EQ7 Series Instruction Manual - TECO-Westinghouse Motor Company

• From the system's safety point of view, it is recommended to employ such a sequence that shuts down
the magnetic contactor (MC) in the inverter input circuit with an alarm output signal ALM issued on
inverter's programmable output terminals. The sequence minimizes the secondary damage even if the
inverter breaks.
When the sequence is employed, connecting the MC's primary power line to the inverter's auxiliary
control power input makes it possible to monitor the inverter's alarm status on the keypad.
• The breakdown of a braking unit or misconnection of an external braking resistor may trigger that of the
inverter's internal parts (e.g., charging resistor). To avoid such a breakdown linkage, introduce an MC
and configure a sequence that shuts down the MC if a DC link voltage establishment signal is not
issued within three seconds after the MC is switched on.
For the braking transistor built-in type of inverters, assign a transistor error output signal DBAL on
inverter's programmable output terminals to switch off the MC in the input circuit.
(7) Magnetic contactor (MC) in the inverter output (secondary) circuit
If a magnetic contactor (MC) is inserted in the inverter's output (secondary) circuit for switching the motor to a
commercial power or for any other purposes, it should be switched on and off when both the inverter and motor
are completely stopped. This prevents the contact point from getting rough due to a switching arc of the MC. The
MC should not be equipped with any main circuit surge killer.
Applying a commercial power to the inverter's output circuit breaks the inverter. To avoid it, interlock the MC on the
motor's commercial power line with the one in the inverter output circuit so that they are not switched ON at the
same time.
(8) Surge absorber/surge killer
Do not install any surge absorber or surge killer in the inverter's output (secondary) lines.
• Noise reduction
If noise generated from the inverter affects other devices, or that generated from peripheral equipment causes the
inverter to malfunction, follow the basic measures outlined below.
(1) If noise generated from the inverter affects the other devices through power wires or grounding wires:
- Isolate the grounding terminals of the inverter from those of the other devices.
- Connect a noise filter to the inverter power wires.
- Isolate the power system of the other devices from that of the inverter with an insulated transformer.
- Decrease the inverter's carrier frequency (F26).
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