Controlling A Contactor Between Drive And Motor; Implementing A Bypass Connection; Protecting The Contacts Of Relay Outputs - ABB ACS880-34 Series Hardware Manual

90 Guidelines for planning the electrical installation

Controlling a contactor between drive and motor

The control of the output contactor depends on how you use the drive, that is, which motor
control mode and which motor stop mode you select.
If you have the DTC motor control mode and the motor ramp stop mode selected, use this
operation sequence to open the contactor:
1. Give a stop command to the drive.
2. Wait until the drive decelerates the motor to zero speed.
3. Open the contactor.
If you have the DTC motor control mode and the motor coast stop, or scalar control mode
selected, open the contactor as follows:
1. Give a stop command to the drive.
2. Open the contactor.
WARNING!
When the DTC motor control mode is in use, never open the output contactor while
the drive controls the motor. The DTC motor control operates extremely fast, much
faster than it takes for the contactor to open its contacts. When the contactor starts
opening while the drive controls the motor, the DTC control will try to maintain the
load current by immediately increasing the drive output voltage to the maximum.
This will damage, or even burn the contactor completely.

Implementing a bypass connection

If bypassing is required, employ mechanically or electrically interlocked contactors between
the motor and the drive and between the motor and the power line. Make sure with
interlocking that the contactors cannot be closed simultaneously. The installation must be
clearly marked as defined in IEC/EN 61800-5-1, subclause 6.5.3, for example, "THIS
MACHINE STARTS AUTOMATICALLY".
WARNING!
Never connect the drive output to the electrical power network. The connection
may damage the drive.

Protecting the contacts of relay outputs

Inductive loads (relays, contactors, motors) cause voltage transients when switched off.
The relay contacts on the drive control unit are protected with varistors (250 V) against
overvoltage peaks. In spite of this, it is highly recommended that inductive loads are equipped
with noise attenuating circuits (varistors, RC filters [AC] or diodes [DC]) to minimize the
EMC emission at switch-off. If not suppressed, the disturbances may connect capacitively
or inductively to other conductors in the control cable and form a risk of malfunction in other
parts of the system.
Install the protective component as close to the inductive load as possible. Do not install
protective components at the relay outputs.