Danfoss VLT 3500 HVAC, Руководство пользователя

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81
VLT
®
3500 HVAC
MG.35.B1.02 – VLT is a registered Danfoss trademark
Section 1Section 1Section 1Section 1Section 1
Section 2Section 2Section 2Section 2Section 2
Section 3Section 3Section 3Section 3Section 3
Section 4Section 4Section 4Section 4Section 4
•••••
Derating for running at low speed Derating for running at low speed Derating for running at low speed Derating for running at low speed Derating for running at low speed
When a centrifugal pump or a fan is controlled by a
VLT 3500 HVAC frequency converter, it is not
necessary to reduce the output current at low speed
because of the load type characteristic of the centrifu-
gal pumps/fans.
•••••
Derating for installing long motor cables or Derating for installing long motor cables or Derating for installing long motor cables or Derating for installing long motor cables or Derating for installing long motor cables or
cables with larger cr
cables with larger cr cables with larger cr cables with larger cr cables with larger cross-section oss-section oss-section oss-section oss-section
VLT 3502-3800 HVAC has been tested using 300 m
unscreened cable and 150 m screened cable (for
3502-3505 this only applies to f
SWITCH
≤
4.5 kHz. For
f
SWITCH
> 4.5 kHz, max. is 40 m).
du/dt and peak voltage on motor
When a transistor in the inverter is activated, the volt-
age applied to the motor will rise by the du/dt ratio
determined by
•
the motor cable (type, cross-section, length,
screened/unscreened)
•
inductors
The self-inductance will cause an overshoot U
PEAK
for
the motor voltage before it stabilizes at a level
determined by the voltage in the intermediate circuit.
Both the du/dt ratio and the peak voltage U
PEAK
influence the lifetime of the motor. Too high values will
primarily affect motors without phase coil insulation.
If the motor cable is short (a few metres), the du/dt
ratio will be quite high, but the peak voltage quite low.
If the motor cable is long (100 m), du/dt will decrease
and U
PEAK
will increase.
To ensure a long service life of the motor, VLT 3500
HVAC features as standard built-in motor coils which
ensure a low value for the du/dt ratio, even with very
short motor cables.
If very small motors are used without phase coil
insulation, it is recommended to mount a clamp filter
or an LC filter after the frequency converter.
Clamp filter, ordering no. 175H5147 (fits all units in
VLT type 3502-3562).
Typical values for the du/dt ratio and the peak voltage
U
PEAK
measured on the terminals of the frequency
converter between two phases (30 m screened motor
cable).
VLT type 3502 - 3562:
•
du/dt du/dt
du/dt du/dt
du/dt ~ 200 - 300 V/
µ
s
•
U U
U U
U
PEAK PEAK PEAK PEAK PEAK
~ 800 - 1100 V
VLT type 3575 - 3800:
•
du/dt du/dt
du/dt du/dt
du/dt ~ 2000 - 2100 V/
µ
s
•
U U
U U
U
PEAK PEAK PEAK PEAK PEAK
~ 900 - 950 V measured with a 20 m
unscreened cable
■
4.5 Special conditions
•••••
Derating for ambient temperatur Derating for ambient temperatur Derating for ambient temperatur Derating for ambient temperatur Derating for ambient temperature e e e e
The ambient temperature (T
AMB,MAX
) is the maximum
temperature allowed. The average (T
AMB,AVG
)
measured over 24 hours must be at least 5ºC lower in
accordance with VDE 160 5.2.1.1.
If VLT 3500 HVAC is operated at temperatures above
40 ºC, a derating of the continuous output current is
necessary.
•••••
Derating for air pr Derating for air pr Derating for air pr Derating for air pr Derating for air pressur essur essur essur essure e e e e
Below 1000 m altitude Below 1000 m altitude Below 1000 m altitude Below 1000 m altitude Below 1000 m altitude no derating is necessary no derating is necessary no derating is necessary no derating is necessary no derating is necessary.....
Above 1000 m the ambient temperature (T
AMB
) or
max. output current (I
VLT,MAX
) must be derated :
1) Derating of output current versus altitude at
T
AMB
= max. 40°C
2) Derating of max. t
AMB
versus altitude at 100%
output current.
VLT 3500 HVAC has been designed to work using a
motor cable with a rated cross-section. If a cable with
a larger cross-section is to be used, it is
recommended to reduce the output current by 5% for
every step the cross-section is increased.
(Increased cable cross-section leads to increased
capacitance to earth, and thus an increased earth
leakage current).
•
Derating for high switching fr Derating for high switching fr
Derating for high switching fr Derating for high switching fr Derating for high switching frequency
equency
equency equency equency
This only applies to VLT 3502-62, since the max.
switching frequency is 4.5 kHz in VLT 3575-3800.
Higher switching frequencies (par. 224) lead to greater
losses and greater heat formation in the transistors
and motor coils of the frequency converter.
Consequently, the frequency converter automatically
derates the maximum permitted constant output
current I
VLT,N
whenever the switching frequency
exceeds 4.5 kHz. The reduction is carried out as a li-
near reduction down to 60% at 14 kHz .
If the ASFM function (Adjustable Switching
Frequency Modulation) is applied (parameter 225) it is
not necessary to derate, since the variable torque
characteristic provides automatic derating.