New Jersey Institute of Technology
Surge voltages only occur for a fraction of a second. For this reason, they are also referred to as transient voltages or short transients. They have very short rise times of a few microseconds before they drop off again relatively slowly over a period of up to 100 microseconds.
The study examines the three different conditions in the electric circuit that result to voltage spikes (surge). It describes the three phenomenons which lead to these conditions and summarizes on the remedies against surge.
There are 6(six) types of voltage transient associated with an electrical circuit. As we know that Current is directly proportional to the Voltage thus these together known as Energy transient.Here we will first discuss the six transient phenomenons possible in an electric circuit and then take the most severe one that has caused 5billion dollars over the last few years.
The first is the voltage Sag, when Short duration decrease in mains supply voltage which generally lasts for several cycles’ voltage during this goes below 80% of rated RMS voltage for 2 or more cycles the common Causes for this phenomenon is Heavy equipment turned on and starting of large electrical motors.
The Second is Brownouts these are long term sags in the mains supply voltage which can last up to several days. In this case a steady state of RMS Voltage under nominal by a relatively constant percentage the common Cause for this is switching of mains supply.
The third is Power Surges and in this there is short duration increase in the main supply voltage which generally lasts several cycles Voltage above 110% of the RMS value for more than 1 cycle the common cause for Heavy equipments being turned off.
The fourth phenomenon is called Electrical Noise High frequency interference in the incoming mains supply. The main reasons for this broadcast transmission and microwave radiation.
The fifth phenomenon is Blackouts it is basically Loss of incoming mains supply. The common causes for blackout are natural calamities & overloading.
The last and the most significant phenomenon is voltage spikes these are very high energy surges or spikes lasting only a few milliseconds. There are two major reasons for voltage spike Magnetization Spikes: Magnetization flux jump & Transport Current Spikes: transport current redistribution
III. REMEDIES C
1. LIMIT LEAD INDUCTANCE The primary way to reduce the inductance is to use shorter, thicker wires. This might not always be practical, but limiting LC transients is just one of several good reasons for avoiding excessively long wires in your designs With the same power switch used earlier but with a battery and shorter leads we see the result is slightly improved. Unfortunately, we’re still left with a potentially destructive transient and in cases such as the bench power supply, reducing lead length can be impossible or very inconvenient.
2. ADDING RESISTANCE TO THE LC CIRCUIT The next thing we can consider is adding resistance in series with the power leads to limit the initial current surge. In low-power applications, even several ohms of resistance might be tolerable since the resulting voltage and power loss under typical conditions might be negligible. However, adding resistance can be very undesirable in high-power applications. One option in such cases is to replace the instantaneous connection of a mechanical switch with the more gradual transition offered by an electronic switch, such as a MOSFET. The MOSFET does add a bit of resistance (typically around 0.01 ohms), but the important factor is the MOSFET’s gradual transition from non-conductive to conductive. With the mechanical switch replaced by a MOSFET, the 40-volt peak we saw was reduced to under 20 V.