Tips to protect your equipment from Lightning surge.
This is my personal opinion getting from basic information to protect equipment from lightning surge.
Home /Internal Lightning /SPD CoordinationCoordination of SPD
In case of several SPDs on one line, each SPD should take care of corresponding surge current so that any SPD do not break down. SPD may be broken or make fire if particular SPD have to take care of too much surge current.
・Panels installed SPD are closely placed.
・Power disribution unit and equipment put into a panels like Cellphone station.
Class 1 (taking care of lightning) places at entrance line form outside and class 2( taking care of induced current)places near equipment.
SPD placed near equipment may break down, if coordination is not achieved, since Class 2 SPD have to take care fo lightning current.
To achieve Coordination of SPD
You can achieve SPD coordination, if you have characteristices data, even SPD from different company. Normally it is difficult to get it and we recomend install SPD from one comapny.
・Coordinaiton SPD for Power and signal
There is No need to think abou coordination of the SPDs, since power and signal line is separated. SPD on power line does not afftect SPD on singnal line.
It may be a good to install SPD for both power and signal lines from one company from the point of maintenace of facility.
Illustration of SPD Coordenation
Coordination Achieved
Coordination Fail
SPD Coordination is important, if several SPD are on one line.
Class 1 SPD will be instaleld to discharge lightning current at the place coming on lines from outside and Class 2 will be installed near equipment to protect from surge current.
If discharge currnt by Class 1 SPD is not enough, Class 2 SPD have to take care of majority part of it and will be broken or damaged seriously
Each SPD have to handle corresponding part of lightning and surge currnt to protect equipment.
In case of Class 1:Gap and Class 2: Varistor
Illustration of the coordination
Gap generally have high capability to by-pass lightning current than other devices and then usually installed the location where lightning current may come. It is important that you consider discharge voltage of the Gap. Varistors start by-pass current from low voltage and expotentially increase amount of by-pass current with increasing voltage. Varistor may be broken if timing of discharge by Gap is too late.
Coordination of Gap and Varistor
Coordination is achieved if discharge voltage of Gap(SPD1）is lower than voltage of Max dischage current（Imax 2） of SPD2. Varistor(SPD2）already starts by-pass before Gap starts dicharge currrent. Discharge voltage of the Gap should be less than voltage(Umax2) of varistor. Wire between has some inductance element and we have some voltage diffenrence Up1 and Up2. It is good idea put Inductance device inbetween the SPDs so that more safe condition for coordination.
In case of Both Class 1 and Class 2 are Varistor
Illustration of the coordination
Coordination is achieved the conditon that by-pass current of SPD 1 is bigger than SPD 2. Charcteristics curve of SPD 1 is lower than it of SPD 2 at any voltage. If the charcteristice curve of both Varistor is the same, coordination will still be achieved, since Up1 is always highter( Ldi/1t) than Up2 an points. Compairing "Varistor voltage" is not good idea to check Coodination conditon. charastatics curve may be crossd over at some voltage, even "Varistor voltage" of SPD1 is lower than it of SPD2.
Coordination of Both are Varistor
Key to achieve coordination is that characteristic curve of SPD1 is lower than it of SPD2 at any point, so that SPD1 is by-pass large amount of surge than SPD2. If you see the above graphic, you can understand that operation points of SPD1(yellow) can flow large amount of surge than SPD2(green). Red point is Max point that SPD2 can take care of surge and coordation will not be achieved over the point.
In case of Coordination Fail
Coordination of Gap and Varistor
The above graphic shows that discharge voltage of SPD1（Gap）exceedsthe voltage of Max flow current of SPD2(Varistor). SPD2 may be broken before SPD1 begine discharge.
Coordination of Both are Varistor
The above graphic shows that charcteristice curve cross over at some point. Surge current of SPD2 is larger than any point after the crossed the curves. "Varistor voltage" is not good idea to check Coodination conditon. We recomend that you check charastatics curve both varistors all area.
Again contents in this Web site is my Personal Opnion. I did my best for the contents of this site, but may have some mistakes. We applogize if such things happen. Please remember that we will Not Take Any Resposibilties, even if you take countermeasures for lighting surge following on this contents and have any damage directly on your equipment and/or some other seconday damages.Please do any lightning protection based on your own resposibilty.