Shravan Garlapati

Agent Based Supervision of Zone 3 Relays to Prevent Hidden Failure Based Tripping

In this paper, we propose a distributed agent based supervisory scheme to make Zone 3 relays robust to hidden failure induced tripping, facilitated by the communication network -- soon to become an integral parts of the smart grid. Possible elimination of Zone 3 relays (remote backup protection) has been studied in the recent past and these remote backup relays have been adjudged to be essential for power system protection [23]. Even though Zone 3 relays are often overly sensitive to remote line overloading, and are known to cause unwarranted trips during cascading failure scenarios, they are prescribed as acceptable means for remote backup. Therefore, providing robustness to Zone 3 relays to minimize the risk of erroneous trips, especially when hidden failures [10, 1] make them vulnerable to over reaction, is an important problem. In our scheme, a synchronous grid is populated with agents at each relay, and an agent hierarchy is maintained in master/slave relationship. The communication established between relay agents decreases the probability of erroneous Zone 3 trips thereby preventing them from aggravating cascading failure scenarios, and reducing the probability of cascading blackouts. Unlike other agent based relay proposals, ours is a nonintrusive approach.

Robust Wide Area Measurement System-Based Control of Inter-area Oscillations

Abstract The application of phasor measurement unit (PMU) measurements and a robust linear matrix inequality-based control based on a polytopic model of the system used to damp inter-area oscillations is investigated. The closed-loop eigenvalues are excluded from a region of the complex plane, guaranteeing that low-frequency modes must be damped. A 68-bus 16-generator system is used as a test system. Three DC lines, three static var compensators, and remote PMU frequencies as added inputs to selected power system stabilizers are used as the example control. Ten different system conditions are used as the vertices of the polytope. The system size is reduced using selective modal analysis.

PHY and MAC layer design of Hybrid Spread Spectrum based smart meter network

The selection of the appropriate communication technology for different smart grid applications has drawn a great attention in the recent past. In this paper, we propose a Hybrid Spread Spectrum (HSS) based Advanced smart Metering Infrastructure (AMI) that reduces the overhead and latency in data transfer when compared to the use of 3G/4G technologies for smart meter data collection. We present a preliminary PHY and MAC layer design of a HSS based AMI network and evaluate their performance using matlab and NS2 simulations.

Performance evaluation of hybrid spread spectrum based wireless smart meter sensor network with multi-user detection techniques

Smart grid is the process of revitalizing the 20th century aging power grid by leveraging the communication, networking and information technological advancements of the 21st century. In the communication and networking industry, the buzz word “smart grid” initiated a discussion on the selection of the appropriate communication and networking technologies for different smart grid applications. In a recent study, a trustworthy source compared different technologies like GPRS, RF mesh, PLC and 3G cellular technologies and concluded that the 3G cellular technologies meet the requirements of distribution side smart grid applications [1]. Even though 3G cellular technologies meet the requirements of smart grid applications, based on the data size specifications of smart grid applications given in [2], an analysis on the use of the current state of the art 3G cellular technologies for smart grid applications gives an indication that their usage results in high data overhead, high latency and high power consumption (during power outage) for data transfer [3]. Therefore, in our prior work we have proposed a Hybrid Spread Spectrum (HSS) based smart meter network design that can reduce the overhead, latency and power consumption in data transfer when compared to the 3G cellular technologies [3].

An algorithm for inferring master agent rules in an agent based robust Zone 3 relay architecture

In order to prevent cascading events caused by hidden failures in zone 3 relays, agent based relay architectures have been suggested in the recent past. In such architectures each zone 3 relay contains agents that require communication with other agents at various relevant relays in order to distinguish a real zone 3 event from a temporary overload. In the presence of hidden failures such temporary conditions may cause unnecessary trip in a Zone 3 relay aggravating the situation towards cascading failures. In a recently proposed scheme, a local master agent is consulted by all Zone 3 agents before a tripping decision is made. The Master agent maintains a rule base which is updated based on the local topology of the network and real time monitoring of the status of other relays and circuit breakers. In this paper we provide an algorithm that uses local grid topology and relay/breaker status information and creates these rules at the master agent. When queried, the rules allow the master agent to appropriately advise the Zone 3 relays on the local conditions which enables them to make robust decisions.

SMAC: A Soft MAC to Reduce Control Overhead and Latency in CDMA-Based AMI Networks

The use of state-of-the-art 3G cellular CDMA technologies in a utility owned AMI network results in a large amount of control traffic relative to data traffic, increases the average packet delay and hence are not an appropriate choice for smart grid distribution applications. Like the CDG, we consider a utility owned cellular like CDMA network for smart grid distribution applications and classify the distribution smart grid data as scheduled data and random data. Also, we propose SMAC protocol, which changes its mode of operation based on the type of the data being collected to reduce the data collection latency and control overhead when compared to 3G cellular CDMA2000 MAC. The reduction in the data collection latency and control overhead aids in increasing the number of smart meters served by a base station within the periodic data collection interval, which further reduces the number of base stations needed by a utility or reduces the bandwidth needed to collect data from all the smart meters. The reduction in the number of base stations and/or the reduction in the data transmission bandwidth reduces the CAPital EXpenditure (CAPEX) and OPerational EXpenditure (OPEX) of the AMI network. The proposed SMAC protocol is analyzed using markov chain, analytical expressions for average throughput and average packet delay are derived, and simulation results are also provided to verify the analysis.

OTRA-THS MAC to reduce Power Outage Data Collection Latency in a smart meter network

The deployment of advanced metering infrastructure by electric utilities poses unique communication challenges, particularly as the number of meters per aggregator increases. When there is a power outage, a smart meter tries to report it instantaneously to the electric utility. In a densely populated residential/industrial locality, it is possible that a large number of smart meters simultaneously try to get access to the communication network to report the power outage. If the number of smart meters is very high on the order of tens of thousands (metropolitan areas), the power outage data flooding can lead to Random Access CHannel (RACH) congestion. Several utilities are considering the use of cellular network for smart meter communications. In 3G/4G cellular networks, RACH congestion not only leads to collisions, retransmissions and increased RACH delays, but also has the potential to disrupt the dedicated traffic flow by increasing the interference levels (3G CDMA). In order to overcome this problem, in this paper we propose a Time Hierarchical Scheme (THS) that reduces the intensity of power outage data flooding and power outage reporting delay by 6/7th, and 17/18th when compared to their respective values without THS. Also, we propose an Optimum Transmission Rate Adaptive (OTRA) MAC to optimize the latency in power outage data collection. The analysis and simulation results presented in this paper show that both the OTRA and THS features of the proposed MAC results in a Power Outage Data Collection Latency (PODCL) that is 1/10th of the 4G LTE PODCL.

Optimum location of master agents in an agent based zone 3 protection scheme designed for robustness against hidden failure induced trips

The post-mortem analysis of few blackouts in US and Europe concluded that the hidden failure induced tripping of distance relays is one of the primary causes of blackouts. In order to provide the distance relays with situational awareness and improve their robustness to hidden failures, a non-intrusive agent based relay supervised distance protection scheme is proposed in [1] and their results seemed promising. Each relay is associated with an agent who has the ability to sense and communicate. The communication between hierarchically distinguished master and slave agents aid relays to differentiate a fault as a true fault or a hidden failure induced fault and respectively to trip or not to trip. The methodology presented in [1] is limited to single master agent and multiple slave agents communication therefore it can only be applied to smaller power system networks. In order to adapt the relay supervision scheme to a geographically widely distributed larger bus system, more than one master agent is required because the use of a single master agent may result in slave agent to master agent round trip communication delays greater than the relay fault clearing times which defeats the purpose of the relay supervision scheme. Therefore for a larger power grid that needs multiple master agents, finding the number of master agents required and the location of the master agents is an issue that has to be addressed. In this paper we modelled the problem of minimizing the number of master agents required to serve the slave agent queries and finding an optimum location for the master agents as a multiple facility location problem. Networking simulations are performed using OPNET and optimization models are developed and simulated using IBM ILOG CPLEX.