When we are about to discuss the concept of breakdown voltage, first we need to think about the concept of why it is needed and why it has to be implemented? So, let’s go with a clear interpretation. For the functioning of power transmission systems, there will be a requirement of power transformers. The insulation medium in the transformers gets reduced when it is made in contact with moisture, acids, oxygen, and heat. Of all these, heat is the foremost factor that causes insulation degradation and so it reduces electrical functioning and mechanical intensity. On behalf of this, conditional evaluation of maintenance and operation has to be done and it will be done through Breakdown Voltage. So, let’s consider the same discussion to be continued.
What is Breakdown Voltage?
It is considered as the threshold voltage where the breakdown starts to initiate. Before the movement of current starts, the voltage that exists at an open gap raises until it forms an ionization way all the way of the dielectric. When the current movement is initiated, then the voltage will be reduced, and it becomes stable at the operating gap level. The voltage that exists between the electrode gap and the work part is considered as the voltage gap. The operating voltage defines the complete energy of the ignition. Extended voltages enhance the gap that increases the flooding scenarios and assists to balance the functioning and enhance the MRR level. Whereas, extended voltages also stands as a factor for weak surface density.
Breakdown Voltage of Zener Diode
This is the different type of diode that functions both in the reverse and forward directions which means it allows current movement in both directions. Certain diodes, when operated in reverse bias, will get harmed after a specific limit. And this specific limit is termed to be “Breakdown Voltage”. Zener diode has two kinds of reverse breakdown regions and those are Zener and avalanche breakdown.
Avalanche Breakdown Voltage
This breakdown happens in Zener diode at extended reverse voltages. When the p-n junction diode is passed through extended reverse voltage, the minority carriers gain more energy and get accelerated to greater velocities.
This breakdown happens in the condition of extensively doped p. junction diodes as they have very thin depletion regions. The application of reverse voltage to the diode creates a solid electric field.
- Zener breakdown mainly occurs at minimal reverse breakdown voltage while avalanche breakdown occurs at extreme reverse voltages.
- Zener breakdown occurs only in the Zener diodes as they have narrow depletion regions.
- The breakdown region is considered the general functioning region in the case of Zener.
- Zener breakdown happens when the Vz is <6V.
Diode Breakdown Voltage
Diodes are considered as the semiconductors as they have partial insulators and conductors’ electrical properties. A diode is developed through P and N-type materials. PN junction diodes are with certain bandgap where there is a movement of holes and electrons. When there is the application of the forward bias, the current movement will be in the forward direction and there happens conduction. While, when there is the application of reverse bias, there will no conduction. But the minority charge carriers develop minima reverse flow of current and it is called leakage current.
Breakdown Voltage in Reverse Bias
When there is a reverse current flow, the PN junction width will be increased. The enhancement in the reverse bias voltage follows a steady manner and at a specific point, there will be sudden escalation on the flow of reverse current. This point is considered to be “Breakdown Voltage of pn junction diode” and the particular voltage is called “Diode Breakdown Voltage”. This might be sometimes termed as “Reverse Breakdown Voltage”.
Vb in Solids, Liquids, and Gaseous Substances
Breakdown conditions vary in liquids, solids and gaseous substances and the breakdown mechanism are dependent on size between the electrodes, material density, electrode material that is used, and the deep curvature that was for the conductors. In addition to solids, other liquids and gases do have insulator properties and they too experience the breakdown voltage mechanism. Though the below formula, the dielectric power of the silicon at room temperature can be known.
| εbr| = (12 ×105)/ (3-log(N/1016)) V/cm
In solid substances, an extended period of partial discharge usually happens before the breakdown that destroys the insulators and the metals that are close to the voltage gap. In the domain of electrical engineering, all the three substances are mostly implemented in many of the applications and it is, therefore, to know about the breakdown mechanism of those.
At general or room temperatures, gaseous substances are perfect insulators and their current conduction is in the order of 10-10 A/cm2. And at the time of the elastic collision, most of the kinetic energy in the molecules is converted into potential energy through the ionization mechanism attacked by the molecule. So, electron ionization influence with the strong electric field results in the breakdown mechanism of gases. And also, the breakdown happens in the case when the dielectric strength of the gaseous substances are topped. As per the statistics and other physical tables, the breakdown voltage of air is in the range of 20 – 75 kV and this breakdown is also based on the factors of moisture levels, thickness and temperature ranges.
With the help of Paschen’s principle and the dielectric strength of two metals separated by an inch, the breakdown voltages of gas can be known.
So, when we consider ‘A’ = 112.50 (kPacm)-1
And ‘B’ = 2737.50 (kPacm)-1
And ‘Yse ‘= 0.01 and ‘P’ = 101325 Pa
Integrating these two values in the Paschen law equation, then
Vb = (= 2737.50 × 101325 × 2.54 10-2)/[ln (112.50 ×101325 ×2.54 10-2 )] – ln(ln(1+1/0.01))]
Vb = 20.3 kV
The transformer oil’s dielectric strength is even termed as the breakdown voltage of transformer oil. This voltage can be calculated by knowing the values of the voltage, triggering strands that are absorbed in the oil and having a certain distance between those. When there is minimal breakdown voltage, it specifies that humidity and conducting material exists there.
So, to calculate the BDV of transformer oil, few kits are available. In these kits, the oil will be in a pot having electrodes immersed in that oil. Gradually voltage is increased between the electrodes and it is at the rate of 2 Kv per every second. The voltage where the sparking starts is observed, and this is considered to be breakdown voltage and it is at 30 kV.
Generally, silicon diodes are with forward-biased voltage and it is closer to 0.7 volts. The greatest reverse bias voltage for a diode is called a breakdown voltage of silicon. It is also termed as “Peak Inverse Voltage”.
1). How do you calculate breakdown voltage?
Every type of material experience different kinds of methods of calculating breakdown voltage. For example, in a capacitor, it is known by measuring the distance of the dielectric medium in between the conducting points.
2). What is knee voltage?
The forward voltage where the current flow for a diode starts to increase is called knee voltage.
3). Why does Vb occur?
To make the material electrically conductive, breakdown voltage happens.
4). How does dielectric breakdown occur?
Dielectric breakdown happens when the electrical field is more enough to trigger a few portions of the dielectric to suddenly switch over from that of the electrical insulator to that of the partial conductor.
5). What is the difference between dielectric strength and breakdown voltage?
Vb differs based on the material thickness whereas the dielectric strength stays as constant.
Thus, this is all about an overview of breakdown voltage, this voltage can also be measured in cables that have the flow of current. The breakdown voltage of a cable depends on the factors of existence of humidity levels in the atmosphere, the time of functioning of voltage and the operating temperature of cables. Get to know more concepts on why does breakdown voltage happens and in what substances?