bus capacitors, and the current will be limited by the precharge resistors. This 12 second period
is called the precharge time. After 12 seconds has passed, a small relay will close, and cause the
supply contactor to close. Shortly, after this time the precharge contactor will open. The drive is
now precharged and ready to run. All of the precharge faults will remain the same as when the Aux.
power device is used to precharge the drive.
The 0490A, 0612A, and 0730A amp drives contain only one power assembly. It is very similar to the
assembly used on the 0490 drive. The power assembly contains two bus capacitors. The 0612A uses
12 modules, and the 0730A uses 15 modules. A pair of power devices share a gate driver board.
A power supply board mounted on top of the power assembly provides power to the gate driver
boards.
The 1278A amp drive contains three power assemblies like the 0774 amp drive, but two capacitors
and more power devices are required on each assembly. Due to the size of the 1278A amp drive, it
has three doors. The center and right doors cannot be opened unless the circuit breaker is placed
in the off position, and the left door is open.
Harmonic filter benefits
The OptiSpeed Compressor Drive (OSCD) system now includes an input Harmonic filter and
high frequency filter trap designed to meet the IEEE Std 519, “IEEE Recommended Practices and
Requirements for Harmonic Control in Electrical Power Systems”. The Harmonic filter provides
a means to improve the input current waveform drawn by the OSCD from the AC line, thus
reducing the possibility of causing electrical interference with other sensitive electronic equipment
connected to the same power source, and reduce 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. Over correcting the power factor may cause voltage
ringing that may 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, thus allowing 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 52 and Figure 53.
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.
YMC
2
Mod B with OptiView
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Control Center
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