What are surges, transients, and temporary over-voltages, and what are their typical characteristics?
These are all forms of overvoltages and confused by the often loose and interchangeable use of terminology. The significance of the terms usually relates to their understood duration. For example, a transient is generally considered of very short duration (<10 m) and relatively low energy content. Such electrical activity is often characterized by voltage switching spikes, which in themselves contain relatively little energy content, but are sufficient in voltage to cause junction breakdown in the substrates of semiconductors and failure. Surges (>10 m & <1 ms), on the other hand, have a greater energy component and it is generally this which causes the damage and charring of electronic components and appliances. SPDs are designed to protect equipment against surges and transients. Temporary over voltages (TOVs) are created by faults on the utility power distribution system and can cause extensive damage since their time domain is much longer (ms to seconds to hours). Note that while U
Although often used as separate terms in the surge industry, Transients and Surges are the same phenomenon. Transients and Surges can be current, voltage, or both and can have peak values in excess of 10kA or 10kV. They are typically of very short duration (usually >10 s & <1 ms), with a waveform that has a very rapid rise to the peak and then falls off at a much slower rate. Transients and Surges can be caused by external sources such as lightning or a short circuit, or from internal sources such as Contactor switching, Variable Speed Drives, Capacitor switching, etc. Temporary over voltages (TOVs) are oscillatory phase-to-ground or phase-to-phase overvoltages that can last as little as a few seconds or as long as several minutes. Sources of TOVs include fault reclosing, load switching, ground impedance shifts, single-phase faults and ferroresonance effects to name a few. Due to their potentially high voltage and long duration, TOVs can be very detrimental to MOV-based SPDs. An extend
