Ontario (IESO Market Rules App. 4.2) ride-through requirements
Frequency ride-through for Canada. Every breakpoint below is read from the code itself, and where a point was taken off a published figure rather than stated in the clause, the section under that chart says so — a boundary charted as approximate.
What is the frequency ride-through envelope for Ontario (IESO Market Rules App. 4.2)?
The plant must ride through between the upper and lower bands. The upper (over-frequency) band holds 61.8 Hz to 8 s, then descends through 17 further breakpoints to 60.6 Hz from 10 min onward — the last band the envelope defines, with no stated end time. Every vertex is in the table below. The lower (under-frequency) band holds 57 Hz to 3.3 s, then climbs through 17 further breakpoints to 59 Hz from 5 min onward — the last band the envelope defines, with no stated end time. Every vertex is in the table below.
The clause states this boundary as a line, but does not give its vertices numerically — the points plotted here were read off the published figure. The last band has no stated end time. The clause below states a continuous region — highlighted; check which band it covers, because it is not always the last one.
Applies to Generation and storage on the IESO-controlled grid
Upper limit
| From | To | Frequency | Between the points |
|---|---|---|---|
| 0 | 8 s | 61.8 Hz | Held flat |
| 8 s | 10.3 s | 61.8 → 61.73 Hz | Ramps linearly |
| 10.3 s | 13.3 s | 61.73 → 61.659 Hz | Ramps linearly |
| 13.3 s | 17.2 s | 61.659 → 61.587 Hz | Ramps linearly |
| 17.2 s | 22.2 s | 61.587 → 61.516 Hz | Ramps linearly |
| 22.2 s | 28.6 s | 61.516 → 61.446 Hz | Ramps linearly |
| 28.6 s | 36.9 s | 61.446 → 61.375 Hz | Ramps linearly |
| 36.9 s | 47.6 s | 61.375 → 61.304 Hz | Ramps linearly |
| 47.6 s | 61.3 s | 61.304 → 61.234 Hz | Ramps linearly |
| 61.3 s | 79.1 s | 61.234 → 61.163 Hz | Ramps linearly |
| 79.1 s | 102 s | 61.163 → 61.092 Hz | Ramps linearly |
| 102 s | 131 s | 61.092 → 61.023 Hz | Ramps linearly |
| 131 s | 169 s | 61.023 → 60.952 Hz | Ramps linearly |
| 169 s | 218 s | 60.952 → 60.881 Hz | Ramps linearly |
| 218 s | 281 s | 60.881 → 60.811 Hz | Ramps linearly |
| 281 s | 363 s | 60.811 → 60.74 Hz | Ramps linearly |
| 363 s | 468 s | 60.74 → 60.669 Hz | Ramps linearly |
| 468 s | 10 min | 60.669 → 60.6 Hz | Ramps linearly |
| 10 min | no stated end | 60.6 Hz | Held flat |
Lower limit
| From | To | Frequency | Between the points |
|---|---|---|---|
| 0 | 3.3 s | 57 Hz | Held flat |
| 3.3 s | 4.3 s | 57 → 57.117 Hz | Ramps linearly |
| 4.3 s | 5.6 s | 57.117 → 57.235 Hz | Ramps linearly |
| 5.6 s | 7.3 s | 57.235 → 57.352 Hz | Ramps linearly |
| 7.3 s | 9.5 s | 57.352 → 57.469 Hz | Ramps linearly |
| 9.5 s | 12.4 s | 57.469 → 57.587 Hz | Ramps linearly |
| 12.4 s | 16 s | 57.587 → 57.7 Hz | Ramps linearly |
| 16 s | 21 s | 57.7 → 57.821 Hz | Ramps linearly |
| 21 s | 27 s | 57.821 → 57.932 Hz | Ramps linearly |
| 27 s | 35 s | 57.932 → 58.047 Hz | Ramps linearly |
| 35 s | 46 s | 58.047 → 58.168 Hz | Ramps linearly |
| 46 s | 60 s | 58.168 → 58.286 Hz | Ramps linearly |
| 60 s | 78 s | 58.286 → 58.403 Hz | Ramps linearly |
| 78 s | 101 s | 58.403 → 58.517 Hz | Ramps linearly |
| 101 s | 132 s | 58.517 → 58.636 Hz | Ramps linearly |
| 132 s | 172 s | 58.636 → 58.753 Hz | Ramps linearly |
| 172 s | 224 s | 58.753 → 58.87 Hz | Ramps linearly |
| 224 s | 5 min | 58.87 → 59 Hz | Ramps linearly |
| 5 min | no stated end | 59 Hz | Held flat |
The clause this came from
IESO Renewed Market Rules, Chapter 4 'Grid Connection Requirements - Appendices', Library Record No. RUL-12, Issue 2.0, Effective December 3, 2025; Appendix 4.2, Category 1 'Off-Nominal Frequency Operation' - continuous 59.4-60.6 Hz, plus the log-linear regions bounded by (0.0 s, 57.0 Hz), (3.3 s, 57.0 Hz), (300 s, 59.0 Hz) and by (0.0 s, 61.8 Hz), (8 s, 61.8 Hz), (600 s, 60.6 Hz). Boundary is a continuous log-linear ramp; the plotted staircase is a conservative inner approximation of it.
Operating requirements beyond the envelopes.
The envelopes above are what Ontario (IESO Market Rules App. 4.2) demands during a disturbance. The rows below are the same regime’s operating and fault-response requirements — reactive capability, frequency response, continuous operating range and fault-current injection — each researched from the document its own row cites, separately from the plotted corpus. Every row carries its clause and a verbatim quote, so you can check it the same way.
| Requirement | What the code states | Clause |
|---|---|---|
| Steady-state dynamic reactive range ±33% of rated active power Reactive capability | Continuously (dynamically) inject or withdraw reactive power up to 33% of the applicable rated active power, at all levels of active power, measured at the high-voltage terminal of the main output transformer, at typical transmission system voltage. Basis: 'applicable rated active power' per Category 4, which for electricity storage facilities is separately specified for injection and withdrawal. Binds storage explicitly: the requirement table column header reads 'Generation facilities or electricity storage facilities directly connected to the IESO-controlled grid shall have the capability to:', and the appendix preamble states the performance requirements 'shall also apply to electricity storage units at all times while connected to the IESO-controlled grid'. Point of application is the HV terminal of the main output transformer, not the connection point — reactive losses/charging between that terminal and the connection point 'shall be addressed in a manner permitted by IESO approval'. A lesser continually available capability is possible only with IESO approval. The clause also deems acceptable a conventional synchronous unit with 0.90 lagging / 0.95 leading power factor at rated active power via a transformer of ≤13% impedance. (Preamble carve-outs apply: the storage-binding sentence covers performance requirements finalized after 18 January 2021 'unless the IESO identifies specific performance requirements that are not applicable to an electricity storage unit', and facilities connected before 21 September 2020 are grandfathered.) | Chapter 4, Appendix 4.2, Category 5 'Reactive Power' + Chapter 4, Appendix 4.2, Category 4 'Active Power' |
The clauses this row citesChapter 4, Appendix 4.2, Category 5 'Reactive Power' — “ Continuously (i.e., dynamically) inject or withdraw reactive power at the high-voltage terminal of the main output transformer up to 33% of the applicable rated active power at all levels of active power, and at the typical transmission system voltage, except where a lesser continually available capability is permitted with the IESO's approval. ” (Renewed Market Rules – Chapter 4: Grid Connection Requirements - Appendices, Issue 2.0, accessed 2026-08-08) Chapter 4, Appendix 4.2, Category 4 'Active Power' — “ Rated active power is the smaller output at either rated ambient conditions (e.g. temperature, head, wind speed, solar radiation) or 90% of rated apparent power. For electricity storage facilities, rated active power values shall be separately specified for both injection and withdrawal operations. ” (Renewed Market Rules – Chapter 4: Grid Connection Requirements - Appendices, Issue 2.0, accessed 2026-08-08) | ||
| Dynamic reactive step response: 30% of rated apparent power within 3 s Reactive capability | Sustained reactive power change of 30% of the facility's rated apparent power (measured at the LV terminal of the main output transformer) achieved within 3 s following a step change of no more than 4% to the AVR voltage reference, with constant voltage held at the HV terminal. Binds storage explicitly — the clause text itself names 'generation facility or electricity storage facility rated apparent power', and the category heading scopes it to inverter-based units ('Reactive Power Response to Voltage Changes of Inverter-Based Units'). This is a small-disturbance AVR-reference step-response requirement (voltage-control dynamics), not a fault-current injection gain. Measurement point for the reactive change is the low-voltage terminal of the main output transformer. | Chapter 4, Appendix 4.2, Category 12 'Reactive Power Response to Voltage Changes of Inverter-Based Units' |
The clause this row citesChapter 4, Appendix 4.2, Category 12 'Reactive Power Response to Voltage Changes of Inverter-Based Units' — “ For a constant voltage at the high-voltage terminal of the main output transformer, achieve a sustained reactive power change of 30% of generation facility or electricity storage facility rated apparent power at the low-voltage terminal of the main output transformer within 3s following a step change no larger than 4% to the AVR voltage reference. AVR response to the voltage error signal must be consistent over the entire operating range. ” (Renewed Market Rules – Chapter 4: Grid Connection Requirements - Appendices, Issue 2.0, accessed 2026-08-08) | ||
| Speed/frequency droop 3–7% (default 4%), deadband ≤ ±0.06% Frequency response | Average droop based on maximum active power, adjustable 3%–7% and set at 4% unless the IESO specifies otherwise; regulation deadband no wider than ±0.06%; a sustained 9% change of applicable rated active power after 10 s in response to a 0.5% step change of speed must be achievable during interconnected operation. Binds storage via the appendix's generation-and-storage scope: the requirement table header covers 'Generation facilities or electricity storage facilities directly connected to the IESO-controlled grid', and the preamble applies the requirements to electricity storage units at all times while connected. 'Applicable rated active power' is as defined in Category 4 (separately specified for injection and withdrawal for storage). Control systems that inhibit primary frequency response shall not be enabled without IESO approval. (Preamble carve-outs apply: the storage-binding sentence covers performance requirements finalized after 18 January 2021 'unless the IESO identifies specific performance requirements that are not applicable to an electricity storage unit', and facilities connected before 21 September 2020 are grandfathered.) The source states the deadband percentage without a base; ±0.06% of 60 Hz = ±0.036 Hz (computed from the printed percentage), matching AESO 503.6's explicit ±0.036 Hz. | Chapter 4, Appendix 4.2, Category 2 'Speed/Frequency Regulation' |
The clause this row citesChapter 4, Appendix 4.2, Category 2 'Speed/Frequency Regulation' — “ Regulate speed/frequency with an average droop based on maximum active power adjustable between 3% and 7% and set at 4% unless otherwise specified by the IESO. Regulation deadband shall not be wider than ±0.06%. Speed/frequency shall be controlled in a stable fashion in both interconnected and island operation. A sustained 9% change of applicable rated active power as defined in category 4 after 10 s in response to a step change of speed of 0.5% during interconnected operation shall be achievable. ” (Renewed Market Rules – Chapter 4: Grid Connection Requirements - Appendices, Issue 2.0, accessed 2026-08-08) | ||
| Frequency: continuous 59.4–60.6 Hz plus time-limited log-linear bands to 57.0/61.8 Hz Continuous operating range | Continuous operation 59.4–60.6 Hz. Time-limited operation in the region bounded (on a log-linear scale) by straight lines through (0.0 s, 57.0 Hz), (3.3 s, 57.0 Hz), (300 s, 59.0 Hz) on the under-frequency side and (0.0 s, 61.8 Hz), (8 s, 61.8 Hz), (600 s, 60.6 Hz) on the over-frequency side. Binds storage explicitly via the requirement table header ('Generation facilities or electricity storage facilities directly connected to the IESO-controlled grid shall have the capability to:') and the appendix preamble applying the requirements to electricity storage units at all times while connected. This is the facility off-nominal frequency capability envelope; the separate IESO-Controlled Grid performance standard (Appendix 4.1, Ref 1, PDF p.7) states the grid environment as 'All equipment shall be capable of continuously operating in the range between 59.5 Hz and 60.5 Hz.' No voltage-band table is given in Appendix 4.2 itself; Category 4 requires supplying all active power levels within ±5% of rated terminal voltage (see the ±5% voltage row below), and transmission voltage ranges live in Appendix 4.1 Ref 2. (Preamble carve-outs apply: the storage-binding sentence covers performance requirements finalized after 18 January 2021 'unless the IESO identifies specific performance requirements that are not applicable to an electricity storage unit', and facilities connected before 21 September 2020 are grandfathered.) | Chapter 4, Appendix 4.2, Category 1 'Off-Nominal Frequency Operation' |
The clause this row citesChapter 4, Appendix 4.2, Category 1 'Off-Nominal Frequency Operation' — “ Operate continuously between 59.4 Hz and 60.6 Hz and for a limited period of time in the region bounded by straight lines on a log-linear scale defined by the points (0.0 s, 57.0 Hz), (3.3 s, 57.0 Hz), and (300 s, 59.0 Hz) and the straight lines on a log-linear scale defined by the points (0.0 s, 61.8 Hz), (8 s, 61.8 Hz), and (600 s, 60.6 Hz). ” (Renewed Market Rules – Chapter 4: Grid Connection Requirements - Appendices, Issue 2.0, accessed 2026-08-08) | ||
| Voltage: full active power across ±5% of rated terminal voltage; storage rated separately for injection and withdrawal Continuous operating range | Continuously supply all levels of active power output within a ± 5% range of rated terminal voltage. Rated active power = the smaller of output at rated ambient conditions or 90% of rated apparent power; for electricity storage facilities, rated active power is separately specified for injection and withdrawal. Binds storage explicitly — the clause names electricity storage facilities and requires separate injection/withdrawal ratings. The ±5% band is at the facility's rated terminal voltage (generator/inverter terminals), not a connection-point voltage band; connection-point transmission voltage limits are stated as grid performance standards in Appendix 4.1 Ref 2 (e.g. 500 kV nominal: 550 kV max / 490 kV min continuous). Active power reductions to rated active power are permitted in order to satisfy steady-state reactive power requirements. | Chapter 4, Appendix 4.2, Category 4 'Active Power' |
The clause this row citesChapter 4, Appendix 4.2, Category 4 'Active Power' — “ Continuously supply all levels of active power output within a +/- 5% range of its rated terminal voltage. Rated active power is the smaller output at either rated ambient conditions (e.g. temperature, head, wind speed, solar radiation) or 90% of rated apparent power. For electricity storage facilities, rated active power values shall be separately specified for both injection and withdrawal operations. To satisfy steady-state reactive power requirements, active power reductions to rated active power are permitted. ” (Renewed Market Rules – Chapter 4: Grid Connection Requirements - Appendices, Issue 2.0, accessed 2026-08-08) | ||
| No momentary cessation or current reduction for inverter-based units during disturbances Fault-current injection | No momentary cessation or reduction of output current by inverter-based units is permitted during system disturbances without IESO approval. No quantified reactive-current injection gain (k-factor), response time, or negative-sequence requirement is stated. Binds storage via the appendix's generation-and-storage scope (table header covers 'Generation facilities or electricity storage facilities directly connected to the IESO-controlled grid'; the preamble applies the requirements to electricity storage units at all times while connected). This is a fault-behavior current requirement (no blocking/momentary cessation while riding through routine switching events and design criteria contingencies), not a proportional reactive-current-support specification — Appendix 4.2 contains no k-gain, no % current per % voltage deviation, and no P/Q priority rule during faults. (Preamble carve-outs apply: the storage-binding sentence covers performance requirements finalized after 18 January 2021 'unless the IESO identifies specific performance requirements that are not applicable to an electricity storage unit', and facilities connected before 21 September 2020 are grandfathered.) | Chapter 4, Appendix 4.2, Category 3 'Voltage Ride-Through' |
The clause this row citesChapter 4, Appendix 4.2, Category 3 'Voltage Ride-Through' — “ Ride through routine switching events and design criteria contingencies assuming standard fault detection, auxiliary relaying, communication, and rated breaker interrupting times unless disconnected by configuration. For Inverter-based units, momentary current cessation or reduction of output current during system disturbances is not permitted without IESO approval. ” (Renewed Market Rules – Chapter 4: Grid Connection Requirements - Appendices, Issue 2.0, accessed 2026-08-08) | ||
Who does Ontario (IESO Market Rules App. 4.2) bind, and since when?
Generation and storage on the IESO-controlled grid. The FRT clause quoted above carries the date of effect — "Effective December 3, 2025".
These figures are a reading aid, not legal advice. Grid codes are reissued: verify against the current edition before you design to them.
Curve data last checked against the code on — 66 standards, 130 envelopes, published by bess.engineer under CC BY 4.0.
Questions this page answers about Ontario (IESO Market Rules App. 4.2)
- Does Ontario (IESO Market Rules App. 4.2) require ride-through, or only that the plant does not trip?
- Ride-through. Every envelope on this page is a performance duty the plant must meet, not a protection-setting no-trip boundary — they are different obligations. That is what these curves are; they are not everything Ontario (IESO Market Rules App. 4.2) contains. The requirement sentence under each chart says which side of the curve is the compliant one.
- Are the numbers on this page taken from Ontario (IESO Market Rules App. 4.2) itself?
- Every breakpoint is read from the code, and where a point was taken off a published figure rather than stated in the clause, the section under that chart says so — on this page that includes a boundary charted as approximate. The clause each curve came from is quoted under it.
- Which events are charted for Ontario (IESO Market Rules App. 4.2)?
- Ontario (IESO Market Rules App. 4.2) is charted here with 1 envelope — frequency ride-through (FRT). No low-voltage or high-voltage envelope is charted here — check Ontario (IESO Market Rules App. 4.2) itself before concluding it sets none.
Ride-through, in context.
An envelope is a compliance boundary; understanding why it exists is a different question. The ride-through and grid-forming entries cover the engineering, and the Engineering Foundations course builds it from the physics up.
Also for Canada: Quebec (Hydro-Quebec D-2022-088), Canada (Alberta AESO)
Elsewhere in North America: Mexico (Codigo de Red), NERC PRC-029-1 (Table 1: AC-connected wind IBR), ERCOT (NOG 2.6.2.1), ERCOT (NOG 2.9.1.2 legacy), and 9 more