Sharif Digital Repository

A wind turbine transformer resonance can occur due to high frequency transients at its terminal i.e.; under its energization through a length of cable. Occurrence of resonance can be addressed by a sophisticated transformer design procedure. The goal is to obtain an optimum design capable of controlling the frequency response of the winding in such a way to avoid occurrence of any resonance under transient conditions. Three insulation clearances parameters which are employed for the wind turbine transformer winding design have been investigated in design of a (800 kVA, 690/20,000 V) wind turbine transformer to determine effect of their variation on its frequency response. It is shown that... 

The standard power flow (PF) equations are nonlinear, and their integration in the optimal PF (OPF) problem leads to a nonconvex hard-to-solve model. To attack the issue, this paper presents a linear PF model wherein real and imaginary parts of nodal voltages are variables. In the model, loads are interpreted via ZIP model including constant impedance, constant current, and constant power components. To preserve linearity of the model, the complex power is represented via a quadratic function of the hosting node voltage. The function coefficients are derived via curve fitting approaches. Since the model is linear, its solution does not need repetition and can be effectively integrated in the... 

Demand response enabled by time-varying prices can propel the power industry toward a greater efficiency. However, a noncoordinated response of customers may lead to severe peak rebounds at periods with lower prices. In this regard, a coordinated demand response scheme can mitigate concerns about the peak rebounds. This paper presents a system-wide demand response management model to coordinate demand response provided by residential customers. The objective of the model is to flatten the total load profile that is subject to minimum individual cost of customers. The model is first formulated as a bi-level optimization problem. It is then casted into equivalent single-level problems, which... 

One way of more efficiently utilizing the existing gas and electrical infrastructures is to consider them as one integrated system in planning and operation of energy systems. The energy hub framework is adopted to determine a modeling procedure for such multi carrier energy systems. This paper presents a residential energy hub model for a smart home. A residential combined heat and power (CHP) as a cogeneration technology, and a plug-in hybrid electric vehicle are employed in the model. Operation of the hub is optimized through a proposed optimization-based formulation. The objective is to minimize customer payment cost. Solving the problem determines how much of each energy carrier the... 

Time-varying electricity rates enable demand-side potentials, which provide an opportunity for distribution companies (DisCos) to hedge against the financial risk imposed by volatile spot market prices and uncertain customers' load. In particular, time-varying rates can be effective alternatives for at least a portion of costly forward contracts. This paper establishes a stochastic framework to determine optimal forward market purchases under time-varying rates. Various electricity rating strategies with different time intervals covering flat, time-of-use, and real-time pricing schemes are considered. The objective of the framework is to maximize DisCo's expected profit while the exposure... 

Real-time electricity prices along with demand-side potentials can provide distribution companies (DisCos) with considerable financial and technical benefits compared to the conventional flat prices. This paper incorporates demand response in DisCos' short-term decision model in a real-time pricing (RTP) environment wherein consumers are charged based on hourly varying prices. Besides the hourly RTP sale prices, the established model deals with other DisCo's short-term activities including hourly purchases from the grid, commitment of distributed generation (DG) units, dispatch of shunt compensators, and invocation of load curtailments (LCs). The stochastic nature of wholesale market prices... 

This paper presents a stochastic framework for short-term operation of a distribution company (disco). The proposed framework optimizes disco's operational decisions in two hierarchical stages. The first stage, called day-ahead operation stage (DAOS), deals with the operational decisions on purchases from the day-ahead market and commitment of distributed generation (DG) units. The objective of this stage is to minimize the expected operating cost while the financial risk exposed by uncertain real-time prices and loads is restricted to a given level. The model associated with this stage is based on the mixed-integer programming (MIP) format. The second stage, named real-time operation stage... 

One way of more efficiently utilizing the existing gas and electrical infrastructures is to consider them as one integrated system in planning and operation of energy systems. The energy hub framework is adopted to determine a modeling procedure for such multi carrier energy systems. This paper presents a residential energy hub model for a smart home. A residential combined heat and power (CHP) as a cogeneration technology, and a plug-in hybrid electric vehicle are employed in the model. Operation of the hub is optimized through a proposed optimization-based formulation. The objective is to minimize customer payment cost. Solving the problem determines how much of each energy carrier the... 

Severe peak rebounds are likely in absence of a system-wide coordination among customers participating in demand response programs. This paper aims to establish a decentralized system-wide framework to coordinate demand response of residential customers in a smart grid. The objective of the framework is to modify system load profile provided that customers' payments are minimized, and their comfort and privacy are preserved. Home load management (HLM) modules, embedded in customers' smart meters are autonomous agents of the framework. The energy service provider iteratively exchanges load information with HLM modules in the hope of achieving his desired load profile. In each iteration, the... 

Time varying prices by motivating customers to reduce their consumption in peak periods propel the electricity industry towards a higher efficiency compared to that of common flat prices. Focusing on time-of-use (TOU) sale prices, this paper establishes a stochastic model for the medium-term decision making problem faced by a distribution company (DisCo). The developed model deals with the DisCo's decisions on the level of involvement in forward contracts and in the pool as well as the sale prices offered to customers. The demand response to TOU prices is captured using a price elasticity matrix (PEM). The objective is to maximize the DisCo's profit while the exposure risk imposed by... 

Despite of the great focus of attention dedicated to demand response (DR), the potential benefits of DR on distribution networks have not yet been quantitatively studied. This paper aims to assess DR potential impacts on major attributes of the operation of a residential distribution network. For doing so, grossly metered usage of more than 1600 residential consumers from Kainuu, Finland, is disaggregated to appliance-level load profiles. The flexibility of the load profiles is also estimated from the survey data and questionnaires. The individual profiles are then adjusted within their flexibility such that the most evenly distributed aggregated load profile is realized. Finally, the... 

The proliferation of more sensitive loads has obliged distribution companies to pay greater attention to the voltage sag mitigation potential of different design alternatives in network planning studies. In doing so, a company has to have effective tools for estimating the voltage sag performance of its network. In this regard, this paper establishes a three-step framework for evaluating voltage sag performance of a distribution network. The first step, designated as state selection, is to select a network state in which voltage sag is likely. Although voltage sags have various causes, those that originated from faults in distribution networks are considered in this paper. The stochastic... 

With the rapid proliferation of residential rooftop photovoltaic (PV) systems, current and voltage unbalance issues have become a matter of great concern in low voltage (LV) distribution feeders. To overcome the issues, this study proposes a model to optimally rephase customers and PVs among the three phases via static transfer switches (STSs). The optimal STS placement is also considered in the model to achieve a cost effective solution with optimum number and location of STSs. The objective is to minimise total energy losses caused by current unbalance, minimise the number of STSs, and keep voltage unbalance along the feeder within the acceptable range. The model is solved via a... 

Implementing automation system in distribution networks needs a huge investment that usually cannot be funded entirely in a short period of time. So distribution companies (DISCOs) should develop long-term plans to equip their network with automation technologies as far as economically justifiable. Aiming to provide a methodology for development such plans, this paper presents a novel multistage planning model for implementing distribution automation system considering all main hardware and software infrastructures. The proposed method optimally determines the type, location, and time in which an equipment or infrastructure must be added to network considering the network capacity expansion... 

Feeder Automation (FA) has been recognized by researchers and utilities as one of the attractive remedial measures to enhance service reliability in the electric power distribution systems. Until now, several kinds of FA schemes have been developed for automating of distribution feeders. They can be categorized into three main approaches: semiautomatic, distributed and centralized schemes. The challenge for the utilities, especially in today's competitive electricity market, is to identify and evaluate potential FA schemes and determine that appropriate for implementation. In this context, reliability cost/worth assessment plays an important role. This paper aims to propose a step by step... 

This article proposes a new three-stage stochastic framework for dealing with predictable two-phase natural disasters in distribution systems. This framework is a multiobjective optimization, in which the amount of curtailed energy, the number of switching actions, and the vulnerability of operational components are selected as the main criteria for decision-making process. The optimization problem is formulated in the form of a stochastic mixed-integer linear programming (MILP) problem. In this article, a windstorm event followed by flooding is analyzed as a two-phase natural disaster. In this regard, the uncertainties associated with gust-wind speed, floodwater depths, and load demands are...