The following is a summary description of the events that took place during the interruptions of power to Mackinac Island from July 22 through 29, 2000, through August 2, 2000. It is based on information from Edison Sault personnel, external consultants and contractors, and recloser event recorders to establish the approximate times of outage events. At times, all of Edison Sault’s 900 customers on Mackinac Island were affected by the power supply cable failures that caused the interruptions.

The efforts to locate and repair the cable problems described below were very time-consuming. The repair and restoration effort required 12 days (with many activities consuming 16 to 24 hours per day) to complete the tedious activity to locate failed cables, test and retest the cable system, make splices in failed cables, and repair cable of questionable integrity identified during testing. Ultimately, more than 24 cable splices were made, with each splice requiring several hours to complete. In addition, 12 cable terminations had to be made within two substation locations as part of the final restoration effort.

Edison Sault crews together with technicians brought in from other utilities, the cable manufacturer and other support personnel worked virtually non-stop day and night, around the clock during the outage period to restore electric power to customers on Mackinac island.

It is important to note that although considerable demands were placed on everyone involved throughout the outage, at no time was the public placed in jeopardy.

At 1025 hours EDT on Saturday morning, the downtown area and the Grand Hotel on Mackinac Island experienced a power outage. At the Edison Sault service center in St. Ignace, it was noted that the circuit breaker for the 26N2 circuit had tripped. (Two 13.2 kV, 3 phase circuits, utilizing special submarine cable serve Mackinac Island from the Edison Sault substation at St. Ignace. These two circuits are designated as 26N1 and 26N2. Three individual submarine cables are used for each circuit. There is also a spare cable that can be used in case of a failure of one of the six cables.)

Edison Sault personnel were immediately dispatched to investigate the situation. After going through the standard procedures of isolating sections of the circuit to locate the problem, it was determined that one of the three cables used for the 26N2 circuit had failed (faulted) between the St. Ignace Substation and the Pat Chambers Switching Station (a distance of more than 3 miles, most of it connected by underwater submarine cable). In order to restore power to the affected area on Mackinac Island as quickly as possible, the faulted cable was disconnected, and the spare cable was connected.

Power was restored on both circuits to Mackinac Island at approximately 1830 hours early Saturday evening.

Six Edison Sault employees were involved in investigating and repairing this problem.

1. At 1030 hours on Sunday morning, a second failure of the 26N2 circuit occurred. Edison Sault personnel were again promptly dispatched to locate the fault. They determined that the spare cable, which was being used as part of the 26N2 circuit to serve Mackinac Island, had failed. Fault current readings indicated that the fault was on Mackinac Island or possibly in the water near the Island. Visual inspections were conducted of the exposed portions of the cable at St. Ignace Substation and on Mackinac Island at the switching station and the Block House (a cable splice location near the shoreline), but the fault could not be located.

Each supply circuit to Mackinac Island requires 3 cables (for a total of 6 cables). Because only 5 of the 7 supply cables were available, only one supply circuit (26N1) to Mackinac Island could be maintained. By early afternoon, the entire Island load was being served by both of the Mackinac Island distribution circuits (44N1 and 44N2) which were connected to the 26N1 cable.

2. At 1520 hours Sunday afternoon the third cable failure occurred, this time to one of the cables on the 26N1 circuit serving Mackinac Island from St. Ignace Substation. This resulted in a power outage to the entire Island. With 3 of the 7 supply cables now unavailable, it was necessary to reconfigure the remaining four cables so that three of them could be used to supply power to the Island. Power was restored by isolating the failed 26N1 cable and reconnecting one of the two remaining cables from the 26N1 circuit to re-establish the 26N2 circuit and create one good circuit to serve the Island.

3. At 2115 hours Sunday evening, the fourth cable failed (affecting circuit 26N2, the only remaining power supply circuit to Mackinac Island). The failed cable was isolated, and the remaining three usable cables were connected to re-establish the 26N1 circuit and restore power supply to the Island. At this point only three supply cables remained from which to configure a circuit to supply power to Mackinac Island.

The fourth cable failure created a fault current of 5400 amperes and caused the 2507 transmission circuit supplying the St. Ignace Substation (and both of the 26N circuits that serve the Island) to trip out. A fault current of this magnitude indicated that this fault was located close to the St. Ignace substation and not on the Island.

During the evening, plans were made to request assistance on Monday morning from other utilities (Consumers Energy, Detroit Edison and Wisconsin Electric Power Company) to help locate cable faults and repair them to restore both power supply circuits to Mackinac Island. Discussions also took place about bringing in additional consultants from the cable manufacturers and other outside engineering firms.

1. At 1020 hours on Monday morning, the fifth failure occurred on the 26N2 circuit. This failure left the entire Island without power. With five of the seven cables damaged, it was not possible to configure a complete circuit to serve the Island. By late afternoon, a failed cable on the St. Ignace side was located and repaired by Edison Sault’s St. Ignace line crew.

This enabled power to be restored to Mackinac Island using the 26N2 circuit. However, at this point no spare cable was available should one of the 3 remaining cables fail.

Technicians from Consumers Power Company arrived on site late Monday morning to help locate the problem cable areas. Technicians from Detroit Edison Company arrived on site by mid-afternoon to test for cable reliability. Wisconsin Electric Power Company technicians were en-route during the day.

The manufacturer of the Kerite submarine cable was contacted and arranged for a splicing technician to be sent to the Island, and Edison Sault also mobilized a tug and barge contractor in Cheboygan, Michigan in case cables needed to be raised from the lake bottom to repair a failed cable.

2. At 2230 hours on Monday evening, the sixth cable failure occurred on the 26N2 circuit, again leaving the Island without power. The damaged cable was located in the Block House on Mackinac Island. Personnel worked through the night repairing the cable, and reconfiguring the cable to complete the 26N1 circuit. Cable testing continued throughout the night on the remaining cables, and additional repairs were made. Appendix 3.1 shows a typical cable repair in progress.

(The Block House is Edison Sault’s term for a small concrete block building—hence, the name—that was located on the Island side of the road near the shoreline where the supply cables from St. Ignace enter Mackinac Island. The supply cables were formerly routed through the Block House before being routed up the bluff onto the Island. In 1996, the Block House was removed (along with a riser facility), except for several course of block below grade which formed the "basement" of the Block House and was used as a splice location for cables. Once the Block House and riser facilities were removed, the seven cables were then spliced in the Block House.

Power was restored at approximately 0500 hours, Tuesday morning.

At 0830 hours, the seventh failure occurred. It was on the 26N1 circuit which again left Mackinac Island without power.

Technicians from Detroit Edison, Consumers Power Company, and Wisconsin Electric Power Company were on site during the day. Later Tuesday afternoon, the technicians from Consumers Power returned to Traverse City. The technician from the cable supplier remained on site to continue a detailed review of the problems and to recommend further action to restore full power to the Island. Edison Sault continued to have more than a dozen employees on site along with technicians from Wisconsin Electric and Detroit Edison.

At 0300 hours early Wednesday morning, the eighth failure occurred. Shortly after this failure, a fire ignited at the Block House on Mackinac Island, and a portion of all seven cables were destroyed. The Mackinac Island Fire Department was called in to extinguish the fire. Because of the cable damage from the fire, none of the circuits could be utilized to supply power to the Island. A failed cable was repaired, and power was restored to the 26N1 circuit late Wednesday morning. Again, no spare cable was available.

A technical representative from the Kerite. Inc. (the company that supplied and installed the submarine cables in 1988) arrived to oversee the work necessary to splice in new sections of cable to replace the fire-damaged portions of the affected cables. The technical representative was also involved in helping assess the likely causes for the cable failures.

Wisconsin Electric and Detroit Edison technicians remained on site. Splicing and repairs were made throughout the day and into Wednesday night.

After the 3:00 AM cable fire, the Island was without power for the balance of Wednesday.

Edison Sault officials met with Mackinac Island local leaders and residents at a town hall meeting early Wednesday afternoon to apprise local residents of the efforts to date and the plans to restore power.

Working in conjunction with Edison Sault, the City of Mackinac Island made plans to obtain diesel generators and use them to provide power to the Island. City Attorney Tom Waters arranged for six diesel generators to be relocated from Coldwater, Michigan and electric transformers from Pennsylvania to be moved to the Island under an emergency request. Edison Sault helped coordinate activity on the Island to unload and move the generators to a location adjacent to the Company’s switching station and then to connect them to supply the Island’s electric distribution system.

A dual effort was now underway to restore power to the Island. Testing and repair of the damaged cable supply system continued along with plans to install the diesel generators. The goal was to restore full power to the Island as quickly as possible by either approach.

Preparations and arrangement were made for the arrival of diesel generators capable of handling the Island's electrical needs. While this was underway, the 26N2 circuit was restored to supply half of Mackinac Island with power.

Durocher Dock & Dredge Company delivered six 1.8-megawatt diesel generators to Mackinac Island during the afternoon. A site near the Pat Chambers Switching Station was chosen, and set-up activities commenced. With a combined capacity of 10.8 megawatts, the diesel generators would be capable of serving the nominal 9 megawatt electrical demand on the Island. To ensure uninterrupted service by the generators, arrangements were made for fuel trucks to be on site to continually refill the generators.

An informational meeting was held at 4:00 PM at the town hall to update residents on the power restoration activities.

At this time, the total work force on site exceeded 40 persons, including more than 20 employees from Edison Sault as well as technicians from Wisconsin Electric and Detroit Edison, representatives from the cable manufacturer, and technicians for the diesel generators.

Motor Shop Electric Company workers prepared the electrical components of the generators, while Edison Sault line crew personnel from Sault Ste. Marie terminated cable at the generator transformers and the Switching Station.

At 1515 hours Friday afternoon, the ninth and last failure occurred. It was to the 26N2 circuit, leaving Mackinac Island without power. Repair of failed cables continued, and power was restored to the 26N1 circuit at approximately 1830 hours.

Because of the repeated cable failures and recommendations of onsite contractor personnel, Edison Sault determined that the best course of action was to replace all of the land-based cable on Mackinac Island and at St. Ignace. This was to be done once the diesel generators were able to supply the Island’s power needs. Once the cable replacement was completed, the entire cable system from the St. Ignace Substation to the Pat Chambers Switching Station on the Island would be tested again and then placed back in service.

As of 1000 hours, Mackinac Island was being supplied from three generators connected to the 26N2 circuit, and the 26N1 circuit was being supplied from the St. Ignace Substation. Please refer to Appendix 3.2 for a view of the diesel generators.

At 1650 hours, all six generators were running and supplying Mackinac Island with power through both of the Island’s local distribution circuits. Electric service to the Island’s business and residential customers returned to near normal operation.

Once the Island’s power was being supplied from the generators, Edison Sault crews began work to replace all the submarine cable from the Block House at the shoreline up the bluff to the Pat Chambers Switching Station with standard 350 MCM underground cable. The majority of the cable failures were in this section of submarine cables, and replacement was deemed necessary to restore reliable service. Installation of the new cables continued on an around-the-clock basis until the work was completed on Tuesday, August 1. Please refer to Appendix 3.3 for a view of spliced cables at the Block House.

At St. Ignace, Edison Sault crews from the Manistique and Sault Ste. Marie Divisions began installing new overhead facilities to replace the submarine cable from the shoreline to the St. Ignace Substation. Work was begun to set poles and run new 336.4 MCM overhead conductor to install two overhead circuits from the substation to a point near the shoreline. At this point, the overhead circuits would be connected to new 350 MCM underground cable being used to replace the remainder of the submarine cable at the shoreline. Please refer to Appendices 3.4, 3.5 and 3.6 for views of underground and overhead facilities being installed at St. Ignace. The underground cable facilities are similar to those installed on Mackinac Island.

The St. Ignace line crew worked through Sunday night on Mackinac Island to expose the submarine cables, cut the nearby blacktop road, install cable duct under the road, and feed the 350 MCM underground cable through the ducts where they would be spliced to the submarine cable.

Customers on Mackinac Island continued to be supplied by the six diesel generators. Preparations were made to switch back to the submarine supply cables from the St. Ignace Substation. A major effort was also in progress to make all splices necessary for the changeover to the submarine supply cables.

Mackinac Island continued to be supplied by the diesel generators. Splicing of the 350 MCM replacement cables on shore at Mackinac Island and St. Ignace continued. Twelve splices were completed on the St. Ignace side and on Mackinac Island, setting the stage for switching back to the submarine supply cables.

At 0230 hours early Wednesday morning, switching activity began to disconnect all six generators and reconnect the submarine cables to supply Mackinac Island. By 0430 hours the switching was completed, and service to Mackinac Island was back to a near normal condition with both of the cable supply circuits from St. Ignace in operation. Partial discharge testing of the energized cables along with special infrared testing was then performed, and these tests determined that the entire cable supply system from St. Ignace to the Pat Chambers Switching Station on the Island was functionally sound.

With the cable supply system operating again, most business and other activity on the Island was back to normal. Edison Sault cautioned its customers to reduce electrical use to help reduce the load on the submarine cables for the rest of the summer. Internal discussions at Edison Sault were already underway to replace the entire system of submarine cables from St. Ignace to Mackinac Island as quickly as possible.

As the preceding chronology shows, Edison Sault (together with its utility partners, consultants, technicians and contractors) mounted a massive effort to restore reliable electric service to its customers on Mackinac Island. During the outage period, repair and restoration efforts had to be coordinated and supervised, significant decisions made, and numerous logistical issues had to be resolved. This activity is summarized in Appendix 3.7

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Last modified: August 16, 2002