The Hertel–New York interconnection project involves building a converter substation. The Québec and U.S. systems operate at the same frequency (60 Hz), but not at the same phase. In other words, their electrical waves do not reach their maximum value at the same time. They are not synchronous. A converter substation is required to link these two asynchronous power systems. Here is how the conversion works.
- Alternating current from the Québec grid arrives at 735,000 volts. It goes through circuit breakers, disconnect switches and busbars. These devices direct the current and protect the line against electric overloads, which can be caused by lightning.
- Power transformers lower the voltage to 400,000 volts to optimize converter operation.
- The current enters the converter. It then goes through transistors, which electronically convert alternating current into direct current. The frequency of the resulting current is zero.
- Once the conversion is complete, the direct current is ready to be sent to the American power system. The Québec and American systems will be connected by two underground cables. Once it reaches the American power system, the direct current will be converted back to alternating current to be used.