GOST 721-77 PDF

Full title and description

GOST 721-77 — "Системы электроснабжения, сети, источники, преобразователи и приемники электрической энергии. Номинальные напряжения свыше 1000 В" (Power supply systems, networks, sources, converters and receivers of electric energy. Rated voltages above 1000 V). This national (USSR) standard specifies the recommended nominal voltages and related classification for alternating-current power systems and the equipment connected to them at voltages above 1 kV.

Abstract

GOST 721-77 defines series of nominal (rated) voltages for three-phase and other AC power systems with phase-to-phase voltages above 1000 V, indicates the highest permissible long-term working voltages for equipment insulation, and sets the standard nominal-voltage values to be used for power sources, converters and consumers in general-purpose electrical networks. The standard was developed for coordinated use with related GOSTs and international practice.

General information

• Status: Active / in force (document widely listed as действующий — reissued and maintained with amendments and reprints).
• Publication date: Approved by Gosstandart (USSR) May 27, 1977; introduced into force July 1, 1978 (various reprints/editions and integrated amendments published later).
• Publisher: State Committee for Standards (Gosstandart of the USSR) / IPC (Publishing House of Standards) — developed under the Ministry of Energy and Electrification of the USSR.
• ICS / categories: Electrotechnics — OKС/ICS classification related to 29.020 (electrotechnics / power engineering).
• Edition / version: Original designation GOST 721-77 (1977); includes amendments published in 1979, 1982 and 1989 (integrated in later reprints); reissued editions/reprints available (notably republications in later years).
• Number of pages: Typically published as a short normative instruction (about 8–9 pages depending on publisher edition).

Scope

The standard applies to general-purpose alternating-current electrical networks (nominal 50 Hz) with rated phase-to-phase voltages above 1000 V and to the sources, converters and receivers of electric energy connected to those networks. It also covers electrical equipment connected to such networks (complete devices and substations, switching gear, current and voltage transformers, reactors, coupling capacitors, etc.), except where other standards specifically establish different nominal voltages (for special networks or transport traction systems).

Key topics and requirements

• Definition of standard nominal (rated) voltages for three-phase and other AC power systems above 1 kV (series of nominal values recommended for sources, converters and receivers).
• Specification of the largest long-term working (interphase) voltages permissible for equipment insulation under normal service conditions.
• Guidance on assignment/classification of electrical equipment by rated voltage (whether treated as source, converter or receiver depends on equipment documentation and application).
• Notes on exceptions and special networks (traction systems, specialized industrial circuits) and recommendation to adopt standard values where practicable.
• Cross-references to related GOSTs and harmonization with CMEA (SEV) and IEC voltage practices of the era.

Typical use and users

Engineers and designers of power systems, substation and switchgear manufacturers, utilities and transmission/distribution planners, standards and regulatory personnel, and technical libraries use GOST 721-77 when selecting and specifying nominal voltages for high-voltage equipment and network planning where USSR/Russian GOST practice is required or accepted. It is also used as a normative reference in technical documentation and regulatory acts that require standardized nominal-voltage values.

Related standards

GOST 721-77 is used together with and references other GOSTs that establish nominal voltages, frequency values and insulation requirements — for example GOST 23366-78 (nominal voltages for products and equipment), GOST 6697-83 (frequencies and permissible deviations) and various equipment-specific standards. It was prepared in alignment with the corresponding CMEA/ST SEV and IEC recommendations in force at the time.

Keywords

GOST 721-77; nominal voltages; rated voltages; high-voltage networks; power supply systems; electrical equipment classification; USSR standard; electrotechnics; OKC 29.020.

FAQ

Q: What is this standard?

A: GOST 721-77 is a State Standard introduced by the USSR that sets standard (nominal) voltage series and related rules for AC power systems and connected equipment at phase-to-phase voltages above 1000 V.

Q: What does it cover?

A: It covers recommended nominal voltages for high-voltage (over 1 kV) power systems, the highest long-term working voltages acceptable for equipment insulation, and classification guidance for sources, converters and receivers of electrical energy connected to general-purpose networks; special networks may be excluded or handled by separate standards.

Q: Who typically uses it?

A: Power-system designers, utilities, equipment manufacturers, regulatory bodies and standards specialists working with Soviet-era or GOST-based technical requirements use this standard for selecting and harmonizing nominal voltages.

Q: Is it current or superseded?

A: The document is widely listed as действующий (active) in Russian standards databases; its original approval was in 1977 with introduction in 1978, and several amendments/reissues were published afterward (limitations on the period of validity were removed by a later Gosstandart decree). Users should verify whether any national or industry-specific regulations have replaced or supplemented its requirements for a given project.

Q: Is it part of a series?

A: Yes — GOST 721-77 forms part of the set of standards that define nominal voltages and electrotechnical parameters (it references and is coordinated with other GOSTs such as GOST 23366-78 and complements frequency-related standards like GOST 6697-83).

Q: What are the key keywords?

A: Key keywords include nominal voltage, rated voltage, high voltage, power supply systems, networks, sources, converters, receivers, electrotechnics, and GOST 721-77.