Load flow analysis of 138/69 kV substation using ETAP (Electrical Transient & Analysis Program)

Improving voltage profile of feeders

In this paper, a load flow analysis is performed to a 138/69 kV substation using ETAP software (shortener for Electrical Transient & Analysis Program). The scope of this report encompasses the load flow results, and explains how these were used to implement changes on the feeders that resulted in an improved voltage profile.

The substation layout and equipment choice were provided by Black & Veatch (B&V) as part of a Senior Design project. In this context, the load flow study is performed for different operating conditions or scenarios to determine what control measurements are necessary to prevent system breakdown.

They yield the updated size of fixed or switched shunt capacitor banks required to compensate the inductive effect of the loads. To verify that the theoretical results are accurate, the load flow is performed with the updated parameters for the capacitor banks.

As introduced earlier, the power flow study for this substation will be performed on ETAP. The acronym ETAP stands for Electrical Transient and Analysis Program.

This software is a comprehensive platform for the design, simulation, and protection of electrical networks.

ETAP not only provides solutions to substation designs, but also specializes in generation, transmission, and distribution of power systems.

The software relies on predictive simulation. This allows the user to perform analysis using real-time system parameters and may also simulate “what if” scenarios to predict equipment malfunctioning.

The one-line diagram of the electrical system in question is composed by several pieces of equipment, each with a specific function. All of the components for this substation are high-voltage components.

Some of the most important components are:

• Power source,
• Disconnect switches,
• Circuit breakers,
• Capacitor banks,
• Transmission lines,
• Power transformers,
• Potential (voltage) transformers, and
• Current transformers.

The layout for the substation and the operation parameters for each component on the one-line were specified in the documentation provided by Black & Veatch, with the exception of the transmission line parameters. The process of choosing the most suitable type of conductors for the transmission lines is also discussed in this thesis.

Performing load flow analysis

For a deeper understanding of this thesis, it is important to cover important information about the load flow analysis. The load flow is analysis is performed to determine whether the system voltages operate within the specified voltage limits under normal or fault operating conditions.

It is used to determine the voltage drop at different points of the system, the voltage reading at each bus, and real and reactive power losses through each branch and feeder. ETAP creates warnings if a feeder bus is below the nominal voltage.

Likewise, the load flow study is often performed to identify the need for additional generation units, and the addition or replacement of capacitors and/or reactors to maintain system voltages within specified limits.