VOLTAGE REDUCTION QUESTIONS & ANSWERS

What is a voltage reduction and why does the IESO implement voltage reductions?

A voltage reduction is one tool used by the Independent Electricity System Operator (IESO) to manage the reliability of Ontario’s power system when demand for electricity exceeds available supply. This action is among the final steps taken before having to implement rotating blackouts. The IESO performs voltage reduction tests every 18 months to simulate emergency actions and to measure the load reduction resulting from voltage reductions of three and five per cent.

What is the impact of a voltage reduction on consumers?

Most consumers will not notice voltage reductions as supplied voltages are still expected to be within established industry standards for electrical equipment used by residential and commercial consumers. However, sensitive equipment may be affected by a wide variety of causes such as local distribution conditions and consumer equipment configurations.

Voltage reductions have been performed in the past as part of the IESO’s routine testing protocols and, under extreme circumstances, to prevent blackouts. If you have not noticed any impact on your equipment in the past, you should not notice it during this test.

Can I request an exclusion from a voltage reduction?

Consumers may request a temporary exclusion from voltage reductions through their LDC to address public health and safety concerns or prevent equipment damage. Many LDCs need to coordinate exclusion requests with Hydro One, which controls most high-voltage transformers in Ontario. Any exclusion would be temporary, until LDCs or consumers resolve the problem locally.

Voltage reductions are implemented at certain high-voltage transformers that serve large numbers of consumers. Excluding one consumer on a shared transformer can severely reduce the effectiveness of voltage reductions as an emergency control action. Under the Ontario Energy Board (OEB)’s Distribution System Code¹, local distribution companies (LDCs) must ensure their systems can supply adequate voltage to consumers, even when a province-wide five per cent voltage reduction is required. Similarly, consumers are expected to manage their equipment and operations to withstand a five per cent voltage reduction². For example, equipment nominally rated at 120 volts should be able to operate within voltage ranges of 108-125 volts under normal conditions, and 104-127 volts under extreme conditions.

Province-wide implementation of a five per cent voltage reduction reduces demand for electricity by about 500 MW, and any decline in this amount through exclusions increases the possibility of rotating blackouts during emergencies.

If you wish to request a temporary exclusion, please contact your LDC. Your LDC is responsible for identifying any temporary exclusion requests and communicating them to Hydro One and the IESO through the Outage Management Process. The IESO will continue to monitor any impact on the effectiveness of voltage reductions as an emergency control action.

¹ Ref. OEB Distribution System Code, Section 4.1.2 and CSA Standard CAN-3-C235-83 Preferred Voltage Levels for AC Systems, Sections 4 and 5.

² Ref. OEB Distribution System Code, Section 4.1.3.