Keeping the lights on
Keeping the lights on
Keeping the lights on
Keeping the lights on
Keeping t
Keeping the lights on
Keeping the lights on
Keeping the lights on
PAC.MARCH.2010
by Xi-cai ZHAO, Shu-chao WANG, Shao-jun CHEN, NR Electric Co., China
Data Acquisition
SCADA
46 47
in Substation for the
Future
the lights on
Today, almost everyone is talking about Smart Grid. However, data and
information are the basis for the operating of the electric power system, and data
acquisition is the key issue. There are several independent systems between
substations and control
centers :
SCADA system
Relay Protection & Fault
Information Management
System (PMIS)
Special
Protection Scheme (SPS)
Wide Area Monitoring
System (WAMS)
Tele-metering system
(TMS), etc.
Each system is for a unique purpose and has its own data acquisition
devices in the substation, dedicated communication channel between substations
and control centers, and dedicated processing workstation in control centers.
Furthermore, each system is maintained by a separate team, thus the maintenance
of common system data models, parameters, and data itself is done repeatedly, and
there is inconsistency between these systems. With the application of electronic
instrument transformers and IEC 61850, it is possible to integrate these systems,
optimize hardware configuration, re-allocate functions, unify data models and the
communication interface, so as to share the power grid models, parameters, data
and other resources, make it easy to maintenance or add new functions, and save
investment. The roadmap to achieve a universal data acquisition platform proposed
in this article includes the following steps:
Update the conventional bay control unit to include functions of Phasor
Measurement Unit (PMU) and that of Disturbance & Fault Recorder (DFR)
Update substation gateway interfaced with control centers to handle all the
data collected by substation automation systems
Design a new communication protocol to transmit all kinds of data between
substations and control centers via a single communication channel (IEC
61850-90-2 may be the answer)
PAC.MARCH.2010
Data Acquisition
SCADA
48
Data acquisition
is the key issue.
It is feasible
to re-design
substation
automation
system,
Update the front end terminals at control centers to
handle all the data for different purposes
Set up a universal platform at control centers for data
acquisition, data sharing, data display, and various
applications, which are part of smart EMS (Energy
Management System)
Reliability plays a significant part in the design process
of a Universal Data Acquisition Platform, which should be
taken into consideration during the hardware and software
design of the whole system and can be achieved in four
aspects: redundancy, security, robustness and resilience.
Data requirements for different purpose
Today, there are several departments in control center
that care about real time data from substations. In China
they are: Operating Operation Planning Market and
Trading Protection Automation Communication
Departments.
Other utilities may have different organization
structure, but with similar functions. For operators on
duty at control centers, the data or information should
assist them to manage the entire system during steady
state, fault clearance period, and post-fault restoration.
The data required for the monitoring and control of the
power system can be classified into three types:
Real Time Data
Real time data from the physical process, including
alarms, events, status, analogue measures of generation,
load, flow, voltage, current, etc.
Real time data generated by data processing and by
11
operator input, including derived values operator
controls/commands/comments, output of close-loop
algorithms, etc.
Real time data imported from other information
systems, e.g. from other SCADA nodes, from external
SCADA systems, etc.
Historical/Archived Data
Long term storage of selective real time data for
trending, analysis and planning purposes
Semi-static Data
Data describing the physical processes such as power
system topology, asset parameters, etc.
Data supporting the processing functions such as
conversion parameters, displays, etc.
On the other hand, protection people want to upload
protection parameters, fault recordings from substations
to do post-fault analysis, protection setting check and
protection performance evaluation. Recently, many
literatures researched feasibility of system modeling, state
monitoring, state estimation, stability analysis, post-fault
analysis or even close-loop control for stability purpose
based on data collected by PMUs. The requirements on
refreshing cycles and propagation delay of PMU data for
different purposes are shown in Table 1.
Roadmap to achieve a Universal Data
Acquisition Platform
The main idea of a universal data acquisition platform is
to merge the existing independent systems and at the same
time fulfill the various requirements on data acquisition
Existing systems between substations and control center
Control Center
networks
between
EMS
PMIS
AAC
SPS
TMR
FE
FE
FE
FE
FE
Proprietary
IEC 60870-5-102
substations and
control centers,
and automation
system in the
control center,
IEC 60870-5-101
IEC 60870-5-104
Proprietary
IEEE C37.118
Substation
Gateway
Gateway
PDC
Gateway
Gateway
DFR
PMU
SPS
MET
to have better
protection,
BCU
PROT
monitoring and
SCADA
control of the
electric power
system.
AAC
EMS
PDC
PMIS
SCADA
Analysis and Application Center
Energy Management System
Phasor Data Concentrator
Relay Protection & Fault Information Management System
Supervisory Control and Data Acquisition
PAC.MARCH.2010
PMIS
BCU
FE
PMU
SPS
WAMS
Bay Control Unit
Front End
Phasor Measurment Unit
Special Protection Scheme
SPS
DFR
MET
PROT
TMR
WMAS
TMR
Disturbance & Fault Recorder
Meter
Protection
Tele-Metering Reading System
Wide Area Management System
by Xi-cai ZHAO, Shu-chao WANG, Shao-jun CHEN, NR Electric Co., China
49
from system operation point of view. After investigating
the existing systems, a roadmap has been proposed as
shown in Figure 2.
Update BCU: (Figure 2(A)). Update bay control unit
as a universal bay control unit (UBCU). It integrates
functions of conventional bay control unit (BCU), phasor
measuring unit (PMU), and dynamic and fault recorder
(DFR), and it can sample data of steady state, dynamic
state and transient state. All the samples are time tagged.
For traditional instrument transformers, different
secondary coils are provided for different purposes,
i.e. protection, measuring and tariff metering. For
non-conventional instrument transformers, different
communication data channels are provided for different
purposes, i.e. protection, measuring / metering, as defined
in IEC 60044-8. The UBCU may adopt data of different
quality regarding steady state accuracy and transient
performance from instrument transformers. If process
bus is applied, such a new design reduces the number of
secondary equipments connected to process bus for a
different purpose, thus reducing the load flow on process
bus. Thanks to the development of micro-controllers and
DSPs, there is no doubt that a bay control unit can handle
all the data efficiently. The sample rate can be high enough
to process steady state, dynamic and transient data.
Under normal condition, only time-tagged steady state
analogue signals are sent at lower rate, for example one
package per second. During a dynamic period, when a
low frequency oscillation occurs, the event and oscillation
frequency are reported or the low frequency oscillation can
be detected in the control center, if the data sampling rate
is high enough. When a fault occurs, the brief report will
be sent at first, and the total recording will be sent after the
recovery from the fault for further analysis.
Update Gateway: Update the gateway as a universal
communication interface to the control centers (see Figure
2(B)). Such a gateway can handle all the data collected
by substation automation systems, and transmit them
to control centers: SCADA data, protection settings
and fault reports, fault recording, etc. At this stage, the
communication channels are still separated between
normal SCADA and other applications.
As an optional solution, if it is not feasible to update
BCU at once as described earlier, the steady state sample
without time tag received from BCUs can be time-tagged
by the Gateway before being transmitted to the control
centre. The inaccuracy of time synchronization of this
solution can be minimized by increasing the data refresh
rate and decreasing propagation delay of communication
between BCUs and the Gateway.
Another idea related to Gateway is to set up a
substation-level sub-database as a part of entire SCADA
system. The raw data will be processed; the bad data
will be checked and corrected. Furthermore, part of state
estimation function can be completed at substation level,
which is done in the control center today.
Data and information are the
basis of the operation of the
electric power system.
Update Tele-communication Facilities: Today, the
wide area communication networks are available for all
the applications described in this article, for example,
Synchronous Digital Hierarchy (SDH) and Synchronous
Optical Networks (SONET) links in fiber optic networks.
One obstacle to improving the efficient operation of the
electric power system is the number of communication
protocols used. Today we have different standards for
different applications; some of them are still proprietary
ones, as shown in Figure 1. Measured value with time
tag can be transmitted via IEC 60870-5-101 or IEC
60870-5-104, but this kind of ASDU (Application Service
Data Unit) is seldom used practically today.
To transmit all kinds of data between substations
and control centers via a single communication channel,
one solution may be IEC 61850-90-2: Using IEC 61850
for the communication between substations and control
centers. Whether or not this future standard can cover all
the applications is unknown yet.
Update Front End Terminals: Figure 2(C) shows a
front end terminal that handles all the data for a different
purpose. Its function is almost the same as in the past.
Update Data Collection Platform: The last step is
to set up a universal data collection platform for data
acquisition, data processing, and data management at
control centers for various applications (Figure 2(D)). This
centralized solution leads to the controlled consistency of
redundant data, a high level of data integrity, standard data
types and the sharing of common data.
Control Center Organization and Workflow: The
organizational structure of the control center is one main
factor which leads to the fact that many independent
systems exist in parallel. Each department in the control
center only cares about the data they need. Once they
feel it necessary, they will design a dedicated system with
its own data acquisition devices in substation, dedicated
communication channels between substations and the
control center, and dedicated processing workstations
table 1 Requirements on:
Refreshing Cycles and Propagation delay of PMU Data
Function in Control Center
Refreshing
cycles
Propagation
delay
25-50
25-50
25-50
25-50
25-50
25-100
≤1
≤1
Several
Several
≤1
≤ 0.1
(per sec.)
Frequency monitoring
Reactive power & voltage monitoring
State estimation
Model & parameter verification
Low frequency oscillation monitoring
Stability assessment and emergency control
(sec.)
PAC.MARCH.2010
Xi-cai ZHAO
- received his
master degree from
Electrical Engineering Department of
Shanghai Jiaotong
University (SJTU) in
1997. From then on,
he has been working for Nanjing NARIRELAYS Electric Co.,
Ltd (NR Electric).
He was involved
in development of
digital protective
relays, bay control
units, protocol
converters, special
protection scheme,
electronic instrument transformers,
etc. Now, he is the
deputy chief engineer of NR Electric,
Secretary General
of Protection Study
Committee of
Chinese Society of
Electrical Engineering (CSEE), member
of Chinese National
standard Technical
Committee of Measuring Relays and
Protection Equipments, Member
of IEC TC95 MT1,
MT3 & MT4, and
regular member of
CIGRE SC B5. E-mail:
xczhao@nari-relays.
com
by Xi-cai ZHAO, Shu-chao WANG, Shao-jun CHEN, NR Electric Co., China
Data Acquisition
SCADA
50
Shu-chao
WANG
received his master
degree from Huazhong University of
Science and Technology (HUST) in
2004. Since then he
joined NR Electric
as a R&D engineer.
He involved in
development of IEC
61850 based digital
protective relays,
bay control units
etc. Now he is also
a member of CIGRE
WG B5.36. E-mail:
wangsc@nari-relays.
com
in the control center. The seamless universal platform
solution may break the boundaries between them, and
change the way they work today.
Redundancy and Reliability
The automation industry’s rapid movement toward
computer controls has increased the importance of
reliability in data acquisition systems. Reliability plays
a significant part in the design process of our Universal
Data Acquisition Platform. According to IEC 60870-4,
reliability is defined as a measure of the ability of
equipment or a system to perform its intended function
under specified conditions for a specified period of time.
The Universal Data Acquisition Platform shall continue
to be operable, according to the “graceful degradation”
principle described in "Distributed Control System
Reliability" by Emmanuel G. Diaz and Iliya A. Dormishev,
as well as "Reliability investigations for SA communication
architectures based on IEC 61850" by Lars Andersson,
Christoph Brunner. This principle should be valid if any
component of the data acquisition system fails, such as a
failure in UBCU, gateway, FE or any of the above SCADA
or other application computers. In Barry C. Ezell’s thesis
on vulnerabilities of the SCADA system, it is said that a
reliable system depends on its survivability. Survivability
is a measure of how a system will function and recover
after failure and is dependent on the system’s redundancy,
security, robustness and resilience. For the Universal Data
Acquisition Platform, these principles directly involve the
hardware and software design of the whole system.
Redundancy: Redundancy plays a crucial role in
maintaining high reliability of the whole Universal Data
Acquisition Platform. Redundancy in a system “…refers
to the ability of certain components of a system to assume
functions of failed components without adversely affecting
the performance of the system itself”. Some events, such as
device power off, network physical or logical disconnect,
systems crash, can make the whole system out of service.
Yet, these events are avoidable using redundant data
acquisition methods. For example, a redundant power
supply can take the UBCU unaffected when one power
supply is out of service. A hot standby redundant UBCU
can avoid data loss when the other UBCU crashes for an
unknown reason. What’s more, the physical topology
of the system network connections must support
redundancy, and the network software must be intelligent
enough to recover from various physical failures. On the
substation side, a redundant station bus should also be
adopted for redundant data acquisition of the UBCU. By
combining these different redundancy methods, many
hybrid systems can be created.
Security: Security deals with prevention, detection
and defence from internal and external attacks. If there is
nothing preventing a hacker from breaking into SCADA
networks, anyone with enough knowledge of computers
can disrupt communications, change program parameters,
and eventually cause the system to malfunction. Therefore,
PAC.MARCH.2010
Tariff metering needs to be
separate from the other
secondary equipment .
it is important to design a system that provides protection
against unauthorized access to operator displays,
control operations, database modification, and access to
applications and critical functions. With the introduction
of the international security standard IEC 62351, a
role based access control solution will be established to
safeguard the whole communication system. The role
based access control can not only be applied to field device
UBCU, gateway, but also to the whole data acquisition
platform, consisting of field devices, station control and
network control – the complete pyramid, in order to
support end to end security. This can secure the universal
data acquisition system against all kinds of cyber attacks,
improving the reliability of the whole system especially in
case of increasing network crimes.
Robustness: The third principle of survivability
involves a system’s robustness. It “…refers to the degree
of insensitivity of a system design to errors”. The Universal
Data Acquisition system should be robust enough to
maintain all components, both software and hardware,
functioning well to keep the system running after an
attack or failure. And the function code implemented
in the system should have the ability to function under
abnormal conditions. Code in each of the network
components can be wide-awake so that if there is a failure
in communication, it will be detected and then a new set
of rules are given to the system. The purpose of this set
of rules is to keep the system stable under the presence of
failure and increase failure tolerance.
Resilience: “Resilience is the ability of a system
to operate close to its intended design, technically and
institutionally, over a short time after the attack, such
that the losses are within manageable limits”. Basic
examples of resilience to SCADA system are virus
protection programs. If the data acquisition systems have
connections to the Internet, it runs the risk of having the
system infected by a computer virus. The virus protection
software is constantly searching through system files for
a virus, and if found, destroying it before it corrupts any
data. In addition, if an attack is successful, a plan of action
has to be in place so that system operators and technicians
can deal with the situation to bring the system back
online as soon as possible. In SCADA system, resilience is
normally limited to the code used to program the gateway
and UBCUs. The code has numerous checks between each
unit and the supervisor, which creates a set of alarms that
will be displayed through the HMI. From here, operators
would attempt to correct the errors, and return the system
to its normal operational mode.
by Xi-cai ZHAO, Shu-chao WANG, Shao-jun CHEN, NR Electric Co., China
51
12
Steps towards the universal solution
Control Center
Control Center
SCADA
APP
SCADA
APP
FE
FE
FE
FE
Substation
Gateway
Substation
Gateway
UBCU (BCU + PMU + DFR)
A
Gateway
B
UBCU (BCU + PMU + DFR)
Control Center
SCADA
APP
APP
SCADA +APP
FE
FE
Substation
Substation
Gateway
Gateway
UBCU (BCU + PMU + DFR)
C
13
Control Center
D
Various applications
Substation overview
UBCU (BCU + PMU + DFR)
UBCU
14
Universal Bay Control Unit
The team work environment
PAC.MARCH.2010
Shao-jun CHEN
became a protective relay engineer
for East China
Power Grid
Co. (ECPGC) in
1983. Since 1989,
he has been a
department manger
of relaying
protection in
ECPGC, and had ten
years’ professional experience
on power
system operation
and protection from
1983 to 1992. From
1993 to 1996, he
was a
chief and professional engineer at
Grid Control Center
in ECPGC being
responsible for
power system
stability control. He
joined in Schweitzer
Engineering
Laboratories, Inc.
(SEL) in 1996 and
has ten years’
experienced
with SEL on
schematic design,
project management and technical
application
respectively for
international
customers, and
became a RSM for
East Asia since
2002. At present, he
has been working
for NR Electric since
2006 as a Vice
President
E-mail: sjchen@narirelays.com.