Atlas Copco QAS 275-325, Instruction Manual, Page: 60 / 114

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Connecting the generator
Precautions for non-linear and
sensitive loads
The most common non-linear, 3-phase loads are
thyristor/rectifier-controlled loads, such as convertors
supplying voltage to variable speed motors,
uninterruptable power supplies and Telecom
supplies. Gas-discharge lighting arranged in single-
phase circuits generate high 3rd harmonics and risk
for excessive neutral current.
Loads most sensitive to voltage distortion include
incandescent lamps, discharge lamps, computers, X-
ray equipment, audio amplifiers and elevators.
Consult Atlas Copco for measures against the adverse
influence of non-linear loads.
Quality, minimum section and
maximum length of cables
The cable connected to the terminal board of the
generator must be selected in accordance with local
legislation. The type of cable, its rated voltage and
current carrying capacity are determined by
installation conditions, stress and ambient
temperature. For flexible wiring, rubber-sheathed,
flexible core conductors of the type H07 RN-F
(Cenelec HD.22) or better must be used.
The following table indicates the maximum allowable
3-phase currents (in A), in an ambient temperature of
40°C, for cable types (multiple and single core PVC
insulated conductors and H07 RN-F multiple core
conductors) and wire sections as listed, in accordance
with VDE 0298 installation method C3. Local
regulations remain applicable if they are stricter than
those proposed below.
The lowest acceptable wire section and the
corresponding maximum cable or conductor length
for multiple core cable or H07 RN-F, at rated current,
for a voltage drop e lower than 5% and at a power
factor of 0.80, are respectively 2.5 mm² and 144 m. In
case electric motors must be started, oversizing the
cable is advisable.
The voltage drop across a cable can be determined as
follows:
e = Voltage drop (V)
I = Rated current (A)
L = Length of conductors (m)
R = Resistance (

/km to VDE 0102)
X = Reactance (

/km to VDE 0102)
Connecting the load
Site distribution panel
If outlet sockets are provided, they must be mounted
on a site distribution panel supplied from the terminal
board of the generator and in compliance with local
regulations for power installations on building sites.
Non-linear loads draw currents with
high contents in harmonics, causing
distortion in the wave form of the
voltage generated by the alternator.
Wire section Max. current (A)
(mm
²
)
Multiple core Single core H07 RN-F
25 94 101 88
35 114 123 110
50 138 155 138
70 176 191 170
95 212 228 205
120 245 273 239
150 282 314 275
185 323 358 313
240 379 421 371
300 429 477 428
e
3 I L R

cos

X

sin

+
    
1000
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