Fuji Electric frenic mini series, User Manual

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9-50
H12 Instantaneous Overcurrent Limiting
Data Function
0 Disable
1 Enable
The inverter features a hardware-controlled output
current limiter to protect it from an overload hazard.
The moment that the output current exceeds the limited
level due to overload or other factor, the inverter
controls the output switching circuits so as to slow
down the output frequency and suppress the output
current momentarily.
This control of the switching circuits may cause an instantaneous reduction in motor output
torque. However, instantaneous torque reduction may not be allowable in some systems
when the system is in a short time overloaded state. To solve this problem, this function
should be disabled and the system set up with a proper facility that is activated by the alarm
output from the inverter when it detects an overcurrent.
The same functions to limit the output current are implemented by software as
function codes F43 and F44. Generally, software features have an operational
delay, so enable function code H12 as well.
Depending upon the load property, acceleration in an extremely short period may
activate the current limiter to suppress the increase of the inverter output
frequency so as to cause the system oscillate (hunting) or to make the inverter
enter the 0V alarm mode and trip. When setting the acceleration time, therefore,
you need to take into account the load property and moment of inertia. (Refer to
Chapter 7, Section 7.1, "Selecting Motors and Inverters" for details about the
calculation of acceleration/deceleration time.)
H26 Thermistor (Selection)
H27 Thermistor (Operation level)
Set these function codes to protect the motor from an overheat hazard using the PTC
(Positive Temperature Coefficient) thermistor embedded in the motor.
Thermistor (Select) (H26)
Data Function
0
Disable overheating
protection
Enables or disables overheating protection
for the motor using the PTC thermistor,
which senses motor temperature.
1
Enable overheating
protection
Thermistor (Operation Level) (H27)
Determines the operation level for the overheating protection.
- Data setting range: 0.00 to 5.00 (V)
Connect the PTC thermistor as shown
in the figure at right. The input current
from terminal [C1] flows across the
resistor R
2
and yields the voltage. If the
voltage exceeds the operation level set
by function code H27, the overheating
protection is activated, and the inverter
enters alarm mode and issues the alarm
"
0H4 " (motor protection).