Cim And Iec 61850.pdf

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CIM and IEC 61850 Integration Issues: Application to Power Systems Yemula Pradeep, Student Member, IEEE, P. Seshuraju, S. A. Khaparde, Senior Member, IEEE, Vinoo S. Warrier, and Sushil Cherian, Member, IEEE

Abstract—Common Information Model (CIM) is emerging as a standard for information modelling for power control centers. While, IEC 61850 by International Electrotechnical Commission (IEC) is emerging as a standard for achieving interoperability and automation at the substation level. In future, once these two standards are well adopted, the issue of integration of these standards becomes imminent. Some efforts reported towards the integration of these standards have been surveyed. This paper describes a possible approach for the integration of IEC 61850 and CIM standards based on mapping between the representation of elements of these two standards. This enables seamless data transfer from one standard to the other. Mapping between the objects of IEC 61850 and CIM standards both in the static and dynamic models is discussed. A CIM based topology processing application is used to demonstrate the design of the data transfer between the standards. The scope and status of implementation of CIM in the Indian power sector is briefed.

I. I NTRODUCTION URRENT trend in the electricity business all over the world is towards restructuring of the power industry and inter connection of power networks at all levels. These steps are being taken to achieve a competitive market for energy and higher reliability. But the existing infrastructure typically consists of heterogenous software and hardware systems, built on dissimilar information models and communication protocols, thus creating hurdles for integration. This scenario makes it imperative to define and adopt open information standards and open system architectures. Over the last decade, this has lead to the development of standards like Common Information Model (CIM) and IEC 61850 which are now well known in the power industry. CIM is an information model from the perspective of a power control center addressing the needs of data exchange, model exchange and applications at the level of control centers, which involve Supervisory Control And Data Acquisition (SCADA), Energy Management System (EMS) and Business Management System (BMS). On the other hand, IEC 61850 is a standard from the perspective of a power substation which enables substation automation, autonomous control, advanced protection systems, self describing equipment, integration of Intelligent Electronic Devices (IEDs) and

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Yemula Pradeep is with Department of Electrical Engineering, Indian Institute of Technology Bombay. email: [email protected] Seshuraju. P is with Department of Computer Science Engineering, Indian Institute of Technology Bombay. email: [email protected] S. A. Khaparde is with Department of Electrical Engineering, Indian Institute of Technology Bombay. email: [email protected] Vinoo S.Warrier is with Kalkitech, India. email: [email protected] Sushil Cherian is with Kalkitech, USA. email: [email protected]

978-1-4244-4241-6/09/$25.00 ©2009 IEEE

communication within substation as well as with the master control center. IEC 61850 is the most detailed description of substation equipment and their monitoring and control aspects, while CIM is the detailed description of connectivity between various equipment, substations and their static and dynamic information. CIM is gaining worldwide recognition and acceptance as a standard for power system data representation and exchange [1]. Many utilities are adopting CIM and vendors are developing CIM compliant products. Considerable literature is reported on CIM covering the need for CIM standard [2], inception and evolution of CIM standard [3], how power system data is represented in CIM standard [4], and how CIM facilitates semantic understanding of the model and data exchanged through static and dynamic extensible markup languageresource description framework (XML-RDF) files [5], [6]. Converters from proprietary to CIM format have also been developed [7], [8]. In view of this, CIM is a natural choice of data representation for the development of an open architecture at the control centers level. Technical overview and benefits of adopting IEC 61850 standard are well explained in [9]. Reference [10] discusses the scope of the IEC 61850 as a communication protocol for substation IEDs. Implementation of few control and automation applications are also presented. Reference [11] describes the issues in migration form the conventional to the IEC 61850 compliant substation automation system. A comprehensive study on modelling, simulation and performance evaluation of substation automation system built on IEC 61850 standard is reported in [12]. To automate the control operations within the substation, designs of autonomous controllers which interact with IEDs using the IEC 61850 standard is presented in [13]. As reported in [14], a first substation with IEC 61850 complaint automation system has been commissioned and tested successfully in October 2005 in America. It is evident from the above discussion that in the near future, introduction of these standards in power systems worldwide would increase. Interdependency of the standards will require integration of these standards. There have been few efforts reported in the literature towards integration of these standards. Reference [15] presents a design of power automation platform for integrating the various power automation subsystems. A framework incorporating IEC61970, IEC61968, IEC61850 standards is described. References [16] and [17], argue about the need for integration of the important and emerging standards. It also provides a method for formal integration and bi-directional mapping of objects in both the

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Fig. 1.

Comparison of IEC 61850 and CIM Representations.

standards. The following are the salient contributions of this paper. 1) Mapping between the Substation Configuration Description (SCD) file and the static CIM XML/RDF file that constitutes the static part of the power network. 2) Mapping between IEC 61850 data values to CIM dynamic file that constitutes the time varying dynamic part. 3) Integration architecture of CIM and IEC 61850 standards. 4) Design of CIM based topology processing algorithm. The above connotion of mappings is specific to the topology processing application discussed in this paper. Based on a similar methodology the mapping can be extended to other objects. II. R EPRESENTATION IN IEC 61850 AND CIM STANDARDS A. Two bus one breaker system For the purpose of this paper, we are mainly interested in describing how mapping can be made between the objects of IEC 61850 standard and the CIM standard to cater to the data requirements of a specific application such as a CIM based network topology processor. This exercise would later pave way for a broader and generic mapping of the standards at the class level. We first begin by considering a part of a network consisting of two bus bars connected by a circuit breaker. This network is then modelled in both the standards and the resulting XML or XML/RDF files are presented. The next step is to map the individual elements in files of one standard to the corresponding elements in the other. Once the mapping is defined, a mechanism for the integration of standards and data flow is presented in the next section. The sample network and its representation is shown in Fig. 1. B. Representation in IEC 61850 standard The IEC 61850 standards consists of set of specifications to model the substation data in a standardized manner, an abstract protocol to define the models for exchange of data at

the bay and process levels, mappings of this abstract protocol to concrete carrier protocols, and also an XML standard for interoperable exchange of engineering/configuration data. Part 6 of the IEC 61850 standard defines an XML Schema that provides a node that contains an XML tree depicting the actual definitions of the Logical Nodes (LNs), Common Data Classes (CDCs), Data Attributes (DAs) and Enumerations (Enums). This information is typically provided in ICD (IED Capability Description) files by the manufacturer and is carried through to the SCD file, with both categories of files being implemented using the XML Schema. In this section, we first look at the general contents and structure of ICD and SCD files. The ICD and SCD files for the above sample system are then presented. 1) ICD File Description: The implementation of IEC 61850 standard is housed in IEDs, such as relays, fault recorders etc and in station Human Machine Interface (HMIs). IEDs contain IEC 61850 servers where as the station HMIs contain IEC 61850 clients. IEC 61850 defines a tree of objects starting from the Server object, and containing a hierarchy of Logical Devices (LDs), logical nodes and Data Objects (DOs). The server object is an approximation of the physical device or IED that houses the 61850 protocol driver which acts as a container for the other objects that finally represent the substation data monitored and controlled by the particular IED. Each substation function (e.g. circuit-breaking) is represented by a standard logical node class (e.g. XCBR). Each instance of a circuit-breaker in the substation will be represented by an instance of the XCBR class. However, the final instance will actually be an instance of a sub-class or derived class of the XCBR class. The definition of the XCBR super-class is specified in the 61850 standard, but the definition of the subclasses used in IEDs is defined by the implementation of the logical node by that particular manufacturer and can vary from another instance of an XCBR sub-class used in another IED. However, the XCBR super class contains a set of mandatory elements (data containing data attributes) which will be present in every sub-class in every implementation. Hence, the data available in any given implementation of an XCBR class can only vary as far as the optional elements of the XCBR superclass. Another level of complexity can be introduced to this mix, since the 61850 standards allow for extensions of the base class under private name-spaces. This is beyond the scope of this paper. The structure of the Logical Node contains Data Objects (DO) which are usually instances of specializations of the Data class, called Common Data Classes (CDCs). For example, the XCBR class is defined as the collection of the following DO, with the parent CDC in parentheses 1) Pos (DPC) Represents the position of the breaker as an instance of a DPC (Controllable Double Point) CDC. 2) BlkOpn (SPC) An instance of an SPC (Controllable Single Point) CDC used to block opening of the breaker. 3) BlkCls (SPC) Used to block closing of the breaker. 4) ChaMotEna (SPC) Used to trigger the spring charging motor. The above represent only the controls related DO in the XCBR LN. There are other categories of DO related to

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Fig. 2.

Description of static and dynamic parts of the sample two bus - one breaker system in IEC 61850 and CIM standards.

common information, measured and metered information and configuration of the circuit breaking function. In the list above the last DO is optional and may or may not be present in any given LN implementation. A second level of variation may be introduced since the CDCs themselves also contain mandatory and optional data attributes. Any DO (e.g. Pos) once again can be an instance of a derived class that implements all the Mandatory DA of the parent DO (in this case DPC) and may implement any subset of the Optional DA therein. This concept of extensibility carries through to the DAs as well. For the example shown in Fig. 1, a typical IED configured into a Substation will appear as an node inside the substation SCD file as shown in Fig. 2 2) SCD File Description: The SCD file also provides for a substation node that can describe the substation power structure along with a mapping of the substation functions to the different IED logical nodes. For example the representation

of a circuit breaker in the power system structure that is mapped to the XCBR1 LN instance of the IED represented above would appear within the substation node of the SCD. At the substation end, a SCD file as per IEC 61850 Standard specification has to be created. The SCD file is an XML file with a tree structure which contains all the information pertaining to the substation, as shown in the Fig. 2. The basic structure of SCD file consists of header, substation, communication, IEDs, CDCs and data templates. In this work, a GUI tool called “SCL Manager” developed by Kalki Technologies is used to create the SCD file. It is clear that the LNode tag is used to map the power system depiction of the circuit breaker (CECBR1 inside Bay2 in Voltage Level VL1) to the XCBR1 LN in the IED that actually controls that breaker. The Terminal tags indicate the connections of the breaker to different Connectivity nodes, thus providing the electrical network topology description.

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Hence, the SCD file format specified by the 61850 standards provides a detailed description of each element of the data served by an IED as well as its mapping to the power system SLD. 3) Mapping of IED with SCD: The problem definition for the mapping to CIM requires a resolution of the following questions: 1) How do we derive the actual structure of any data within a logical node served by an IED? 2) How do we map the data to the power system description (the single line diagram)? The IED above has an instance of circuit breaker LN named XCBR1, which is instance of a class derived from XCBR called XCBR2. The structure of this lnType is provided in the SCD file under a DataTypeTemplates section which can be drilled down into, to eventually find the list of all leaf data items and their basic types. This provides a standardized mechanism for mapping. Once the complete SCD file is known, any data attribute can be identified and extracted by its tag. For the example system shown in Fig. 1, the object name structure of the breaker status value would be represented by the string, “IED1/XCBR2$ST$Pos$stVal”. In other words, the status of the breaker can be known by retrieving the value of this tag from the IEC 61850 server.

Fig. 3. Overview of the mapping of IEC 61850 and CIM Standards. A is the mapping of both standards pertaining to static configuration of power system network. B is the Mapping of dynamic time-stamped data objects of both standards.

Id shown as ”Discrete1” for the sample system. This connection establishes a physical location to the measurements. Measurements can either be defined on the terminals or on the equipment as per the nature of the measurement and thus contain the correponding RDF Id of the terminal or equipment in their definition. Thus to make practical sense of the data in the CIM dynamic file one needs a corresponding CIM static file. III. M APPING OF IEC 61850 AND CIM S TANDARDS

C. Representation in CIM Standard 1) CIM Static File Description: The static data describes the configuration of power system network infrastructure. It includes exhaustive information about the different components like busbars, circuit breakers, generators and loads. that exist in the network of interest. This data changes only when there is any change in the physical structure of the network due to removal or addition of equipment. Consequently, the power system model represented in the CIM static file is to be maintained up to date with that of the network. Models can be exchanged between the utilities for their relevant studies. The sample two bus one breaker system shown in Fig. 1 contains ten objects under the CIM representation. Once these objects are identified their configuration and connectivity data can be represented as an XML/RDF file shown below. Unlike the SCD file which has a tree structure, the structure of CIM static file is flat and the interconnections between the equipment, their terminals and connectivity nodes are represented through RDF IDs. For example, in element 1 of CIM static file, ConnectivityNode1 is shown to be connecting Termina1 and Terminal3. The CIM static file for the sample system of Fig. 1 is shown in Fig. 2. 2) CIM Dynamic File Description: CIM dynamic file contains the time stamped real-time measurement data. For the sample system being modelled, there is only one measurement which is, status of the circuit breaker. This information is held in the measurement element identified by RDF Id ‘Measure1’ as shown in Fig. 2. Similarly, CIM dynamic file is a flat XML/RDF file with collection of all the measurements and their values at a time stamp. 3) Mapping of CIM Static File with Dynamic File: The CIM static and Dynamic files are connected with the RDF

In the last section, we have seen the description of four files, containing static and dynamic data of the system in both the standards. The mapping between these four files can be summarized as shown in Fig. 3. The left side files belong to the IEC 61850 standard where as the right side files belong to the CIM standard. Mapping of the elements of these files within the corresponding standards is shown as vertical arrows and is defined in the design of the standards itself. The mapping between the configuration files represented as ‘A’ and the mapping between the data files represented as ‘B’ is addressed in this paper keeping in view the requirements of a typical topology processing application. Fig. 3 can be further expanded to get the element-wise mapping details of the files. This is depicted in fig. 4. For clarity and better understanding, a tree structure of the SCD file and the IED file are shown with the essentially individual elements of the CIM static and CIM dynamic files as shown being interconnected with a line representing the linking by RDF Id. The mappings identified as A1, A2, etc., in the Fig. 4 are further explained below. A1 : The breaker elements of both standards are mapped. A2 : Logical node associated with breaker is analogous to the CIM DescreteValue object. A3 and A4 : The terminals associated with breaker in both the standards are also mapped. A5 : There is no Busbar element in the IEC 61850 standard and it uses Connectivity Nodes as Busbars. But in CIM, connectivity nodes are abstract constructs to show interconnection by tying together the terminals which belong to the connected equipment. In this process, the Connectivity Node, Terminal of Busbar and the Busbar elements of the CIM standard are mapped to the Connectivity node of the IEC61850 standard.

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Fig. 4.

Fig. 5. Model.

Detailed Mapping of standards IEC 61850 and CIM

Integration Mechanism for IEC61850 and Common Information

A6 : Similar to the mapping of A5, the other connectivity node of IEC 61850 is mapped to the combination of Busbar2, Terminal4 and Connectivity Node2 of the CIM. The example only shows the mapping of Busbars, Circuit Breakers, connectivity nodes and terminals. A similar approach can be used to map the elements of configuration data in either standards. B1 : Once the other three mappings as shown in Fig. 3 are defined, the mapping between the data objects gets defined. An integration mechanism for transfer of data from IEC 61850 compliant substation to a control center with CIM based topology processing application is shown in Fig. 5. The CIM dynamic file converter can be connected to multiple IEC 61850 clients which receive data from various IEC 61850 servers located at different substions. IV. CIM BASED T OPOLOGY P ROCESSING A PPLICATIONS CIM is primarily intended to achieve information interoperability, but can also be leveraged to achieve interoperability at application level. This can be done by designing applications that are CIM compliant, which does not need any adapters or converters to work on the data. A CIM Level application is an application which acquires its input data directly from

a set of CIM/XML files by sending queries which contain tags that are defined in the CIM standard. Such application can also take advantage of the object oriented structure of the CIM standard in the design of its internal algorithms for performing its function. For example, CIM based Network Topology Processing algorithm described below exploits the CIM defined hierarchy i.e. Equipment → Terminal → Connectivity node → Topology Node → Topology Island, for performing the topology processing. The CIM based topology processing algorithm takes both static and dynamic CIM files as inputs. In terms of objects defined in the CIM standard, the output of the topology processor is a grouping of connectivity nodes into topological nodes and further grouping of topological nodes into topological islands. The first grouping is done based on circuit breaker status information found in the dynamic CIM file, and the second level of grouping is done based on connectivity information found in the static CIM file. The algorithm design facilitates that entire file be processed once and then onwards only incremental changes be considered for updation of current topology. The topology processing algorithm first processes the static CIM file. Based on the information available in the static CIM file, the algorithm creates two lookup tables: 1. Conducting Equipment ↔ Terminal, and 2. Terminal ↔ Connectivity Node. These lookup tables are subsequently used to lookup corresponding values. For example, using the second lookup table created above, given the Terminal ID, we can look up which Connectivity Node is connected to it; or given a connectivity node we can know which terminals are connected to it. The processing of the Static CIM file and creating the lookup tables is a one-time job, and the lookup tables can be incrementally updated whenever there are any changes made to the system network configuration. The dynamic CIM file contains the timestamped information of status of all the circuit breakers. As and when the topology processing algorithm receives information about the status change of a circuit breaker, it acts up on it and updates the topology output. The algorithm for the topology analysis works on two rules as listed below. 1) If two connectivity nodes are connected by a circuit breaker (or a switching equipment) and the breaker status is “Closed”, then the collectivization nodes belong to the same topology node. 2) If two topology nodes are connected by any other equipment, then they belong to the same topology island. V. CIM IN I NDIAN S CENARIO Indian power sector is one of the fastest growing in the world with a current installed capacity of 146.7 GW. At the same time, it is also undergoing major restructuring. The five regional grids are being connected with strong inter-regional links to form a national grid to facilitate sharing of resources nationwide. Power Grid Corporation of India Limited (PGCIL) is the Central Transmission Utility and is responsible for management of the Grid. Each of the regional grids are operated by Regional Load Despatch Centers (RLDC) which are also being integrated to form a National Load Despatch Center

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(NLDC). Challenges in terms of interoperability, application integration and vendor independence are being faced. The power scenario is in a state of drastic change warranting creative, innovative and yet cost effective solutions for system integration. Research is going on in the field of design of open architecture for power control centers. Reference [18] describes the role of interoperability in the Indian power grid and argues the need of adopting CIM as a standard for information representation. Reference [19] outlines the initiatives towards achieving an Intelligent grid in India. Workshops on “Intelligent Grid” and “Substation Automation” are being conducted by various transmission and distribution utilities on a regular basis. Awareness on CIM and IEC 61850 standards is being generated among the personnel of utilities and the industry. In India, all the new substations that are being commissioned are IEC 61850 compliant. Thus, at the substation level IEC 61850 has already made its presence felt. Typical lifecycle for the control centers at regional level is around 10 - 15 years. India is geared towards adoption of standards and interoperability in the future. VI. C ONCLUSIONS This paper described an approach for mapping the objects of IEC 61850 and CIM standards keeping in view the requirements of a topology processing application. The mapping is then used to design an integration and data exchange mechanism between the two standards. Topology processing application based on CIM standard is also outlined. Eventually when both the standards are adopted by utilities in the future, a more exhaustive and concrete mapping of the complete standards would be needed. The scope and awareness of CIM in Indian power sector is also briefed. R EFERENCES [1] I. Xtensible Solutions, “CIM tutorial,” CIM User Group Meeting, Salt Lake City, Utah, pp. 87–89, Dec. 2006. [2] S. T. Lee, “The EPRI common information model for operation and planning,” in Proc. IEEE Power Eng. Soc. Summer Meeting, vol. 2, pp. 866–871, July 1999. [3] J. P. Britton and A. N. deVo, “CIM-based standards and CIM evolution,” IEEE Trans. on Power Syst., vol. 20, pp. 758–764, May 2005. [4] A. W. McMorran, “An introduction to iec 61970-301 and 6196811: The common information model,” University of Strathclyde, UK, Specification formal / 97-02-25, Jan 2007. [5] G. M. Huang and N. K. C. Nair, “Static and dynamic CIM-XML documents for proprietary EMS,” in Proc. IEEE Power Eng. Soc. General Meeting, vol. 2, pp. 1081–1086, July 2003. [6] A. W. McMorran, G. W. Ault, C. Morgan, I. M. Elders and J. R. McDonald, “A common information model (CIM) toolkit framework implemented in java,” IEEE Trans. on Power Syst., vol. 21, pp. 194– 201, Feb. 2006. [7] A. W. McMorran, G. W. Ault, I. M. Elders, C. E. T. Foote, G. M. Burt and J. R. McDonald, “Translating CIM XML power system data to a proprietary format for system simulation,” IEEE Trans. Power Syst., vol. 19, pp. 229–235, Feb 2004. [8] J. Wu and N. N. Schulz, “Overview of CIM-oriented database design and data exchanging in power system applications,” in Proc. of the 37th Annual North American Power Symposium, pp. 16–20, Oct. 2005. [9] R. Mackiewicz, “Overview of IEC 61850 and benefits,” in Proc. IEEE PES Power Systems Conference and Exposition PSCE’06, pp. 623–630, Oct. 2006. [10] T. S. Sidhu and P. K. Gangadharan, “Control and automation of power system substation using iec61850 communication,” in Proc. IEEE Conference on Control Applications (CCA) 2005., pp. 1331–1336, Aug. 2005.

[11] C. Hoga and G. Wong, “IEC 61850: open communication in practice in substations,” in Proc. IEEE PES Power Systems Conference and Exposition PSCE’04, vol. 2, pp. 618–623, Oct. 2004. [12] T. S. Sidhu and Y. Yin, “Modelling and simulation for performance evaluation of IEC61850-based substation communication systems,” IEEE Trans. on Power Delivery, vol. 22, no. 3, pp. 1482–1489, July 2007. [13] A. Taylor and D. Meadows, “Autonomous control algorithms using IEC61850,” IET 9th Intl. Conf. on Developments in Power System Protection, pp. 621–625, Mar. 2008. [14] J. Rodrigues, L. Soldani and G. Wong, “First substation with IEC61850 commissioned in the americas,” Transmission and Distribution Conference and Exposition: Latin America, 2006. TDC ’06. IEEE/PES, pp. 1–5, Aug. 2006. [15] J. Fan, H. Zhao, X. Wang, Y. Liu, and L. Ge, “A new design of modern power automation platform,” IEEE/PES Transmission and Distribution Conference and Exhibition: Asia and Pacific, Dilian, China, pp. 1–5, Aug. 2005. [16] T. Kostic, O. Preiss and C. Frei, “Towards the formal integration of two upcoming standards: IEC 61970 and IEC 61850,” IEEE Large Engineering Systems Conference on Power Engineering, pp. 24–29, May 2003. [17] Y. Serizawa, E. Ohba, T. Otani, S. Sato, T. Tanaka and T. Kobayashi, “Conceptual design for distributed real-time computer network architecture,” IEEE/PES Transmission and Distribution Conference and Exhibition 2002: Asia Pacific, vol. 1, pp. 26–31, Oct. 2002. [18] Y. Pradeep, A. Medhekar, P. Maheshwari, S. A. Khaparde, and R. K. Joshi, “Role of interoperability in indian power sector,” in Proc. GRID INTEROP FORUM Conference, Albuquerque, New Mexico, Nov. 2007. [19] Y. Pradeep, S. A. Khaparde, and R. Kumar, “Intelligent grid initiatives in India,” 14th IEEE International Conference on Intelligent Systems Applications to Power Systems (ISAP), Kaoshiung, Taiwan, Nov. 2007.

Yemula Pradeep is currently working towards Ph.D. degree in Electrical Engineering Department at IIT Bombay, India. His research interests include IT application in power systems and power systems restructuring issues. P. Seshuraju is currently working towards Masters degree in Computer Science Engineering Department at IIT Bombay, India. His research interests include system architecture, complex event processing applications to power systems. Shrikrishna A. Khaparde (M’87-SM’91) is a Professor, Department of Electrical Engineering, Indian Institute of Technology Bombay, India. He is a member of the Advisory Committee of Maharashtra Electricity Regulatory Commission (MERC). He has co-authored books titled, ”Computational Methods for Large Sparse Power System Analysis: An Object Oriented Approach,” and, ”Transformer Engineering: Design & Practice,” published by Kluwer Academic Publishers and Marcel Dekker, respectively. His research area includes distributed generation and power system restructuring. Vinoo S Warrier completed his engineering degree in production engineering and management from REC, Calicut University, India in 1995. He worked with MICO-Bosch in bangalore India for a period of 3 years before joining Kalkitech in 1999 and has been with Kalkitech since then in various capacities. He currently serves as the vertical head for the communication solutions vertical and oversees the product Engineering and Communication products business units of Kalkitech. His major Interest areas are Control and Automation, Embedded Systems and communication protocols. Sushil Cherian, Member IEEE, is President at Kalkitech Inc.,. He completed his B-Tech in Mechanical Engineering from NIT Calicut in 1995, and MS in Mechanical Engineering, Specializing in Control Systems from Colorado State University in 1998. He is an active member of the North American Synchro Phasor Initiative and his research interests include Wide Area Monitoring and Control and Advanced Control Applications.