5.3 Description of Function Codes 5.3.1 F codes (Fundamental functions)
Electronic thermal overload protection for braking resistor
(Discharging capability, Allowable average loss and Braking resistance value)
These function codes specify the electronic thermal overload protection feature for the braking resistor.
Set the discharging capability, allowable average loss and resistance to F50, F51 and F52, respectively. These
values are determined by the inverter and braking resistor models. For the discharging capability, allowable average
loss and resistance, refer to Chapter 11 “11.8.3 Specifications.”
The values listed in the tables are for standard models and 10% ED models of the braking resistors which Fuji
Electric provides. When using a braking resistor of any other manufacturer, confirm the corresponding values with
the manufacturer and set the function codes accordingly.
Depending on the thermal characteristics of the braking resistor, the electronic thermal overload
protection feature may act so that the inverter issues the overheat protection alarm dbH even if the actual
temperature rise is not large enough. If this happens, review the relationship between the performance
index of the braking resistor and settings of related function codes.
Using the standard models of braking resistor or using the braking unit and braking resistor together can
output temperature detection signal for overheat. Assign terminal command THR (“Enable external alarm
trip”) to any of digital input terminals [X1] to [X9], [FWD] and [REV] and connect that terminal and its
common terminal to braking resistor’s terminals [1] and [2]. Set OFF for function code F50.
Calculating the discharging capability and allowable average loss
If the discharge withstand current rating and permissible average loss are unknown when using a non-Fuji resistor,
as long as the applicable motor capacity, %ED, and maximum braking time (*) resistor specifications are known,
the discharge withstand current rating and permissible average loss can be calculated. When doing so, the
calculation method differs depending on the resistor specifications %ED concept (how braking load is applied.)
* The maximum braking time is not the inverter deceleration time setting value, but is the length of time that the
braking resistor is able to continuously block regenerative electric power.
<If expressed with %ED for deceleration>
In usual deceleration, the braking load decreases as the speed slows down. In the deceleration with constant torque,
the braking load decreases in proportion to the speed. Discharge withstand current rating and permissible average
loss can be calculated with the following formula.
<If expressed with %ED for constant speed>
Unlike when decelerating, the braking load is constant if an external braking load is applied at constant speed.
Discharge withstand current rating and permissible average loss can be calculated with the following formula.
(kWs)
(s)(kW)
2
(kW)
(kW)
2
%ED(%)
100
(kWs)(s)(kW)
(kW) (kW)
%ED(%)
100
Discharge withstand
current rating (kWs)
Max. braking time (s) x motor capacity (kW)
Permissible average
loss (kW)
Permissible average
loss (kW)
Discharge withstand
current rating (kWs)
Max. braking time (s) x motor capacity (kW)
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