For permanent PD monitoring installations we make the Model 831. It is produced in a number of formats according to the customer's requirements. One of the most popular applications of the 831 is transformer monitoring. In this instance it is supplied with a number of sensors to detect PD activity, such as ultrasonic detectors and high frequency CTs which are connected to earthing cables.

Another important application is HV underground cable monitoring where a number of cubicles are installed at locations along the length of cable, each one checking the PD activity of a cable section through a high frequency CT installed on an earth connection.

For portable PD testing applications the model 832 is supplied with a number of sensors which allow PD activity to be detected in the equipment assets that are vital to the utility.

The lightweight 832 has a laptop PC which can display PD activity in various types of graph to help engineers determine the maintenance requirements needed to prevent deterioration.

Up to 4 channels of PD input can be monitored simultaneously, and 4 noise channel inputs are provided to monitor ambient electrical noise so that spurious signals can be eliminated.

Auxiliary inputs are provided to measure temperature, humidity or other variables.

These sensors are used to amplify the very low level PD signals and transmit them via coaxial cable to the Model 831 and Model 832 units. The 834B is a split core high frequency CT with 66mm window. For transformer testing a good choice is the 835B ultrasonic sensor which has a strong magnetic base capable of gripping the steel tank of the transformer.

Rejecting spurious signals is important when performing PD tests, and for this purpose we have the 836B noise sensor. This sensor picks up and amplifies ambient electrical noise with its aerial, and the signal is then sent to the 831 or 832 so they can discard any apparent PD which occurs at the same time which may be due to noise.

To help in maintaining GIS ( gas insulated switchgear ) equipment we make a Model 840 GIS tester which is designed to take the output signal from a Model 841 GIS sensor. The signal is interpretated by a dedicated micrprocessor unit in the 840 which in turn sends digital data to the laptop PC. In the laptop PC the digital data is used to construct graphical representations of the PD activity.

The portable Model 841 is fitted with a high frequency amplifier matched to the typical PD signature of GIS equipment. It has a rechargeable LiOn battery for extended field use, and is connected to the 840 with a coaxial test cable. There is a swivel attachment on the 841 so it can be used on the end of a hot stick when required.