Power Quality

Transmission system

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.

Distribution system

Hydro-Québec guarantees that voltages will at all times remain 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.

Nominal voltages*

Low-Voltage

Voltage limits at the connection point as specified in CAN3 C235 83
	Normal operating conditions		Extreme operating conditions
	Minimum (volts)	Maximum (volts)	Minimum (volts)	Maximum (volts)
Single-phase system 120/240 V 600 V	110/220 550	125/250 625	106/212 530	127/254 635
Three-phase system 4 wire 120/208 V (Y)* 347/600 V (Y)*	112/194 318/550	125/216 360/625	110/190 306/530	127/220 367/635
Three-phase system 3 wire 240 V 600 V	220 550	250 625	212 530	254 635

*Y: Three-phase grounded wye

Note: If the voltage remains within the limits for normal operating conditions, no improvements or remedial measures are necessary. If it exceeds normal limits but remains within the limits for extreme operating conditions, improvements or remedial measures must be planned according to a clearly defined program though urgent action is not necessarily required. If the voltage exceeds the broader limits, however, urgent action must be taken to remedy the situation.

Medium-Voltage

According to CAN3-C235-83, the voltage at the connection point must not differ by more than ±6% from the nominal voltage (usually 25 kV, that is, 14.4/24.94 kV three-phase grounded wye).

Power disturbances

Power disturbances are waveform distortions very often due to the use of devices like powerful motors and air conditioners, which affect the grid. They may affect the operation of equipment depending on how sensitive it is and on the degree of waveform distortion.

The problem can be corrected, however, and equipment can be made more compatible with the supply voltage. Solutions must be assessed on a case-by-case basis by a specialist (master electrician or engineer), who factors in costs and impacts on your company's productivity.

Main sources of power disturbances

Indoors	Outdoors
Air conditioners Arc welders Escalators and passenger/freight elevators Fans Fluorescent lights Motors with variable-speed drives Photocopiers Telephone switching systems Vending machines	Accidents Air pollution Lightning Magnetic storms Strong winds Tree limbs in contact with lines