Specialists at KEMA have developed an application named REMA-T to provide energy distribution companies such as Stedin (formerly known as Eneco Netbeheer) with optimized transformer replacement and maintenance schedules. REMA-T allows energy distribution companies to determine the optimal balance between the reliability of the power supply network and investment costs.
KEMA has selected the AIMMS modeling system because of the easy interfacing with the front-end spreadsheets, convenient definition of optimization models and its powerful embedded solvers.

Optimized transformer replacement and maintenance schedules for energy distribution companies


Power transformers connect different voltage networks and are critical and costly components in the power supply infrastructure. A failing transformer can have large impact on the power supply to industry and consumers. Based on age and condition, transformers are monitored, maintained, refurbished and finally replaced.

The Challenge

In energy distribution companies such as Stedin, the asset manager is in charge of determining the maintenance schedule and strategy of the power transformers.
In order to prioritize the activities, the asset manager has to balance:
- Overall system reliability (during normal conditions and maintenance)
- Investment budget
- Maintenance budget
The maintenance schedule of one transformer can easily be managed by hand. However, the power grid of Stedin includes 220 transformers of different age and condition, distributed over 100 sub-stations with different risk profiles. The number of activities and scheduling options becomes so large that a decision-support tool is needed.

The Solution

Specialists of KEMA have developed REMA-T to support the asset manager in making optimal decisions for scheduling transformer maintenance.
REMA-T calculates all activities and optimizes the schedule to the specific energy distribution company’s objectives and constraints. Transformer information (e.g. age, condition based on analysis and diagnostics, failure data), and the company’s specific requirements are included. The result is an optimal timing of maintenance and replacement per transformer per year, the type of maintenance and the effect of replacement on the total reliability of the system.

The Benefits

REMA-T provides the asset manager and the energy distribution company with quantitative foundations for annual investment and maintenance budgets. A direct relation between investments and network reliability is calculated and the output is presented in such a way that it is easily communicated to the management team. Upcoming replacement waves are identified and can be optimized.

For Stedin applying REMA-T resulted in a tailor-made replacement and maintenance schedule for a combination of substations. This schedule is regularly updated and optimized to the current market insights. High and low risk substations are identified and monitoring schedules are adjusted to the constraints.
The total costs of maintenance, refurbishment and replacement have been decreased. The investment in the tailored model was earned back in less than three months.

Advantages of AIMMS

REMA-T is built up from different modules: reliability and cost models for a single solution form the center. The powerful solvers embedded in AIMMS are used to determine the best solution considering multiple solutions.
AIMMS offers a good link to MS Excel, so that the results can be presented in Excel for managers who are not familiar with AIMMS. This link also gives the opportunity to perform a sensitivity analysis while varying the inputs.

Customer Quotes

Sonja Bouwman, consultant of KEMA: “AIMMS is very easy to use, with good solvers, a very pragmatic tool. With AIMMS we could make this model very user friendly and the solvers were very fast. We made the first demo version of the model in MS Excel and it took a whole day just to optimize one substation. With AIMMS it takes just minutes to optimize 100 substations.”
Herman Arts, Expert Asset Management of Stedin: ”We yearly use the REMA-T application (built in AIMMS) for optimizing our maintenance, refurbishment, and replacement program of power transformers for a complete regional network. Thus we can postpone the refurbishment or replacement for several years guarding the risks we take. “

About KEMA

KEMA is a global company specializing in strategic and technical energy consulting, operational support, measurements and inspection, and testing and certification. As part of its innovative services, KEMA develops and implements OR models for energy and gas distribution companies.

About Stedin

Stedin provides and manages a safe and continuous transport of gas and electricity to more than two million customers in the Netherlands. In addition, Stedin is responsible for the development and maintenance of this network.

View this case study as a PDF.

Further information: STAtOR, December 2009,  pages 14-19 (Dutch only).