Warning: not all SPDs are the same, in fact three macro-categories can be distinguished:
Switching or trigger : the main role is assigned to the spark gap . This is a device made with 2 electrodes spaced in the air. When an overvoltage occurs, an electric arc will be generated between these 2 electrodes. The advantages of this type of SPD are: reliability, galvanic isolation, size and high discharge currents local electrician in Charleston, WV.
A limitation : the most used technology are varistors made with a ceramic mixture and zinc oxide particles . When a voltage occurs, these are always crossed by a small leakage current, and their main characteristic is the constant maintenance of the voltage at the terminals during the absorption of the overvoltage. The advantages of these mechanisms are: very short intervention times, precision in the repeatability of ignition, low level of protection Up and finally absence of the following current .
Combined type : it is simply the connection in series or in parallel of the first two types of SPDs . The advantages of a series connection are the galvanic isolation and the absence of follow current . In the case of parallel connection, the advantages are: reduced tripping time, high discharge currents, low level of protection Up and tripping precision.
Which one to choose
After understanding what surge arresters are and what they are for, it is equally important to understand how to choose the type of SPD to install in your system. In order to make the best choice, it is necessary to be aware of the “nameplate data” of each type of SPD. The wording “plate data” refers to specific characteristics, the most important of which are:
Rated voltage [Un] : indicates the rated voltage of the power supply system.
Maximum continuous voltage [Uc] : indicates the voltage value below which the SPD does not intervene.
Protection voltage level [Up] : represents the maximum voltage value that persists across the SPD during its intervention.
No-load voltage [Uoc] : this parameter is peculiar to Class III SPDs and corresponds to the peak value of the no-load voltage of the combined type test generator capable of delivering at the same time a current with an 8/20 micro waveform seconds.