Thyristors problem in a 1800v capacitor discharge system

Thread Starter

gordi

Joined Oct 20, 2019
4
I have two thyristors R1275nc21x, they are Westcode thyristor and have some issues in my application.

I want to make a capacitor draining system with 1800V charged and it can discharge to the coil (8uH, 10mΩ)resonantly (with 166us duty cycle and up to 30Hz). But our thyristors(S2) burned, maybe to causes: high dv/dt or high voltage or not suitable snubber.

Of course, I used another thyristor Y89kkm for Techsem that higher voltage than “R1275nc21x”, but it has burned too.

It is necessary to mention that Scr2 always burn.

Please guide me select right SCR and snubber or right circuit.
chargeDischargeSys.JPG


chargingAndDrainingCap_test_Circuit_Transient_Result.JPG

This is one cycle of draining 166us in 1 to 30Hz.

scrTrigger.JPG
before connect to G K of SCR.

Of course, I trigged thyristors gates separately with pulse transformer,2 or 3 pulse every cycle (1 to 30Hz), 5 volts and 10ms Duty cycle and 20us period.
 

crutschow

Joined Mar 14, 2008
23,499
The R1275nc21x is one healthy size SCR so it's not obvious what could be zapping it.
The peak current should be no more than about 1500 amperes.

Can you look at the voltage across the inductor during the discharge?
 

Hymie

Joined Mar 30, 2018
711
I suspect you are breaching one or more of the parameters on the data sheet for the device.

Interestingly it lists a maximum gate voltage of 3V, you appear to be applying 5V.

The energy stored in the 65uF capacitor is around 100 Joules; looking at the data sheet figures 9 & 10 (note the figure 9 Y axis is in mJ), you may be exceeding this.

It might be worth contacting IXYS technical department asking for their advice.
 

Thread Starter

gordi

Joined Oct 20, 2019
4
The R1275nc21x is one healthy size SCR so it's not obvious what could be zapping it.
The peak current should be no more than about 1500 amperes.

Can you look at the voltage across the inductor during the discharge?
Thanks reply. my circuit current un 166us is 5500A but the SCRs have higher in non-dc current. I will add some information.
 

Thread Starter

gordi

Joined Oct 20, 2019
4
I added some additional informations.
SCRsVoltage.JPG
SCRs voltage

scrtriggervoltage_in negetiveSide.JPG

real SCR trigger voltage that I measured by oscilloscope.



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