Thyristor Checking
Thyristor Checking
(OP)
Hello Everybody
I have a question regarding checking thyristors. What is the correct way to check a thyristor? Recently I got problem in a DC drive and I have to replace the thyristor board. On checking I got ohm readings as shown in attached table, but not sure what is the ideal ohm value for a thyristor? DC drive is of 640 Volts and 540 amps. Tyhristors are EUPEC- TT250N16KOF.
I have a question regarding checking thyristors. What is the correct way to check a thyristor? Recently I got problem in a DC drive and I have to replace the thyristor board. On checking I got ohm readings as shown in attached table, but not sure what is the ideal ohm value for a thyristor? DC drive is of 640 Volts and 540 amps. Tyhristors are EUPEC- TT250N16KOF.





RE: Thyristor Checking
A thyristor in good shape shall not light the lamp. Applying a gate gurrent (around 100 mA, negative to K1 and positive to G) shall light the lamp. The lamp shall not burn brightly, since the current is half-wave rectified. Remove the gate current and the lamp shall go out.
PLEASE NOTE: You will be dealing with lethal voltages. Use insulating gloves and do not work on your own!
If you really want to characterize your thyristors, you can use a special thyristor check instrument. But that is seldom needed.
The values in your table look good. Not much to worry about. They show the normal spread. Don't think any of your thyristors is faulty - it usually shows in gate resistance either being very low or very high.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Thyristor Checking
The correct way is to apply a voltage and measure the leakage current, then apply a gate voltage and measure at what level it turns on. Both of these will be in the specification for the device.
Typically, the gate resistance will measure shorted or open or the SCR will measure shorted anode to cathode if it is bad. The gate resistance is usually between about 4-40ohms.
RE: Thyristor Checking
RE: Thyristor Checking
The gate include a silicon junction so there is a threshold voltage. If the source voltage for you resistance measurement is too low, the resistance will appear to be high.
The resistance of a given gate cathode with change depending on the actual meter used. The good old analog meter virtually always works, but some digital do not.
Best regards,
Mark Empson
L M Photonics Ltd
RE: Thyristor Checking
I've used the method Skogsgurra suggests although my supply was a big 110V DC source loaded with a bank of 500W halogen floodlamps. Blocking in the forward and reverse directions was proven by a Megger test, then conduction and gate firing was tested with a pulse of about 100mA or so. Worked very well. Also scared one of the managers who walked into the makeshift test area only to be blasted by a few kW of floodlamps as I triggered the gate. Highly entertaining for those of us who knew what was going on!
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If we learn from our mistakes I'm getting a great education!
RE: Thyristor Checking
Out of curiosity, I checked a medium size thyristor (a couple of hundred amps in a six pulse bridge) and got the results in the attached pdf.
I remember that I wondered about this before. The characteristic is much more linear than one would think.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Thyristor Checking
RE: Thyristor Checking
I missed it before but device #2 AK-K is likely bad if it is only 8.9 ohms. I hope you meant 8.9M??