2.11 Custom Application Functions
2.11.1 Brake Resistor
When the servo drives are decelerating, the motors act like
a generator. This means that the energy coming back from
the servo drives is collected in the DC-link. The function of
the brake resistor is to provide a load on the DC-link
during braking, thereby ensuring that the brake power is
absorbed by the brake resistor. If no brake resistor is used
and the servo drives are decelerating, the DC-link voltage
will rise to a dangerous level. The SAB disconnects the ISD
lines when the DC-link voltage is too high. A DC-link
overvoltage will result in damage to the SAB and the servo
drives.
2.11.1.1 Mechanical Installation
The brake resistors are cooled by natural convection.
The ventilation must be efficient enough to dispatch the
regenerative power in the brake resistor.
2.11.1.2 Electrical Installation
EMC precautions
The following EMC precautions are recommended to
achieve interference-free operation of fieldbus cables, and
digital and analog inputs and outputs.
Observe any relevant national and local regulations, for
example regarding protective earth connection.
Keep the fieldbus cables away from the brake resistor
cables to avoid coupling of high frequency noise from one
cable to the other. The minimum distance of 200 mm is
sufficient, however a greater distance between the cables
is recommended, especially where the cables run in
parallel over long distances. When crossing is unavoidable,
the fieldbus cables must cross the brake cable at an angle
of 90
°
.
Cable connection
To comply with the EMC emission and immunity specifi-
cation, the use of shielded/armored cables is mandatory.
Brake cable
Maximum length: 20 m shielded cable
Ensure that the connection cable to the brake resistor is
shielded. Use cable clamps to connect the shielding to the
conductive decoupling plate of the SAB, and to the brake
resistor metal cabinet.
Protective functions
The VLT
®
Brake Resistor MCE 101 is equipped with a
galvanic isolated temperature switch (PELV) that is closed
under normal operating conditions and opens if the brake
resistor overheats.
The temperature switch can be used as an overtem-
perature protection feature to prevent damage to the
brake resistor caused by overtemperature.
The temperature switch can also be used to disable the
mains supply to the SAB by a contactor.
1.
Connect the built-in thermal switch on the brake
resistor to the K1 input contactor.
2.
Connect the start and stop push buttons in series
with the thermal switch.
3.
Connect to a contactor in the mains supply on
the front of the SAB.
Thermal overheating in the brake resistor disables the
mains supply of the SAB.
91 92 93 95
L1 L2 L3 PE
Line
1
Line
2
SAB
MCE 101
Brake resistor
T1
T2
RB1
RB2
R–81
R+82
PE99
PE
L1
L2
L3
N
PE
F1
S1
K1
F2
S2
K1
K1
130BF779.10
Illustration 2.14 Temperature Switch Disconnecting the Mains
from the SAB
In addition, the brake power monitor function enables
readouts of the momentary power and the mean power
for a selected period. A brake power limit can be set and if
the brake power exceeds the set limit, the SAB issues a
warning or an error. When the SAB issues a warning, the
UDC output remains enabled. However, when an error is
issued, the UDC output to the servo drives is disconnected.
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.
2.11.1.3 Brake Resistor Calculation
To select the most suitable brake resistor for a given
application, the following information is required:
•
The number of servo drives in the application.
•
The inertia connected to the servo drives.
•
The braking/accelerating profile.
System Overview
VLT
®
Integrated Servo Drive ISD
®
510 System
26
Danfoss A/S © 08/2017 All rights reserved.
MG36C102
2
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