Mechanical Brake Control - Danfoss VLT AutomationDrive FC 300 Design Manual

Introduction
3.8.5 Control with Brake Function
The brake is protected against short-circuiting of the brake
resistor, and the brake transistor is monitored to ensure
that short-circuiting of the transistor is detected. A relay/
digital output can be used for protecting the brake resistor
against overloading in connection with a fault in the
frequency converter.
In addition, the brake makes it possible to read out the
momentary power and the mean power for the latest 120
s. The brake can also monitor the power energizing and
make sure it does not exceed a limit selected in 2-12 Brake
Power Limit (kW). In 2-13 Brake Power Monitoring, select the
function to carry out when the power transmitted to the
brake resistor exceeds the limit set in 2-12 Brake Power
Limit (kW).
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
Start
1=on
term.18
0=o
Par 1-71
Start delay time
Shaft speed
Output current
Pre-magnetizing
current or
DC hold current
Par 2-23
Brake delay time
on
Relay 01
o
Mechanical brake
locked
Mechanical brake
free
Illustration 3.33 Mechanical brake control in open loop
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®
VLT AutomationDrive FC 300 Design Guide, 0.25-75 kW
Par 1-74
Start speed
Par 1-76 Start current/
Par 2-00 DC hold current
Reaction time EMK brake
®
MG33BE02 - VLT is a registered Danfoss trademark
since tripping of the frequency converter is avoided. In this
situation the ramp-down time is extended.
NOTE
OVC can not be activated when running a PM motor
(when 1-10 Motor Construction is set to [1] PM non salient
SPM).

3.9 Mechanical brake control

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 [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 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.
Par 2-20
Release brake current
3
Par 2-21
Activate brake
speed
Time
47
3