Braking In The Agy System; Braking Unit - gefran AGy-EV Series Instruction Manual

5.8 Braking in the AGy System

Two means of braking are possible:
- Internal Braking Unit
- Injection of direct current from the Inverter into the motor (D.C. braking)
There are two essential differences between the two braking methods:
- A braking unit can be used for speed reduction (e.g.: from 1000 to 800 rpm), whereas D.C. braking can only be used
for braking to standstill.
- The energy in the drive is converted into heat in both cases. This conversion takes place in a braking resistor encased
in the braking unit. With D.C. braking, the energy is converted into heat in the motor itself, resulting in a further rise in
motor temperature.

5.8.1 Braking Unit

In oversynchronous or regenerative operation, the frequency-controlled three-phase motor feeds energy back to the DC
link circuit via the Drive. This leads to an increase in the intermediate circuit voltage. Braking units (BU) are therefore used
in order to prevent the DC voltage rising to an impermissible value. When used, these activate a braking resistor that is
connected in parallel to the capacitors of the intermediate circuit. The feedback energy is converted to heat via the braking
resistor (R ), thus providing very short deceleration times and restricted four-quadrant operation.
BR
_
Drive sizes 1007 up to 3150 (230V...480V) and 2002 up to 3020 (575V) have as standard an internal braking unit.
Drive sizes 4185 up to 5550 (230V...480V) and 4025 up to 5075 (575V) can be equipped with an internal braking unit (see
section 3.1.2, Inverter type designation) factory mounted on request.
All the standard AGy... drive can be equipped with an external braking unit (BU-32... or BUy) connected to the terminals C and D.
The braking resistor is optional and has always to be mounted externally.
When the circuit terminals C and D are connected to external devices, the AC Input must be protected
N !
OTE
with superfast semiconductor fuses! Observe the mounting instruction concerned.
The braking resistors can be subject to unforeseen overloads due to possible failures.
The resistors have to be protected using thermal protection devices. Such devices do not have to
interrupt the circuit where the resistor is inserted but their auxiliary contact must interrupt the power
Warning!
supply of the drive power section. In case the resistor foresees the precence of a protection contact,
such contact has to be used together with the one belonging to the thermal protection device.
The braking threshold for the internal braking unit is dependent on the value of the supply voltage of the drive.
54 • Chapter 5 - Wiring Procedure
Figure 5.8.1: Operation with Braking Unit (Principle)
R
BR
U
ZK
BU
E
M
3
AGy-EV Instruction manual