Airedale TurboChill FreeCool 200kW - 1830kW - Manual (Page 118)

118 Chiller Technical Manual 7525355 V1.1.0_04_2013
Chillers TurboChill™ Air Cooled and FreeCool
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Power Quality & Harmonics
Variable speed drives are now common place due to their efficiency and versatility. Not ignoring these facts, care must
be taken when installing VSD technology into new and existing installations. This is due to the effect the introduction of
such technology may have on line harmonics of a buildings electrical system. VSDs by their nature cause distortion of
the AC line by drawing current in pulses, rather than continuously from the supply resulting in harmonic generation. The
useful power to a motor is that obtained from the fundamental frequency of 50Hz. The additional currents at the higher
frequencies are not useful to the appliance and are therefore transmitted back onto the line.
Examples of other non-linear loads that cause harmonics are:-
Single phase loads, e.g.
• Switched mode power supplies
• Personal computers
• HF fluorescent ballasts
• Compact fluorescent lamps
Three phase loads, e.g.
• Variable frequency drives
• Inverters
• Large UPS systems
The distortion of the line caused by harmonics can cause the following associated issues:-
• Erroneous operation of control systems
• Nuisance tripping of circuit breakers
• Overloading of transformers
• Overloading of capacitors
• Overvoltage problems
• Excessive currents in neutral conductor
The 3rd, 5th, 7th and 9th harmonics are considered to be the predominant frequencies produced by non-linear loads.
To minimize the harmonic effect, each Turbocor compressor is fitted with a 5% line reactor to help reduce the harmonics
and improve the displacement power factor above 0.95 (1). However, to further reduce the effects and to help meet limits
for engineering recommendation (ER) G5/4, the following guidelines can be followed.
Current Harmonics
Harmonic currents contribute to system losses. Mitigation measures can be implemented in the following ways:
a) Install passive/active harmonic filters
b) Install the unit as far from the source transformer as possible
Voltage Harmonics
Harmonic voltage distortion causes disturbance to other loads and increases losses in them. Methods for harmonic
voltage reduction can be achieved in the following ways:
a) Increase the size of the supply transformer
b) Connect the unit to a point with a high fault level (low impedance)
c) Keep the unit as far from the point of common coupling (PCC) as possible
Engineering Recommendation G5/4
It is important to understand that G5/4 is effectively an “Installation Standard” and applies to the total harmonic
generating equipment installed by a consumer. G5/4 identifies consumers by their PCC to the supply and applies limits
at that point. G5/4 is not a product or equipment standard and therefore no single item of equipment can be said to
comply.
Note: (1) Based at full load conditions.