Daikin WMC Specifications download pdf (Page 26)

26 Centrifugal Chillers IMM WMC-2

1. Keep the PCC as far from the drives (close to the power source) as possible.

2. Increase the size (decrease the impedance) of the source transformer.

3. Increase the capacity (decrease the impedance) of the busway or cables from the source to the PCC.

4. Make sure that added reactance is "downstream" (closer to the VFD than the source) from the PCC.

Line Reactors

Five-percent line reactors are standard equipment on WMC chillers and located in each compressors power

panel. They are employed to improve the power factor by reducing the effects of harmonics.

Harmonic Filter

The harmonic filter is an option for field mounting and wiring outside of the power panel. It works in

conjunction with the line reactor to further minimize harmonic distortion. It is wired between the line reactor

and compressor. IEEE 519-1991 Standard defines acceptable limits.

See the WMC certified drawings for harmonic filter dimensions and wiring information.

EMI (Electro Magnetic Interference) and RFI (Radio Frequency Interference) Filter

This filter is a factory-installed option. The terms EMI and RFI are often used interchangeably. EMI is actually

any frequency of electrical noise, whereas RFI is a specific subset of electrical noise on the EMI spectrum.

There are two types of EMI. Conducted EMI is unwanted high frequencies that ride on the AC wave form.

EMI

Radiated EMI is similar to an unwanted radio broadcast being emitted from the power lines. There are many

pieces of equipment that can generate EMI, variable frequency drives included. In the case of variable frequency

drives, the electrical noise produced is primarily contained in the switching edges of the pulse width modulation

(PWM) controller.

As the technology of drives evolves, switching frequencies increase. These increases also increase the effective

edge frequencies produced, thereby increasing the amount of electrical noise.

The power line noise emissions associated with variable frequency and variable speed drives can cause

disturbances in nearby equipment. Typical disturbances include:

• Dimmer and ballast instability

• Lighting disturbances such as flashing

• Poor radio reception

• Poor television reception

• Instability of control systems

• Flow meter totalizing

• Flow metering fluctuation

• Computer system failures including the loss of data

• Thermostat control problems

• Radar disruption

• Sonar disruption

RFI

Three-phase filters are supplied as an option for factory mounting in the compressor power panels. They use a

combination of high frequency inductors and capacitors to reduce noise in the critical 150 kHz to 30 MHz

frequency range. The inductors act as open circuits and the capacitors act as short circuits at high frequencies

while allowing the lower power line frequencies to pass untouched. The filters assist with cost effective

compliance to Electro Magnetic Compatibility (EMC) directives, in a compact, efficient, light-weight design.

The high common mode and differential mode reduction in the critical 150kHz to 30MHz frequencies assures

that potential interference from AC drives is reduced or eliminated.

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Daikin WMC Specifications Page 26

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