Information Modeling for Distributed Energy Resource ...

Information Modeling for Distributed Energy Resource Integration in IEC 61850 based Substations Ikbal Alia, Mini S. Thomasb, Sunil Guptac and S. M. Suhail Hussaind a,b,d

c

Department of Electrical Engineering, Jamia Millia Islamia, New Delhi, India. Department of Electrical & Electronics Engineering, Maharaja Surajmal Institute of Technology, New Delhi, India Email: a [email protected], b [email protected], c [email protected], d [email protected]

Abstract— With the increasing deployment of Distributed Energy Resources (DERs) in the distribution system, DERs presents many challenges for smooth and stable operation of the grid. For the effective management of DERs extensive communication between different components of DER and distribution system is required. To standardize the communication methods and modeling of logical nodes required for Intelligent Electronic Devices (IEDs) in DERs, data modeling of DERs is issued in IEC 61850-7-420 standard. This paper has contributed communication modeling of Green Energy Resources (GERs) and other DERs, modeling of messages exchanged among different IEDs with regard to their optimum structure & size and a Substation Communication Network (SCN) topology. End to End (ETE) time delay performance of the designed communication configuration architecture is presented using OPtimized Network Engineering Tool (OPNET). The dynamic performance result in the SCN has demonstrated the successful communication configuration for integrating the DERs in distribution system. Keywords— Communication Modeling, Distributed Energy Resources, IEC 61850; OPNET, Substation Automation System; SCN

I. INTRODUCTION Generation of electrical energy from fossil fuels is currently the single largest source of carbon dioxide emission in the world's atmosphere, making it a significant contributor to climate change or global warming [1]. This has negative consequences for society in general [2]. Though Green Energy Resources (GERs), especially solar and wind, provide alternative energy source in abundance but there is an uncertainty associated with their power output levels due to their dependence on climatic conditions [3]. Hence, are not fit to provide required quality power to the end user’s needs when acting alone [4]. In a scenario, when load demand is growing rapidly, to mitigate the consequences of climate change and to satisfy the increasing demand for power, integration of GERs/Distributed Energy Resources (DERs) to the traditional power grid becomes inevitable [5], [6]. However, increased penetration of DERs in the distribution system has posed many challenges in the operation of distribution system. The communication architecture plays an important role in smooth functioning of DER integrated distribution system. 978-1-4673-6540-6/15/$31.00 ©2015 IEEE

Robust, deterministic and interoperable communication architecture is essential in order to ensure that all DER components exchange information, control commands and real time measurements effectively without any delay or loss. High cost and complexity involved with proprietary communication protocols for integrating DER devices in distribution system has come up with major issues, and demands for communication interoperability among multivendor devices for implementation of communication architectures. IEC 61850-7-420 [7] as an extension to IEC 61850 [8] is a widely accepted standard to standardize the communications between DERs and other equipment. In literature IEC 61850 based communication architectures for automation, protection and monitoring of substations has largely been reported [9], [10]. References [11], [12] have proposed IEC 61850 communication based distribution system protection schemes. Taha et al. [13] and Apostolov [14] presented the object modeling of DERs with IEC 61850-7-420 and its extensions from the control and communication point of view. Kanabar et al. [15] presented the study of different communication systems between DERs and IEC 61850 based distribution system. Communication modeling of GERs/DERs and modeling of messages has led to smooth integration of Green Energy, e.g. solar and wind etc., in the distribution system. SMART, i.e. Standard based, Multi-layered, Available, Resilient and Timely, management has provided secure, reliable and stable electricity supply to the end users. SMART management is made possible through a robust, redundant and deterministic SCN topology. Therefore a hybrid of the GERs and other DERs, SMARTly managed and integrated through robust, redundant and deterministic SCN, is crucial to provide a sustainable, environment friendly and energy efficient power system. This paper presents the information modeling of DER IEDs according to IEC 61850-7-420 and its extensions. Further, an innovative SCN architecture incorporating both communication and components redundancy is proposed. OPtimized Network Engineering Tool (OPNET) modeler is used for the performance simulation of this proposed SCN architecture integrated with DER in distribution system using wired communication technologies [16]. The paper is organized as follows: Section II provides a brief description of IEC 61850 object modeling and communication approach, Section III explains the

communication modeling of IEC 61850 substation IEDs and different DERs system according to IEC 61850-7-420, and Section IV discusses the detailed modeling and the simulation study of communication between different DERs and distribution system using wired communication technologies in OPNET. Finally, Section V presents conclusion. II.

IEC 61850 OBJECT MODELING & COMMUNICATION APPROACH

IEC 61850 provides an object oriented modeling approach for power system devices to organize data, configure objects and map them on to protocols, so that they are consistent and interoperable. IEC 61850 standardized data models and ACSI services are mapped over standard communication protocols and hardware such as Transmission Control Protocol (TCP)/Manufacturing Message Specification (MMS) and Switched Ethernet, to make this standard a future proof standard. To reduce the additional overhead caused by TCP/IP layers in transmission time performance, real-time and mission-sensitive messages such as Sampled Values (SVs) from Merging Units (MUs) and Generic Object Oriented Substation Event (GOOSE) messages are mapped to the Ethernet layer of the ISO/OSI communication stack as shown in Fig.1. Further, Network traffic segregation and prioritization through network management features in switched Ethernet avoids delays and plays an important role in the design and real time performance protection applications. Thus, IEC 61850 communication approach and switched Ethernet ‘QoS’ features such as RSTP (IEEE 802.1w), full duplex, priority tagging (IEEE 802.1p), VLAN (IEEE 802.1q), multicast filtering and others allow system designer to optimize the SCN architecture as per IEC 61850-5 performance requirements taking into consideration the constraints of the system [17].

IEDs to the substation. Table I gives the time requirements of different messages of distribution substation and DERs. TABLE I. Information Type Protection information Monitoring and control information

MAXIMUM MESSAGE DELIVERY TIME Internal in substation (ms) 0-4 16

External (DER) to substation (ms) 8-12 1s

IEC 61850 was initially proposed for substation automation systems SASs) later it was extended to utility automation. The new extensions of the standard such as part 7420 defines the logical nodes for DERs, part 90-1 describes the communication between two substations, part 90-5 describes the use of IEC 61850 to transmit synchrophasors information according to IEEE C37.118, part 90-7 describes the Object Models for DER inverters, etc. III.

COMMUNICATION MODELLING OF SMART SUBSTATION AND DER SYSTEM

Non-Conventional Instrument Transformers (NCITs), MUs, Protection & Control IEDs (P&C IEDs), Ethernet switches (ESs), Time Synchronization (TS) sources, and Circuit Breaker IEDs (CB_IEDs) etc. are a part of IEC 61850 SAS. Bay level P&C IEDs are independently connected to process level equipments such as MUs, NCITs through a process bus network. MU IEDs transmits process level data in the sampled value format, as per IEC 61850-9-2 ‘LE’ guidelines, to the bay level IEDs for necessary protection and control functions. CB_IEDs controls the status and condition of circuit breaker on the basis of tripping, status and interlocking commands from P&C IEDs.

Fig. 2. Single line diagram of a typical 220/132 kV D2-1 type substation. Fig.1. ISO/OSI 7-layer communication stack of IEC 61850

The IEC 61850-5 standard specifies the time requirements of IEC 61850 SAS messages, but the time requirements for DERs connected to distribution system are not specified. IEEE 1646 standard [18] gives the time requirements to different types of information messages for external or remote or DER

Fig.2 shows the single line diagram of D2-1 type substation that consists of six (F1-F6) feeder bays), two (TI&T2) transformer bays and one(S) bus section bay [9]. Fig. 3 shows the redundant SCN architecture, drawn for 220/132 kV substation, as shown in Fig.2, where each feeder bay has one MU IED, two P&C IEDs, and one CB_IED. Each transformer bay and bus section bay has two MU IEDs, one CB_IED, and two P&C IEDs.

F2_IEDS_MAIN_2

F6_IEDS_MAIN2

TS

T1_IEDS_MAIN2

T2_IEDS_MAIN2

S_IEDS_MAIN2

STATION_SWITCH_2

CB_IED2 MU_IED2

Process Data P&C_IED2

Trip Signal

STATION_SWITCH_1

Interconnected Links connecting inter-bay Ethernet switches of two ring networks F1_ES11

F2_ES22

F6_ES66

T1_ES11

T2_ES22

S_ES22

Ring 1 Network Ring 2 Network

F1_ES1

F2_ES2

F6_ES6

T1_ES1

T2_ES2

S_ES1

Links connecting Bay IEDs to its own bay switch Links connecting Bay IEDs to the adjacent bay switch

P&C_IED1 TS CB_IED_1 MU_IED1

F2_IEDS_MAIN1

F6_IEDS_MAIN1

T1_IEDS_MAIN1

T2_IEDS_MAIN1

S_IEDS_MAIN1

Redundant NCITs & CB Trip Coils

Fig. 3. Innovative IEC 61850 SCN architecture.

This design of this innovative and conceptual SCN architecture is based on the fact that current substation IEDs have redundant Ethernet communication ports. These IEDs run DHP to automatically switch over the communication to back up port when the primary port fails, and hence maintains the continuity and stability in substation operations [19]. This SCN architecture can be generalized to any substation. The way network component redundancy as well as the communication links redundancy is incorporated is the USP of this innovative SCN architecture. This makes this architecture free of single-point-failure, link failure, component failure and

even a protection systems failure. The communication model of GERs/DERs and Substation components is developed using the basic logical nodes (LN) in IEDs. Logical nodes are group of data objects which serve specific functions. The IEDs associated with specific GER/DER/substation components contains the relevant logical nodes needed for communication, according to functions performed by them. The logical nodes associated with different types of GERs like photovoltaic, wind plant and DERs like diesel plant, CHP plant are shown in Fig. 4.

Fig. 4. Organization of DER logical nodes and Logical devices at ECP [7]

IEC 61850-7-420 defines the logical nodes for DER systems except for wind power plant which are defined in a separate standard IEC 61400-25-2 [20]. These logical nodes and data classes are in accordance or compatible with the nodes defined part 7-4.The DER system communication IEDs are modeled with relevant logical nodes defined in the IEC 61850 standards. Modeling of following types of DER systems is presented: 1. Photo Voltaic (PV) system 2. Diesel Generator system 3. Wind plant system Each DER plant is connected to the distribution substation via Electrical Connection Point (ECP). At this point of connection a circuit breaker and metering devices are present. Fig. 4 shows different logical nodes associated with the DER system components. Every DER plant is modeled to have 4 IEDs – ECP control IED, DER control IED, Breaker IED and Measuring Unit (MU) IED. ECP control IED receives the settings, commands or modes from the control center and sets the implement the same at DER. DER control IED corresponds to the controller of each DER which sets or controls the different parameters of the DER plant. Breaker IED corresponds to the circuit breaker connecting DER to the substation and Merging Unit IED corresponds to the CT and PT at the ECP. IV. MODELLING AND SIMULATION USING OPNET

standard and customized network nodes. Table II enlist different network nodes with their description. Fig. 5 shows the customized node models developed in OPNET node model editor, which supports GOOSE, Sample Values and MMS type of traffic. The Merging Unit IED only sends Sample values to other IEDs, in which data is directly mapped on to the MAC layer, is modeled as ‘ethernet_station_adv’ node.

(a)

A. IED Modeling Opnet modeler provides Proto-C based object-oriented modeling approach, with many editors such as Project editor, Node editor, Process editor, Packet editor for detailed customization of the dynamic models of IEC 61850 substation/DER system IEDs, Ethernet switches and fiber optics communication links. TABLE II.

NETWORK NODES AVAILABLE IN SIMULATED SCN ARCHITECTURE

SCN component Type

OPNET Node Model

MU IED

ethernet_station_adv

P&C IED

ethernet_wkstn_adv

CB_IED

ethernet_wkstn_adv

Ethernet switch

ethernet16_switch_ adv

Full Duplex, 100 Mbps

100BaseFX_adv

Full Duplex, 100 Mbps

ethernet_wkstn_adv ethernet_server_adv

Standard Standard

Fiber optics communication links Station PC Server

Description Standard (Support SVs Stack) Customized (MMS & GOOSE stack) Customized (MMS & GOOSE stack)

From Fig. 4 it quite clear that the breaker IED, DER Control IED and ECP control IEDs receive or send the GOOSE, Sample Values and MMS type messages. Hence, the simulated SCNs and DER system make use of the available

(b) Fig. 5. Customized Node models (a) MU IED, (b) Breaker and control IEDs.

B. Simulation and Traffic Modelling Fig. 6 shows the OPNET modeler’s simulated DER system integrated with the proposed SCN. The detail modeling and simulation of the substation can be obtained from [9]. The DER system and all the substation bays are modeled as subnets in project window of OPNET. Each subnet contains

Fig. 6. OPNET’s simulated Innovative SCN architecture with DERs integration.

its corresponding bay IEDs and a bay Ethernet switch. The SCN also consist station server and station PC which are connected to station switch, also all bay switches are connected to the station switch. The DER’s subnet, which contains the DER IEDs and a switch, is connected to the station switches of SCN. The IEC 61850 substation/DER IEDs basically exchange three types of messages. First are the trip/open commands which are exchanged between substation P&C IEDs/DER control and Breaker IEDs. Sometimes these commands are also issued from substation control PC to DER breaker IED. TABLE III.

SIZE OF DIFFERENT MESSAGES EXCHANGED BY DER IEDS

Type of message Trip commands

Source IED

Destination IED

DER Control IED P&C IEDs (substation) Station PC

Sample Values

MU IED

Status Update

DER control IED DER Breaker IED

Packet Size (bytes) 98

DER Breaker IED

substation server/station PC. Table III & IV gives details of the traffic configured in SCN through ‘Application Configuration’, ‘Profile Configuration’, and ‘Task Configuration’ windows of OPNET for all the SAS applications [10]. TABLE IV.

Type of Message

Source IED

Sampled Packets Protection Controls

MU IED

102

DER Control IED Server

150

200

Second types of messages are the sample values of process data from substation CTs/VTs or the current and voltage values at the ECP of DERs. The Merging Unit IEDs send these messages to their corresponding substation P&C IEDs/DER control IED. Third type of messages is status updates in which the substation P&C IEDs/DER controls IEDs and breaker IEDs constantly updates their status to the

Value

P&C IED

File Transfer Status Update

TABLE V.

DER Control IED Server

SIZE OF DIFFERENT MESSAGES EXCHANGED BY SUBSTATION IEDS

Message Type GOOSE Sampled Values MMS Traffic

P&C IED, CB IED

Destination IED P&C IED

Size (Bytes) 102

CB IED P&C IED, CB IED Server Server

104 200 1 MB 200

PERFORMANCE EVALUATION OF 100 MBPS WIRED LAN FOR MESSAGES FROM DER TO SUBSTATION Delay (ms) 0.11 0.14 0.22

100 Mbps Throughput (Kbps) 80 3500 1000

1000 Mbps Delay Throughput (ms) (Kbps) 0.08 80 0.106 3500 0.203

1000

The performance of the communication network is studied for wired configurations. In Fig. 6, the simulation of SCN using wired technology in OPNET Modeler software is presented. Here 100 Mbps wired communication links between DER IEDs and DER switch; and between DER subnet and substation switch are considered. The distance between the substation and DER for the simulation is considered to be 5 km. For the performance evaluation of the SCN architecture, the ETE delay for time-critical messages

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