The components of a SPD
The SPD chiefly consists of (see Fig.1):
1) one or more nonlinear components: the live part (varistor, gas discharge tube, etc.);
2) a thermal protective device (internal disconnector) which protects it from thermal runaway at end of life (SPD with varistor);
3) an indicator which indicates end of life of the SPD;
Some SPDs allow remote reporting of this indication;
4) an external SCPD which provides protection against short circuits (this device can be integrated into the SPD).
Technology of the live part
Several technologies are available to implement the live part. They each have advantages and disadvantages:
•Zener diodes;
•The gas discharge tube (controlled or not controlled);
•The varistor (zinc oxide varistor).
The table below shows the characteristics and the arrangements of 3 commonly used technologies.
Fig.2 – Summary performance table
A surge protective device (SPD) is designed to protect electrical systems and equipment from surge events by limiting transient voltages and diverting surge currents. Surges can originate externally, most intensely by lightning, or internally by the switching of electrical loads. The sources of these internal surges, which account for 65% of all transients, can include […]
DC SPD applied to the Din rail type protects the DC electric system from surge. Also, the system allows replacement of the protective element (MOV), ensuring convenience and reduced cost. However, as only the protective module is provided, other components should be added when the system is installed in accordance with the site condition.
Knowing individual surge components is helpful to understand, but what drives the standards for SPDs are performance aspects or features for each device. After identifying the power distribution system to which the SPD is to be connected, one should compare different available devices by the following: 1. Maximum Continuous Operating Voltage (MCOV). The MCOV is the […]
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