Siemens 411 Manual De Usuario

 

MICROMASTER 411 & COMBIMASTER 411    Operating Instructions  

118 

6SE6400-5CA00-0BP0  

Fast Current Limit (FCL) is a cycle-by-cycle hardware current limit built into the 
inverter.

The current is rapidly reduced by pulse dropping, that is by turning off the 

Insulated Gate Bipolar Transistors (IGBTs) on a pulse by pulse (cycle by cycle) 
basis.

The normal current limit operation then takes over. 

The FCL threshold is set slightly below the software overcurrent trip threshold and 
reacts much quicker (i.e. in milliseconds), thus preventing spurious and unwanted 
trips when sudden loads are applied or fast accelerations requested. 

FCL is especially useful when working in open loop control to override unwanted 
currents. 

Many motors are available with a Positive Temperature Coefficient (PTC) resistor 
built into the windings.

The resistance of the resistor rises rapidly at a particular 

temperature and this change can be detected by the inverter.

If the resistor is 

connected to the inverter terminals as shown in Figure 10-2 and the PTC input 
enabled by setting parameter P0703=29, then if the resistance rises above 2 k

Ω

, 

the inverter will trip and Fault Code F0085 displayed. 

Most Motor Protection PTC resistors have a resistance of 200-300 ohms when cold 
and this value rises rapidly at the ‘knee point’ to typically 10 k

Ω

 and greater.

The 

PTC

input is set so that it will operate at 1 k

Ω

 minimum, 1.5 k

Ω

 nominal, and 2 k

Ω

 

maximum.

On this basis two or three PTCs may be connected in series when a 

motor has more than one PTC built in, or if two or three motors are connected to 
the inverter output and require individual protection. 

1      2       3      4      5      6        7

 

Figure 10-2  PTC Resistor Connections