Figure 111 - Current Transformers; Figure 112 - Dv/Dt Output Suppression Network; Figure 113 - Flash Tank Feed And Drain Valve Controller - York YCIV0157 Installation Operation & Maintenance

Section 6 - Technical data
Current transformers
CURRENT
TRANSFORMERS

Figure 111 - Current transformers

A current transformer on each phase sends current sig-
nals proportional to phase current to the VSD Logic
Board. The output of each CT is buffered, scaled, and
sent to RMS to DC converters. These signals are then
sent to an A-D converter, scaled, and sent to the Chiller
Control Board for current display and current limiting
control.
The highest current is also compared to the setting of
the Overload Adjustment Potentiometer on the VSD
Logic Board for overload safety sensing.
DV/DT output suppression network
DV/DT
RESISTORS

Figure 112 - DV/DT output suppression network

The dV/dT Output Suppression Network limits the rate
of rise of voltage and the peak voltage of the PWM
198
LD10617
LD10618
DV/DT
CAPACITORS
pulses applied to the motor windings. This eliminates
the possibility of causing a turn-to-turn short in the mo-
tor due to winding insulation breakdown. The suppres-
sion network is made up of a 3-phase RC network.
Flash tank feed and drain valve controller
Figure 113 - Flash tank feed and drain valve
controller
The Flash Tank Feed and Drain Valve Controller is a
microprocessor driven controller that operates the Feed
and Drain Valves based on commands from the Chiller
Control Board. The Feed and Drain Valves control the
level of liquid in the flash tank and the superheat to
the evaporator. The controller is a stand-alone valve
control module in the Control/VSD panel. The flash
tank liquid level is controlled by sequencing a stepper
motor valve (Feed Valve) on the inlet of the flash tank.
The controller opens and closes the Feed Valve to con-
trol the liquid level of the refrigerant in the flash tank
based on commands from the Chiller Control Board.
Superheat is controlled by sequencing a stepper motor
valve (Drain Valve) on the outlet of the flash tank. The
controller opens and closes the Drain Valve to control
flow to the evaporator and ultimately superheat to the
compressor based on commands from the Chiller Con-
trol Board.
Drain Valve superheat control is controlled by a PI
control algorithm based on suction pressure and suc-
tion temperature in the Chiller Control Board software.
The control algorithms will attempt to control the level
in the flash tank to approx 35% when the economizer is
energized. If the level exceeds 87.5%, the system will
fault. The normal 35% level may fluctuate apprecia-
bly when the economizer is off as the flash tank acts
as nothing more than a reservoir as the Drain Valve
controls superheat. The level will also vary when the
economizer is first energized or a system transient oc-
curs such as fan cycling, etc.
Form 201.23-NM2
Issue date: 12/19/2023
LD10619
Johnson Controls