NEMA has issued a new revision of ANSI C84.1-2020-Electric Power Systems and Equipment — Voltage Ratings (60 Hertz). This edition carefully explores higher allowable voltage ranges considering high-penetration Distributed Energy Resources (DER) such as solar, wind, and other sources of renewable energy. C84.1 has a new Annex D that describes the acceptable voltage ranges for dedicated circuits to DER and the point where those circuits connect to the point of common coupling with supply to other equipment.
Previous versions of C84.1 have generally assumed voltage drop was caused by power flowing from remote generation sources. It allocated voltage drop to various parts of the electric supply system to electrical outlets in buildings. This produced a preferred range of voltages whereby utilities, building designers, supply equipment manufacturers, and utilization equipment manufacturers would design and test for known voltage ranges.
The advent of high penetration DER introduces the strong possibility that energy will often flow in the opposite direction, causing voltage rise instead of voltage drop. This has the potential to generate higher than expected voltages at many locations along with electric supply systems. One Standard, IEEE 1547 allows for continuous operation 10 percent above nominal at the terminals of the DER but not at the point of common coupling.
ANSI C84.1 Members carefully considered allowing higher voltages, even at the point of common coupling. This might allow higher penetration of DER and possibly reduce any need for DER output curtailment to prevent high voltage.
ANSI C84.1 Members concluded the preferred voltage range at the point of common coupling should not change for many good reasons. Some of those reasons include:
- Legacy equipment—the complete base of supply and utilization equipment has been designed and tested for safe operation and proper performance within existing voltages ranges. Operating outside these ranges may degrade performance or create safety risks.
- Reduction of useful life—Operating at higher voltages would reduce the useful life of supply and utilization equipment.
- Overloads and nuisance tripping—Operating at higher voltage causes some equipment to draw more current. This might overload the supply circuit or cause circuit breakers to trip.
- Over excitation of transformers—Higher excitation currents increase heating and reduce capacity of transformers
- Higher short circuit currents—The higher voltages can increase short circuit currents. This increases arc flash energy and may exceed the interrupting rating of some fuses or circuit breakers.
- Standards revisions—Standards for design and testing for all sorts of supply and utilization equipment would need to be updated. Test equipment would need to be updated to apply the revised testing protocol
These and other reasons convinced C84.1 Members that voltages should not change at the point of common coupling. Annex D describes an allowance for five percent voltage rise from the point of common coupling to the point of connection for DER. However, these systems should give proper consideration for equipment ratings and performance for the higher voltages.
NEMA, as the secretariat of ANSI ASC on Preferred Voltage Ratings for AC Systems and Equipment, C84, is looking for industry experts specifically in the categories of “Producers” and “General Interest” to participate in Standards development activities. Please contact NEMA at firstname.lastname@example.org if you are interested and indicate your interest category and area of expertise.