GE AF-650 GP Series, Design And Installation Manual

Page: 79 / 166

6.6.2.2 Brake Resistor Cabling
EMC (twisted cables/shielding)
To reduce the electrical noise from the wires between the
brake resistor and the adjustable frequency drive, the wires
must be twisted.
For enhanced EMC performance, a metal shield can be
used.
6.6.2.3 Overvoltage Control
Overvoltage control (OVC) (exclusive brake resistor) can be
selected as an alternative brake function in B-17 Over-
voltage Control . This function is active for all units. The
function ensures that a trip can be avoided if the DC link
voltage increases. This is done by increasing the output
frequency to limit the voltage from the DC link. It is a very
useful function, e.g. if the decel time is too short since
tripping of the adjustable frequency drive is avoided. In
this situation, the decel time is extended.
NOTE!
OVC cannot be activated when running a PM motor (when
P-20 Motor Construction is set to [1] PM non-salient SPM).
6.6.3 Mechanical Brake Control
For hoisting applications, it is necessary to be able to
control an electro-magnetic brake. For controlling the
brake, a relay output (relay1 or relay2) or a programmed
digital output (terminal 27 or 29) is required. Normally, this
output must be closed for as long as the adjustable
frequency drive is unable to 'hold' the motor, due to a
load that is too large, for example. In
E-24 Function Relay
(Array parameter), E-20 Terminal 27 Digital Output , or
E-21 Terminal 29 Digital Output , select mechanical brake
control [32] for applications with an electro-magnetic
brake.
When mechanical brake control [32] is selected, the
mechanical brake relay stays closed during start until the
output current is above the level selected in
B-20 Release
Brake Current . During stop, the mechanical brake will close
when the speed is below the level selected in B-21 Activate
Brake Speed [RPM] . If the adjustable frequency drive is
brought into an alarm condition, i.e. an overvoltage
situation, the mechanical brake immediately cuts in. This is
also the case during safe stop.
Figure 6.23
In hoisting/lowering applications, it must be possible to
control an electro-mechanical brake.
Application Setup Examples AF-650 GP
TM
Design and Installation Guide
6-24 DET-767A
6 6