An alternative is to lower the ambient temperature at high
altitudes and thereby ensure 100% output current at high
altitudes. Example: At an altitude of 2000 m and a
temperature of 45
°
C (T
AMB, MAX
- 3.3 K), 91% of the rated
output current is available. At a temperature of 41.7
°
C,
100% of the rated output current is available.
80
0
500
100
95
90
85
1000
1500
2000
2500
3000
Altitude (metres above sea level)*
130BB008.10
I
OUT
(%)
Illustration 3.12 Example
0
500
1000
1500
2000
2500
3000
Altitude (meters above sea level)*
30
35
40
45
(°C)
A
mb
. T
emp
.
130BB009.10
HO
NO
Illustration 3.13 Derating of Output Current versus Altitude at
T
AMB, MAX
3.5.5 Extreme Running Conditions
Short circuit (motor phase-phase)
The frequency converter is protected against short circuits
by current measurement in each of the 3 motor phases or
in the DC link. A short circuit between 2 output phases
causes an overcurrent in the inverter. The inverter turns off
when the short-circuit current exceeds the allowed value
(
Alarm 16, Trip Lock
).
Switching on the output
Switching on the output between the motor and the
frequency converter is allowed. Fault messages can appear.
To catch a spinning motor, select
[2] Enabled always
in
parameter 1-73 Flying Start
.
Motor-generated overvoltage
The voltage in the DC link is increased when the motor
acts as a generator. This voltage increase occurs in the
following cases:
•
The load drives the motor at constant output
frequency from the frequency converter. That is,
the load generates energy.
•
During deceleration (ramp-down) when the
inertia moment is high, the friction is low, and
the ramp-down time is too short for the energy
to be dissipated as a loss in the frequency
converter, the motor, and the installation.
•
Incorrect slip compensation setting can cause
higher DC-link voltage.
•
Back EMF from PM motor operation. When
coasted at high RPM, the PM motor back EMF can
potentially exceed the maximum voltage
tolerance of the frequency converter and cause
damage. To help prevent this risk of damage, the
value of
parameter 4-19 Max Output Frequency
is
automatically limited. The limit is based on an
internal calculation, based on the values of:
-
Parameter 1-40 Back EMF at 1000 RPM
.
-
Parameter 1-25 Motor Nominal Speed
.
-
Parameter 1-39 Motor Poles
.
When the motor risks overspeed (for example,
due to excessive windmilling effects), use a brake
resistor.
The control unit can attempt to correct the ramp
(
parameter 2-17 Over-voltage Control
).
When a certain voltage level is reached, the inverter turns
off to protect the transistors and the DC-link capacitors.
Select the method used for controlling the DC-link voltage
level via:
•
Parameter 2-10 Brake Function
.
•
Parameter 2-17 Over-voltage Control
.
NOTICE
OVC cannot be activated when running a PM motor (that
is, when
parameter 1-10 Motor Construction
is set to
[1]
PM non-salient SPM
).
Mains dropout
During a mains dropout, the frequency converter keeps
running until the DC-link voltage drops below the
minimum stop level. The minimum stop level is typically
15% below the lowest rated supply voltage of the
frequency converter. The mains voltage before the dropout
and the motor load determines how long it takes for the
frequency converter to coast.
System Integration
Design Guide
MG03M202
Danfoss A/S © 06/2016 All rights reserved.
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