Daikin WMC Specifications download pdf (Page 39)

Catalog 602-2 39

Power Factor Correction

Do not use power factor correction capacitors with

WMC chillers. Doing so can cause harmful

electrical resonance in the system. Correction

capacitors are not necessary since VFDs inherently

maintain high power factors.

The full load power factor exceeds 0.90 for all

units.

VFD Line Harmonics

Despite their many benefits, care must be taken

when applying VFDs due to the effect of line

harmonics on the building electric system. VFDs

cause distortion of the AC line because they are

nonlinear loads, that is, they don't draw sinusoidal

current from the line. They draw their current from

only the peaks of the AC line, thereby flattening

the top of the voltage waveform. Some other

nonlinear loads are electronic ballasts and

uninterruptible power supplies.

Line harmonics and their associated distortion can

be critical to ac-drives for three reasons:

1. Current harmonics can cause additional

heating to transformers, conductors, and

switchgear.

2. Voltage harmonics upset the smooth

voltage sinusoidal waveform.

3. High-frequency components of voltage

distortion can interfere with signals

transmitted on the AC line for some

control systems.

The harmonics of concern are the 5

, 7

, 11

, and

. Even harmonics, harmonics divisible by three,

and high magnitude harmonics are usually not a

problem.

Current Harmonics

An increase in reactive impedance in front of the

VFD helps reduce the harmonic currents. Reactive

impedance can be added in the following ways:

1. Mount the drive far from the source

transformer.

2. Add line reactors. They are standard

equipment on Magnitude chillers.

3. Use an isolation transformer.

4. Use a harmonic filter.

Voltage Harmonics

Voltage distortion is caused by the flow of

harmonic currents through a source impedance. A

reduction in source impedance to the point of

common coupling (PCC) will result in a reduction

in voltage harmonics. This can be done in the

following ways:

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 Magnitude 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. IEEE 519-1991

Standard defines acceptable limits.

See the Magnitude installation manual and

certified drawings for harmonic filter installation

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.

1 2 ... 34 35 36 37 38 39 40 41 42 43 44 ... 63 64

Comments to this Manuals

No comments

Daikin WMC Specifications Page 39

Comments to this Manuals

Related products and manuals for Heat pumps Daikin WMC