Playing Roulette

Getting some people to pay attention to power quality issues is often like trying to sell them insurance; they wonder, “Why bother? It never happens to me.” It becomes a gamble, or as Dirty Harry would say, “Do you feel lucky?”

Power quality issues have been around since Westinghouse and Edison debated whether generation should be AC or DC power. But what has been changing is the increase in PQ pollution and the susceptibility of equipment to such. Even industries such as hospitality and gaming are becoming increasingly vulnerable. It is no longer a matter of “if” but rather “when” it will affect the facility.

Hotels and gaming facilities have become increasingly dependent on having continuous and compatible electric power provided to their facilities and the equipment within them. Reservation and check-in/out systems are dependent on a network of interconnected computers, which have the same vulnerabilities to sags, swells and transients as those in an office or industrial facility. Even with backup systems in place, they’re not immune to problems.

Many articles in the PQ industry refer to the fact that the majority (anywhere from 50 percent to 85 percent depending on the source) of the power quality-related problems that occur in a facility are related to the wiring and grounding. Inadequate neutral conductors, illegal neutral-to-ground bonds, ground loops formed by improperly terminated LAN cabling, insufficient transient suppression, and just too many harmonic-producing single phase loads, such as personal computers, faxes and printers, make such facilities prime candidates for PQ problems. Additional harmonic distortion comes from the proliferation of adjustable speed drives to control elevators and HVAC systems, adding lots of fifth, seventh, ninth, and 11th harmonic currents. These harmonic currents can turn the sinusoidal voltage waveform that most equipment is designed to be powered from, into a variety of distorted waveforms, as shown in the figure above.

“But why should I care; what’s the downside to me?” ask the facility managers. How do you measure the revenue loss from a customer who can’t check in because the “system is down,” or whose reservation was lost when a transient occurred and corrupted the memory, or who can’t get into their room because an instantaneous sag tripped the room key security system off-line, or when the slot machine made an “unanticipated” large payout because the microprocessor inside the machine was confused by a power factor capacitor switching transient … and so on? These power quality phenomena are out there, lurking in the wires, every day.

Many of these facilities do have protection from longer duration power outages, or sustained interruptions as they are known in the industry. This is from backup generators that can power part or even all of the facility, depending on their size and the load. Many times, these generators suffer from inadequate maintenance and testing, so they don’t perform as desired when such an event occurs. They also take several seconds to get up to speed and provide adequate voltage for the system. This transition time may require UPS units to be placed on critical circuits, such as computer systems and elevator controls, to provide ride-through until the generator is fully functioning.

The generators may also have been designed for a load profile that is quite different from what is presently in the facility. Backup generators typically have a higher source impedance than the utility system, which means that the same large increase in current from load energization will result in a much deeper voltage sag than would have occurred when powered from the utility electrical distribution system. The harmonic impedance may also be higher, which means the same harmonic currents will produce a more distorted voltage waveform. So equipment that had run just fine off the grid may now malfunction when powered off the backup generator.

However, these generators may also be a source of revenue. There is a growing program for providing additional peak capacity through the use of distributed generation. The local electric utility or the ISO (Independent System Operator) may have programs available that allow this standby capacity to be “sold” as reserve capacity for times of peak demands that the local utility may not have adequate capacity to provide with the proper safety margins. Payments come in the form of capacity payments (just for being there) and energy payments (should the need arise to actually run the generators).

The winning ticket is to be proactive, to know what your system’s requirements, susceptibilities, and quality of supply are before the PQ-related problems become more than just an inconvenience to your customers. It doesn’t take much to do such, and the payoffs can be huge.

BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680. 


About the Author

Richard P. Bingham

Power Quality Columnist
Richard P. Bingham, a contributing editor for power quality, can be reached at 732.287.3680.

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