Influencing factors of 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 note that your supply voltage is outside normal limits (for example, not between 110 V and 125 V for a 120-V supply), please call Customer Services at 1 800 790-2424 or contact your commercial officer.
Standards and characteristics
Voltage limits at the connection point of delivery as specified in CAN3-C235-83
Normal operating conditions
|Minimum (volts)||Maximum (volts)|
|Single-phase 120/240 V||112/194||125/216|
|3-phase quadruplex 120/208 V (Y)||112/194||125/216|
|3-phase quadruplex 347/600 V (Y)||318/550||360/625|
|3-phase triplex 600 V||550||625|
Extreme operating conditions
|Minimum (volts)||Maximum (volts)|
|Single-phase 120/240 V||106/212||127/254|
|3-phase quadruplex 120/208 V (Y)||110/190||127/220|
|3-phase quadruplex 347/600 V (Y)||306/530||367/635|
|3-phase triplex 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 falls into the range for extreme operating conditions, improvements or corrective action should be planned according to a definite schedule though not necessarily on an emergency basis. If the voltage surpasses 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 [PDF 894 Kb - in French only].
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 [PDF 894 Kb - in French only].
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. This 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 impact on your company’s productivity.
Main sources of power disturbances
- Escalators and passenger/freight elevators
- Air conditioners
- Fluorescent lights
- Vending machines
- Variable-frequency drive motors
- Welding machines
- Telephone switching systems
- Tree limbs in contact with lines
- Air pollution
- Magnetic storms
Electromagnetic compatibility refers to the ability of equipment to function satisfactorily in its electromagnetic environment without introducing intolerable disturbances to anything in that environment 1.
How to ensure the electromagnetic compatibility of your equipment?
Under the Conditions of Electricity Service [PDF 4.69 MB], your electrical installation must be designed, built, connected, protected, used and maintained in such a way that it does not cause disturbances in 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 of its power system. If necessary, Hydro‑Québec will ask you to conduct the appropriate studies. For example, standards C.22-03 [PDF 1 MB – in French only] and C.25-01 [PDF 1 MB – 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 power disturbances (the CAN/CSA-CEI/IEC 61000-4-X series). 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.
Low-voltage electrical service
To find out more about the requirements for low-voltage connections, see Hydro‑Québec standards E.21‑10 (Blue Book) [PDF 7.66 MB – in French only] and E.21-11 (Green Book) [PDF 2,6 MB – in French only]. Hydro‑Québec reserves the right to require that you conduct an electromagnetic compatibility assessment in accordance with C.22-03 [PDF 1 MB – in French only] and C.25-01 [PDF 252 Kb - in French only].
Medium-voltage electrical services
To find out more about the requirements for medium-voltage connections, see Hydro‑Québec standard E.21-12 (Red Book) [PDF 6.5 MB – in French only]. Hydro‑Québec reserves the right to require that you conduct an electromagnetic compatibility assessment in accordance with C.22-03 [PDF 1 Mo - in French only] and C.25-01 [PDF 252 Kb - in French only].
Filters placed in series at the entrance to a variable-frequency drive can improve immunity against transient surges on the power grid.
It is your responsibility to guard against the consequences of a power loss, particularly on just one phase, whether or not your equipment is protected by fuses.
Questions about power quality?
Characteristics and Target Values of the Voltage Supplied by the Hydro‑Québec Medium and Low Voltage Systems [PDF 894 kB - in French only]
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
- New facilities and adding equipment [PDF 98 kB – in French only]
- Protection against phase loss [PDF 113 kB – in French only]
- Voltage dips [PDF 113 kB – in French only]
- Steady stage voltage [PDF 291 kB – in French only]
- Variable-speed drives [PDF 118 kB]
- Voltage and current imbalances [PDF 99 kB – in French only]
- Industrial programmable controllers [PDF 49 kB – in French only]
- Power factor [PDF 47 kB – in French only]
To find all the PDF files mentioned on this page, go to:
three-phase star connection, grounded neutral.
As defined by the International Electrotechnical Commission (IEC)
CSA/IEC 61000-4-11 Electromagnetic Compatibility (EMC) – Part 4-11: Testing and measurement techniques – Voltage dips, short interruptions and voltage variations immunity tests
CSA/IEC 61000-4-34 Electromagnetic Compatibility (EMC) – Part 4-34: Testing and measurement techniques – Voltage dips, short interruptions and voltage variations immunity tests for equipment with mains current more than 16&nbps;A per phase