Better Electric Distribution Systems Begin with “Knowing the Load”

By Tyler Oberly, Safety Program Manager

Those familiar with electrical concepts know that load basically refers to the power an electrical system draws in order to keep its network of equipment operating. There can be a big difference between the actual electrical load a system draws and the load it is capable of drawing.
Often, this cuts both ways:
- Under-loading – If the system is drawing less power than it could, it is under-loaded (i.e., it could safely, efficiently power more equipment).
- Overloading – If the system draws more power than it is designed for, it is overloaded. Damaged equipment, shutdowns, lost product, and other problems could result.

Along with knowing a system’s overall load, it’s key to know how the load is distributed (balanced): a balanced system is an efficient system.

The best way to know your system’s load is with a load flow study, or “power flow” study. A load flow study is numerical analysis that compares an electrical system’s use with its
capacity. Its purpose is two-fold:

- Improvement – Evaluate how the system is performing now to decide if changes can improve operations.
- Planning – Predict how future hypothetical or emergency situations might impact its performance (e.g., adding equipment and significant amounts of new load, or shutting down a transmission line for servicing, creating the need to transfer its load to other parts of the system…and the question, “Can they handle this without overloading?”).

If you want to boil it down to simplest terms, the load flow study answers two questions: “Load-wise, is my power system as good as it could be today?” and “Will it be adequate for what I need tomorrow?”

Every industrial electrical power system can benefit from a load flow study, but a particularly good time to conduct one is before making a major change to the existing equipment network. A good rule of thumb is if the change involves the addition of 200 amps or more of new service requirements, a load flow study is warranted.

Generally, there are two types of load flow studies: a design load flow study and a metered load flow study. The design load flow study entails reviewing the electrical system, and using calculations to estimate its electrical loading at different points. The analysis from this study can be used for many purposes, like deciding if it’s okay to temporarily connect a piece of equipment to an undersized circuit breaker in order to test the equipment.

The metered load flow study involves using electrical metering equipment to measure the system’s actual electrical load at different operating points and times to get an overall – and very accurate – view of its normal, steady-state operation. The meters capture information for just about any aspect of system performance pertinent to the load flow study, including watts, amps, volts, voltage angles, vars, disturbances (harmonics), and power factor.

What benefits does a load flow study offer? Helping to prevent an overload is one. For instance, too often, if a switchgear has a spare breaker, the assumption is, “It’s okay to add equipment here.” But just because a breaker is available doesn’t mean the system isn’t loaded heavy or already overloaded. Adding more load might be “the straw that breaks the camel’s back.” As a result, a vital – and expensive – transformer can overheat and be damaged or destroyed.

Load balancing is another valuable benefit. Sometimes, electrical systems have distribution equipment that is underutilized. A load flow study will point this out, allowing electrical planners to shift and combine loads for better equipment use. This normally helps save money by promoting more economical operations and also frees up distribution equipment for service in other parts of the system.

Recently, D.L. Steiner did a load flow study for a client that was planning to add two new transformers to handle its present and future load requirement. Our study showed that by consolidating and shifting loads within the existing transformer setup, the need for new transformers could be eliminated. The result was a $300,000 net savings to the client!

Anyone with electrical knowledge can complete a load flow study, but experienced electrical distribution professionals usually deliver the best results. They have the background necessary to interpret the study data, spot issues, and make recommendations that will fine-tune the electrical system for maximum performance, both now and as its load requirements change in the future.

For more details on D.L. Steiner’s load flow study services – or if you want D.L. Steiner to review and analyze the electrical system load flow data you’ve collected – please contact D.L. Steiner, Inc.