Hello,

I am having problems measuring the voltage of a 600 kW six pulse
bridge rectifier with a simple multimeter ....
it is runing through 3 pairs of thyristors (1800 V, 1500 A 200 ìs
typical time) the AC burs after a Current transformer (???) attached
to each one passes current to thyristors in pair
When I power ON at around 250 kW , it is an induction furnace solid
state inverter at 600 kW - yet I am reaching just the 500 kW for the
moment ... and I measure (multimeter in AC V scale) the AC bars in
one end and the other to DC (upper thyristors blocks) I get
respectively say 1-2 ~ 650 V 1-3 ~ 1000 V(!) and 2-3 1350 V (!!!),
to the lower thyristor block from AC bars again , low voltage like
120-220 Volts
DC+DC- around 1000 Volts
when power of the generator is OFF , normal 400 V AC is coming through
the 3 AC bars ....
measuring the AC burs at the exit of the main switch from my board to
the cabinet I get 500, 730, 840 Volts respectively
the AC bars leading to the thyristor pairs usualy overheats, I suspect
it is a thyristor triggering related problem but cant measure them
correct , though in 200 Ohms none is showing short circuit

thyristors are like ...

1 3 5
2 6 2

and bus bars 1 2 3


I would apreciate if someone could enlighten me on how to measure the
voltages and/or thyristors thanks !