Metropolitan Kansas City Has Enjoyed Consistent Growth in New Customer Loads over the years, highlighted most recently by a resurgence of the downtown area. In the past couple of years, new, large downtown loads, such as a new sports arena and Federal Reserve and Internal Revenue Service buildings, have come on-line.
Kansas City Power & Light (KCP&L; Kansas City, Missouri, U.S.) serves the metropolitan area, which includes customers in both Kansas and Missouri. The utility also has seen significant growth in other residential and commercial loads, both downtown and in the surrounding service area. At the same time major infrastructure additions and modifications were going on to accommodate this new load, commodity prices — and, therefore, material prices — were escalating 15% a year on average, driving up construction costs. In order to use capital in the most efficient manner possible and maximize the value of the existing distribution assets, the distribution engineering group decided to take another look at how it does capacity planning and additions.
A NEW APPROACH
In the past, KCP&L designed and built a system based on N-1 contingency planning design criteria that could handle the loss of any one piece of equipment at a given time. The circuit loads used in this type of planning were seasonal peak loads, which were not always coincident peak loads. The highest load a circuit reached in a given year was assumed to be coincident to a neighboring circuit's highest load.
This presumed coincident peak load was used to determine how much load could be shifted to another circuit during failure conditions. If a cable rating was violated during this simulated load-shifting procedure, capital improvements were designed and built to resolve the switching issue. On one hand, this could be as simple as installing a feeder-class switch to sectionalize a circuit differently and break apart the load onto neighboring circuits. On the other hand, it could be as complex as installing a new substation with new distribution circuits to cut over loads that would otherwise overload neighboring circuits in failure conditions. In any case, the coincidence or non-coincidence of these loads was not examined.
The original non-coincident contingency method should still be used as a first screening of which circuits might be problematic. If a non-coincident contingency switching order works, there is no need for further examination. If it doesn't work, the engineer should look more closely at those days of the year where there could be overload. During that examination, the engineer would be able to tell how many hours and by how much a circuit is overloaded — both key pieces of information when making decisions based on risk and for use with energy-efficiency and demand-response programs.
FEEDER DATA AND PLANNING PROCESS
There are four levels in which to examine the behavior of a given feeder or feeders: multiple-year seasonal demand, single-year daily demand, multiple-day hourly demand and single-day hourly demand. All these may be based on hourly amp-flow at a feeder breaker from a distribution supervisory control and data acquisition (SCADA) system, which can be sorted to find a 3-phase daily peak kilovolt-amp. Each level of examination serves a different purpose in distribution planning. For example, a multiple-year seasonal demand would be used to determine a circuit's future growth rate.
A multiple-day hourly demand between several feeders would be used to determine if distribution ties would be overloaded if one feeder failed. Generally speaking, if a feeder has five distribution ties and equal peak demand to its tie circuits, then each circuit in the area should have at least one-fifth of its capacity reserved for contingency switching. Another use of multiple-day hourly demand between feeders that serve a given geographic area is to analyze a geographic area's power usage, which is valuable when determining a neighborhood's growth rate.
By looking at the behavior of multiple feeders simultaneously, it is possible to determine if the distribution ties between the circuits will be overloaded during failure conditions on a seasonal, daily or hourly basis, also called an N-1 coincident contingency analysis. There is a method to reduce the level of analysis required for such a study.
First, perform a seasonal peak contingency study. By taking the apparent peak demand of several circuits during a given summer, determine what switching operations are necessary to restore all customers if one of the feeders were to fail. Then determine what effect that switching operation will have to see which tie circuits are overloaded. Identify the demand level at which the tie circuit would not be overloaded when switched around and set a desired threshold.
Once the threshold is determined, examine those days in the summer where the circuit's demand was higher than the threshold. By looking at this closely for a circuit, the number of hours of risk is apparent (and a necessary piece of information needed for decision-making). The number of hours curtailment needed in a summer is also required for curtailment programs, also called energy efficiency and demand response (EE/DR). A logical step-by-step process for this analysis is outlined in the nearby sidebar.
ENERGY EFFICIENCY AND DEMAND RESPONSE
KCP&L also is using this new analysis approach in a unique way by partnering with its Energy Solutions (ES) department to integrate energy-efficiency and demand-response opportunities into the distribution-planning process. With detailed information about when a problematic circuit peaks, the peak duration, the magnitude of the peak and when the peak occurs, the ES group can target existing EE/DR programs to help relieve circuit problems and avoid capital costs. If one of the existing EE/DR programs does not seem to fit, the programs can be modified or new ones developed to address the specific circuit issue. Costs of addressing the issue with an EE/DR solution can then be compared against a traditional engineering solution to select the most economical plan.
Today, KCP&L's ES team is using three EE/DR programs: Energy Optimizer, MPower and CoolHomes. By taking Distribution Engineering's necessary hours per summer of curtailment and how many kilowatts of curtailment are needed, these three programs can be targeted at customers served by problematic circuits to reduce peak demand where it's needed most — to resolve the N-1 contingency scenarios that could potentially overload distribution ties.
The Energy Optimizer program is an air-conditioning cycling program by which KCP&L can reduce residential and small commercial air-conditioning load during peak summer days. The utility achieves this load reduction by sending a paging signal to a control device attached to the customer's air conditioner. The control device then turns the air conditioner off and on over a period of time, depending on the control and load-reduction strategy established by the utility.
MPower is a contracted load-curtailment program for large commercial and industrial customers that provide a capacity and energy payment to participating customers to curtail their usage during summer months when high electric demand occurs. Customers are eligible for participation in the program by providing a minimum load reduction of 200 kW during KCP&L's high-usage/high-cost periods.
The Cool Homes program will encourage residential customers to purchase and install energy-efficient air conditioning and heat pumps by providing financial incentives to offset a portion of the equipment's higher initial cost. The program's long-range goal is to encourage contractors and distributors to use energy efficiency as a marketing tool, thereby stocking and selling more efficient units and moving the entire central air-conditioner and heat-pump market toward greater energy efficiency.
In just one district, the contingency coincidence analysis has already yielded a significant decrease in the number of capital-improvement projects required to meet the needs of the KCP&L distribution system.
After following the aforementioned analysis procedure, KCP&L deferred more than US$2 million by at least two years when the level of risk was shown as low or nonexistent. Eight different feeder peak violations were determined using non-coincident loads, and these were further analyzed on a daily basis showing there were only three remaining coincident violations. These three violations were insignificant enough to delay the capital improvements for at least two years, given the local growth rate. EE/DR programs were then deployed in the area to further defer the capital spend.
Engineers now better understand the behavior of specific circuits at a more granular level and can plan accordingly to meet the needs of this dynamic system. Armed with the hours at risk and kilowatts required to resolve a contingency scenario, the engineers can make more informed decisions, and energy-efficiency programs can be targeted to specific circuits to achieve the same effect as a new feeder tie.
In the end, KCP&L is spending capital dollars more efficiently and better utilizing the existing distribution infrastructure.
Greg Elliott joined KCP&L in 2006 after graduating from Iowa State University with a BSEE degree. He is an EIT and has been leading the distribution infrastructure enhancements in support of the ongoing Kansas City downtown revitalization projects.
Scott Grafelman is manager of Distribution Engineering with KCP&L. He has more than 27 years experience with KCP&L, having held a variety of distribution positions in energy management, customer service, field design, system operations and restoration, engineering and field construction. Grafelman earned a BS degree in thermal and environmental engineering from Southern Illinois University - Carbondale and an MBA in finance from the University of Missouri - Kansas City. He is a registered professional engineer in Missouri.
PLANNING FLOW CHART
The adjacent pseudo code is used to quickly identify possible coincident contingency scenarios that may be problematic. If varying granularity levels of data are available, sorting through entire power-distribution systems' worth of load data can be daunting.
By following this process, non-problematic scenarios can be eliminated quickly, narrowing down the search for hourly contingency switching overages. This program points the engineer toward those few scenarios that require further analysis.
The key to this kind of analysis is used to reduce very quickly the number of feeders that must be examined on an hourly basis. There would be an enormous amount of information to analyze with very little benefit otherwise. This step process to identify problematic circuits is vital for the engineer to discover the most useful information and use the capital dollars in an efficient manner.