Category | Protection Measures

Reliability Engineering in Power Electronics

Posted on 11 January 2020

    Reliability in power electronics is the extent to which a system can be expected to perform its intended function within the required tolerances. In other words, reliability is the system's ability to operate correctly under certain conditions over a given time period.     The definition of failure rate (FR) to be used [...]

Electromagnetic Interference in Converters (EMI)

Posted on 21 December 2020

              The processes that take place in a converter system will always produce unwelcome electromagnetic interference due to the switching of the power semiconductors, on the one hand (Figure 1), and welcome energy transmission with corresponding signal processing, on the other hand. Figure 1. Energy processes in converters These [...]

High Voltage Power Thyristor with Built-in Protective Elements

Posted on 16 November 2020

  Despite the possibility of “outer” protection, usage of thyristors with built-in elements for protection against excess voltage may also be attractive to customers if such a thyristor has the same quality as a the standard one at a lower price. There are two types of protective elements that are different in principle of operation. [...]

Capacitor Protection with Semiconductor Fuses

Posted on 24 October 2020

  The primary responsibility of a capacitor fuse is to isolate a shorted capacitor before the capacitor can damage surrounding equipment or personnel. Typical capacitor failure occurs when the dielectric in the capacitor is no longer able to withstand the applied voltage. A low impedance current path results. The excessive heat generated builds pressure and [...]

Varistor Applications

Posted on 16 July 2020

              Varistors in protective circuits Varistors are commonly used in protective circuits. Varistors used in applications must always be connected in parallel to the electronic circuits to be protected. Typical examples of this principle are given by the cicuit diagrams below. Figure 1. AC/DC single-phase protection Figure 2. AC [...]

Protection of Automotive Electrical Systems Using Varistors

Posted on 13 July 2020

              Requirements for Automotive Electrical Systems Electronic equipment must work reliably in its electromagnetic environment without, in turn, unduly influencing this environment. This requirement, known as electromagnetic compatibility (EMC), is especially important in automotive electrical systems, where energy of mJ levels is sufficient to disturb or destroy devices that [...]

Preventing Overvoltages with Varistors

Posted on 12 July 2020

              Industrial and commercial systems, as well as building, automation, and household appliances, are often destroyed by overvoltages, necessitating their repair or replacement. To avoid this damage, variable resistors, known as varistors, are incorporated into the electrical network or circuit. Varistors are voltage dependent resistors whose resistance decreases with [...]

Interruption of DC Fault Currents

Posted on 11 July 2020

              For a fault in a DC circuit, the prospective (available) short circuit current is the final constant value VDC /R, where VDC is the source voltage and R is the resistance of the circuit. After a fault occurs, the current in the circuit increases exponentially, as shown in figure [...]

Protection Against Overcurrents with Fuses

Posted on 10 July 2020

  Overcurrents can be roughly classified into two groups; overloads and short-circuits. In all cases, when a fuse interrupts a fault there are two stages: Prearc arc Overloads The term "overload" is used for excess current flowing in a circuit which is electrically sound. Overload currents are usually not much greater than the normal full-load [...]

AC Side Snubber Circuits

Posted on 09 July 2020

              Very high voltage spikes occur when transformers are turned on and off under low load or no load at all. In addition to these occasional non-periodic switching operations, periodic switching operations caused by the thyristor firing also occur in controllable converter circuits. This is particularly true for diode [...]