RK3000 High Frequency Power Supply
Operating Manual
Page 52 of 73
CHAPTER 10
DISCUSSION OF TYPICAL CONTROL WAVEFORMS
The waveforms on the following pages show the precipitator peak current waveform
versus time for various programmable parameter settings. These waveforms can be
duplicated on an oscilloscope with single sweep and storage capability by connecting the
positive scope lead to Interface Unit terminal TB7 points 1 (ma) and the ground lead to
Interface Unit TB7point 3 (ISOGND). These waveforms show the envelope (peak values
connected together) of the secondary current signal.
Waveform #1, Quench Mode, Arc Only, Pedestal Programmed to 1 Cycle
Starting in the upper left-hand corner, the precipitator current is at its maximum rating.
The current is stable at this level until a Spark occurs. The RK3000 sense the Spark and
reduces the conduction angle of the IGBTs, causing an almost instantaneous reduction in
precipitator current. This current reduction after a Spark is called the Phase Back. Phase
Back is a discrete key programmable parameter.
Sketch 1: Quench Mode Arc Only
Within one-half cycle after reaching the Phase Back current level, the
RK3000 starts to
increase current towards it’s rating by increasing the conduction angle of the IGBTs. The
period of time it takes for the current to increase from the Phase Back level to the current
level where the spark occurred is called the Ramp Rate. The Ramp Rate is a discrete
key programmable parameter.
If an arc occurs in the precipitator, the RK3000 detects the arc and quenches the arc
within one-half cycle by interrupting the firing pulse to the IGBTs. This turns off the power
to the precipitator for the programmed Quench Time, forcing the arc to extinguish. After
the Quench Time, the IGBTs are again turned on and the power increases to the Phase
Back level in the programmed 1 cycle pedestal rate. At the Phase Back level, the rate of
current increase is transferred to the Ramp Rate, which continues to increase the current,
but at a slower rate.
This control action repeats every time an Arc and/or Spark occur in the precipitator.
