2330 - 301 exam question

[pedro1961]

I sat the 301 on line last night at college, may have well not bothered learning formulaes as so much was on machines, but little on calulations ,eg what would improve the torque on a 3Ph induction motor,option were to add capacitors or resistors in rotor or stator windings etc. Absolutley nothing on lighting or power factors.

One question was something like " semi conductor diode , supplied with 10 v what will be the PIV ", options were .707v, 14v, 20v or 40 v, i've looked up explanations of PIV but can't work out what the answer would be, ( the course leader couldn't figure it out either, he thought it should be 10v but that wasn't an option.. I guessed at 20v but not sure if i was right).

Anyone have simple explanation of how you would work it out.

thanks

 

[markyboy2782]

Pedro

Not 100% on this as i'm still a student myself but vaguely remember touching on this in college.

PIV stands for Peak Inverse Voltage - This is the maximum voltage that a diode can withstand in the reverse direction without breaking down.

I think the simplest way to calculate this would be PIV = 10V x sqrt(2) = 14.142V.

Not good that your tutor didn't know what this was though.

Mark

 

[Technician]

Torque improvement on a 3 phase machine would

entail adding resistance to the rotor windings.

Peak torque in these machines takes place when

rotor resistance equals rotor reactance and thus

adding resistance causes the peak torque speed

to alter. Sufficient resistance can be added so that

peak torque takes place at start up.