Electrical
Systems
Abnormal heating associated with high resistance or excessive current flow is
the main cause of many problems in electrical systems. Infrared thermography
allows us to see these invisible thermal signatures of impending damage before
the damage occurs. When current flows through an electric circuit, part of the
electrical energy is converted into heat energy. This is normal. But, if there
is an abnormally high resistance in the circuit or abnormally high current flow,
abnormally high heat is generated which is wasteful, potentially damaging and
not normal.
Ohm¡¯s law (P=I2R) describes the relationship between current, electrical
resistance, and the power or heat energy generated. We use high electrical
resistance for positive results like heat in a toaster or light in a light bulb.
However sometimes unwanted heat is generated that result in costly damage.
Under-sized conductors, loose connections or excessive current flow may cause
abnormally high unwanted heating that result in dangerously hot electrical
circuits. Components can literally become hot enough to melt.
Infrared Solutions cameras enable us to see the heat signatures associated with
high electrical resistance long before the circuit becomes hot enough to cause
an outage or explosion. Be aware of two basic thermal patterns associated with
electrical failure: 1) a high resistance caused by poor surface contact and 2)
an over loaded circuit or multi-phase imbalance problem.
Contact Problems
Heat is produced by current flow through a contact with high electrical
resistance. This type of problem is typically associated with switch contacts
and connectors. The actual point of heating may often be very small, less than a
1/16 inch when it begins. Below are several examples found with the IR SnapShot
during customer demonstrations.
Thermogram A) is a motor controller for an elevator in a large hotel. One of the
three phase connections was loose, causing increased resistance at the
connector. The excess heating produced a temperature rise of 50 degrees C (90F).
Thermogram B) is a 3-phase fuse installation where one end of one fuse has poor
electrical contact with the circuit. The increased contact resistance caused a
45C (81F) hotter temperature at that connection than at the other fuse
connections. Thermogram C) is a fuse clip where one contact is 55C (99F) hotter
than the others. And thermogram D) is a two-phase wall plug-in where the wire
connections were loose causing the terminals to heat 55C (100F) hotter than the
ambient.
 |
 |
 |
 |
| A)
Controller |
B) 3 Phase
Fuse |
C) Fuse
Clip |
D) Wall
Plug |
All four of these examples were serious and needed immediate attention.
Thermogram B) shows an interesting principal used in interpreting thermal
patterns of electrical circuit. The fuse is hot at one end only. If the fuse
were hot at both ends, the problem would be interpreted differently. An
overloaded circuit, phase imbalance, or an undersized fuse would cause both ends
of the fuse to overheat. Being hot at one end only suggests that the problem is
high contact resistance at the heated end.
The wall plug in Thermogram D) was seriously damaged as seen in the visual
picture to the right, however, it continued to operate until it was replaced.
 |
Overloaded Circuit Problems
The following thermograms show overloaded circuits. Thermogram E) shows a
circuit panel in which the main breaker at the top is over heated 75C (135F)
above ambient. This total panel is overloaded and in need of immediate
attention. Thermograms E) and F) show all the standard circuit breakers over
heated. Their temperatures were 60C (108F) above ambient. Although in the
thermogram the wires are blue in color they are also hot, 45 to 50C (81 to 90F).
This entire electrical system needs to be redone.
 |
 |
 |
 |
| E) Circuit
Panel |
F) Circuit
Panel |
G)
Controller |
H) Current
Xformer |
Thermogram G) shows one line of a controller that is about 20C (36F) above the
others. This needs further investigation to determine why one wire is that much
hotter than the others are and to determine the repair needed. Thermogram H)
shows a current transformer that is 14C (25F) warmer than the other two
transformers in a 3-phase service installation. This indicates a serious
imbalance of the service or a faulty current transformer that could seriously
impact the customer¡¯s utility bill.
Load Requirements
When making an inspection it is important that the system is under load. Wait
with the inspection for ¡°worst case¡± or peak loads, or when the load is at
least 40% (according to NFPA 70B). Heat generated by a loose connection rises as
the square of the load; the higher the load, the easier it is to find problems.
Don¡¯t forget to consider the cooling effect of wind or other air movement.
Surface Temperatures Only
Infrared cameras cannot see through electrical cabinets or solid metal bus
trays. Whenever possible open enclosures so the camera can directly see the
electrical circuits and components. If you find an abnormally high temperature
on the outside surface of an enclosure, rest assured that the temperature is
even higher, and usually much higher, inside the enclosure. Below are some
thermograms taken of a bus enclosure, which identify a serious problem with the
electrical buses inside the enclosure. The hot spots were on the order of 10C
hotter than the ambient and 6C hotter than other parts of the bus enclosure.
I) J) K) L) Bus enclosures
Electric Distribution
Literally hundreds of different pieces of equipment may be found in an
electrical system. They start with the utility electricity production, high
voltage distribution, switchyards and substations, and end with service
transformers, switchgear, breakers, meters, local distribution, and appliance
panels. Many utilities have purchased the FlexCam¢ç or SnapShot¢ç to help with
their maintenance. And nearly every type of industry has bought Infrared
Solutions cameras to help with maintenance on their end of the electrical
distribution system.
Thermogram M) is a service transformer that had leaked some cooling oil,
resulting in dangerously over heated coils near the top. One connection was 160C
(288F) above ambient. This transformer needed immediate replacement but the
company wanted to delay the repair one month so it could be done during a
scheduled total plant shutdown. They used the IR SnapShot camera to monitor the
state of the transformer and successfully delayed the repair. Thermogram N) is
for a pole mounted service transformer that has a connection 30C (54F) hotter
than ambient. Such a condition required maintenance at the next convenient
opportunity. Thermogram O) shows a hot main connection on an interrupter at a
substation in Mexico. The connection was found to be 14C (25F) hotter than the
others. This was believed to be a problem that needed attention. Thermogram P)
shows an overhead connection in a Peru substation. It was less than 10C or (18F)
above ambient and not of immediate concern.
 |
 |
 |
 |
| M)
Transformer |
N)
Transformer |
O)
Interrupter |
P)
Connection |