Whether it’s your first infrared inspection or you’re a
veteran with hundreds of surveys under your belt, it’s important
to realize that in order to successfully identify and analyze thermal
is beneficial to understand the operation of the equipment under inspection.
This paper will provide guidelines for performing infrared inspections
of motor control centers, identifying key components and potential problem
areas, illustrating both common and not-so-common thermal anomalies.
|Figure 2: The bus stabs at the back
of the MCC are where the incoming connections to the main horizontal
bus occur. These are important IR inspection points and are often
overlooked or misdiagnosed. The thermal image to the right reveals
a hot spot indicating a potential problem.
control center, or MCC, is a modular cabinet system for powering and
controlling motors in a factory. MCCs are quite common in factories
having heavy machinery. Typically, an MCC cabinet consists of a metal
enclosure with doors providing access. Although the contents may vary,
MCC contains a motor starter, circuit breaker and possibly a power transformer.
The MCC enclosure protects personnel from contact with current carrying
devices, and it protects the components from various environmental conditions.
There are different classes and types of MCCs, but generally speaking,
an MCC looks like a row of file cabinets with each cabinet representing
an MCC section. The drawers of the file cabinet represent the plug-in
units that contain the motor control components. Three phase power is
within the MCC by bus bars, large metal current carrying bars. The horizontal
bus provides three-phase power distribution from the main power supply.
Vertical bus in each section is connected from it to individual MCCs.
Bracing and isolation barriers are provided to protect against fault conditions.
The plug-in units of an MCC have power stabs on the back to allow it to
be plugged into the vertical power bus bars of the structure.
Your MCC Infrared Inspection:
Before opening the panel or door on a
motor controller, prescan the enclosure to assure a safe opening condition.
If excessive heat appears on the surface
of the door, extra care should be taken when opening it. The thermographer
or escort may decide to note the condition as unacceptable and not take
a chance on opening it under load. Once the unit is open, begin with
both an infrared and a visual inspection to assure no dangerous conditions
this white paper to learn more about
the recommended guidelines for inspecting the motor control
center (MCC). The paper describes
how to identify key components and potential problem areas and illustrates
both common and not-so-common thermal anomalies.