From its early beginnings in 1905, ENMAX Power Corp. has provided safe and reliable electricity to Calgary, Alberta, Canada. Now a new, uniquely designed substation in northeast Calgary helps the utility continue its history of reliable customer service.

In 2001, the electricity industry in Alberta was restructured to introduce innovation and competition into the market. That summer, the organization responsible for maintaining the transmission system in Alberta invited companies to bid on a new substation project through a request for proposal (RFP) process. The RFP was for the design, construction, ownership, and operation and maintenance of a 240-kV substation in northeast Calgary. On completion of the substation, the successful bidder would enter into a service agreement to own, operate and maintain the substation for 40 years.

The substation project was the first of its kind to go forward in Alberta's newly restructured market. The project set a precedent for being the first bid to contractually prescribe reliability standards as a part of ownership. Moreover, there was a financial penalty for missing the in-service date — a penalty of as much as $100,000 per day, with a maximum total penalty of $2 million — should the project be delayed.

In September 2001, ENMAX was awarded the contract to design and build the substation.

Substation Configuration

The substation needed to connect a 300-MW cogeneration plant to the Alberta transmission system and to provide a major source for the ENMAX electric system in north Calgary.

The project was divided into two phases. The first phase was to design, construct and commission the 240-kV substation with an in-service date of July 1, 2002. The second phase was to construct a 138-kV portion of the project by May 2003. Both phases had similar challenges, including permit and licensing, adverse winter weather conditions and tight timelines for procurement of major equipment.

ENMAX proposed the 240-kV bus consisting of six circuit breakers configured in a breaker-and-a-half scheme. Connected to the 240-kV bus are the cogeneration plant (two generators — a steam turbine and a combustion turbine generator), two transmission lines and two 240/320/400 MVA autotransformers.

The 138-kV bus is configured in a breaker-and-a-third scheme consisting of four circuit breakers. Currently, three 138-kV circuits are terminated in the substation — one from the substation that links to the rest of the Alberta grid and two that link to other ENMAX substations in Calgary. Some of the designs and technology used in the substation include:

• Unique hexagonal steel structure of the substation to reduce materials, space, labor and cost.

• Real-time transformer monitoring system to monitor the transformers 24 hours a day, 7 days a week.

• Dual redundant local-area network (LAN) communications that connect devices in a peer-to-peer network through fiber optics.

• Human Machine Interface (HMI) that allows the substation to be controlled and monitored from a single point.

Construction

ENMAX was awarded the contract in September 2001. With an in-service deadline of July 2002, all the civil work had to be completed before winter.

Site preparation involved excavating 8000 sq m (86,111 sq ft) of topsoil and saturated till. The fill material, which needed to be granular, had to cover an area of 105 by 105 m (345 by 345 ft) to a 2 m (6 ft) depth (24,000 cu m [31.391 cu yd]). The city of Calgary was constructing a wet pond at the same time, and ENMAX negotiated to remove the clay fill for the cost of hauling charges. No offsite drainage was allowed, so an on-site retention pond was developed and designed to withstand a 100-year flood. Initial grade was stopped 450 mm (18 inches) below final grade to allow grounding and trench work without excavation.

The construction of the foundations was a critical step. Much of Calgary is situated on an old riverbed so bedrock exists 5 to 6 m (16 to 19 ft) below grade. ENMAX designed the foundations to bear on the rock. Three types of piles were designed to support the bus work, breakers and building.

A grounding design software program was used to design the ground grid for a 40,000-A fault level. This design enabled ENMAX to reduce the amount of insulating gravel required under the Alberta Electrical and Communication Utility Code from 150 to 100 mm (6 to 4 inches).

ENMAX used underground trenching over the conventional pull box and duct system for the cable system. This method allowed more flexibility because of the uncertainty of the generator's cable needs during construction. It also met industry wheel loading requirements for heavy equipment and provided flexibility for future expansion plans.

ENMAX introduced a new family of bus work structures designed to meet the equipment support needs of the substation. Structures are of a galvanized, tapered break-formed, tubular design. Design advantages include:

• Improved appearance — single support columns reduce the number of structures required by 50%, and the graceful tapered pole shaft and arm lend an architecturally designed appearance to the substation.

• The single support columns reduced grounding requirements and foundations required by 50%, compared to conventional structures.

• The number of assembly components is less than traditional designs, thus reducing construction labor costs.

The tubular-shaped receiving structures saved caisson, cage and anchor bolt costs. These structures were designed as semi-deadend structures, so no deadends were required outside the yard. The generator company was impressed with the design and, as a result, hired ENMAX to perform the engineering, procurement and construction for its structures as well.

Real-time Transformer Monitoring

ENMAX installed an online transformer monitoring system that improves reliability, reduces maintenance cost and minimizes out-of-service time for the substation. Through a remote terminal unit (RTU), ENMAX continually collects data and monitors the health of the transformer. Some of the key elements monitored online are gas-in-oil, the condition of the bushing and the tap changer.

The online gas-monitoring sensor is sensitive to hydrogen, carbon monoxide, ethylene and acetylene, which are the primary indicators of transformer faults. A moisture-in-oil sensor measures the relative humidity and temperature of the oil. The sensors are connected to the RTU through a communications link, and software for the monitor allows the user to set alarm parameters and view readings. Water content in oil, gas levels, hourly gas trends and daily gas trends can be alarmed. The alarms and trending can be viewed on the HMI.

The online bushing monitor performs an analysis on the bushing leakage current. The system calculates power changes and capacity of the bushings. A benchmark value is set, and once a change is detected, the system will identify the bushing that is experiencing a problem. The information is passed to the LAN for display on the HMI.

The online tap changer monitor analyzes and reports key load tap changer (LTC) parameters such as the tap position, LTC motor current, load current, number of tap changes per day and wear factor on the last tap change. A communications link to the RTU allows data flow through the LAN to the HMI. Software on the HMI allows a user to view real-time values, alarms and trending. Alarms are passed to the substation RTU and on to the company's system control center.

Winding temperatures and top and bottom oil temperatures also are monitored by the system. Winding hot spot, winding temperatures and oil temperature are alarmed and trended, and can be viewed on the HMI.

ENMAX presently does a gas-in-oil sample on transformers on a yearly basis. Tap changer maintenance and bushing tests are performed on a five-year cycle. A first-year inspection will be performed in 2004 to assess the accuracy of the online monitoring. Once the reliability and accuracy of the monitoring has been verified, it is planned to base maintenance on condition monitoring rather than fixed maintenance cycles.

Advantages of the transformer online monitoring include:

• Real-time monitoring

  The company's control center receives alarms and real-time readings through the HMI system at the station.

• Trending

  The RTU monitors incipient faults occurring over time. Rather than look for specific readings, the company looks for trends before they become serious problems and can prevent catastrophic failures.

• Reduced maintenance cost

  The trending allows for maintenance to occur on an as-needed basis directly where the problem is, rather than on a planned maintenance cycle. This significantly reduces the time required to have the substation out of service and allows for more efficient maintenance procedures.

• Reduced wiring

  The fiber-optic LAN communications system greatly reduced the amount of wiring required between the control building and the transformer, which saved on construction and maintenance cost.

• Extended life of transformers

  Online monitoring of the health of the transformers extends the lifetime of the units because corrective action can be taken quickly when problems are detected rather than waiting for routine maintenance.

Protection and Control

As the substation is a critical component of power supply for the city of Calgary, ENMAX developed protection systems to significantly reduce risk of failure. Two independent protection schemes, “A” and “B,” are used. The schemes use different families of relays, and in some cases, different protection methods. Seventeen relays are in the “A” protection scheme and nine are on “B.” Some noncritical functions such as synchronism check, reclosing and breaker failure are not duplicated in both schemes.

The concept for the overall protection system is to work normally for any single type of failure, including communications, relay or breaker fail. While this concept is common to many protection schemes, the method of connecting the relays to the system has been done using fiber optics rather than traditional “hardwired copper” schemes.

Local Area Network

On the “A” protection scheme, the relays are connected with fiber-optic cables through a redundant LAN. This allows the relays to communicate peer-to-peer (back and forth). If communications in one port (or LAN) fails, the other available communications port is automatically selected. The fiber link replaces the need for wiring every relay and adds extra flexibility to transfer information from one relay to another on the network.

The peer-to-peer communications is used extensively to record system disturbances at the substation instead of using a digital fault recorder. It is also used to initiate breaker failure signals. Due to the complexity of the substation, an elaborate breaker failure scheme was designed by programming the logic in the relays using information received from relays on the LAN.

However, it is difficult to isolate the breaker failure initiate signal using the peer-to-peer communications when testing the relays, so precautions must be made to prevent inadvertent trips resulting from the testing.

The relays on the “B” protection have only one connection to the LAN. This connection is used to provide information back to the HMI and RTU only and does not have peer-to-peer functionality.

Logic schematic drawings, not previously used by ENMAX, were created and are used as tools by the engineering and field staff to describe the functionality of the protection system. These drawings show the peer-to-peer communications, SCADA inputs and outputs, hardwire inputs and outputs and the internal logic programmed for each relay.

Human Machine Interface

Connected to the LAN is an HMI, which is a dual-screen computer in the substation that provides a single access point to all the relays in the substation. The HMI:

• Displays single-line diagrams of the substation. The data on these diagrams are displayed in real time and include current, voltage and power values, and breaker and switch status.

• Provides local control to operate (open and close) motorized disconnect switches and breakers.

• Acts as a site event recorder by gathering information from all connected devices, creating a sequence of events list.

• Provides substation status at a glance — alarms and protection trip targets are displayed on screen.

• Provides access to each relay using the relay manufacturer's programming software.

• Enables programming, uploading and downloading information to and from each relay.

• Provides access to the online transformer monitoring.

To keep the HMI running in the event of a power failure, a high-speed switch with a built-in inverter is connected to the HMI computers. The switch is connected to both an ac service and the substation battery bank.

Remote access to the HMI is also available. Instead of sending a crew out to the substation to obtain information, this can be done remotely from the office. Security measures are in place to prevent unauthorized access.

Conclusion

This was the first major 240-kV to 138-kV substation to be competitively procured in Alberta. ENMAX won the bid by submitting an innovative proposal for a state-of-the-art substation using innovative technology, the first of its kind in western Canada.

It was also the first project in Alberta to prescribe reliability standards and propose financial penalties for not meeting the in-service dates. ENMAX completed the entire project on time and on budget, and saved money through strong construction management and providing project management, engineering design, procurement and commissioning services in-house.

The competitive process encouraged the development of an innovative new substation, challenged the company to new heights and, most important, helped ensure the lights stay on for citizens in and around Calgary.

Joseph Lee is a registered professional engineer in Alberta, Canada, where he has accrued 20 years of electric industry experience with three major utility companies in the province of Alberta. He was the project manager of the Beddington Substation Project and is currently responsible for asset management in the transmission department at ENMAX Power Corp. He has a BSEE degree from University of Calgary.
jlee@enmax.com