455-461 Series
In the 455 and 461 series, the thyristors are fired by a trigger
pulse train
of a maximum
of 5 ms.
To reduce the cost price of the electronics, it is possible, in most single-phase applications,
to send trigger pulses every
10 ms
so that the thyristors are polarized directly (anode
positive in relation to cathode) or inversely (anode negative). Each thyristor will only fire
when its voltage is positive; when it is negative, the anti-parallel thyristor fires.
In certain applications, trigger pulses on the inversely polarized thyristor may lead to
operating problems: firing instability, fuse blow-out.
It is therefore essential to eliminate the trigger pulses when the thyristor is inversely
polarized: this function is performed by the
gating
circuit available in the standard version
of models 456 to 458 and 462 to 464.
This selective locking of the trigger pulses is essential for configurations in which several
units are distributed between the phases of a three-phase supply with an electrical coupling
by the load which causes a voltage
phase shift.
For example:
• monitoring of heating electrodes (in the transformer secondary circuit) immersed
in the same glass bath
• load in star with neutral, with the central point of the star connected to the neutral
of the supply by a wire of a non-negligible resistance in relation to that of the
load.
451-461
User
Manual
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