John L. Hullett

On the development of transfer function method for fault identification in large power transformers on load

Frequency Response Analysis (FRA) is now established as a proven tool in identifying some typical mechanical faults in power transformers. However, all FRA measurements so far have been off-line. An on-line technique is very much desired by the utilities, as this will prevent continued operation of the transformer while it is carrying a fault to failure stage. In this paper, challenges and some progress made so far toward the development of an on-line FRA technique has been presented. The paper also reports on the development of a high frequency magnetic coupler for this purpose. Results on some sensitivity analysis on a large reactor coil showing significant but characteristic changes on the FRA signatures to parameter variations. Observations of results obtained show that an on-line FRA tool is achievable but still there are some issues that need to be addressed.

Size and speed insensitive distributed queue network

A shared medium ATM switch in the form of a distributed queue dual bus (DQDB) network is described. Access to the network is in multiple stages, a separate stage for each branch of the network. Performance of the queue protocol is affected by distance within a stage, but not by distances between stages. In consequence a DQDT network can be of arbitrary extent without thereby limiting the rate, and DQDT networks can be designed with a speed-distance product that is orders of magnitude larger than is possible for DQDB, FDDI and other high speed LANs.