The ComEd system is characterised by a peak load of more than 22 300 MW and 3.5 million connected meters with old equipment and infrastructure throughout much of the central system.

Constant service reliability problems reached a crisis level in the summer of 1999, with two lengthy interruptions of supply to major areas of downtown Chicago. Irony of ironies, even the Chicago Board of Trade and its Illinois Electricity Exchange were blacked out for extended periods resulting in “public, political and internal outrage.” Commonwealth Edison has invested more than $1.5 billion in a massive overhaul of the utility’s transmission and distribution system.

On April 11 ComEd reported that with the summer less than three months away, more than 70 per cent of critical improvement work slated for this summer has been completed and the company was on target to have all critical projects finished by June 1.

On March 24 ComEd announced the construction of a five storey high substation building at 369 West Ohio Street, designed as a “brick attractive structure” to harmonise with current area architecture and fit in with future construction.

The Kingsbury/Ohio project is part of a six sub-station (known as the “six-pack”) building and refurbishment programme. ComEd awarded ABB the contract for five of the six substations. The sixth project went to General Electric.

Grid modelling and simulation

ABB has used advanced grid modelling and simulation techniques to design a network capable of rerouting power around any disturbance that might occur in the network. It took about three weeks to identify deep systematic problems.

ABB’s project schedule involved three integrated parallel tasks starting from August 1999:

1. System study and plan development:

identify immediate steps for improvement;

develop short-term plan for maximum improvement possible by summer 2000.

2. Plan development:

develop a long term (five year) optimum plan building from this;

stress high system performance (high reliability at low cost).

3. Turnkey substation implementation:

rebuild/expand four large substations in core of downtown including the largest substation in the USA (Northwest, 435 MW);

emphasis on upgraded capacity and changing configuration (buses, breaker combinations and layout) for high reliability;

one new substation;

planning to completion in only seven months.

The longer term plan aims to fill in other needs to achieve world class performance, provide for significant load growth, and improve economy and reliability.

Substation project

ABB’s substation project, consisting of the delivery of four upgraded and one new substation by June 2000, was worth over $100 million. A major part of the effort was modification of the switchgear–breaker configuration for high reliability and operating flexibility. The key elements of the ABB substation project were: Building Diversey, a new 200 MVA 138/12.47 kV substation on the north side of downtown:

new site with existing old buildings;

revisions to 138 kV cable lines for network strength.

Rebuild/reinforce Lakeview, a 103 year old site on Lincoln and Diversey:

rebuilt several times since 1897 but now a very constricted site with access problems;

a key area of downtown.

Building Kingsbury and Ohio substations:

total of 900 MVA;

close together, with only 30 foot alley between them;

electrically separate sites.

Refurbish and revise Northwest substation on California and Addison:

435 MW, with 78 MV circuits

Directing power

Nothing so sophisticated and expensive as FACTS systems were envisaged, but static phase shifting transformers are being used to direct power in different direction in some cases. High priority was placed on improvements in SCADA and the use of improved digital relays. A key aim is to be able to calculate reliability simultaneously in every part of the system 8760 hours in the year.

An interesting development is the use in recent months of some 300 small – 1.5 to 2.5 MWe – mobile generating sets at a number of smaller substations around Chicago. These are mainly natural gas fired reciprocating engine systems. This suggests an opportunity for potential merchant IPP peak power suppliers in the region.