NOTE
Monitoring the brake power is not a safety function; a
thermal switch is required for that purpose. The brake
resistor circuit is not earth leakage protected.
Over voltage control (OVC)
(exclusive brake resistor) can be
selected as an alternative brake function in
2-17 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 ramp-down time is too short
since tripping of the frequency converter is avoided. In this
situation the ramp-down time is extended.
3.9.1 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 frequency
converter is unable to ’hold’ the motor, e.g. because of too
big load. In
5-40 Function Relay
(Array parameter),
5-30 Terminal 27 Digital Output
, or
5-31 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
2-20 Release
Brake Current
. During stop, the mechanical brake will close
when the speed is below the level selected in
2-21 Activate
Brake Speed [RPM]
. If the frequency converter is brought
into an alarm condition, i.e. over-voltage situation, the
mechanical brake immediately cuts in. This is also the case
during safe stop.
Start
term.18
1=on
0=off
Shaft speed
Start delay time
on
off
Brake delay time
Time
Output current
Relay 01
Pre-magnetizing
current or
DC hold current
Reaction time EMK brake
Par 2-20
Release brake current
Par 1-76 Start current/
Par 2-00 DC hold current
Par 1-74
Start speed
Par 2-21
Activate brake
speed
Mechanical brake
locked
Mechanical brake
free
Par 1-71
Par 2-23
130BA074.12
In hoisting/lowering applications, it must be possible to
control an electro-mehanical brake.
Step-by-step Description
•
To control the mechanical brake any relay output
or digital output (terminal 27 or 29) can be used.
If necessary use a suitable contactor.
•
Ensure that the output is switched off as long as
the frequency converter is unable to drive the
motor, for example due to the load being too
heavy or due to the fact that the motor has not
been mounted yet.
•
Select
Mechanical brake control
[32] in parameter
group5-4* (or in group 5-3*) before connecting
the mechanical brake.
•
The brake is released when the motor current
exceeds the preset value in
2-20 Release Brake
Current
.
•
The brake is engaged when the output frequency
is less than the frequency set in
2-21 Activate
Brake Speed [RPM]
or
2-22 Activate Brake Speed
Introduction to FC 300
FC 300 Design Guide
MG.33.BD.02 - VLT
®
is a registered Danfoss trademark
45
3
3