Siemens A1 ユーザーズマニュアル
Simple Applications
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24
MICROMASTER Applications Handbook
5.6
Current Limit and Protection Systems
The inverter must protect itself, the motor and system from overload and possible
damage. Current limit now operates very rapidly, limiting the current and
preventing a trip occurring.
damage. Current limit now operates very rapidly, limiting the current and
preventing a trip occurring.
Most inverters have several levels of current limiting:
Electronic
Trip.
Trip.
This is a very fast current limit which operates if there is a
short circuit (line to line or line to earth) on the output. It is a
fixed level trip and operates within a few microseconds.
short circuit (line to line or line to earth) on the output. It is a
fixed level trip and operates within a few microseconds.
Overload
Limit.
Limit.
This is a fast limit, which operates within a few microseconds,
and removes some of the output pulses to limit the current and
protect the inverter. If this pulse dropping occurs during
overload, the operating condition will usually recover and the
motor continue to operate without tripping.
and removes some of the output pulses to limit the current and
protect the inverter. If this pulse dropping occurs during
overload, the operating condition will usually recover and the
motor continue to operate without tripping.
Long Term
Overload limit.
Overload limit.
This is a slower limit, which allows an overload of at least 60
seconds when the current lies above the motor limit, but below
the instantaneous limit values described above.
seconds when the current lies above the motor limit, but below
the instantaneous limit values described above.
Continuous
Limit.
Limit.
This is the level set as the maxiumum continuous motor
current. The inverter will control the current to this level after
the overloads described above have timed out.
current. The inverter will control the current to this level after
the overloads described above have timed out.
For further details refer to the Operating Instructions and Reference Manual.
5.7
Other Protection Features
5.7.1 I
2
t Protection
When the motor is running at low speed and high load, the built in cooling fan may
not provide enough cooling and the motor may overheat. Parameters can be set to
calculate the motor temperature, based on a motor model and operating history
such that the inverter will take action to protect the motor under these conditions.
Further information is given in the Reference Manual.
not provide enough cooling and the motor may overheat. Parameters can be set to
calculate the motor temperature, based on a motor model and operating history
such that the inverter will take action to protect the motor under these conditions.
Further information is given in the Reference Manual.
5.7.2 PTC
Resistor
Protection
Many motors are available with a PTC (Positive Temperature Coefficient) resistor
built into the windings. The resistance of the PTC rises rapidly at a particular
temperature, and this change can be detected by the inverter. The input terminals
of the inverter may be configured to accept a PTC signal and trip the inverter in the
event of overheating.
built into the windings. The resistance of the PTC rises rapidly at a particular
temperature, and this change can be detected by the inverter. The input terminals
of the inverter may be configured to accept a PTC signal and trip the inverter in the
event of overheating.
5.7.3 Overvoltage
If the inverter is connected to a high voltage, or if the internal voltage is forced high
by energy from an external load, then the inverter will trip. Overvoltage usually
occurs as a result of a braking or regenerative load. See section 8.2. If the supply
voltage is too high the inverter may be damaged even if it trips.
by energy from an external load, then the inverter will trip. Overvoltage usually
occurs as a result of a braking or regenerative load. See section 8.2. If the supply
voltage is too high the inverter may be damaged even if it trips.
5.7.4 Internal
Overtemperture
The inverter is protected from overheating. The heatsink temperature is monitored
using a PTC and if the maximum temperature exceeded the inverter will trip.
using a PTC and if the maximum temperature exceeded the inverter will trip.