Isolated Phase Bus Duct Testing with Dr. Kevin Linfield, P.E.

A brief look at Isolated Phase Bus Duct Testing. A short video featuring Dr. Kevin Linfield, P.E.
As nuclear power plants are functioning longer and increasing their output, the efficiency of the cooling system in the isolated phase bus duct system becomes more important. An isophase bus duct carries very large currents, typically between a generator and a transformer. Maximum cooling capacity can be achieved by balancing air flow, whether in an existing system, or as part of an upgrade. By measuring the flow in each branch of the ducts, the plant is able to ensure balanced flow and improve the cooling ability. The goal of this testing is to accurately measure the flows in these ducts and perform iterative balancing as necessary. Much of the testing is performed with 3-D velocity probes and hot wires with a sophisticated data acquisition system.
An overview of the testing and balancing procedure is as follows: the field testing crew and plant personnel agree on test port locations, and the number of test points are selected to exceed EPA Method 2/2F guidelines. The bus is de-energized to fully characterize the flow paths inside the conductor and enclosure. The degree of existing flow imbalance is determined, and fan outputs and various damper opening positions are noted. The flow is balanced through an iterative process of fan operation and damper position changes. The final results include proper damper settings for improved and balanced cooling flow.
For particularly challenging duct geometry, a full scale mock-up of the ducts can be fabricated and tested in the laboratory. The purpose of the physical model is to understand flow patterns and to develop correlation curves for the flow rate vs damper settings in various branches. Results of this type of flow study allow accurate, repeatable flow measurements in the ducts, giving the ability to balance flow between the branches. Shown here is an example of generator-side ducts tested in ASC's lab.
For more information on flow modeling and testing, please contact Airflow Sciences. Thank you, and have a wonderful day.
Copyright Airflow Sciences Corporation. With contributions by Dr. Kevin Linfield, P.Eng., P.E.