MPS is involved in a joint venture to build, own and operate electric transmission facilities in Indiana. The project consists of the construction of approximately 290 miles of 765kV transmission lines extending from a substation near Kokomo and terminating near Evansville. MPS was awarded all of the line material (insulators and hardware) for the initial 60 miles of the line.

Ultra high voltage (UHV) 765 is used to transmit bulk power. We commonly supply 345kV and 500kV transmission projects, which in transportation terms would be 4 lane interstate highways. 765kV would be an 8-lane highway.

MPS was tasked with proving the corona and radio interference voltage (RIV) for the assemblies. The corona/RIV is the buzz, snap and crackle sometimes associated with high voltage lines. For residents near the line corridor, the audible noise is objectionable. Directly linked to this audible noise is the radio interference voltage which can disrupt radio and television signals in residential areas.

For most projects, RIV/Corona testing consists of raising the voltage in the test lab and recording the values. In the case of extra high voltage, 765kV, the size of the test hall due to limited height and absence of the other two phases used in the field will reduce the values in the lab, from what they could expect in service. Because of this, project designers use a unique method of measurement. Designers calculate the maximum voltage stress on the conductor in service, and then calibrate the voltage required in the lab to create an equivalent voltage stress in the smaller confines of a test lab.

One of the design tools utilized for the project is an electric field computer-modeling program. The MPS team uses this tool to help the customer refine their assembly design, as well as predict where the voltage stresses will be on the hardware and insulators. The program uses 3D drawings of all of the shapes in the assembly to determine the voltage level for corona.  Computing hardware utilized on this project is the same used by Pixar to create the animated film, Shrek.

The test lab that was utilized for this project is one of only three labs in the world that can test full assemblies (insulators and hardware) at 765kV indoors. Assemblies had to operate without visible corona and RIV levels less than 1000 micro volts at over 1 million volts (1045kV – 28% above normal operating conditions). Within the lab conditions, this translated to an applied voltage of more than 900kV. In the test hall, we were within 30 feet of the energized assembly and the field strength was enough to literally make your hair stand-up. MPS passed all 5 assembly types. This project will continue over the next several years.

Inside view of the 200,000 lb. quad dead end string assembly.

Double V string setup in test hall before test.

Single V string assembly with positive corona discharge at more than 600,000 volts.