JUMO 709040 TYA-110 thyristor power unit Operating Manual - Manual (Page 16)

2 Operating modes
16 Power units 02.06
For transformer loads, the thyristor power unit operates in burst-firing mode
with a cut-back (retarded) phase-angle for the first half-wave. The factory set-
ting is an angle
α = 90°. This value can be altered on the front panel over a
range
α = 0 — 90°.
v Section 5.4 “Setting the phase angle for the first half-wave”
H
We recommend that this setting is not changed!