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5
R BRAKE OPTION (Continued)
Technical Overview
The pulsed R brake electronics operate
completely independently of the inverter
electronics, monitoring the DC link voltage.
During braking, the motor will regenerate,
causing the DC link voltage to rise.
When a set threshold is reached, the
pulsed R brake electronics will switch the
resistor onto the DC link. This will cause
the regenerated energy to be dissipated as
heat in the resistor, thus preventing an
over-voltage trip.
Whilst the resistor is switched onto the DC
link, the resistor temperature will rise.
When the threshold temperature (Tmax), is
reached, the electronics will limit the power
in the integrated resistor to approximately
5% of the peak power. If the temperature
continues to rise, the resistor will be
disabled completely, until the temperature
has fallen.
P1
P2
T1
Tmax
T1
Maximum duty cycle is 5%.
The actual duty cycle depends on the
braking energy required.
P1 – 7kW
P2 – 350W (5%)
© Siemens plc 2000 ¦ G85139-H1731-U450-B1
T2
T2
Fig. 3 R Brake Option Duty Cycle
T1 and T2 are variables up to the following
maximums:
In the event of a fault the
resistor may become
permanently connected
and overheat.
The resistor temperature is
monitored by an internal
circuit, which will indicate
resistor overheating by
means of a fault relay
(RL100).
The fault relay (RL100) is
provided to connect to an
external contactor, wired
to isolate the inverter, if
the relay detects an over-
heat condition.
If heatsink <90 deg C
T1 = 10s max (so, T2 = 190s).
If heatsink >90 deg C
T1 = 3s max (so, T2 = 57s).
If heatsink >105 deg C
Inverter Trips.
7

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