A synchronized generic substation events tripping circuit monitor for ...

INTERNATIONAL TRANSACTIONS ON ELECTRICAL ENERGY SYSTEMS Int. Trans. Electr. Energ. Syst. 2015; 25:1–16 Published online 24 October 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/etep.1814

A synchronized generic substation events tripping circuit monitor for electric substation applications Yang Liu1,2*,†, Rastko Zivanovic2 and Said Al-Sarawi2 2

1 ElectraNet Pty Ltd, 52-55 East Terrace, Rymill Park, Adelaide, SA 5000, Australia School of Electrical and Electronic Engineering, The University of Adelaide, SA 5005, Australia

SUMMARY Substation automation system consists of intelligent electronic devices, substation computer and a communication network between them. The network is used for control implementation, protection and monitoring tasks in substations. This paper presents a tripping circuit monitor (TCM) that accurately translates substation event information into a binary data representation using nonintrusive current transducers. The data are then transmitted using generic object oriented substation event message format, which is defined in the latest substation communication standard IEC 61850, onto local Ethernet network. The TCM is also capable of implementing either IEEE 1588–2002 or IEEE 1588–2008 standards to provide synchronized time stamp value for each translated binary data within sub-microsecond accuracy. The substation event data, which is captured by the TCM module, have a number of applications in current electric substations. The main application of the TCM device is to provide a communication interface between electromechanical relays and modern numerical intelligent electronic devices. Other possible applications include improving substation system-wide testing and enhancing substation topology processing in supervisory control and data acquisition systems. Test results that demonstrate the operation of the new TCM module are also presented in the paper. Copyright © 2013 John Wiley & Sons, Ltd. key words:

GOOSE; IEC 61850; synchronization; IEEE 1588; substation events

1. INTRODUCTORY BACKGROUND Under the growing demand of power consumption, electric utilities face the challenge on how to make the power system operation more cost effective and preserve a high level of reliability and security [1]. In response to the challenge, it is desired to integrate advanced technologies with existing power system. This article provides a practical approach of utilizing the developed tripping circuit monitor (TCM) module to address this challenge and discusses the benefits in applying this approach for electric utilities. Electrical substations generally include primary devices, such as power transformers, bus bars, circuit breakers (CBs) and instrument transformers, which are arranged in switch yards. These primary devices are operated in an automated way via a substation automation system (SAS), which is responsible for controlling, protecting, measuring and monitoring in substations. The SAS often comprises of intelligent electronic devices (IEDs) that are interconnected using a communication network, which is needed to facilitate the required interaction with the primary devices via a process-level interface. In a traditional SAS system, the binary input/output information is transmitted via conventional control circuits with copper wires. The binary information is mainly utilized in two ways: First, it allows confirming the current status of both primary equipment and secondary IEDs outputs. This status data are used for real-time substation protection and control functions (e.g. inter-tripping and interlocking).

*Correspondence to: Yang Liu, School of Electrical and Electronic Engineering, The University of Adelaide, SA 5005, Australia. † E-mail: [email protected] Copyright © 2013 John Wiley & Sons, Ltd.

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Second, the binary information is used for monitoring and recording all state changes during the operation of primary and secondary plants that are initiated by substation events. Collected data are then utilized in event analysis of the system. In recent years, substation communication standard IEC 61850 [2] has been well accepted by transmission and distribution network service providers. The preliminary goal of the IEC 61850 standard is to define an interoperable communication system via Ethernet for exchanging the information between devices within a substation and standardize protection and control designs for better reusability with plug-and-play solutions [3]. The interoperability and flexibility of the IEC 61850 standard has enabled enormous applications in electric transmission and distribution networks. The recent discussion has brought the IEC 61850 standard towards the concept of Smart Grid [4–8]. There are also many proposals on applying the IEC 61850 standard at distribution level as well as microgrid [9–12]. In particular, the IEC 61850-7-420 [13], which is an extension of the IEC 61850 standards, is aimed to cover the information model of distributed generation under the concept of microgrid [10]. Due to the popularity of electric vehicles, a further extension to define the information model of electric vehicles in IEC 61850-7-420 standard has also been proposed in [14]. The greatest benefit of implementing the IEC 61850 standard is the lowered installation, maintenance and engineering costs, because the traditional copper wires for protection and control applications can be replaced with a digital communication over Ethernet cables [2]. The projected view on the new generation of substation communication infrastructure introduces many challenges on substation communication network topology, redundancy, clock synchronization and management options that drive the adoption of new IEDs to be applied to future electric substations [15–18]. Because of the nature of the IEC 61850 standard, it can be only realized in modern numerical protection relays while there are still a large number of legacy electromechanical (EM) relays in service in electric substations at present. In order to unify the protection and control equipment during substation extension or network augmentation, the electricity utilities tend to replace the EM relays with numerical IEDs. Such replacement process could significantly reduce the economic value of the substation asset [19] because the EM relays are still reliable and able to meet all protection and control requirements in a substation, especially in the substation with harsh environment. Therefore, a communication interface between legacy EM protection system and numerical IEDs is needed under such situation. The framework of the integration between the legacy protection system and modern IEDs has been introduced in [20]. The communication interface shall be reliable, low cost, nonintrusive and interoperable with numerical IEDs to raise the economic value of the substation instead of replacing the whole legacy EM protection and control system. Because of the earlier reasons, a TCM module was developed. The module is capable of translating any direct current (DC) control signals (e.g. EM relay trip circuit) in a substation into binary data very accurately using nonintrusive current transducers. Such data are then transmitted via generic object oriented substation event (GOOSE) messages on an Ethernet network, which is defined in IEC 61850 standard. To the best of our knowledge, there is currently no commercial product that could provide the same level of service. A brief system configuration is shown in Figure 1. The GOOSE messages are received by numerical IEDs to establish the needed translation between the old and new protection systems. The developed TCM module also implements a highly accurate time synchronization standard, IEEE 1588. The reason for providing a precise time value for each status change is that the TCM modules would be installed at various points on a local area network (LAN) within a substation control room, and it is sensible that the captured control signals have a precise common time reference. The TCM module utilizes either IEEE 1588–2002 or IEEE 1588–2008 time synchronization standard [21,22], which are also known as Precise Time Protocol version 1 (PTPv1) and version 2 (PTPv2), respectively. In addition, both IEC Smart Grid Vision and US National Institute of Standards and Technology standardization ‘roadmaps’ recommend the use of PTP for high accuracy time synchronization in substations [23,24]. Although introducing the new TCM device in a substation is an additional risk of device failure or malfunction, the TCM device could still be a more attractive option from financial perspective against entire secondary system replacement in a substation. Moreover, the TCM device would be applied to a redundant protection system in a substation that eliminates certain probabilities of device failure from occurring. Copyright © 2013 John Wiley & Sons, Ltd.

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Figure 1. Brief configuration of TCM.

The novel approach of applying the TCM module as a communication interface between legacy EM relays and numerical IEDs could be further extended in system-wide testing and topology processing for supervisory control and data acquisition (SCADA) system. This paper highlights the construction of the developed TCM device and illustrates the benefits of applying the device in industrial projects. This paper is organized as follows: Section 2 provides a brief review on the characteristics of the IEC 61850 and the IEEE 1588 standards. Section 3 describes the components of TCM module. Then, the test results and functionalities of the TCM module are presented and discussed in Section 4. Finally, the TCM module applications are provided in Section 5.

2. CHARACTERISTICS OF THE IEC 61850 AND THE IEEE 1588 STANDARDS 2.1. Characteristics of the IEC 61850 standard The developed IEC 61850 standard is an abstract application layer protocol [11,25] that specifies two main group of communication models, the client/server [26] and publisher/subscriber [27] models. The term ‘abstract’ indicates the standard only describes the provided services of a substation device. In terms of how such services are built in the device are not described in the standard. The IEC 61850 standard supports substation related functions by using object oriented data models. Such data models outline the processes that shall be implemented and controlled in all substation functions. As a result, IEC 61850 standard divides the SAS functions into sub-functions, which are also known as logical nodes (LN). Each LN includes a number of data attributes to provide better representation of a subfunction in a substation device. There are two specific infrastructure LNs defined, the physical device logical node and logical node zero. Physical device logical node is utilized for accessing hardware related data of an IED, whereas logical node zero is utilized for accessing logical device related data of an IED [11]. In addition to the object oriented data models, the IEC 61850 standard also defines generic services on the foundation of publisher/subscriber communication structure between devices, such as GOOSE, to transmit data under the transmission requirements of speed, reliability and security [25]. The high speed characteristic of GOOSE communication is well suited for the transfer of time-critical data where reliability and security are achieved by repeating the messages a number of times [28]. Copyright © 2013 John Wiley & Sons, Ltd.

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2.2. Characteristics of the IEEE 1588 standard The mechanism of IEEE 1588 (PTP) is based on a master/slave protocol. The PTP synchronization is generally achieved by running two procedures in parallel. The first procedure is called syntonisation, which is responsible to run the slave clock at the same pace as the master. At each configured synchronization interval, the time master sends a Sync Message, which contains the send time t1k, to time slaves on the network. The time slave records both the send time t1k and the receive time t2k in order to adjust its clock until the time intervals are equal on both clocks. This process can be represented as the following equations: t1 kþ1 –t 1 k ¼ t 2 kþ1 –t 2 k t2 kþ1 –t1 kþ1 ¼ t2 k –t1 k According to the standards [21,22], there are two options to transport time stamp t1k from the master to the slave. One option is known as one-step mode. In this configuration, the time master inserts the precisely measured time at which the message leaves the master into the Sync Message and sends to the connected slaves. The other option is known as two-step mode. In this mode, the time master sends Sync Messages with estimated time values. In parallel to this process, the time master also sends a separate Follow_Up message that contains the precise time to the connected slaves. The second procedure is to determine the delay from the slave to the master. This is achieved by measuring the two-way delay, which is the round trip time between the master and slave. For the downlink from the master to the slave, t1 and t2 are available from the last Sync Message. The uplink from the slave to the master is acquired by exchanging Delay_Req and Delay_Resp messages. The slave sends a Delay_Req to the master and marks the time t3 when message leaves. In responding to the request message from the slave, the master sends back a Delay_Resp, which contains the time t4 that it received the Delay_Req message. The slave records both t3 and t4 calculates the one-way delay and offset from the master under the assumption of a symmetric transmission path as the following: Delay ¼ ½ðt 2 –t 1 Þ þ ðt 4 –t 3 Þ=2 Offset ¼ ½ðt 2 –t 1 Þ–ðt 4 –t 3 Þ=2 As an improvement of IEEE 1588–2002 (PTPv1), the IEEE 1588–2008 (PTPv2) software is designed with the potential of much higher synchronization accuracy. This is achieved by raising the limit of time stamp resolution from 1 ns in PTPv1 messages [21] to 216 ns in PTPv2 [22]. Another main difference between the two versions is the structure of the Sync Message. The Sync Message in PTPv1 is 124 octets long, which consist of a time stamp and additional information for best master clock algorithm [21]. In contrast, the functions of Sync Message in PTPv2 are split into two messages [22]. One of the messages is a 44 octet long Sync Message that is dedicated for synchronization. The other message is an Announce Message for best master clock algorithm. Therefore, the message rate can be configured individually. It is typical that the Sync Message is sent at higher rate than Announce Message. Two synchronization tests were performed to acknowledge the difference between PTPv1 and PTPv2. A Precise Time Protocol daemon, available as open source software [29], was implemented to achieve the synchronization of PTPv1. The synchronization of PTPv2 is achieved via commercial PTP software from IXXAT Automation GmbH [30].

3. TRIPPING CIRCUIT MONITOR COMPONENTS In a substation, every status change of a target device (i.e. circuit breaker or CB) is associated with a change of DC flowing through the control wire of the CB. The typical CB control wiring in a substation is shown in Figure 2. Such DC current change can be captured via current transducers. The current transducer is designed with Hall effect sensor that was built in a small clamp to detect the magnetic field that is associated with current change in the wires of relay device. Such design ensures a nonintrusive measurement making it attractive for use in all running substations. The use of current transducer in a live substation has also been considered as much safer than running hard wired analogue signals. A picture that illustrates the design of the current sensor is shown in Figure 3. Copyright © 2013 John Wiley & Sons, Ltd.

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Figure 2. Typical circuit breaker control wiring.

Figure 3. Hall Effect current transducer device.

For example, a relay closes its output contact to trip a CB as illustrated in Figure 2. Any current change in the control wires of the relay can be detected by clamping a current transducer onto it. The current transducer then produces a short voltage pulse to indicate the action from the protection relay. The voltage pulse is then passed to the conditioning circuit to convert it to a suitable voltage level for an embedded computer. The detailed design of TCM module is illustrated in Figure 4. Such conditional circuit board acts as a two-channelled bridge between the transducer and an embedded computer. For each channel, the signal from the sensor is amplified, reshaped and conditioned to a suitable voltage level for the embedded computer. The current transducers together with the conditioning circuit have a sensitivity of picking up any current flowing at value over 200 mA without any turns on the wire. The processed signals are then sent to the general purpose input/output ports of the embedded computer board and stored in binary format. The second channel of the conditioning circuit

Figure 4. Developed TCM module. Copyright © 2013 John Wiley & Sons, Ltd.

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generates an interrupt pulse using a simple combinational logic. The generated interrupt is a 1 μs pulse width with +3.3 V amplitude. Such pulse is then delivered to an IEEE 1588 pin-header on the embedded computer board to trigger a time-stamping function. The embedded computer board is the core component of the monitoring module. It performs timestamping function and transmits the collected data via GOOSE messages on an Ethernet network. The following characteristics were considered during the selection of embedded board: • Support for IEEE 1588 standards (PTPv1 and PTPv2). This ensures high level system synchronization with a known time reference. • Hardware assisted time-stamping to allow for accurate time stamp value [31]. Therefore, each substation event is recorded with precise time information. • Ethernet networking to implement the IEC 61850 standard. • Easy to programme communication under IEC 61850 standard. • Low cost. With the earlier criteria in mind, the MPC8313E development system [32] from Freescale Semiconductor was selected. This board has a 32 bit PowerPC microprocessor, a GNU/Linux operating system and an on-board network switch with five Ethernet ports. Most importantly, the system provides hardware time-stamping function when exchanging PTP messages. Such feature can be utilized when implementing either PTPv1 or PTPv2 algorithms for accurate calculation of the time offset [31]. The software in the project is developed using C programming language. As a part of the software, a Linux kernel driver has been developed for acquiring memory regions as the data of current transducers, as well as handling the interrupt from the conditional circuit. The IED capability description (ICD) file of the TCM module and the data encoding to GOOSE messages are based on a commercial library provided by OMICRON electronics GmbH. In general, the ICD file of an IED describes all functionalities in the device by accommodating relevant LNs. The ICD file is in Substation Configuration Language format based on eXtensible Markup Language version 1.0. The ICD file of the TCM module contains several Generic Process I/O [33] LN, which specified the most suitable data attributes for the device, status input data and its time stamp value. Both information is encoded into GOOSE messages and transmitted over an Ethernet network.

4. TEST RESULTS The synchronization accuracy was tested separately via PTPv1 and PTPv2 because of the different structure of synchronization messages. The setup diagram of PTPv1 synchronization test is shown in Figure 5, where two identical MPC8313E boards (TCM 1 & 2) were synchronizing with the time master. The MEINBERG M600 PTPv1 time server [34], which was the time master, was connected to a GPS antenna to obtain an absolute time reference. The test was carried out for over 14 h, and the results are shown in Figure 6. The figure shows the relationship between 1-pulse-per-second (1-PPS) signal from the master and two 1-PPS signals from the two TCM modules. The oscilloscope was configured as infinite persistence for the entire period of testing. From the figure, it is clear that the two 1-PPS signals from the two TCM modules are within the range of 200 ns from the 1-PPS signal of the master. The test result indicates that the integration of Precise Time Protocol daemon and hardware time-stamping feature can achieve a high level of synchronization. The PTPv2 synchronization test setup is shown in Figure 7. The setup consists of one MPC8313E board (TCM module) with its on-board network switch and MEINBERG M600 PTPv2 time server [34]. A GPS antenna was also connected to the time server to obtain an absolute time reference. The synchronization was achieved by executing IXXAT PTPv2 programme on MPC8313E board with a minimum filter in order to eliminate the white noise of the nonindustrial network switch. The synchronization interval on both the PTP Master and the TCM module was configured as 3, which is 8 Sync Messages per second. A total number of 28 443 samples were collected and analysed. The test results are shown in Figures 8 and 9. The data from synchronization start-up phase are shown in Figure 8. The TCM module was synchronized with the PTP Master within 100 ns range in 20 Sync Message packets, which is Copyright © 2013 John Wiley & Sons, Ltd.

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Figure 5. PTPv1 synchronization test setup diagram.

Figure 6. PTPv1 synchronization test result.

approximately 2.5 s. The synchronization accuracy was stabilized to be within 50 ns in 40 Sync Message packets, which is approximately 5 s. The PTP performance upon the stabilized synchronization is shown in Figure 9. The test result indicates the synchronization accuracy was well maintained at ±50 ns level during the test with standard deviation of 22.16 ns. The test result also confirmed that PTPv2 has significantly improved from PTPv1 in terms of synchronization accuracy. As a result, it is expected that PTPv2 will dominate future applications in a substation with synchronization requirement, especially in the areas that IEC 61850 standard is implemented. Copyright © 2013 John Wiley & Sons, Ltd.

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Figure 7. PTPv2 synchronization test setup.

Figure 8. PTPv2 performance at synchronization start-up phase.

Although the PTP software test results were satisfactory, there was an additional delay within the TCM system that should be taken into account. The delay is due to the signal propagation between the actual state change in a DC control wiring and obtaining a synchronized time stamp value for the detected change. This delay is caused by the response time of the Hall effect sensor together with the employed logic circuit. According to the manufacture datasheet of the current transducer, a typical response time of 3 μs is specified [35]. In order to further prove the response time specification, an additional test report has been provided by the manufacturer. The test report has shown the response time of the current transducer is less than 3 μs under different strength of electromagnetic field. Furthermore, the time delay of the employed logic circuit in the TCM module was measured separately. The result of this measurement is shown in Figure 10. From the measurement value at the bottom of Copyright © 2013 John Wiley & Sons, Ltd.

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Figure 9. PTPv2 performance histogram and standard deviation.

Figure 10. Combinational logic delay measurement.

Figure 10, the delay between receiving the sensor signal (bottom signal) and generating an interrupt pulse (top signal) is found to be 16.20 ns. As a result, an overall delay of 2.0162 μs has been compensated at the programming level when capturing time stamp values. Therefore, the overall system time synchronization performance is achieved at ±1 μs level. Copyright © 2013 John Wiley & Sons, Ltd.

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The GOOSE transmission test was performed to verify that the monitored status data, and its time stamp value are properly encoded in the GOOSE messages from the TCM module. The test was performed by using Wireshark software [36]. The free software is able to capture any GOOSE messages on Ethernet network and display its content. A screenshot of Wireshark software during the test is shown in Figure 11. At the top of Figure 11, several GOOSE messages, which were from the TCM module, are shown in coloured background. The message No. 14 is described in detail in the middle section of the figure. Among the subscribed information, the status data of three control signals are shown at the bottom of the figure. The status data are labelled as Boolean (TRUE/FALSE). The synchronized time value of each event is displayed in hex format as labelled ‘t’ in the figure. The rest information such as GOOSE control block reference, goID and GOOSE state number are also displayed in the figure. The test result confirmed that the monitored status and its time stamp value are properly encoded in the GOOSE messages. It has been well established in IEC 61850–5 standard that the total network transfer time for a Type 1A trip in Performance Class P2/3 shall be in the order of 3 ms [37]. The transfer time is further specified in IEC 61850–10 standard that an IED shall take 40% of 3 ms (1.2 ms) to encode a GOOSE message and deliver it on Ethernet network [38]. A speed test that measures the time for both data encoding and GOOSE delivery was also developed as part of the software. The speed test confirmed that the GOOSE message has been encoded and delivered in approximately 48 μs when a state change was detected in a DC control wire. It is clear that the demonstrated GOOSE delivery time is well below the specified time by the IEC 61850–10 standard. Although the GOOSE communication has been established, it is not guaranteed that the TCM module is interoperable with other protection relays from different vendors [39]. Therefore, a compatibility

Figure 11. GOOSE message transmission test. Copyright © 2013 John Wiley & Sons, Ltd.

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test has been performed between the TCM module and SEL-387 current differential relay. The setup diagram of the test is shown in Figure 12. In the test, the TCM module was used to monitor the flowing current in the wire, which is connected to a DC power supply and a thermal resistor. When there was a current flowing in the wire, the TCM module would detect the change on the flowing current and drive its encoded status data to high in the GOOSE messages. The ‘Remote Bit 1’ of the SEL-387 relay was configured to subscribe to the status data in the GOOSE messages from the TCM module. The configuration screen of SEL-387 relay is shown in Figure 13. The value of the ‘Remote Bit 1’ in SEL-387 relay is expected to be high when the status data in TCM GOOSE messages is high. As a result, the SEL-387 relay shall drive one of its outputs (denoted as ‘TR1’ or ‘Trip 1’, which is shown in the Appendix) to high. Therefore, it is expected that both ‘Remote Bit 1’ and ‘Trip 1’ in SEL-387 relay were driven to high when the status data in the TCM GOOSE messages was high. The event log, which was downloaded from SEL-387 relay, is shown in Figure 14. It is clear that the SEL-387 relay has been successfully operated by the GOOSE messages from the TCM module as expected.

Figure 12. Compatibility test setup.

Figure 13. SEL-387 relay configuration screen. Copyright © 2013 John Wiley & Sons, Ltd.

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Figure 14. SEL-387 relay event log.

5. TRIPPING CIRCUIT MONITOR MODULE APPLICATIONS 5.1. Tripping circuit monitor module as communication interface ElectraNet, the transmission network service provider in South Australia, will be establishing a new substation named ‘Whyalla Central’ adjacent to the Whyalla township to support the existing power supply demand. As a result, both primary and secondary equipment in the old substation named ‘Whyalla Terminal’ shall be partly replaced to accommodate such change. The secondary system of the old Whyalla Terminal substation consists of EM relays. Due to project implementation constraints on this part of the transmission network, only the protection relays for the 132 kV feeder to Whyalla Central substation and the ‘Y’ current differential protection relay for the transformer will be replaced with numerical relays that are IEC 61850 standard compatible. The rest protection devices, such as overcurrent and restrict earth fault protection on transformer high voltage and low voltage winding, will remain in service as EM protection relays. Table I lists all protection schemes at Whyalla Terminal substation and its associated relay technology. Because the modified Whyalla Terminal substation contains mixed relay technologies, the communication among the different generations of protection devices would have to be hardwired as the communication specification of the EM devices is limited to predominantly hardwired interfaces. Hence, the integration of the hardwired system would be very complicated to implement, especially on this brown field site. The developed TCM could be utilized to implement a modern open communication architecture on the basis of an Ethernet LAN technology for this type of application. The theoretical application of the TCM module as a communication interface on the project is illustrated in Figure 15. The TCM device could be applied to monitor the DC tripping wires of the installed EM relays by simply clamping the current transducer onto the wires. If there is any operation on the EM relays, the TCM device would detect the DC current change and publish such information via GOOSE messages on the Ethernet LAN. The published GOOSE messages would be subscribed and interoperated by the modern IEDs at the Whyalla Terminal substation to enable different technology devices to communicate and cooperate together to establish a complete protection system. It is also important to emphasize that the nonintrusive feature will make the TCM device even more practical for brown field site applications. Table I. Protection schemes and associated relay technology at Whyalla Terminal substation. 132 kV FDR X protection

Relay technology

CDIFF Backup distance protection CB fail DDR and fault location

IED IED IED IED

TF X protection scheme

Relay technology

CDIFF HV REF LV REF Pressure release device Buchholz protection Winding temperature X protection

EM EM EM EM EM EM

132 kV FDR Y protection CDIFF Backup distance protection CB fail DDR and fault location TF Y protection scheme

Relay technology IED IED IED IED Relay technology

CDIFF Tertiary winding OC HV OC LV OC Winding temperature Y protection Oil temperature Y protection

IED EM EM IED EM EM

DDR

IED

CDIFF, current differential; IED, intelligent electronic device; CB, circuit breaker; DDR, digital disturbance recording; HV, high voltage; LV, low voltage; EM, electromechanical; OC, overcurrent.

Copyright © 2013 John Wiley & Sons, Ltd.

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Figure 15. Demonstrated TCM application as communication interface.

In addition to the earlier benefits, the TCM device is capable of being synchronized on the same Ehternet LAN via IEEE 1588 standard. This feature will provide sub-microseconds synchronization accuracy to the translated tripping signals from EM relays. As a result, the proposed TCM application could enable a unified communication system in the brownfield site project with lowered installation and wiring cost. 5.2. Tripping circuit monitor module contribution in system-wide testing During the commissioning on a protection and control system in a substation, it is important to prove system-wide protection schemes are working as they are designed. Such testing procedure often involves confirming the inter-tripping signals from different protection relays. In a large and hardwired protection and control system, this process could be time consuming and complex, especially with mixed communication technologies in a control room as the previous example. The developed TCM module could significantly simplify the system-wide testing. The TCM device could be attached to any intermediate relay that is involved in the protection system and continuously monitors the intertripping signals. The monitored tripping signals are translated to GOOSE messages once they are detected, hence acknowledged by other testing IEDs. Consequently, any incorrect tripping could be easily located and diagnosed in the protection system. 5.3. Tripping circuit monitor module contribution in topology processing In modern EMS, state estimation is an essential tool to determine the most likely state of the power system for more efficient operation [40]. Conventionally, the state estimator software is operated on the basis of substation data that is collected by SCADA system via the installed remote terminal units. The state estimation involves three programmes that are usually solved sequentially [41]: (1) Topology processor that utilizes the real-time CB status; (2) A mathematical calculation that solves the complex voltage at each bus based on analogue measurements; (3) Bad data detection to identify bad measurements in the obtained solution. It is obvious that the traditional information system architecture that supports power system state estimation is a star connection between the control centre and all the substation remote terminal units. The substation level of information is generally polled by the SCADA system with a periodicity of Copyright © 2013 John Wiley & Sons, Ltd.

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Figure 16. Overview of EMS System architecture with TCM device.

a few seconds [41]. In recent years, there have been some discussions regarding the implementation of two-level state estimation to split the state estimation into substation level and control centre level [41,42]. The main scope of substation level state estimation is to construct substation level topology based on substation connectivity data and real-time measurements from protective IEDs at the substation. As it is mentioned earlier, there is a large number of EM relays still in service and not capable of providing the digitalized information. Therefore, in order to easily generate the substation topology together with numerical IEDs, it is necessary to apply the TCM module to translate the EM relays’ process-level information into digital format and publish the data on the communication network. The proposed architecture of the substation level topology processing is illustrated in Figure 16. As similar to the architecture that is introduced in [41], the proposed substation level topology processing is based on local calculations only handle the simple Kirchhoff’s law equations. The locally determined substation topology allows a large number of EM relays that are still in operation to benefit from the implementation of the synchronized sequence of substation events.

6. CONCLUSION In summary, the development of the TCM module and its applications are presented in this paper. The test results of the TCM module demonstrated its compatibility with SEL-387 current differential relay and the overall system performance with the time stamp accuracy of ±1 μs. The paper also demonstrated the features of the TCM module in providing a communication interface to legacy EM relays that are still in service in electric substations. Such approach not only significantly enhances the economic value of substations but also reduces the wiring and installation costs under substation expansion or system augmentation in a nonintrusive and safe manner. The proposed approach can also be applied to system-wide testing and the generation of a robust, locally determined substation topology. ACKNOWLEDGEMENTS

The authors would like to thank OMICRON electronics GmbH for their support and contribution to the development of the TCM device. The authors also thank ElectraNet Pty Ltd for their support in publishing this paper. The authors also appreciate for the kind support from Mr Kiet To in developing the TCM. Copyright © 2013 John Wiley & Sons, Ltd.

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APPENDIX SEL-387 configuration summary data: FID = FID = SEL-387E-R702-V0-Z101003-D20071025 TR1 =50P11T + 51P1T + 51Q1T + OC1 + LB3 + RB1 TR2 =51P2T + 51Q2T + OC2 TR3 =50P31 + 51P3T + OC3 TR4 =87R + 87U ULTR1 = !50P13 ULTR2 = !50P23 ULTR3 = !50P33 ULTR4 = !(50P13 + 50P23 + 50P33) CL1 = CC1 + LB4 + /IN104 CL2 = CC2 + /IN105 CL3 = CC3 + /IN106 ULCL1 = TRIP1 + TRIP4 ULCL2 = TRIP2 + TRIP4 ULCL3 = TRIP3 + TRIP4 ER =/50P11 + /51P1 + /51Q1 + /51P2 + /51Q2 + /51P3 OUT101 = TRIP1 OUT102 = TRIP2 OUT103 = TRIP3 OUT104 = TRIP4 OUT105 = CLS1 OUT106 = CLS2 OUT107 = CLS3 Copyright © 2013 John Wiley & Sons, Ltd.

Int. Trans. Electr. Energ. Syst. 2015; 25:1–16 DOI: 10.1002/etep