Thank you for the detailed information regarding the Refurbishment Project at Marchwood MTS. This project will facilitate equipment maintainability.

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1 November 30, 2007 Mr. Ed Donkersteeg Hydro Ottawa Ltd Merivale Road Nepean Ontario K2G 6Y9 Dear Mr. Donkersteeg, Marchwood MTS Refurbishment Project Notification of Conditional Approval of Connection Proposal CAA ID Number: 2007-EX343 Thank you for the detailed information regarding the Refurbishment Project at Marchwood MTS. This project will facilitate equipment maintainability. Since the ratings of the refurbished 115 kv equipment are the same or higher than the original 115 kv equipment, we have concluded that the proposed change will not result in a material adverse effect on the reliability of the IESO-controlled grid. The IESO is therefore pleased to grant conditional approval for the modification detailed in the attached assessment report subject to your signed acknowledgment below. Any material changes to your proposal may require re-assessment by the IESO in accordance with Market Manual 2.10, and may nullify your conditional approval. Final approval to connect the facility to the IESO-controlled grid will be granted upon successful completion of the IESO Facility Registration process including, without limitation, satisfactory completion of the requirements set out in the System Impact Assessment report. During this process you shall demonstrate the requirements have been fulfilled and the equipment installed has characteristics no worse than those in the proposal assessed by the IESO. Please contact market.entry@ieso.ca if you have not received a Facility Registration Summary package within the next 10 days. For further information, please contact the undersigned. Yours truly Michael Falvo Manager - Transmission Assessments & Performance Telephone: (905) Fax: (905) mike.falvo@ieso.ca cc: IESO Records Page 1 of 6

2 Hydro Ottawa Ltd. acknowledges receipt of the System Impact Assessment Report setting out the IESO requirements for final approval, and commits to fulfill these requirements, and all other applicable Market Rules, before receiving final approval to connect to the IESO-controlled grid. Dated: Per: Name: Title:

3 ASSESSMENT SUMMARY Hydro Ottawa Ltd. 1.0 GENERAL DESCRIPTION Marchwood MTS consists of two three phase 115/27.6 kv transformers (20/26/33 MVA) with four 27.6 kv feeders. The MTS is connected to the IESO-controlled grid via circuit S7M. Hydro Ottawa Ltd. is proposing to refurbish two existing 115 kv circuit switchers and to replace the existing 27.6 kv Metalclad switchgear. Hydro Ottawa Ltd. is not making any P&C changes that affect 115 kv lines and does not have any equipment subject to transfer tripping. All work is scheduled to be complete in spring of PROPOSED MODIFICATION The locations of the equipment identified in the following sections can be seen in figure 1 (existing configuration) and figure 2 (final configuration). The 27.6 kv bus configuration will be altered from a Single Bus configuration to a Breaker and a Half configuration. The technical assessment of the new 27.6 kv Metalclad switch gear specifications are not part of this assessment. Two existing circuit switchers will be refurbished. Specifications are shown in the table below: Marchwood MTS Original Circuit Switchers Refurbished Circuit Switchers Identifiers MWD-CS1 & MWD-CS2 MWDCST1 & MWDCST2 Manufacturer S&C S&C Model Rated Voltage (kv) Maximum Voltage (kv) Rated Continuous Current (A) 1,200 1,200 Rated Symmetrical Short Circuit Capability (ka) Serial Number MWDT1: MWDT2: T-L MWDT1: MWDT2: T-L Serial #s will remain the same as the equipment is being refurbished. 3.0 ASSESSMENT The Transmission System Code (TSC), Appendix 2, identifies the maximum permissible 3 phase fault level for the 115 kv system as 50 ka phase to phase. The installation of a 40 ka rated short circuit capability circuit switcher instead of an 50 ka rated circuit switcher is a risk assumed completely by Hydro Ottawa Ltd. Should future system changes result in fault currents greater than 40 ka, Hydro Ottawa Ltd. will be required to change the circuit switchers at their expense. Some recognized contingencies (e.g. load shedding, open line end) can cause a temporary voltage increase above the maximum continuous voltage of 115 kv. For these conditions, connection equipment may be exposed to voltages slightly above its maximum continuous rating for the short period of time that it takes the IESO to direct operations to restore a normal voltage profile, and to prepare for the next contingency. This reparation period will be as short as possible, but it will not take longer than 30 minutes. Therefore, the IESO requires that the 115 kv connection equipment have the following requirements:

4 connection equipment must have a maximum continuous voltage rating of at least 127 kv in southern Ontario; and equipment must remain in service, and not automatically trip, for voltages up to 5% above the maximum continuous rating (133.4 kv), for up to 30 minutes, to allow the system to be re-dispatched to return voltages within their normal range. The new equipment meets the Market Rules requirements for maximum voltage. 4.0 CONCLUSIONS The refurbishment project at Marchwood MTS will have no material adverse effect on the IESO-controlled grid. 5.0 REQUIREMENTS Hydro Ottawa Ltd. must notify the IESO as soon as it becomes aware of any changes to the assumptions made in the connection assessment. The IESO will determine whether these changes require a re-assessment. The installation of a 40 ka rated short circuit capability circuit switchers instead of 50 ka rated circuit switchers is a risk assumed completely by Hydro Ottawa Ltd. Should future system changes result in fault currents greater than 40 ka, Hydro Ottawa Ltd. will be required to change the circuit switchers at their expense. Hydro Ottawa Ltd. is required to meet the transmitters' requirements with respect to protection systems, as outlined in the Transmission System Code. The Market rules (Chapter 4 section 7.4) require that transmitters shall provide the IESO on a continual basis with on-line monitored quantities and status as specified in Appendix For this proposed project, the IESO will require the status of the circuit switchers. 6.0 NOTIFICATION OF CONDITIONAL APPROVAL This expedited System Impact Assessment concludes that the installation of replacement 115 kv equipment is not expected to have a material adverse effect on the IESO-controlled grid. It is therefore recommended that a Notification of Conditional Approval of the Connection Proposal be issued, subject to the requirements detailed above.

5 Figure 1: Marchwood MTS - Existing Station Configuration Page 5 of 6

6 Figure 2: Marchwood MTS - Final Station Configuration