As electrical professionals, many of us have been coming across the terms LV or LT, MV, HV or HT & EHV or EHT in our day-to-day professional lives. But are we aware of the limits of these voltages as per Indian Standards and/or International Standards?
This article aims to analyse the limits set for these voltages in Indian as well as International Standards.
Voltage levels have been defined and classified by various National and International Standards as also by certain electric power utility companies.
The following are the definitions given in various National & International Standards for AC Voltages:
As per the (erstwhile) Indian Electricity Rules, 1956, vide Rule 2(av), the following were the limits:
-Low Voltage: Not exceeding 250 V.
-Medium Voltage: Not exceeding 650 V.
-High Voltage: Not exceeding 33000 V.
-Extra High Voltage: Exceeding 33000 V
However, it may be noted that the IE Rules have now been superseded by the Central Electricity Authority (Measures Relating to Safety and Electric Supply) Regulations, 2010 and the above definition is removed in the CEA Regulations, 2010.
As such, as per the latest Regulations in vogue in India, there is no such classifications as LV, MV, HV & EHV.
The National Electric Code (of India) 2011 (Reaffirmed in 2016): Part 1 – Section 2
-Low Voltage: The voltage which does not normally exceed 250 V (Cl. 3.3.37)
-Medium Voltage: The voltage which normally exceeds 250 V but does not exceed 650 V (Cl. 3.3.38)
-High Voltage: The voltage which normally exceeds 650 V (but less than 33 kV) (Cl. 3.3.39)
-Extra High Voltage: The voltage exceeding 33 kV under normal conditions (Cl. 3.3.40)
Note: The definitions given in 3.3.37 to 3.3.40 are based on the provisions of IE Rules. It may, however, be noted that voltage ranges as defined internationally are at variance with the above definitions.
IS/IEC 60071-1 & IEC 60071-1: Insulation Coordination – Definitions, principles, and rules:
-Low Voltage: Um < 1 kV
-High Voltage – Range I: 1 kV < Um ≤ 245 kV.
-High Voltage – Range II: Um > 245 kV
IS 13234 / IEC 60909: Short-circuit currents in three-phase AC systems:
-Low Voltage: 100 V to 1000 V
-Medium Voltage: > 1 kV to 35 kV
-High Voltage: > 35 kV to 230 kV
ANSI C84.1-1989: American National Standard for Electric Power Systems and Equipment – Voltage Ratings (60 Hertz):
-Low Voltage: From 120 V to 600 V
-Medium Voltage: From 2.4 kV to 69 kV
-High Voltage: From 115 kV to 230 kV
ANSI C92.2-1987: IEEE/ANSI C92.2-1987: American National Standard for Power Systems – Alternating-Current Electrical Systems and Equipment Operating at Voltages Above 230 kV Nominal-Preferred Voltage Ratings:
-Extra High Voltage: From 345 kV to 765 kV
-Ultra High Voltage: 1100 kV & above
IEEE 141-1993: The RED Book: IEEE Recommended Practice for Electric Power Distribution for Industrial Plants & IEEE 241-1990: The GREY Book: IEEE Recommended Practice for Electric Power Systems in Commercial Buildings:
-Low Voltage: 120 V to 600 V
-Medium Voltage: 2.4 kV to 34.5 kV
-High Voltage: 46 kV to 230 kV
-Extra High Voltage: 345 kV to 1100 kV
IEEE 1623-2020: IEEE Guide for the Functional Specification of Medium Voltage (1kV to 35kV) Electronic Shunt Devices for Dynamic Voltage Compensation:
-Medium Voltage: 1 kV to 35 kV
NECA/NEMA 600-2003: Standard for Installing and Maintaining Medium-Voltage Cable (ANSI):
-Medium Voltage: From 600 V to 69 kV
French Standard: Vide a publication dated 14th November 1998, the French Regulations define three voltage levels as below:
-Low Voltage: < 1 kV
-High Voltage A (HTA): > 1 kV but </= 50 kV
-High Voltage B (HTB): > 50 kV
CENELEC (The European Electrotechnical Standardization Committee): Vide a publication dated 27th July 1992, the CENELEC recognizes the following voltage levels:
-Low Voltage: < 1 kV
-Medium Voltage: > 1 kV but </= 35 kV
-High Voltage: > 35 kV
IEC 62271-1: High-voltage switchgear and controlgear – Part 1: Common specifications for alternating current switchgear and controlgear:
-Cl. 1.1: Note: For the use of this standard, high voltage is the rated voltage above 1, 000 V. However, the term medium voltage is commonly used for distribution systems with voltages above 1 kV and generally applied up to and including 52 kV.
IEC 60038: IEC standard voltages:
-In many discussions on the classification of AC Voltages, like LV, MV, HV & EHV, many people incorrectly quote that such a clear & precise classification is available in IEC 60038. But this is not true.
-IEC 60038, in its Section-2.
Tables of Standard Voltages, gives only the following:
-Table 1 – AC systems having a nominal voltage between 100 V and 1 000 V inclusive and related equipment.
-Table 2 – DC and AC traction systems
-Table 3 – AC three-phase systems having a nominal voltage above 1 kV and not exceeding 35 kV and related equipment.
-Table 4 – AC three-phase systems having a nominal voltage above 35 kV and not exceeding 230 kV and related equipment.
-Table 5 – AC three-phase systems having a highest voltage for equipment exceeding 245 kV.
-Table 6 – Equipment having a nominal voltage below 120 V AC or below 750 V DC.
-In fact, in the entire pages of IEC 60038, there is no terminology like Medium Voltage, High Voltage or Extra High Voltage. And the terminology “Low Voltage” is used only once as a foot-note to Table 1 of Section 2, to describe the limits of voltage variation.
-Thus, it is grossly incorrect to quote that IEC 60038 has given the classifications of LV, MV, HV & EHV.
Conclusion
As can be seen from the above, there is no clear-cut demarcation for classification of various voltage levels in AC Electric Power Transmission and Distribution.
Also, there is no single standard across the globe, with various countries defining various limits for these voltages. And, as in the case of India, Europe and USA, even within one country, two standards do not match, when it comes to these limitations.
It is wished that the electrical community across the globe meets and takes a decision soon to bring harmony across the countries of the world in standardizing the limits for various voltage classifications.
Sivakumar
The author is the Head – Technical, Sriwin Electric, Salem
