NORDAC PRO (SK 500P) – Users Manual for Frequency Inverters
30 BU 0600 en-2319
2.2.4 Monitoring of the braking resistor
To prevent overload of the brake resistor, it should be monitored during operation. The most reliable
method is thermal monitoring with a temperature switch which is mounted directly on the braking
resistor.
2.2.4.1 Monitoring with a temperature switch
As standard, SK BR2-… braking resistors are equipped with a suitable temperature switch.
Typically, evaluation of the temperature switch is carried out by an external control system.
Alternatively, the temperature switch can be evaluated directly by the frequency inverter. To do this, it
must be connected to a free digital input. This digital input must be parameterised with the function
{10} "Block voltage".
Example, SK 5xxP
• Connect the temperature switch to digital input 4 (Terminal 43 / 24)
• Parameter P420 to function {10} "Block voltage".
The switch opens if the maximum permissible temperature of the brake
resistor is reached. The output of the frequency inverter is blocked. The
motor runs down to a standstill.
2.2.4.2 Monitoring with current measurement and calculation
As an alternative to monitoring with a temperature switch it is also possible to use an indirect,
arithmetical monitoring of the the brake resistor load on the basis of measurement values.
This software-assisted indirect monitoring is activated by setting parameter P556 "Braking resistor"
and P557 "Braking resistor power". The actual calculated resistor load can be read out in parameter
P737 "Braking resistor load". Overload of the brake resistor results in a shut-down of the frequency
inverter with the error message E3.1 "Overcurrent Chopper I²t“
The supported indirect monitoring using measurement of electrical data and calculation is based on
standard ambient conditions. In addition, the calculated values are reset when the device is switched
off. It is therefore not possible to detect the actual load on the braking resistor.
It is therefore possible that an overload may not be detected or its environment may be damaged due
to excess temperatures.
Reliable temperature monitoring is only possible with the use of a temperature switch.
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