Brake Resistor Cabling; Overvoltage Control; Mechanical Brake In Open Loop - GE AF-650 GP Design And Installation Manual

Application Set-Up Examples
464923
500 V : R = Ω
rec
P
motor
630137
600 V : R = Ω
rec P
motor
832664
690 V : R = Ω
rec P
motor
NOTICE
If a brake resistor with a higher ohmic value is selected,
the 160% braking torque may not be achieved because
there is a risk that the frequency converter cuts out for
safety reasons.
NOTICE
If a short circuit in the brake transistor occurs, power
dissipation in the brake resistor is only prevented by
using a mains switch or contactor to disconnect the
mains for the frequency converter. (The contactor can be
controlled by the frequency converter).
NOTICE
Do not touch the brake resistor as it can get hot while/
after braking. The brake resistor must be placed in a
secure environment to avoid fire risk.
CAUTION
Unit size 4x to 6x frequency converters contain more
than one brake chopper. Therefore, use one brake
resistor per brake chopper for those frame sizes.

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 frequency converter, the wires must
be twisted.
For enhanced EMC performance, a metal shield can be
used.
MG35M402
AF-650 GP™ Design and Installation Guide

6.6.2.3 Overvoltage Control

Overvoltage control (OVC) (exclusive brake resistor) can be
selected as an alternative brake function in
parameter 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 useful function, for example, if the decel
time is too short since tripping of the frequency converter
is avoided. In this situation, the decel time is extended.

6.6.3 Mechanical Brake in Open Loop

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 frequency converter is unable to 'hold' the motor,
for example, because of too large load. In
parameter E-24 Function Relay (Array parameter),
parameter E-20 Terminal 27 Digital Output, or
parameter E-21 Terminal 29 Digital Output, select [32]
Mechanical brake control for applications with an electro-
magnetic brake.
When [32] Mechanical brake control is selected, the
mechanical brake relay stays closed during start until the
output current is above the level selected in
parameter B-20 Release Brake Current. During stop, the
mechanical brake closes when the speed is below the level
selected in parameter B-21 Activate Brake Speed [RPM]. If the
frequency converter is brought into an alarm condition,
that is, overvoltage situation, the mechanical brake
immediately cuts in. This is also the case during Safe
Torque Off.
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