Rating plate explained

A rating plate on a machine carries information about its operational limits. The plate frequently contains the names of the machine and its manufacturer, so the rating plate is often called a name plate (hence the term "nameplate capacity" for a generator), although many devices carry separate nameplates and rating plates.^[1]

For an electric machine, the power rating is the number on its rating plate and corresponds to a maximum electric load it can carry. There is a distinction between the continuous rating (for generators, continuous maximum rating or CMR^[2]), at which the machine can be operational without a time limit and short-term rating that can only be used for a specified amount of time.^[3]

Generators

A typical electrical generator rating plate contains the following parameters:

• power rating is specified in terms of apparent power (KVA or MVA), since the exact power factor will be determined by the external factors;
• power factor (PF) is the nominal power factor for other ratings; usually PF = 0.8;
• insulation class (B, F, H) for the primary coil. Typical value is F, although older generators might use class B;
• type of enclosure (IP code);
• rated voltage can be either line to line ("line voltage") or phase to neutral ("phase voltage");
• rated current is derived from the rated power and voltage:

{ratedCurrent} = (apparentPower)/(lineVoltage) ;

• line frequency (50 Hz or 60 Hz) and rotational speed of the prime mover in RPM;
• connection (star or delta).

See also

• Per-unit system

Sources

• Book: Reddy, B.K. . Electrical Equipment: A Field Guide . Wiley . 2021 . 978-1-119-77168-5 . Rating Plates . https://books.google.com/books?id=OIA_EAAAQBAJ&pg=PA80 . 2023-10-14.

Notes and References

1. Book: National Electric Light Association . Handbook for Electrical Metermen . Franklin printing Company . Nineteenth Century Collections Online (NCCO): Science, Technology, and Medicine: 1780-1925 . 1924 . https://books.google.com/books?id=rh1SAQAAMAAJ&pg=PA1185 . Rating Plate. 2023-07-15 . 1185.
2. Book: Stuart, S. . Electrical (Generator and Electrical Plant): Modern Power Station Practice . Elsevier Science . 2013 . 978-1-4831-5751-1 . https://books.google.com/books?id=gqM3BQAAQBAJ&pg=PA18 . 2023-07-15 . 18 . The Rating of Generators.
3. Book: British Standards Institution . British Standardisation Rules for Electrical Machinery (excluding Motors of Traction Purposes) Rev. September, 1917 . committee . British Standardisation Rules for Electrical Machinery (excluding Motors of Traction Purposes) Rev. September, 1917 . 1917 . https://books.google.com/books?id=LXNtDgXCABIC&pg=PA18 . 2023-07-15 . 18 . Definitions.