Partial discharge and bushing monitoring are terms describing usual processes in high-voltage installations. Whether we're talking about a power plant or a simple underground cable, partial discharge is a usual physical occurrence. To be more precise, a discharge is an electrical breakdown of a small portion of high-voltage electrical insulation system. This kind of discharge is really difficult to detect, given its small magnitude and short duration, in some cases, nanoseconds. As technology evolved, so did the tools we use. So, these days there's a whole variety of partial discharge and bushing monitoring tools to cover every aspect of this usual phenomenon taking place in installations. We'll do a quick analysis for you on this theme to give you an idea about what you can find on the open market.

Let's begin with a few partial discharge instruments, such as the portable 4 channel Acoustical Partial Discharge Analyzer. It has one electrical PD input and it is used to detect, locate and analyze PD in oil filled equipment, GIS, cable joints and other high-voltage equipment. It has 4 sensors that are to be placed 3 feet apart for good readings. They have to be moved around the transformer for a proper measurement. The acoustical partial discharge instrument is complementary with electrical PD measuring systems and can also be connected to a computer for downloading and later viewing of data.

The most advanced PD analyzer in the world is the Expert Partial Discharge Analyzer with Reflectometer. It has 12 PD channels and a Noise Cancellation feature (pulse shape, pulse polarity, pulse comparison, time of arrival and specialized software filters). It has two auxiliary inputs for external temperature and humidity sensors allowing for PD correlations with external dynamics. The partial discharge channels come with protection and high pass filters, as well as isolated input circuitry. Also, the frequency band is 0.5 to 10 MHz. Its unique feature is the built-in reflectometer which assists in locating defects and is capable to record up to three time domain reflectograms per channel with different trigger levels.

Concerning bushing monitoring, there is the Bushing Monitor Performance Test Set - Type ITT, which is the only known test instrument that can be used to test bushing monitoring systems! It can simulate a three phase milli-amp current based on inputted bushing capacitance and power factor. It includes a 100 Ohm RTD calibrator as well as a PD generator with time delay, pulse polarity and magnitude control.

It is known that bushings are the highest failure components on large power transformers. Therefore, there are also bushing sensors available to ease bushing monitoring. They're designed up to 800 kV and there are several mechanical interfaces available (North American and European). The bushing sensors provide both power frequency and partial discharge signal. Their output voltage is limited to less than 20 volts. They are to be installed on bushings? capacitor/potential taps and they monitor and detect problems with the bushing and winding insulation systems. The BAU-type bushing sensors are designed with the best protection known: open circuit protection, surge projection as well as fail safe circuitry if all the above protection fails.

These are just a few of the tools available for partial discharge and bushing monitoring. It is advisable that you log on a few specialized sites on the Internet before going out shopping. It might help you find better tools and even save some money. A place to start is elec-di.com. It's a user-friendly site with a comprehensive database, where you can find detailed information about numerous tools and professional equipment that will ensure the safe and sound development of your installations.