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Power quality

Learn more about the various factors that influence power quality, about power quality standards and about how power quality is assessed.

Our transmission system meets the quality and reliability standards of the Northeast Power Coordinating Council (NPCC), which regulates transmission providers in northeastern North America and has some of the most stringent criteria on the continent.

Our distribution system supplies power at voltages within the limits recommended in CSA Standard CAN3-C235-83 for low- and medium-voltage power systems.

If you find that your supply voltage is outside normal limits (for example, not between 110 V and 125 V for a 120-V supply), contact Customer Services at 1 -800 -790-2424 or your commercial delegate.

Standards and characteristics

Voltage limits at the connection point of delivery
As specified in CAN3-C235-83

Normal operating conditions

Minimum (volts)

Maximum (volts)

120/240 V
110/220 125/250
120/208 V
112/194 125/216
347/600 V
318/550 360/625
600 V
550 625

Extreme operating conditions

Minimum (volts)

Maximum (volts)

120/240 V
106/212 127/254
120/208 V
110/190 127/220
347/600 V
306/530 367/635
600 V
530 635

Note: If the voltage remains within the limits for normal operating conditions, no improvements or corrective action are necessary. If it remains within the range for extreme operating conditions, improvements or corrective action should be planned according to a definite schedule but not necessarily on an emergency basis. If the voltage is outside these limits, Hydro-Québec must take urgent action to remedy the situation.

You’ll find more information about low voltage in Characteristics and Target Values of the Voltage Supplied by the Hydro-Québec Medium- and Low-Voltage Systems.

According to standard CAN3-C235-83, the voltage limits at the connection point correspond to ± 6% of rated voltage (usually 25 kV, that is, 14.4/24.94 kV, 3-phase wye, grounded neutral).

You’ll find more information about medium-voltage supply in Characteristics and Target Values of the Voltage Supplied by the Hydro-Québec Medium- and Low-Voltage Systems.

Voltage disturbances

Power disturbances are waveform distortions that are very often due to the use of high-power electrical equipment, which affects the grid when in use. It can affect the operation of other equipment depending on how sensitive it is and on the degree of waveform distortion.

It is possible to correct the problem and improve the electromagnetic compatibility of your equipment with the supply voltage; however, solutions must be assessed on a case-by-case basis by a specialist (master electrician or engineer), who should factor in the cost and the impact on your company’s productivity.



  • Escalators and passenger/freight elevators
  • Air conditioners
  • Fluorescent lights
  • Vending machines
  • Variable-frequency drive motors
  • Photocopiers
  • Welding machines
  • Telephone switching systems
  • Fans
  • Arc or induction furnaces
  • Accidents
  • Tree limbs in contact with lines
  • Lightning
  • Air pollution
  • Magnetic storms
  • Strong winds

Electromagnetic Compatibility

Electromagnetic compatibility is the ability of equipment to function satisfactorily in its electromagnetic environment without introducing intolerable disturbances to anything in that environment.

Under the Conditions of Electricity Service [PDF], your electrical installation must be designed, built, connected, protected, used and maintained in such a way that it does not cause disturbances on the power system. Disturbances can be caused by a number of phenomena: voltage and current fluctuations, flicker, harmonics, etc. In order to maintain power quality, Hydro-Québec must ensure that the various types of disturbances do not exceed the thresholds on its power system. If necessary, Hydro-Québec will ask you to conduct the appropriate studies. For example, standards C.22-03 [PDF] (in French only)  and C.25-01 [PDF] (in French only)  contain specific requirements regarding flicker and harmonics. It should also be noted that large, disturbance-causing equipment (welding machines, variable-frequency drives, power electronics, etc.) can be incompatible with sensitive equipment and can cause the allowable disturbance thresholds to be exceeded.

Hydro-Québec encourages you to look for equipment that meets the Canadian standards for immunity to disturbances . Equipment with electronic components is highly sensitive to power disturbances. Electromagnetic incompatibility between your equipment and the voltage delivered by Hydro-Québec can lead to damage or malfunction and can even shorten the service life of your equipment.

Take advantage of our technical audit and assessment services

Hydro-Québec offers you the technical support of its power experts. Their help is just what you need if you rely on power electronics or other equipment potentially affected by disturbances such as harmonics or voltage dips.

A two-fold service

  • Preliminary assessment
    • Assessment of your needs
    • Recommendations on the most appropriate remedial measures:
      • Immediate implementation of simple measures
      • Technical audits
  • Technical audits
    • Reliable, objective studies to determine how compatible your equipment and installations are with the power supply
    • Customized solutions with optimum cost/benefit ratio
    • Optional audits to meet more specific needs
    • Complementary technical audits

A cost-effective investment

  • The preliminary assessment lets us identify problems and recommend effective solutions.
  • The cost of the technical audit depends on your company’s industry and demand power, as well as the options you have chosen.
  • Your Hydro-Québec representative will inform you about applicable rates.

Recognized expertise

  • We have a thorough knowledge of our product and our power system.
  • We work hand in hand with experts in electromagnetic compatibility.
  • The work of our research institute (IREQ), especially its energy technologies laboratory (LTE), keeps us at the cutting edge of technologies specially designed to improve the compatibility of your equipment.

For more information, please contact Customer Services or your commercial delegate.

Questions about power quality?

Characteristics and Target Values of the Voltage Supplied by the Hydro-Québec Medium- and Low-Voltage Systems [PDF].

This document describes the main characteristics of the voltage supplied by the Hydro-Québec distribution system. It lists the various phenomena that influence power quality and proposes measures for protecting your equipment and reducing the potential impacts of disturbances.

Bulletins on power quality

To find all the PDF documents mentioned on this page, go to:

˲Technical documentation on electrical service

See also