Your electricity goes through a number of voltage changes before it gets delivered to your home or business. Voltage is coarsely defined as the pressure that pushes the electricity through wires to your devices, often compared to a pump that pushes water through pipes. The higher the voltage the more electricity that can be provided. The device that changes the voltage is called a transformer. A transformer changes alternating current (AC) voltage higher or lower through mutual inductance.
Electricity is generated at a relatively low voltage. A solar panel may generate electricity at only a few volts and even a large hydro generating plant may be only generating at around 10,000 – 25,000 volts. Once the electricity is generated it is usually “stepped-up” on-site to the higher voltages needed by the distribution or transmission system to which it is connected.
For instance, while the individual solar panels may only generate electricity at a few volts, by the time they have been through the inverters and transformers they are connected to the electricity will have been stepped up to 120V. If the solar panels are directly connected to a home or business, such as with a net metering contract, then at 120V the electricity can help power the home or business. If the solar panels are connected to the local grid, such as with a FIT or Micro-FIT contract, then the electricity will go through a local transformer and be further stepped up to the distribution grid voltage.
Likewise, the electricity generated at a large hydro station will be immediately stepped up to the transmission voltage. For instance, the electricity that emerges from the Beck Generating stations in Queenston will be stepped up to 115,000V (115 kV) or 230 kV depending on which transmission line they are connected to. Similarly, the voltage at the generating station on the Welland Canal will be stepped up to 27.6 kV which is the NOTL Hydro distribution voltage.
Transmission grids operate at the highest voltages. The higher the voltage then the more electricity can flow through with the least line losses. As transmission grids are designed to move a lot of power over long distances this is important. In Ontario, the transmission voltages are 115 kV, 230 kV and 500 kV. Manitoba also uses the 115 kV, 230 kV and 500 kV voltages though they also have 138 kV and 66 kV lines. In Quebec most of the transmission voltage is 735 kV. New York State uses 115 kV, 138 kV, 230 kV and 345 kV voltages.
Having different voltages for transmission lines is not necessarily problematic. The equipment is specialized and made to order so being of different voltages in this context is not an issue. Connection points between separate grids are closely monitored so having transformers in place to convert the voltages is also not an issue. The major downside is that it prevents any sharing of equipment in times of emergencies. As an example, Ukraine has not been able to source spare transmission transformers from North America as different voltages are being used.
Some large customers are directly connected to the transmission grid so have their own transformers to get the power to the voltage they need. Mines and large manufacturing facilities are examples of this. Most customers are connected to a distribution grid. Distribution grids are connected to the transmission grid either directly or indirectly. NOTL is an example of a directly connected distribution grid as the voltage is transformed from the 115 kV transmission voltage to the 27.6 kV distribution voltage at our two transmission stations. Other distribution grids may get their electricity indirectly from a 44kV sub-transmission line which is then connected to the transmission grid.
Different distribution grids use different primary voltages. The most common in Ontario are 27.6 kV, 13.8 kV (St. Catharines), 8.32 kV and 4.16 kV. NOTL Hydro uses 27.6 kV and 4.14 kV. Having these different voltages creates some challenges:
- Inventory levels must be kept higher as you need extra transformers for all the voltages used by a distributor.
- You cannot share transformers with another distributor if they use a different voltage. NOTL Hydro has mutual emergency services agreements with many other electricity utilities across Ontario. These are for the provision of manpower and equipment in case of emergency such as a bad storm. An example of this was the ice storm in Fort Erie in 2022. However, if the distributor uses a different voltage, then the transformers are not shareable.
- You cannot connect to systems using s different voltage. The systems of NOTL and St. Catharines are not connected as they are different voltages. This removes a potential source of power in the event of an emergency.
These voltage decisions were made historically based on circumstances at that time. Once in place, it is very hard to change the voltage of a system. Many local distribution companies, like NOTL Hydro, are slowly phasing out their lower voltage infrastructure to standardize on one distribution voltage. Higher voltage systems have lower line losses so are more cost effective. Transformers for the higher voltages are also more readily available as they are more commonly used. Even so, NOTL Hydro is now in its fourth decade of phasing out the 4.16 kV system with another decade to go.
From the primary distribution voltage, the electricity is stepped-down to utilization secondary voltages. Residential homes use 120/240V; 240V for stoves, air conditioners, and electric heat; 120V for all other residential applications across North America. Commercial and industrial customers may use 120/208V and 347/600V three-phase secondary voltages. The transformers that change distribution to secondary voltages are the green boxes for the underground system and the grey cans for the overhead system. However, as anyone who has traveled knows, the voltages used across the world vary. For instance, in Europe it is 220V while in Australia it is 230V. Power adapters are needed to use north American electrical products in these other regions to change voltage and frequency (a topic for another blog …).