandgap temperature sensor

The silicon bandgap temperature sensor is an extremely common form of temperature sensor (thermometer) used in electronic equipment. Its main advantage is that it can be included in a silicon integrated circuit at very low cost. The principle of the sensor is that the forward voltage of a silicon diode, which may be the base-emitter junction of a bipolar junction transistor (BJT), is temperature-dependent, according to the following equation:

In electronics, an avalanche diode is a diode that is designed to experience avalanche breakdown at a specified reverse bias voltage. The junction of an avalanche diode is designed to prevent current concentration and resulting hot spots, so that the diode is undamaged by the breakdown. The avalanche breakdown is due to minority carriers accelerated enough to create ionization in the crystal lattice, producing more carriers which in turn create more ionization. Because the avalanche breakdown is uniform across the whole junction, the breakdown voltage is nearly constant with changing current when compared to a non-avalanche diode.

Spark gap

A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conductors exceeds the breakdown voltage of the gas within the gap, a spark forms, ionizing the gas and drastically reducing its electrical resistance. An electric current then flows until the path of ionized gas is broken or the current reduces below a minimum value called the "holding current". This usually happens when the voltage drops, but in some cases occurs when the heated gas rises, stretching out and then breaking the filament of ionized gas. Usually, the action of ionizing the gas is violent and disruptive, often leading to sound, light and heat.

Differential amplifier electronic amplifier, a circuit component

A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. It is an analog circuit with two inputs and and one output in which the output is ideally proportional to the difference between the two voltages

Schmitt trigger

In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. It is an active circuit which converts an analog input signal to a digital output signal. The circuit is named a "trigger" because the output retains its value until the input changes sufficiently to trigger a change. In the non-inverting configuration, when the input is higher than a chosen threshold, the output is high. When the input is below a different (lower) chosen threshold the output is low, and when the input is between the two levels the output retains its value. This dual threshold action is called hysteresis and implies that the Schmitt trigger possesses memory and can act as a bistable multivibrator. There is a close relation between the two kinds of circuits: a Schmitt trigger can be converted into a latch and a latch can be converted into a Schmitt trigger.

Current source electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it; dual of a voltage source

A current source is an electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it.

Electrical breakdown when current flows through an electrical insulator when the voltage applied across it exceeds the breakdown voltage

Electrical breakdown or dielectric breakdown is when current flows through an electrical insulator when the voltage applied across it exceeds the breakdown voltage. This results in the insulator becoming electrically conductive. Electrical breakdown may be a momentary event, or may lead to a continuous arc if protective devices fail to interrupt the current in a power circuit.

Marx generator

A Marx generator is an electrical circuit first described by Erwin Otto Marx in 1924. Its purpose is to generate a high-voltage pulse from a low-voltage DC supply. Marx generators are used in high-energy physics experiments, as well as to simulate the effects of lightning on power-line gear and aviation equipment. A bank of 36 Marx generators is used by Sandia National Laboratories to generate X-rays in their Z Machine.

Widlar current source

A Widlar current source is a modification of the basic two-transistor current mirror that incorporates an emitter degeneration resistor for only the output transistor, enabling the current source to generate low currents using only moderate resistor values.

An avalanche transistor is a bipolar junction transistor designed for operation in the region of its collector-current/collector-to-emitter voltage characteristics beyond the collector-to-emitter breakdown voltage, called avalanche breakdown region. This region is characterized by avalanche breakdown, which is a phenomenon similar to Townsend discharge for gases, and negative differential resistance. Operation in the avalanche breakdown region is called avalanche-mode operation: it gives avalanche transistors the ability to switch very high currents with less than a nanosecond rise and fall times. Transistors not specifically designed for the purpose can have reasonably consistent avalanche properties; for example 82% of samples of the 15V high-speed switch 2N2369, manufactured over a 12-year period, were capable of generating avalanche breakdown pulses with rise time of 350 ps or less, using a 90V power supply as Jim Williams writes.

Capacitor types Quantitative

Capacitors are manufactured in many forms, styles, lengths, girths, and from many materials. They all contain at least two electrical conductors separated by an insulating layer. Capacitors are widely used as parts of electrical circuits in many common electrical devices.

Capacitor Passive two-terminal electronic component that stores electrical energy in an electric field

A capacitor is a passive two-terminal electronic component that stores electrical energy in an electric field. The effect of a capacitor is known as capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed to add capacitance to a circuit. The capacitor was originally known as a condenser or condensator. The original name is still widely used in many languages, but not commonly in English.

References

  1. J. M. Meek and J. D. Craggs, Electrical Breakdown of Gases, John Wiley & Sons, Chichester, 1978.
  2. Emelyanov, A.A., Izv. Vyssh. Uchebn. Zaved., Fiz., 1989, no. 4, p. 103.
  3. Kalyatskii, I.I., Kassirov, G.M., and Smirnov, G.V., Prib. Tekh. Eksp., 1974, no. 4, p. 84.
  4. G. Cuttone, C. Marchetta, L. Torrisi, G. Della Mea, A. Quaranta, V. Rigato and S. Zandolin, Surface Treatment of HV Electrodes for Superconducting Cyclotron Beam Extraction, IEEE. Trans. DEI, Vol. 4, pp. 218<223, 1997.
  5. H. Moscicka-Grzesiak, H. Gruszka and M. Stroinski, ‘‘Influence of Electrode Curvature on Predischarge Phenomena and Electric Strength at 50 Hz of a Vacuum
  6. R. V. Latham, High Voltage Vacuum Insulation: Basic concepts and technological practice, Academic Press, London, 1995.
  7. D. G. Fink, H. W. Beaty, Standard Handbook for Electrical Engineers, Eleventh Edition, McGraw-Hill, 1978, ISBN   007020974X, page 17-20 ff