use 6 thyriseor as SSR in 3PHASE(But dont WORK it)

Thread Starter

MOHAMAD MAGHSOODI

Joined Dec 22, 2015
2
Hi dear friends
i use 6 thyristor as switch in 3 phase like below:


i trigger each thyristor on zero time in its phase . (i use zero crosing).
it work when neutral is connect on star center .but it don't work when the neutral wire is disconnected .

what is the problem ?

i think for example in first time when thyristor's R phase is triggered because other thyristors are off it can't turn on (there is no way for flow the current in load )like below:


but when the neutral is connected there is a way to flow current in load like below:



-----------
now please help me to solve the problem .
how must i trigger thyristors that work circuit with out neutral wire?
thanks a lot .
best regards.

@i am sorry because my english isn't good.
 

dendad

Joined Feb 20, 2016
3,164
Yes, you need current to keep them turned on, so if you are only triggering at the 0 crossing on each phase then only 1 is being turned on and as soon as the trigger stops it will turn off again as there is no circuit for the current to flow as you have not got another one turned on. You could try continuous triggering but it would be easier to just use a suitable 3 phase contactor.
 

Thread Starter

MOHAMAD MAGHSOODI

Joined Dec 22, 2015
2
hi dear friends
i have use zero crossing . but i don't know when must trigger the thyristors .
i designed a circuit that i trigger on zero crossing each phase respect null . but it just work when we have null wire .
if i don't have null wire , how must i provide zero crossing signal ? must i use of zero crossing or commutation point ?
best regard
 

tcmtech

Joined Nov 4, 2013
2,868
Are you triggering two SCRs at a time, so that two windings at a time are enabled to pass current?
Depending on the orientation of the phases in a cycle two outgoing devices may need to be turned on.

Add in any odd counter EMF feedback or phase shifting due to power factor and its possible that at any one point all six devices could need to be actively turned on to compensate for it.
 
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