Detnet X. Vilajosana, Ed.
Internet-Draft Worldsensing
Intended status: Informational T. Mahmoodi
Expires: January 8, 2017 King's College London
S. Spirou
Intracom Telecom
P. Vizarreta
Technical University of Munich, TUM
July 7, 2016
Wind Park requirements for Detnet
draft-vilajosana-detnet-windfarm-usecase-00
Abstract
This document analyses the use case requirements for deterministic
flows in a wind park network. It inlcudes the intra-domain and
inter-domain requirements.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. Use Case description . . . . . . . . . . . . . . . . . . . . 3
4. Traffic Demand . . . . . . . . . . . . . . . . . . . . . . . 4
5. Intra-Domain network considerations . . . . . . . . . . . . . 6
6. Inter-Domain network considerations . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. Wind Park Networks Future . . . . . . . . . . . . . . . . . . 8
9. Wind Park Network Wish List . . . . . . . . . . . . . . . . . 9
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.1. Normative References . . . . . . . . . . . . . . . . . . 9
11.2. External Informative References . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The wind power industry has been selected as a representative example
of industrial networks with strict performance, security, and
reliability requirements. A Wind Park network is part of a
Supervisory Control and Data Acquisition (SCADA) system that
regulates power production from each wind turbine and from the entire
park. The SCADA system extends beyond the Wind Park, over the
Internet, to a remote control centre. Moreover, this network
interconnects sensors and actuators and a hierarchy of purpose-built
controllers and repositories via domain-specific protocols (e.g., IEC
1041, MODBUS2) in a static and secure topology. In this document the
Intra domain requirements, referring to the network consiserations in
terms of latency, jitter, delay tolerance, within the same
administrative domain will be presented. Analogously, and as Wind
Parks are connected to remote Control Centers the requirements and
considerations for the Inter domain reliability, jitter, latency and
delay tolerance will be outlined.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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3. Use Case description
In a Wind Park, the wind turbines represent a complex system of
sensors, actuators and an internal controller, located offshore or in
remote locations that communicate with a central control or master
SCADA station over reliable communication network. Wind turbines are
grouped in radials to maximize the energy production. The size of
the wind park varies significantly; having the biggest offshore wind
parks up to 200 wind turbines. Depending on the size of the park,
there might be an additional substation located close to turbines to
facilitate power transportation to the utility grid with minimum
losses [Sie13], [Kri03]. On another side, local control center
combines several functionalities necessary for control and management
of the wind park. SCADA comprise power plant control function to
synchronize and coordinate operation of the wind turbines in the
park, network management system (NMS) for network configuration,
performance and fault monitoring and different servers to collect and
store the metering data and status information from sensors, as well
as gateway to the other control centers and Internet [Spe09],
[Pet11]. The communication system between field devices and SCADA
has to be reliable to facilitate control and management of the wind
park. Wind power plant control and monitoring system have stringent
latency requirements, and reconfiguration of the network in the case
of a failure has to be done quickly. The most common way to improve
reliability is to connect wind turbines in a ring in order to provide
resistance to single link or node failure. Additionally, backup
microwave links can be built to improve the overall system
availability.
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Figure 1: Wind turbine control network
|
|
| +-----------------+
| | +----+ |
| | |WTRM| WGEN |
WROT x==|===| | |
| | +----+ WCNV|
| |WNAC |
| +---+---WYAW---+--+
| | |
| | | +----+
|WTRF | |WMET|
| | | |
Wind Turbine | +--+-+
Controller | |
WTUR | | |
WREP | | |
WSLG | | |
WALG | WTOW | |
4. Traffic Demand
Figure 1 presents the subsystems that operate a wind turbine. This
subsystems include the rotor (WROT) control, the nacelle control
(WNAC), the transmission control (WTRM), the generator (WGEN), the
yaw controller of the tower head (WYAW), the in-turbine power
converter (WCNV), the in-tower power transformer (WTRF) and an
external meteorological station providing real time information to
the controllers of the tower (WMET). Traffic characteristics
relevant for the network planning and dimensioning process in a wind
turbine scenario are listed below. The values in this section are
based mainly on the relevant references [Ahm14] [Spe09]. Each
logical node (Figure 1) is a part of the metering network and
produces analogue measurements and status information that must
comply with different specifications in terms of data rate.
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Table 2: Wind turbine data rate constraints
+----------+----------+----------+------------+----------+-------------+
|Subsystem |# Sensors | # Analog | Data rate | # Status | Data rate |
| | | Samples |(bytes/sec) | Samples | (bytes/sec) |
+----------+----------+----------+------------+----------+-------------+
| WROT | 14 | 9 | 642 | 5 | 10 |
| WTRM | 18 | 10 | 2828 | 8 | 16 |
| WGEN | 14 | 12 | 73764 | 2 | 4 |
| WCNV | 14 | 12 | 74060 | 2 | 4 |
| WTRF | 12 | 5 | 73740 | 2 | 4 |
| WNAC | 12 | 9 | 112 | 3 | 6 |
| WYAW | 7 | 8 | 220 | 4 | 8 |
| WTOW | 4 | 1 | 8 | 3 | 6 |
| WMET | 7 | 7 | 228 | - | - |
+----------+----------+----------+------------+----------+-------------+
| Total | 102 | 73 | 225544 | 29 | 58 |
+----------+----------+----------+------------+----------+-------------+
Quality of Service (QoS) requirements of different services are
presented in the Table 2. The requirements are defined by IEEE 1646
standard [IEEE1646] and IEC 61400 standard [IEC61400].
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Table 3: Wind turbine Reliability and Latency constraints
+-----------+----------+-------------+-----------------+
| Service | Latency | Reliability |Packet Loss Rate |
+-----------+----------+-------------+-----------------+
| Analogue | | | |
| measure | 16 ms | 99.99% | < 10-6 |
+-----------+----------+-------------+-----------------+
| Status | | | |
|information| 16 ms | 99.99% | < 10-6 |
+-----------+----------+-------------+-----------------+
|Protection | | | |
| traffic | 4 ms | 100.00% | < 10-9 |
+-----------+----------+-------------+-----------------+
| Reporting | | | |
|and logging| 1 s | 99.99% | < 10-6 |
+-----------+----------+-------------+-----------------+
| Video | | | no specific |
| surveill. | 1 s | 99.00% | requirement |
+-----------+----------+-------------+-----------------+
| Internet | | | no specific |
|connection | 60 min | 99.00% | requirement |
+-----------+----------+-------------+-----------------+
| Control | | | |
| traffic | 16 ms | 100.00% | < 10-9 |
+-----------+----------+-------------+-----------------+
| Data | | | |
| polling | 16 ms | 99.99% | < 10-6 |
+-----------+----------+-------------+-----------------+
5. Intra-Domain network considerations
A Wind turbine is composed of a large set of subsystems (sensors,
actuators) that require time critical operation. The time-
criticallity of different actions is shwon in Table 3. These
subsystems are connected to an intra-domain network used to monitor
and control the operation of the turbine and connect it to the SCADA
subsystems. The different components are inter-connected using fiber
optics, industrial buses, industrial ethernet, EtherCat or a
combination of them. Industrial signaling and control protocols such
as Modbus, Profibus, Profinet and EtherCat are used directly on top
of the L2 or encapsulated over TCP/IP.
The Data collected from sensors or condition monitoring systems is
multiplexed into fiber cables for transmission to the base of the
tower and to remote control centers. The turbine controller
continuously monitors the condition of the wind turbine and collects
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statistics on its operation. As the name implies, the controller
also manages a large number of switches, hydraulic pumps, valves, and
motors within the wind turbine.
There is usually a controller both at the bottom of the tower and in
the nacelle. The communication between these two controllers usually
takes place using fiber optics instead of copper links. Sometimes, a
third controller is installed in the hub of the rotor and manages the
pitch of the blades. That unit usually communicates with the nacelle
unit using serial communications.
6. Inter-Domain network considerations
As mentioned in the introduction, a remote control center that
belongs to a grid operator, regulates the power output, enables
remote actuation and monitors the health of one or more Wind Parks in
tandem. It connects to the local control center in a Wind Park over
the Internet (Figure 2), via firewalls at both ends. The AS path
between the local control center and the Wind Park typically involves
several ISPs at different tiers. For example, a remote control
center in Denmark can regulate a Wind Park in Greece over the normal,
public AS path between the two locations.
The remote control center is part of the SCADA system, setting the
desired power output to the Wind Park and reading off the result once
the new power output level has been set. Traffic between the remote
control center and the Wind Park typically consists of protocols like
IEC 104 [IEC104], OPC XML-DA [OPCXML], Modbus [MODBUS], and SNMP
[RFC3411]. Usually, QoS requirements are not strict, so no SLAs or
service provisioning mechanisms (e.g., VPN) are employed. Traffic
flow across the domains is best effort. In case of events like
equipment failure, tolerance for alarm delay is in the order of
minutes, due to redundant systems already in place.
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+--------------+
| |
| |
| Wind Park #1 +----+
| | | XXXXXX
| | | X XXXXXXXX +----------------+
+--------------+ | XXXX X XXXXX | |
+---+ XXX | Remote Control |
XXX Internet +---------+ Center |
+----+X XXX | |
+--------------+ | XXXXXXX XX | |
| | | XX XXXXXXX +----------------+
| | | XXXXX
| Wind Park #2 +----+
| |
| |
+--------------+
7. Security Considerations
On top of the classical requirements for protection of control
signaling, it must be noted that Wind Farm networks operate on
critical infrastructures with heterogeneous devices and networks.
This includes heterogeneous L2 technologies that must be secured in a
per link model. Control and signaling occur at the transport layer
and therefore end to end security mechanism must be installed.
8. Wind Park Networks Future
In the future we expect cloud-based SCADA systems controlling,
storing and monitoring the critical and non-critical subsystems of
the windfarm. We foresee an increase in the number of sensing
devices and technologies, combining wireless and wired capillars. We
foresee heterogeneous L2 technologies, homogenized by common IPv6
frameworks such as those developed by 6TiSCH, 6lo, LPWAN and 6MAN.
We expect windfarm networks to be operated by standardized and common
management planes, enabling the orchestration of the different
building blocks and underlaying technologies and being able to
Internet-connect enabling service gurantees and remote operation with
quality of service. Therefore protocols for network management, flow
control, increased reliability and security are mandatory in order to
improve the operation of critical infrastructures, including in this
case Wind Farms.
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9. Wind Park Network Wish List
The community would like to see a set of protocols that enable the
inter-domain and the intra-domain operation of a wind park
infrastructure satisfying the timing, security, availability and QoS
constraints described above, such that the resulting converged
network can replace the heterogeneous, sometimes propieatary field
networks. Ideally this connectivity should extend to the open
Internet. This would imply an architecture that can guarantee
Low communication delays from <4 ms to 1000ms in the inter-domain
network
Low communication delays from <150 ms to 5000 ms in the intra-
domain network
Low jitter (< 1 ms)
Tight feedback intervals (4ms - 10ms) in the intra-domain
High network availability (up to 99.9999% )
10. Acknowledgements
This requirements have been extracted from the study of Wind Farms
conducted within the 5GPPP Virtuwind Project. The project is funded
by tge European Union's Horizon 2020 research and innovation
programme under grant agreement No 671648 (VirtuWind).
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
DOI 10.17487/RFC3411, December 2002,
<http://www.rfc-editor.org/info/rfc3411>.
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11.2. External Informative References
[IEC61400]
"International standard 61400-25: Communications for
monitoring and control of wind power plants", June 2013.
[IEEE1646]
"Communication Delivery Time Performance Requirements for
Electric Power Substation Automation", IEEE Standard
1646-2004 , Apr 2004.
[Sie13] "Creating the most from wind, retrieved from siemens.com/
wind-equipment", ACM International Conference on Mobile
Computing and Networking (MobiCom) , June 2013.
[Kri03] Kristoffersen, J. and P. Christiansen, "Horns Rev Offshore
Wind Farm: Its Main Controller and Remote Control
System.", Wind Engineering, p. 351-360. , June 2003.
[Spe09] Sperotto, A., Sadre, R., Vliet, F., and A. Pras, "A First
Look into SCADA Network Traffic", IP Operations and
Management, p. 518-521. , June 2009.
[Ahm14] Ahmed, M. and R. Kim, "Communication network architectures
for smart-wind power farms", Energies, p. 3900-3921. ,
June 2014.
[Pet11] Pettener, A., "SCADA and communication networks for large
scale offshore wind power systems", EIET Conference on
Renewable Power Generation. , June 2011.
[IEC104] International Electrotechnical Commission, "International
Standard IEC 60870-5-104: Network access for IEC
60870-5-101 using standard transport profiles", June 2006.
[OPCXML] OPC Foundation, "OPC XML-Data Access Specification", Dec
2004.
[MODBUS] Modbus Organization, Inc., "MODBUS Application Protocol
Specification", Apr 2012.
Authors' Addresses
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Xavier Vilajosana (editor)
Worldsensing
483 Arago
Barcelona, Catalonia 08013
Spain
Phone: +34 (646) 633 681
Email: xvilajosana@worldsensing.com
Toktam Mahmoodi
King's College London
Strand, London WC2R 2LS
London, London WC2R 2LS
UK
Email: toktam.mahmoodi@kcl.ac.uk
Spiros Spirou
Intracom Telecom
19.7 km Markopoulou Ave.
Peania, Attiki 19002
Greece
Email: spis@intracom-telecom.com
Petra Vizarreta
Technical University of Munich, TUM
Maxvorstadt, Arcisstrasse 21
Munich, Germany 80333
GE
Email: petra.vizarreta@lkn.ei.tum.de
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