electrical power engineering course

Load Factor The load factor on an electric utility company bill is a product of the peak demand and energy usage. It usually is calculated and applied to the customer's bill each month. Reducing either the peak demand or energy usage levels, or both, will decrease this added cost factor. Reducing power factor penalties also will help to reduce load factor charges. Power Factor Power factor charges are the result of heavy inductive loading of the utility company system. A poor PF will result in excessive losses along utility company feeder lines because more current is required to supply a particular load with a low PF than would be demanded if the load had a PF close to unity. (The technical aspects of power factor are discussed in Section 3.2.) The power factor charge is a penalty that customers pay for the extra current needed to magnetize motors and other inductive loads. This magnetizing current does not show up on the service drop wattmeter. It is, instead, measured sepa...

Peak Demand Conserving energy is a big part of the power bill reduction equation, but it is not the whole story. The peak demand of the customer load is an important criterion in the utility company's calculation of rate structures. The peak demand figure is a measure of the maximum load placed on the utility company sys- tem by a customer during a predetermined billing cycle. The measured quantities may be kilowatts, kilo- volt-amperes, or both. Time intervals used for this measurement range from 15 to 60 min. Billing cycles may be annual or semiannual. Figure 23.1 shows an example of varying peak demand. If a facility operated at basically the same power consumption level from one hour to the next and one day to the next, the utility company could predict accurately the demand of the load, and then size its equipment (including the allocation of energy reserves) for only the amount of power actually needed. For the example shown in the figure, however, the utility company must ...

Introduction Utility company power bills are usually a large part of the operating expenses of a facility. To reduce the amount of money spent each month on electricity, engineers must understand the billing methods used by the utility. Saving energy is more complicated than simply turning off unnecessary lights. The amount of money that can be saved through a well-planned energy conservation effort is often substantial. Reductions of 20% are not uncommon, depending upon the facility layout and the extent of energy conservation efforts already under way. Regardless of any monetary savings that might be realized from a power-use-reduction program, the items discussed here should be considered for any well-run facility. The rate structures of utility companies vary widely from one area of the country to another. Some gen- eralizations can be made, however, with respect to the basic rate-determining factors. The four primary parameters used to determine a customer’s bill are • Energy ...

Plant Maintenance Maintenance of the facility electrical system is a key part of any serious energy-management effort. Perform the following steps on a regular basis: • Measure the current drawn on distribution cables. Document the measurements so that a history of power demand can be compiled. • Check terminal and splice connections to make sure they are tight. • Check power-system cables for excessive heating. • Check cables for insulation problems. • Clean switchboard and circuit-breaker panels. • Measure the phase-to-phase load balance at the utility service entrance. Load imbalance can result in inefficient use of ac power. • Measure and chart the power factor of the load. Develop and post a simplified one-line schematic of the entire power net- work as well as other building systems, including heating, air- conditioning, security, and alarm functions. A mimic board is helpful in this process. Construct the mimic board control panel so that it depicts the entire ac power-...

Introduction To achieve high levels of power-system reliability — with the ultimate goal being 24-hour-per-day availability, 365 days per year — some form of power-system redundancy is required, regardless of how reliable the individual power-system components may be [1]. Redundancy, if properly implemented, also provides power-distribution flexibility. By providing more than one path for power flow to the load, the key elements of a system can be shifted from one device or branch to another as required for load balancing, system reno- vations or alterations, or equipment failure isolation. Redundancy also provides a level of fault tolerance. Fault tolerance can be divided into three basic categories: • Rapid recovery from failures • Protection against “slow” power system failures, where there is enough warning of the condition to allow intervention • Protection against “fast” power system failures, where no warning of the power failure is given As with many corrective and prevent...

Introduction When utility company power problems are discussed, most people immediately think of blackouts. The lights go out, and everything stops. With the facility down and in the dark, there is nothing to do but sit and wait until the utility company finds the problem and corrects it. This process generally takes only a few minutes. There are times, however, when it can take hours. In some remote locations, it can even take days. Blackouts are, without a doubt, the most troublesome utility company problem that a facility will have to deal with. Statistics show that power failures are, generally speaking, a rare occurrence in most areas of the country. They are also short in duration. Studies have shown that 50% of blackouts last 6 s or less, and 35% are less than 11 min long. These failure rates usually are not cause for concern to commercial users, except where computer-based operations, transportation control systems, medical facilities, and communications sites are concerned. ...

Cable Routing Good engineering practice dictates that different signal levels be grouped and separated from each other. It is common practice to separate cables into the following groups: • ac power • Speaker lines • Line-level audio • Microphone-level audio • Video lines • Control and data lines Always use two-conductor shielded cable for all audio signal cables. This includes both balanced and unbalanced circuits, and microphone-level and line-level cables. On any audio cable connecting two pieces of equipment, tie the shield at one end only. Connect at the receiving end of signal transmission. On video coaxial cables running to outlet jacks mounted on plates, isolate the connector from the plate. The shield should connect to ground only at the equipment input/output or patch panel. For data cables, carefully follow the recommendations of the equipment manufacturer. The preferred interconnection method for long data cables is fiber optics, which eliminates ground-loop proble...