Johnson Controls YORK YVAM 0350, Operation & Maintenance Manual

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connected to the same power source, and reduces power loss in the customer’s switch gear and
source transformer.
In addition, the power factor of the system with this harmonic filter corrects the OSCD’s input
power factor to nearly unity over the full load range of the product. Some passive filters may over
correct the power factor at lighter loads. Overcorrecting the power factor can cause voltage ringing
that can affect other equipment.
Harmonic filter general information
The Harmonic Filter is no longer an option for this style of OSCD. The function of the Harmonic
Filter is now integrated into the input of the OSCD. The input rectifier has fast switching transistors
instead of SCR’s and diodes. The OSCD can now control the input current waveform to a near sine
wave shape by controlling how the rectifiers are turned on and off. The Harmonic Filter of the past
injected harmonic current into the input of the OSCD to correct the current waveform.
Since the Harmonic Filter is basically the input to the OSCD there is no need for the additional, pre-
charge, power unit, Harmonic Filter logic board, and contactors for the Harmonic filter of yesterday.
The Harmonic Filter does not require its own pre-charge time, which allows the chiller to start or
restart sooner. This is an important benefit to many customers. The reductions in parts counts will
improve the reliability of the OSCD, and ease of repair. See Figure 47 and Figure 48.
A line inductor is still needed to limit the rate of change in the input current. Without the line
inductor, the input current cannot be properly controlled and harmonic currents would be
generated.
115 YVAM Control Center