Page 212 - Root Cause Failure Analysis

200 Root Cause Failure Analysis

INSTALLATION
Inverters must be installed in a reasonably clean, air-conditioned environment. In crit-
ical applications, an extra cooling fan may be required to ensure adequate temperature
control. Wiring from an inverter to a motor, including starter, plugsets, and fuse dis-
connections, must be new or in good working condition.

Motors

Motors to be controlled by an inverter must be of the three-phase, AC type. More than
one motor can be controlled by one inverter, but each motor must have its own set of
three fuses. A positive disconnection must be installed upstream of the dedicated
motor-fuse set.

Short-circuit Protection
Short-circuit fuse coordination is required in all multimotor inverter systems. In the
case of a short circuit in one motor, the individual fuse set will clear without caus-
ing the inverter’s overcurrent-protection system (fuses, electronic trips, etc.) to
operate.

Ground-Fault Protection

Ground-fault fuse coordination is required with multimotor inverter systems for the
same reason as short-circuit fuse coordination. Including ground-fault protection for
each motor will prevent shutting down the inverter should one or more motors trip.

Transformers
Transformers may be required when a different input or output voltage is required for
proper operation. Input transformers are required when the available input voltage is
different than that required by the inverter system or motor. Input isolation transform-
ers also can be used to prevent the electrical noise generated in the inverters from
feeding into other equipment.

An output transformer can be used to match the motor’s load to the inverter. For
example, if the inverter is capable of producing a 480-V output and the motor requires
only 290 V at maximum speed, an output transformer can be used to step down the
inverter’s output voltage.

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Proper operation and maintenance of an inverter system requires adequate feedback to
monitor and troubleshoot the system. As a minimum, inverter systems should have
digital oscillators and a fault-indication system.