Once a year, I focus on the latest trends and changes in power-quality monitors, standards and mitigation equipment. This article initially focused on the latter, but after researching several dozen of the newer products on the market, one thing became apparent. Customers often send me data from power quality monitors that seem to defy the laws of physics. A disturbingly large number of the products claim such impossible things as well. Whether measuring or mitigating, Ohm’s and Kirchoff’s Laws will still apply until someone can disprove Maxwell’s Equations and win the Nobel Prize for Physics.
This table is extracted from the infamous Table 2 in IEEE Std 1159 2009, Recommended Practice for Monitoring Electric Power Quality. It lists the types of power quality phenomena.
To mitigate the phenomena, the solution must either supply or absorb enough energy at the right time, reacting fast enough and long enough to recreate the original sine wave of the voltage and/or current so that the equipment powered from the supply is no longer affected.
An impulsive transient is one of the more common phenomena, especially in lightning-prone areas. Depending on how close the strike is, what it couples into, and the grounding system of the facility and equipment, the typical lightning strike of 20,000 amperes can result in a 1.2 × 5 usec impulsive transient of hundreds or thousands of volts on the electrical distribution wiring and/or communication wiring. Though the old 4-kilovolt breakdown test is more energy than is typically coupled into the wiring within a facility, the energy must either be absorbed by the protection device or diverted from the supply lines and into the ground.
This energy still comes in the wires and will pass through the watt-meter. Therefore, claims that surge-suppression devices can save energy or provide energy to ride through sags are violating these rules. If the device absorbs energy, it must have an adequate joule rating for the application. If the device shunts it into the ground, it should have an adequate grounding wire to an adequate low impedance ground path, or it may result in raising the equipment grounding level to an unsafe voltage for other equipment.
How can devices that are simply inserted in series with the data lines protect the data networks against lightning-induced surges, AC power interference, electrostatic discharge and ground loop energies when they have no separate ground path?
If the device has a grounding wire and recommends grounding on each end of the circuit, doesn’t that create a ground loop? What component inside these devices can provide enough energy to supply voltage and correct for a negative transient (which subtracts from the voltage curve), let alone against utility outages? Notches, a common form of negative transient, can result in damage to motor windings, and the more severe ones can cause zero crossing errors that confuse timing circuits synched to the power frequency.
Harmonic filters are another area where some claims defy the laws of physics. Harmonic filters are generally installed within the facility and often near equipment that produces harmonic currents and propagates other parts of the electrical system, resulting in potentially damaging harmonic-voltage levels. Since the energy already came into the building through the meter, how can anything that occurs downstream make significant savings in your electric bill? The usual capacitors in those devices are not designed to provide a backup power source nor a significant source of volt-amperes reactive to correct power factor.
Speaking of power-factor correction (PFC), there is a dynamic PFC device that claims to react in real-time to improve the power quality, along with improving the power factor for better efficiency and lower demand charges. Elevators and air conditioning systems with adjustable speed drives are a known source of harmonics, as are other nonlinear loads. But the presence of harmonics doesn’t mean they have poor lagging power factors, which a PFC addresses. A power factor of 1.0 does not equal 100 percent efficiency of the equipment in the facility. It just means that the watts consumed equals the volt-amperes supplied.
Next month, I will work through Table 2 from IEEE Std 1159 2009 and demonstrate what can mitigate such phenomena while fully complying with the rules.
About The Author
BINGHAM, a contributing editor for power quality, can be reached at 908.499.5321.