In the recent article, we read about the sources of surges in Industrial & Commercial Power Systems. In this article, we will analyse solutions to protect the electronic equipment from surges. Nowadays, many electronic equipment failures are mainly due to two main reasons mentioned below.
With availability of online harmonic analysers, it is made simple to study harmonics, which comes under AC Power quality. Once you find solution for harmonics but still the problem remains and equipment failure continues due to unknown reasons, then it is mainly attributed towards surges. Surges can be lightning surges and switching surges.
Lightning surge causes radiated and conducted surges.
Radiated surges can be minimized by having Faraday cage type of lightning protection system while SPD’s- Surge Protection Devices are the remedy for conducted surges which pass through power, data and communication cables.
SPD will conduct under surge conditions only, and during normal conditions remain in sleep mode or does nothing similar to a fuse function within its current rating.
The fundamental difference between Fuse & SPD is,
FUSE is current operated device and is connected in series to the load whereas an SPD is a voltage operated device connected parallel to the load, in most power line applications. Unlike a fuse, SPD can be used many times which actually depends on the amount of surge taken by SPD over a period of time.
Surge or over voltage exists only for few microseconds to few milliseconds and hence the total energy is not huge. SPD operates when the voltage across it exceeds a pre- determined level called MCOV- Maximum Continuous Operating Voltage.
Not only selection of SPD for a particular application is important, its installation is much more important. Improper installation can damage both the equipment and SPD. In some cases, equipment continues to fail, while SPD is in good condition. Both are undesirable situations. Also most of the electrical Engineers are well versed in installation of fuses, MCBs etc which are current operated devices where as SPD is voltage operated device, in which short, straight run of wire is more important than thickness of the wire.
Further, SPD earth and equipment earth must be connected to same EBB- Equipotential Bonding bar, preferably SPD earth with shorter length than the equipment that needs protection. Hence, one should do the SPD installation exactly as per the recommendation of instruction/installation manual.
Also, power line SPDs at different locations- Viz. Main DB, Sub DB and equipment side should have insulation co-ordination much like the same of fuse coordination.
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