As with all things ultrasound, the question is: How does the signal reach the instrument?

With high-voltage switchgear, the answer is simple. ultrasound finds its way through any gaps in seals, air vents, etc. If you are using the Ultraprobe, we would recommend scanning from a distance with the scanning module, and closing in on any signals you pick-up using the rubber focusing probe.

In the case of oil-filled or resin-cast equipment, the scanning module is of little use, since the ultrasound is generated internally, and will produce very little in the way of detectable airborne activity. The contact module is the thing to use here. Ideally, you should use this in conjunction with a magnetic mount and extension cable to allow the operator to move away from the transformer under test. The other advantage is that the operator will not be confused by frictional signals generated if he was to simply contact the transformer case.

Both the magnetic mount and extension cable are supplied as standard with the Ultraprobe 10,000, and are also available as accessories for the other models of Ultraprobe. Below we quote a user in the USA using a similar set-up to the one described above...

A 345KV transformer had a fault and within minutes it blew up - sending the usual fire balls hundreds of feet into the air. A secondary transformer connected to the 345KV unit was, of course, spiked. Problems with the gas levels in the oil were reported in the secondary unit. A consultant was called in to do an infrared scan of the transformer, but nothing was found - even though the flammable gas tests were increasing.

Using the Ultraprobe with the contact module, inspectors were able to listen to the arcing in the transformer winding, and could also confirm where it was happening - thus saving them from having to drain all the oil in the transformer as the arcing was happening at the top of the winding.

An arc or corona discharge emits ultrasound at the site of emission. The signal is heard as a frying or buzzing sound in the headset. Switchgear, transformers, circuit breakers, buss bars, relays, junction boxes, insulators can all be checked on line and without direct access.

Thermography is the use of an infrared camera to "see" and "measure" thermal energy emitted from an object.

Thermal, or infrared, energy, is radiation that is not visible because its wavelength is too long to be detected by the human eye; it's the part of the electromagnetic spectrum that we perceive as heat. Unlike visible light, in the infrared world, everything with a temperature above absolute zero emits heat. Even very cold objects, like ice cubes, emit infrared. The higher the object's temperature, the greater the infrared radiation emitted. Infrared allows us to see what our eyes cannot.

Infrared cameras produce images of invisible infrared or "heat" radiation and provide precise non contact monitoring capabilities. Nearly everything gets hot before it fails, particularly electrical equipment making infrared cameras extremely cost-effective and valuable diagnostic tools. Many applications exist in the electrical field for infrared inspections...

• Transfer Switch
• Stand By Batteries
• Motor Control Centre and Motors
• Substation including transformers and capacitor evaluation
• Overhead Bus Duct
• Electrical Panels

See loose connections (left) and incorrectly secured connections (right).

Nearly all of these applications require line of sight with the item being inspected. Infrared cameras cannot "see" through materials such as glass or steel. For inspections of electrical equipment where opening cabinet doors would defeat safety mechanisms we recommend the installation of "infrared sightglasses" which permit inspections without opening cabinet doors.

Infrared cameras have proven over time to be an invaluable resource for predictive maintenance. They can locate problems well in advance of failure, resulting in rapid payback on investment, avoiding costly plant shutdowns in the process. Our Flir range of thermal imaging cameras not only locate problems quickly, but its non-contact precision temperature measurement capabilities deliver the answers you need to decide what repair action - if any - to take and when.

Regular surveys of a steel mill's substations potentially save tens of thousands of Euros per year. A major steel company, for example, discovered a significant temperatue rise in one of their 69 kV breakers. If this problem had gone undetected, it could have cost the company in question 50,000 Euros per hour in lost time due to shutdown of the casters. Total loss of power to a mill was estimated to be over 250,000 Euros an hour.

At a public electric utility company, a thermography survey indicated one of the ouput filter capacitors of a station battery charger was considerably cooler than the others. As a result, the capacitor in question was tested and found to have failed. Replacement of the failing capacitor avoided an outage, saving an estimated 500,000 Euros as a consequence.

Historically, there have been two methods of inspecting electrical equipment...

Scanning the covers - The first is: scanning the equipment with the covers still in place. Although this is a practice still undertaken by some thermographers, it is not a viable option as it does not provide an accurate indication of faults and their locations - if indeed a fault can be determined at all. When the covers are in place, insufficient radiation is emitted from the panel front for the camera to register.

Cover removal - The second method of inspection is: scanning electrical equipment with the covers removed. This method provides excellent fault resolution, and allows simple component identification. Unfortunately, there are important considerations that must be made when choosing this method of electrical inspection...

The answer? Thermographic Inspection Windows. Typical uses of these Inspection Windows include...

• Transfer switch
• Stand by batteries
• Motor Control Centre and motors
• Substation, including transformers and capacitor evaluation
• Overhead bus duct
• Electrical panels

Should you have any questions, or if you would like to discuss any of this further, then please do not hesitate to get in touch.