how to design a rectifier faliure indication circuit 1

[baskings]

hello everyone,
can anyone plz help me out while giving me the solution of desining a rectifier faliure indication circuit.

idea: in a generator the excitor has a rectifier assemly. if any diode gets short circuited then by taking the load on the generotor, it burns the stator or rotor windings. we have to develop a system which can indicate us by turning any indication on either LED or BUZZER during ideal running time of genertor before taking any load on it; that some diode is short circuited.

any suggestions wuld be appreciated. u can ask me if my problem is not clear.

regards

 

[MikeHalloran]

Who stands next to the generator?
How do they see the LEDs? Exciters are usually rotating inside a closed case.
How do they hear the buzzer over the engine noise?
Where does the buzzer get its power?

Would it be simpler to just use two diodes in series?


Mike Halloran
Pembroke Pines, FL, USA

 

[VEBill]

As you mention rectifier assembly, I assume it's a DC output generator.

Perhaps you could use something like a capacitor in series with a speaker (<- conceptual). If the output is noisy, then you'll hear it.

 

[baskings]

generator output is 440v, 3-phase and 60 hz. its remote pannel is installed at a distance place frm whr its monitoring can be done. the rectifiers are installed on exciter to give it a DC supply so that it rotates inside the stator and produes current.

 

[MikeHalloran]

How about installing fuses in series with the diodes?

Hold that thought; the centrifugal force from rotation might change a fuse's effective rating. Maybe fusible links would be better. Mechanical replacement (as of fuses) would not be particularly beneficial since soldering is probably required to replace a shorted diode anyway.



Mike Halloran
Pembroke Pines, FL, USA

 

[eeprom]

So it sounds like the excitation is providing current to the field. If a diode fails, it becomes a short, and the AC current is allowed to flow to the rotor. Instead of checking the diode bridge, which would require one detector on each diode, why not measure the polarity of the field current.

If you able to design on the component level, as in actually making a printed circuit board, this could be done by putting a current shunt in series with the field. A difference op amp can be used to monitor the voltage across the shunt, which would be a scaled version of the current. Many shunts offer 1 mV per amp. The voltage should always be positive, and the change in voltage should be small. You could use one op amp to measure the polarity, this would be the difference op amp. And use another op amp to measure the differential (as in dV/dt). The differential should be small, as this is a DC circuit. If the differential becomes large, then that may be a sign of an AC component into the rotor. Either of these conditions should trip the prime mover and remove the generators load.

Someone else mentioned using fuses, which is very good idea. Although I'm not sure if you lost one diode that you would necessarily reach a current high enough to blow a fuse.

This sounds like a fun project.

 

[VEBill]

Just select some diodes that are similar in form factor, but higher in reverse voltage and forward current ratings. Then they shouldn't ever fail again.

 

[baskings]

@MikeHalloran
sir, we will add two diodes in series to which component ? can u plz make me understand the whole concept.

naser

 

[baskings]

@VE1BLL
sir plz elaborate ur concept. it seems to be interesting. may be we can makeout some solution.

regards

 

[baskings]

@eeprom
sir,
i wuld like to thnku for ur positive response. can u plz guide me further tht whr we can apply shunt ? either in series of the output of bridge rectifer or somewhr else ? further more if we choose the fuses thn wht can be the consequences ? sir plz helpout. may be we will be able to find out some positive solution.

regards

 

[VEBill]

Diodes shouldn't be short-circuiting so often that a Rectifier Failure Indicator Circuit is an attractive option.

Use better diodes. Or provide them with protection from over-voltage spikes.