Puget Sound Energy

Project: Voltage Rise on a Distribution Feeder with a Distributed Generator

Team: Bryce Coomer, Kevin Frei, Andy Wick, Darrin Wright

Advisor: Dr. Juan Bala Jr. / Dr. Peter McKenny

Liaison: Joseph Seabrook

Puget Sound Energy team

Description: This project investigates voltage rise on lightly loaded distribution lines with a distributed generator, as well as the appropriate solutions to correct the problem.

Distributed generation (DG) is an increasingly popular idea taking place in which small generators provide power locally within a distribution circuit. This is a different approach from the traditional electric power system, which can reduce the need for new power plants and transmission lines.

With this project, a small 1500kW generator would be connected to the end of the distribution line and generate power into the grid. The problem that can occur is when the generator produces too much power for the load, and the extra current flows back toward the substation. This in turn brings about a voltage rise on the system, which can raise the voltage above regulation standards. The goal of this project is to lower that rise in voltage. software calculations

The solutions studied to solve this problem were the use of large reactors to absorb reactive power, line drop compensation (LDC), and synchronous generators operating at various power factors. Additionally, the project team used the software PSS/E to simulate power flow and stability analysis with these solutions.

The power flow simulations showed that reactors were able to lower the voltage within specified limits as the generator operated at unity power factor. As well, operating the generator at leading power factor or using line drop compensation with reactors, also solved the problem. Lastly, operating the generator at a lagging power factor greatly increased the overvoltage problem and was deemed to be an undesired operating condition.

The next step was to use the valid solutions obtained and test them in stability analysis simulations. It was seen that the generator could not operate at a leading power factor, as the voltage, powers, and power angle oscillated continuously. The inductors on the other hand were simulated with three phase faults and the generator returned to steady state after the transient. Faults of durations up to 44 cycles were simulated, and the generator recovered from all of them. Line drop compensation also proved successful during the three phase faults and lowers the reactive power needed to be absorbed by the inductor.

T&D instructor Tuan Tran The team also worked with T&D instructor Tuan Tran to brainstorm ideas for the project. Tuan is a Gonzaga Alum and Transmission and Distribution Supervisor for Operations and Planning at Tacoma Power.

The conclusions of the project were that although operating the generator at a leading power factor proved promising in the power flow simulations, this generator with its intrinsic parameters, could not pass the stability analysis simulations (although operating another generator at leading power factor may be a valid solution). The use of a large reactor, however expensive, is the best solution in solving the overvoltage problem. As well, using line drop compensation in conjunction with reactors greatly reduces the amount of reactive power consumption. With these solutions implemented, distributed generation is an effective and reliable advancement in power generation.

The team would like to thank their advisors and liaison engineer, as well as Puget Sound Energy for sponsoring the project.