Debrup Das

Power flow control in networks using controllable network transformers

The drive for higher reliability has motivated many utilities to move toward a more meshed system. Two control areas are often connected together with tie-lines. Power flow through the tie-lines connecting two control areas is difficult to control. This lack of controllability of power flow is one of the major issues in the modern grid. It causes asymmetric stress on the grid assets. This makes some grid assets more vulnerable to failure than others, and therefore, decreases the overall system reliability. Presently utilities can achieve very limited power flow control using devices like load tap-changing transformers and phase-shifting transformers. Controllable network transformers (CNTs) were introduced as a simple, low-cost solution to the power flow problem. This paper develops a theoretical analysis for the operation of CNT in a meshed network. It also shows the various possible applications of the CNT. Experimental validation of the working principle of a small-scale prototype CNT is also provided.

Reducing transmission investment to meet Renewable Portfolio Standards Using Smart Wires

Increasing societal concern for global warming and energy security have led many of the US states to adopt policies like Renewable Portfolio Standards (RPS). Introduction of these environmental policies in the energy market are expected to have significant impact on grid operation as well transmission investment. The energy delivery system has to be upgraded significantly in order to make it capable of handling these changes. It has been claimed that upgrading the present transmission system to a Smart Grid would facilitate the integration of renewable resources. Smart Wires are distributed, low cost, autonomous smart assets that are capable of controlling power flow in a meshed transmission network. This paper studies the benefit of Smart Grid technologies like Smart Wires in reducing transmission investment that is required to implement policies like the RPS.

Smart Wires — A distributed, low-cost solution for controlling power flows and monitoring transmission lines

Smart Wires is a family of three Distributed FACTS (D-FACTS) technologies able to realize low-cost transmission line monitoring and power flow control in meshed networks. Smart Wires will allow utilities to increase power transfers in meshed networks by increasing average line utilization. The technology is projected to have significantly lower cost and lead time than alternatives, namely new line construction, reconductoring, or conventional FACTS technology. This paper overviews the work done to date to demonstrate the feasibility and impact of the technology, including prototype development and system simulations.

Reducing transmission investment to meet Renewable Portfolio Standards using Controlled Energy Flows

Increasing societal concern for global warming and energy security have led many of the US states to adopt policies like Renewable Portfolio Standards (RPS). Introduction of these environmental policies in the energy market are expected to have significant impact on grid operation as well transmission investment. The energy delivery system has to be upgraded significantly in order to make it capable of handling these changes. It has been claimed that upgrading the present transmission system to a Smart Grid would facilitate the integration of renewable resources. Controllable Energy Flows (CEF) is one method to realize power flow control on the Smart Grid. The CEF method controls transactions of incremental power using distributed assets like Distributed Series Impedances of Controllable Network Transformers. The paper studies the benefit of Smart Grid technologies like Controlled Energy Flows in reducing transmission investment that is required to implement policies like the RPS.

Optimal placement of Distributed Facts devices in power networks Using Particle Swarm Optimization

The concept of Distributed Flexible AC Transmission Systems (D-FACTS) was introduced in order to provide a cost-effective solution for power flow control. Determining the location and amount of distributed compensation to be employed is an important problem. Proper deployment of DFACTS is necessary for optimal control of the power flow in a large meshed network. Being a distributed solution, DFACTS provides flexibility in terms of deployment. This often makes the problem even more computationally intensive. Recent studies show that Particle Swarm Optimization (PSO) technique gives better results than classical optimization techniques, when applied to power engineering optimization problems. This paper shows the application of PSO for the optimal deployment of DFACTS. The technique is applied on the IEEE 39 bus system. Details of the method and the results obtained are presented in the paper.

Design and testing of a medium voltage Controllable Network Transformer Prototype with an integrated hybrid active filter

Dynamic control over real and reactive power flow is one of the key areas of concern for the modern grid. Traditional FACTS based devices have proven to be too costly and complex to achieve any significant market penetration. Modifying existing transmission assets to make them controllable may be a cost-effective method of increasing the grid controllability. Controllable Network Transformers (CNTs) have been shown theoretically to be an effective real and reactive power flow controller. The various options for filter design of a CNT are presented in this paper. The paper also discusses the design and testing of a medium voltage CNT prototype with an integrated hybrid active filter, rated at 200 kVA and 2.4 kV.

Ubiquitous power flow control in meshed grids

A new method of power flow control in a meshed network has been presented earlier, to enable power dispatch along a defined path without impacting flows on branches adjacent to the path. This paper explores the type of power converter topology that could optimally provide the desired control function. This includes well known FACTS devices such as Back-to-Back Converters (BTB) and Unified Power Flow Controllers (UPFC), as well as newer devices such as Controllable Network Transformers (CNT), and Distributed Series Impedance (DSI) devices. Equipment ratings are calculated for the BTB, UPFC, CNT and CNT-DSI hybrid solutions. Scalability to grid voltages and power levels is also discussed. Power flow capability, implementing the proposed solution with ideal voltage sources, is shown via simulation for the IEEE 39 bus system. Finally, functionality is simulated in a meshed, four-bus system using switching devices. Proposed functionality would allow more efficient market operation, incentivize transmission investment and ensure physical delivery of contracted energy, thus enabling real-time markets for lowcarbon (green) sources.

Smart tie-line control using Controllable Network Transformers

Increasing load growth, decreasing investments and increasing penetration of dynamic sources and loads have severely increased the stress on the electric grid. This growing stress has forced operators and regulators to think of delivering energy in a smart, controllable and reliable way to the customers. Tie-lines connecting two systems are one of the traditional methods used by utilities to improve the system reliability. However, often specially during contingencies, tie-lines get overloaded due to the lack of power flow controllability through them. Controllable Network Transformers (CNTs) are smart assets which can be realized by augmenting existing Load Tap Changing (LTC) transformers in order to achieve power flow control. This paper proposes the use of CNTs in tie-lines to make them smart and controllable, without compromising the system reliability.

Increasing inter-area available transfer capacity using controllable network transformers

Control areas are often interconnected to each other by tie-lines over which the operators have little or no real-time control. Congestion of any one of the lines in the transmission corridor limits its Available Transfer Capacity (ATC), even if there is available spare capacity in some parallel paths. Increasing inter-area ATC is key to increasing penetration of renewable generation, since the geographical location of renewable generation sites are often far from the load centers. Traditional methods of increasing inter-area ATC like transmission upgrade or FACTS installations are expensive and also require significant lead-time. Controllable Network Transformers (CNTs) are low-cost power flow controllers which can be realized by augmenting existing Load Tap Changing (LTC) transformers. The paper shows from a system level perspective, the application of CNTs to increase inter-area tie-line ATC, thereby allowing increased inter-area green energy transfer.

Energy Budget Reduction by Using Ultracapacitors in Mining Converters

A typical mining facility uses excavation machines like shovels, draglines etc. for removing overburden and ores during the mining process. These machines are characterized by cyclic loads consisting of high peak power demands as well as regenerative energy. The peak power demand is often as high as double the average demand. The regenerated energy is as high as 60% of the peak motoring power. This regenerated energy can be stored temporarily and then reused during peak motoring demand thus leading to peak-shaving of the load. The recent development in the field of ultracapacitors has led to commercial availability of high power ultracapacitor modules rated for reasonably high voltages. The paper proposes the use of ultracapacitors in order to peak load shaving thereby reducing energy costs. The paper also discusses the economic benefits achieved by adopting this technology.