Electric Power System and Equipment – Voltage Ratings

The voltage levels or voltage ratings are defined and classified by various national and international standards and also by some electrical utility companies.

In general, an electrical professional comes across the terms LV / LT, MV, HV / HT, EHV / EHT and UHV in our day-to-day professional lives.

Voltage Rating Standards

The Indian Electricity Rules, 1956, the following were the voltage limits of power system and equipment −

• Low Voltage (LV) − Less than or equal to 250 V.

• Medium Voltage (MV) − Less than or equal to 650 V.

• High Voltage (HV) − Less than 33 kV.

• Extra-High Voltage (EHV) − More than 33 kV.

However, the Indian Electricity Rules have now been lay off by the Central Electricity Authority (CEA) Regulations 2010.

The National Electricity Code (India) 2011(reaffirmed in 2016), the following were the voltage limits of power system and equipment –

• Low Voltage (LV) − Voltage ratings do not exceed 250 V.

• Medium Voltage (MV) − Voltage ratings more than 250 V, but do not exceed 650 V.

• High Voltage (HV) − Voltage ratings more than 650 V, but do not exceed 33 kV.

• Extra-High Voltage (EHV) − More than 33 kV.

The IEC 60071-1 − Insulation Co-ordination (Part 1) – Definitions, Principles and Rules −

• Low Voltage − Voltage ratings Less than 1 kV.

• High Voltage (Range I) − Voltage ratings greater than 1 kV, but less than or equal to 245 kV.

• High Voltage (Range II) − Voltage ratings greater than 245 kV.

The IS 13234 / IEC 60909 − Short circuit current calculation in 3-phase AC systems −

• Low Voltage − From 100 V to 1 kV.

• Medium Voltage − From 1 kV to 35 kV.

• High Voltage − From 35 kV to 230 kV.

The IEEE / ANSI C92.2-1987 − American National Standard for Power Systems − Alternating Current Electricity Systems and Equipment Operating at Voltages above 230 kV Nominal −

Preferred Voltage Ratings −

• Extra-High Voltage (EHV) − From 345 kV to 765 kV.

• Ultra-High Voltage (UHV) − Greater than or equal to 1100 kV.

The IEEE STD 141-1993 − The Red Book: IEEE Recommended Practice for Electric Power Distribution for Industrial Plants and IEEE STD 241-1990: The Grey Book: IEEE Recommended Practice for Electric Power Systems in Commercial Buildings −

• Low Voltage − From 120 V to 600 V.

• Medium Voltage − From 2.4 kV to 34.5 kV.

• High Voltage − From 46 kV to 230 kV.

• Extra-High Voltage − From 345 kV to 1100 kV.

The IEEE 1623-2020 − IEEE Guide for the Functional Specifications of Medium Voltage (1 kV to 35 kV) Electronic Shunt Devices for Dynamic Voltage Compensation −

• Medium Voltage − 1 kV to 35 kV.

The NECA / NEMA 600-2003 − Standard for Installing and Maintaining Medium-Voltage Cable (ANSI) −

• Medium Voltage − From 600 V to 69 kV.

The French Standard − The French Regulations define three voltage levels as follows −

• Low Voltage (BT) − Less than 1 kV.

• High Voltage A (HTA) − From 1 kV to 50 kV.

• High Voltage B (HTB) − Greater than 50 kV.

The CENELEC (European Committee for Electrotechnical Standardization) − the CENELEC defines the following voltage levels −

• Low Voltage – Less than 1 kV.

• Medium Voltage – From 1 kV to 35 kV.

• High Voltage – more than 35 kV.

The IEC 62271-1 − High-voltage switchgear and controlgear – Part 1: Common specifications for alternating current switchgear and control-gear −

• Medium Voltage – From 1 kV to 52 kV.

• High Voltage – Above 1 kV.

Table 1 – Electric Power System (Power Lines) Voltage-Ratings

Table 2 – Electric Equipment Voltage-Ratings