Monday, April 18, 2011

ANSI C84.1 establishes the nominal voltage ratings and operating tolerances for 60-Hz electric power systems above 100 volts (steady-state voltage levels only). Its latest revision, ANSI C84.1-2006 includes preferred voltage ratings up to and including 1200 kV maximum system voltage. However, it does not include momentary disturbances, which may be the result of, but not limited to, utility switching operations, large motor starts, lightning strikes, fault clearing and similar occurrences. ANSI C84.1 makes recommendations to other standardizing groups with respect to voltage ratings for equipment used on power systems and for utilization devices connected to such systems.

In this post, the focus will be on ANSI C84.1 standard nominal system voltages and voltage classes. Refer to this article for voltage tolerances: ANSI C84.1 – Voltage Ranges.

Basically, the standard stated the following objectives:

1.   Promote a better understanding of the voltages associated with power systems and utilization equipment to achieve overall practical and economical design and operation.
2.      Establish uniform nomenclature in the field of voltages
3.   Promote standardization of nominal system voltages and ranges of voltage variations for operating systems
4.      Promote standardization of equipment voltage ratings and tolerances
5.  Promote coordination of relationships between system and equipment voltage ratings and tolerances
6.   Provide a guide for future development and design of equipment to achieve the best possible conformance with the needs of the users
7.    Provide a guide, with respect to choice of voltages, for new power system undertakings and for changes in old ones.

System Voltage Classes

Subsequently, ANSI C84.1 defines the system voltages into classes depending on the system voltage magnitude.

Ø      Low Voltage (LV) –  Nominal voltage 1000 V or less
Ø      Medium Voltage (MV) –Greater than 1000 V but less than 100 kV
Ø      High Voltage (HV) – Class of nominal system voltages from 100 kV to 230 kV
Ø      Extra-High Voltage (EHV) – Greater than 230 kV but less than 1000 kV
Ø      Ultra-High Voltage (UHV) – System voltages that are equal to or greater than 1000 kV

Nominal System Voltages

ANSI C84.1 has published the following standard nominal system voltages:
ANSI C84.1 Standard Nominal System Voltages
ANSI C84.1 Standard Nominal System Voltages
Note: Bold-face type numbers are the preferred system voltages

The medium voltage 3-wire systems of 4160, 6900 and 13800 volts, are particularly suited for industrial systems that supply predominantly polyphase loads, including large motors. This is because these voltages correspond to standard motor ratings of 4000, 6600 and 13200 volts, respectively. It is not intended to recommend the use of these system voltages for utility primary distribution, for which four-wire voltages of 12470Y/7200 volts or higher should be used.

ANSI C84.1-2006

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I am a Professional Electrical Engineer with a Masters Degree in Business Administration. My interest is in Power Quality, Diagnostic Testing and Protective Relaying. I have been working in an electric distribution utility for more than a decade. I handle PQ studies, power system analysis, diagnostic testing, protective relaying and capital budgeting for company projects.