Mikael Nordman

Distributed agent-based State estimation for electrical distribution networks

A new agent concept for state estimation in electrical distribution networks is presented. The responsibility for state estimation is delegated to local agents in secondary substations. These use historical data and probabilistic means to assess the performance of the substation and to detect bad data. Topology and observability analysis as well as bad data identification are performed with a token that traverses the secondary substations of the primary substation feeders. The feasibility of the concept is evaluated in a case study where data from real sensor measurements are used as input. According to the study, the state estimation concept performs well.

An agent concept for managing electrical distribution networks

A new agent concept for managing technically advanced electrical distribution networks is presented. The essence of the concept consists of three aspects: the secondary substation object, decentralized functionality and an information access model. In this framework, a primary substation area is modeled so that secondary substations are represented as copies of the secondary substation object, local function copies in every substation represent functions and they are executed by a token passing procedure that occurs between neighboring secondary substations. The permission to execute a function is delegated to different power system hierarchy levels according to the information access model. The concept is illustrated by the use of case studies of condition assessment and fault management. In addition, a small-scale implementation is described and results of some test runs are presented.

Modeling and experimental verification of on-line PD detection in MV covered-conductor overhead networks

The falling trees on covered-conductor (CC) overhead distribution lines produce partial discharges (PDs). The measurements have been taken in the laboratory and PD signal characteristics under various circumstances have been described. In this paper, an on-line single-phase PD monitoring system using Rogowski coil is simulated in EMTP-ATP. The simulation results are compared with those obtained from the laboratory measurements. The proposed model can be used to estimate the length of the practical CC lines at which PDs due to falling trees can be detected and localized; thus, deciding the number and positioning of the sensors over a particular length of the CC lines. The different noise sources have been described that cause interference with low level PD signals, which is a major challenge for on-line/on-site condition monitoring. The design aspects of the wireless sensor for this specific application are also discussed. Automatic detection of falling trees will reduce visual inspection work after storms and it will improve reliability and safety of the CC distribution system.

A wireless sensor concept for managing electrical distribution networks

In this paper, methods and analysis of a simple wireless sensor concept for detecting and locating faults as well as for load monitoring are presented. The concept is based on distributed wireless sensors that are attached to the incoming and outgoing power lines of secondary substations. A sensor measures only phase current characteristics of the wire it is attached to, is not synchronized to other sensors and does not need configuration of triggering levels. The main novelty of the concept is in detecting and locating faults by combining power distribution network characteristics on system level with low power sampling methods for individual sensors. This concept enables the sensor design to be simple, energy efficient and thus applicable in new installations and for retrofit purposes in both overhead and underground electrical distribution systems.

Design of a concept and a wireless ASIC sensor for locating Earth faults in unearthed electrical distribution networks

In this paper, a new concept for using simple wireless sensors for detecting and locating faults in an unearthed electrical distribution network is presented. The concept is based on distributed wireless sensors that are attached to the incoming and outgoing power lines of different feeders and branches. A sensor measures only the phase current characteristics of the wire it is attached to, is not synchronized to other sensors, and does not need configuration of triggering levels. The main novelty of the concept is in detecting and locating faults by using the electrical distribution system aspects and the Bayesian probability theory. The feasibility and selectivity of the concept is shown with several simulations done with the Matlab SimPowerSystems environment. In addition, a new design of a wireless application-specific integrated circuit sensor for the proposed fault-management concept is presented.

Adaptive autonomy: Smart cooperative cybernetic systems for more humane automation solutions

Smart cooperation of human and computer agents should be harmonized by adapting the automation level of the cybernetic systems to the changing environmental and peripheral situations. This paper presents an adaptive autonomy methodology that is based on an extension of a well-known human-automation interaction model, as well as the expert judgment technique and the performance shaping factors concept. The method is implemented to a power distribution automation system, and the results are discussed through a scenario-based approach. Then, the performance of the proposed methodology and the effectiveness of adaptive autonomy are shown by the wide span of the changes in the resulting automation levels. The trends of the automation levels are investigated versus the criticality of the situations and the automation stages. The application-oriented matters are also discussed to stress on the context-based nature of the human-centered automation models.

Challenges in implementation of human-automation interaction models

This paper presents the practical experience gained in the process of implementing the human-centered automation design methodology to an electric power utility management automation function, along with the analytical discussions on the implementation challenges. This report of implementation challenges and the discussions made on the methods devised to conquer those challenges lead to an alternative approach to the original approach to the well-known human-centered automation design model in the literature.

A method for synchronizing low cost energy aware sensors used in industrial process monitoring

Time synchronization is needed in distributed industrial systems. When wireless low cost energy aware sensors are used for monitoring industrial processes a new concept for time and synchronization must be developed. These sensor systems are much more heterogeneous and energy aware than traditional systems, making standard time synchronization methods inadequate. Implementation differences, energy resources and environmental conditions may greatly vary even inside one cell of sensors. This must be considered in the design. The authors propose a new time synchronization method that scales to the real synchronization requirements of the cell application. The method has been designed to be energy efficient, flexible and robust. It is based on three steps that respectively learn the system and its behavior, make coarse synchronization and perform precise synchronization according to the desired synchronization level and the energy available in each sensor. They show some early simulation results that indicate the potential of the method discussed in the paper.

Synchronizing low-cost energy aware sensors in a short-range wireless cell

Time management and synchronization in distributed systems has been studied thoroughly for many years. Basically the goal has bene to close the gap between local clocks of distributed devices. In systems that need to be both low cost and low power the devices sleep most of the time making standard CMOS timers impractical to use. Instead, imprecise RC oscillators are used to manage the wake up cycles. However, there is also a need to provide time management and synchronization in these systems. This is difficult with RC oscillators being the main device clock references. In this paper we propose a method that uses event timestamps to synchronize low cost, low power sensors with RC oscillators. The method relies on the cooperation of sensors in a wireless cell and a boundary node, which collects data from the sensors. Initial evaluation of the method shows that it is promising and possible can provide good synchronization with greater flexibility, lower costs and less energy than standard CMOS timers.

A task scheduler framework for self-powered wireless sensors

The cost and inconvenience of cabling is a factor limiting widespread use of intelligent sensors. Recent developments in short-range, low-power radio seem to provide an opening to this problem, making development of wireless sensors feasible. However, for these sensors the energy availability is a main concern. The common solution is either to use a battery or to harvest ambient energy. The benefit of harvested ambient energy is that the energy feeder can be considered as lasting a lifetime, thus it saves the user from concerns related to energy management. The problem is, however, the unpredictability and unsteady behavior of ambient energy sources. This becomes a main concern for sensors that run multiple tasks at different priorities. This paper proposes a new scheduler framework that enables the reliable assignment of task priorities and scheduling in sensors powered by ambient energy. The framework being based on environment parameters, virtual queues, and a state machine with transition conditions, dynamically manages task execution according to priorities. The framework is assessed in a test system powered by a solar panel. The results show the functionality of the framework and how task execution reliably is handled without violating the priority scheme that has been assigned to it.