System Reliability

Voltage reduction is an emergency action available to the IESO to maintain reliability in situations when demand on the power grid exceeds the available supply. Voltage reductions can lower demand quickly, minimizing the likelihood of service interruptions. Voltage reductions have minimal or no noticeable impact on the general public as the voltages are still expected to be within established industry standards for electrical equipment used by residential, commercial and industrial consumers.

Regular Voltage Reduction Testing

Every 18 months, the IESO conducts province-wide system voltage reduction tests. These tests are not simulations but actual voltage reductions of three and five per cent. The purpose of voltage reduction tests is:

• To determine how much power can be reduced through the two levels of reduction − three and five per cent
• To identify equipment problems so they can be addressed
• To help keep IESO and market participant staff familiar with procedures, and identify any deficiencies in the procedures that may need correction

The amount of relief provided to the grid is expressed as a percentage of Ontario demand. An example of voltage reduction results during the July 2019 test:

• The three per cent voltage reduction resulted in an average reduction of 0.96% in Ontario demand
• The five per cent voltage reduction resulted in an average reduction of 1.68% in Ontario demand

Participation in voltage reduction tests is important. Broad participation also leads to a better quality of test, which helps support a robust and reliable power grid.

Temporary Exclusions from Voltage Reduction Tests

Consumers may request a temporary exclusion from voltage reduction tests through their local distribution company. That request may be granted if it addresses public health and safety concerns, potential damage to equipment, or undue injury to the environment. In addition, exclusions may be granted where loss of production might occur.

All requests for exclusions must be accompanied by a mitigation plan to remedy the problem or confirmation that the request will not result in a future exclusion during an actual voltage reduction. Participation in voltage reduction tests is important. Tests provide consumers an opportunity to identify and address problems with their equipment. In a real voltage reduction scenario, it is unlikely that there would be many exclusions. Broad participation also leads to a better quality of test, which helps support a robust and reliable power grid.

Read the related: Market Manual 7.1: System Operating Procedures.