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IESO to Conduct Routine Voltage Reduction Test

August 8, 2016

The Independent Electricity System Operator (IESO) will conduct a routine voltage reduction test on Tuesday, August 9, 2016, as part of mandatory testing of its emergency operating measures. The test, which will not impact the public, is an important tool for ensuring the reliability of Ontario's electricity grid.

Voltage reductions lower demand quickly and minimize the likelihood of service interruptions, helping the IESO maintain the reliability of Ontario`s power system during a variety of unplanned occurrences.

A three-percent reduction is expected to occur from 9 a.m. to 10:00 a.m. EST. A five-percent reduction is planned for 1 p.m. to 2 p.m. EST. These tests are normally conducted every 18 months.

Voltage reduction tests have three key purposes:

1. To determine how much power can be reduced through the two levels of reduction.

2. To identify equipment problems so they can be addressed.

3. To help keep IESO and market participant staff familiar with procedures to execute voltage reductions and identify any deficiencies in the procedures that may need correction.

The IESO is responsible for maintaining real time and future reliability of the province's power system. The reliability outlook remains strong, with about 1,150 MW of new supply expected to come online in the next 18 months. Emergency planning, training and testing including voltage reduction tests help the IESO maintain this reliability.

Consumers with questions about the test should contact their local distribution company. A list of local distribution companies is available.

More information about voltage reductions is available on the IESO website at or by contacting IESO customer relations at 1-888-448-7777.

About the IESO

The IESO manages the province's power system so that Ontarians receive power when and where they need it. It plans and prepares for future electricity needs and works with its partners to guide conservation efforts. For more information, please visit

IESO Media Contact:

John Cannella

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