Implementation
Time
IEC
GOOSE
61850
GOOSE
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GOOSE GOO
GOOSE
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by Hachidai Ito and Kenichiro Ohashi , Toshiba Corporation, Japan
of
High Performance
and Protection
Relay Testing
EAF
Transformers
IEC 61850 GOOSE messaging is applied for Substation Automation
Systems and for status interactions between IEDs by replacing the conventional
method of using binary inputs/outputs and wires with communication over
Ethernet cables/fibres.
With its fast transfer characteristics, it is also applied for
GOO protection testing purposes.
SE
In
order to confirm the basic
functionality of IEC 61850 and
GOOSE messaging, conformance
tests are mandatory for basic
multi-vendor interoperability.
IEC 61850, the new communication standard for power
substations, is now being widely used in practical applications. In particular,
GOOSE (Generic Object Oriented Substation Events) messaging has
been applied not only for SAS (Substation Automation System) control
and monitoring of primary equipment and IED status, but also for status
interactions between IEDs including protection relays by replacing the
conventional method of using binary inputs/outputs and wires with
communication by GOOSE messages over Ethernet cables/fibres. This is
achieved through much simpler engineering based on the multi vendor
interoperability described in the IEC 61850 standard, which enables the
easy connection of different IEDs, including relays supplied by different
vendors.
PAC.WINTER.2008
protection
40 41
by Hachidai Ito and Kenichiro Ohashi , Toshiba Corporation, Japan
IEC 61850
protection
42
Hachidai Ito
was born in Osaka,
Japan, in September
15, 1956. He joined
Toshiba in 1981,
and worked as a
development engineer and a manager
of Protection and
Control Development Department.
He is now a Chief
Specialist in Power
System Protection &
Control and is principally responsible
for technology and
overseas marketing
of protection and
control products
in Toshiba Corporation. He is a senior
member of IEEE, and
a member of CIGRE,
IEEJ and IEICE. Also
he is a secretary of
Japanese National
Committee of IEC/
TC95, a convenor
of its MT1 (Maintenance Team 1)
and a member of
its other 3 working
groups, and also a
member of several
working groups in
IEEE/PSRC...
In order to confirm the basic functionality of GOOSE
messaging in protection relays, functional conformance
testing at an independent test laboratory is mandatory for
multi vendor interoperability. However, an IEC 61850
device certificate does not fully ensure conformity to the
IEC 61850 standard. Furthermore, in some cases, the
correct behaviour of an IED is not clearly described in the
standard. Hence, performance testing for GOOSE messaging
must be considered as an important item in the product
type test and/or the routine test because this is critical for
practical substation applications. It should be noticed that
performance testing for GOOSE messaging is not covered
by conformance tests at present.
In order to replace the conventional method of using
contacts and wires, the performance of the GOOSE
messaging, i.e. transfer time should be less than 3ms for
a Trip GOOSE command and 20ms for a Block GOOSE
command as specified in IEC 61850-5 'Communication
requirements for functions and device models’. It is clear
that new methods for testing GOOSE messaging including
performance and interoperability must be carefully
considered, not only by vendors but also by the end users
who evaluate system performance in the field.
GOOSE APPLICATIONS FOR PROTECTION
Advantages of GOOSE for protection devices
GOOSE messaging is a very important function in
achieving multi-vendor interoperability as described in
IEC 61850. The purposes and associated advantages are
considered as follows:
Instead of connecting conventional metallic wiring and
other ancillary equipment between protection devices, or
between protection devices and primary equipment, only a
single LAN cable/fibre is required. This results in a reduced
total cost of building a system in a substation.
Connection between IEDs provided by different
vendors is much easier to achieve.
Modification or addition of data communications
between IEDs can be easily achieved by the simple
re-configuration of the IEDs’ GOOSE settings, rather than
by complex metallic wiring.
Figures 1 and 2 show an example of the differences
between the conventional method and that utilising GOOSE
messages where communication between a protection
relay and a primary CB (Circuit Breaker) is required for an
Autoreclose function.
Possible GOOSE application for protection and
related ongoing activities
GOOSE messaging in IEC 61850 can also be utilised in
the following protection functions:
Autoreclose (between relay and CB)
Intertripping (between relay and relay)
Interlocking (between bay control unit and relay)
Some utilities consider and plan contingencies in
the case of a protection failure in a system. In order to
minimize the damage caused in the case of a primary fault
to the zone protected by the equipment that has failed,
messaging between protection relays is very important.
This subject is being discussed in CIGRE/SCB5/WG16:
Busbar protection. There is a possibility to use GOOSE
messages for information communication between
the various items of equipment contained within the
substation
ACHIEVING INTEROPERABILITY
Functional conformance test See Figure 3.
UCAIUG (http://www.ucausersgroup.org) defines
the conformance test procedure which is detailed in IEC
61850 part 10 (Conformance testing). The test procedure
contains two types of test;
11
22
Connections between Relay
and CB by conventional methods
Connections between Relay
and CB by GOOSE
Protection Relay
Binary output
Trip/Autoreclose
GOOSE for Trip/Autoreclose
Binary
input
100 BASE/10 BASE HUB
Primary CB
GOOSE for CB Condition
CB Condition
Dedicated metalic cable (s)
PAC.WINTER.2008
A LAN cable
by Hachidai Ito and Kenichiro Ohashi , Toshiba Corporation, Japan
Positive test: Checks with correct parameters.
Negative test: Checks with incorrect parameters.
However, there are some points that we must be
cognizant of with regard to conformance testing;
‘Conformance’ does not mean ‘Interoperability’.
Only basic functional tests are undertaken, no
performance tests are carried out at present.
IEC 61850 communication interfaces in the IED form
the main part of the test, but the connections between
prot ec t ion applic at ions and their IEC 61850
communication interfaces are too complex and varied to be
comprehensively tested.
Regarding standardisation and guidance on testing,
functional testing of IEC 61850 based systems is now
being discussed in CIGRE Subcommittee B5 Task Force
92. The technical brochure will define the functional
aspects of testing which are not defined in IEC 61850-10
(Communication networks and systems in substations
-Part 10: Conformance testing). It deals with the functional
parts not covered by the IEC 61850 device certificate
which is based only on IEC 61850-10. This will have an
impact on the work of the protection engineer, and this
kind of functional testing approach should naturally be
carried out for all existing IEC 61850 conformant devices
and systems.
Importance of performance testing for GOOSE
messaging
In order to achieve multi vendor interoperability in
GOOSE messaging in consideration of an actual practical
situation within a substation, it is important that not only
the functional conformity to IEC 61850 be tested, but also
performance conformity to IEC 61850 must be tested, by
vendors, as a type test of the IED.
Performance criteria examples of GOOSE messaging
defined in IEC 61850-5 'Communication requirements for
functions and device models’ are given as follows:
3ms: ‘TRIP’ GOOSE information (class P2/P3)
20ms: ‘BLOCK’ GOOSE information (class P2/P3)
The transfer time definition is described in IEC 61850-5
(see Figure 4). IEC 61850-5 states that the transfer time
of GOOSE messaging for a Trip command shall be such
that the command should arrive at the destination IED
within 3ms. For a single IED, by assuming the time for
the publishing process and the subscribing process are
approximately equal and if ‘tb’ can practically be ignored,
then at least half of the defined time is needed for the IEDs
to process the message (i.e. 1.5ms for ‘TRIP’ GOOSE). See
Figure 4.
PROTECTION RELAY TESTING USING GOOSE
Comparison with the conventional method
Figures 5 and Figure 6 simply show the difference
between the conventional test method used to measure
tripping time and the method used to measure the ‘Trip’
GOOSE transfer time using an IEC 61850 GOOSE
enabled test set. In order to simulate network traffic,
possibly caused by other equipment connected to the same
network, a network traffic simulator running on a PC is
used. It is considered very important for the product type
test to have a similar environment to that found within the
23
24
An IEC 61850 device certificate
IEC 61850
Conformance with
the performance criteria
defined in IEC 61850-5
should be tested.
protection
43
Kenichiro
Ohashi
was born in MiyagiPref., Japan, on
March 5, 1973. He
joined Toshiba in
1995. He is currently responsible
for product development of protection and control
systems as a quality
assurance/testing
engineer in Toshiba.
He is a member
of IEC/TC95/MT2
(Maintenance Team
2: EMC standards
for measuring relays
and protection
equipment).
GOOSE transfer time
IEC 61850 -5
The UCA International
Transfer time t = ta + tb + tc
Users Group defines
ta
tb
tc
the conformance test
procedures required for
issuing IED conformance
f1
Communication
processor
Communication
processor
f2
GOOSE
transfer time
is the time
certificates.
between
Physical device PD1
Physical device PD2
fuctions in two
devices
PAC.WINTER.2008
by Hachidai Ito and Kenichiro Ohashi , Toshiba Corporation, Japan
IEC 61850
protection
44
Implementation and test
results satisfying the
performance criteria are
described along with methods
for evaluation.
substation, and this is a key point in GOOSE testing. See
Figure 5/ Figure 6.
The advantages in testing with GOOSE messaging are
considered as follows:
Dedicated metallic cables in the connection between
the relay and test equipment and/or cables used for testing
can be reduced.
Performance evaluation is more accurately achieved
in GOOSE messaging since hardware overhead time on
conventional binary inputs/outputs can be ignored.
The limitation in the number of binary inputs/
outputs can be covered by GOOSE.
The timing of all GOOSE can be monitored by an
external IEC 61850 protocol analyzer connected to the
network.
Expanding flexibility in testing with GOOSE
IEC 61850 GOOSE, with its fast transfer characteristics
within a network environment (<3ms as defined by
the standard), is now being widely used for protection
purposes in place of conventional dedicated wiring. As
described, this brings great benefits to the user since
dedicated wiring can be reduced.
In the same way, GOOSE can be applied for testing
purposes. All signals, even those used internally in the
execution process of software for a numerical protection
relay, can be assigned to GOOSE. This results in reduced
wiring during testing and also facilitates the realisation of
more detailed testing.
Figure 7 shows a practical example of the test result of
a switch-on-to-fault case utilizing GOOSE for a certified
IEC 61850 conformant numerical transformer protection
relay.
In this case, the COMTRADE waveforms calculated
by RTDS with a simulation of both CT saturation and
transformer inrush under a switch-on-to-fault condition
were played on a test set. At the same time the relay’s
internal signals for 2nd harmonic inrush current detection
and CT saturation detection which are used to block
tripping were observed along with the trip signal, without
any wiring connection but by monitoring GOOSE
messages on the network.
The waveform can be seen to consist of fault current
and transformer inrush components. In response to
this unusual waveform, the relay firstly detects second
harmonic to temporarily block tripping and then
subsequently issues a trip, which is considered to be the
expected result.
In the past, there would have been many limitations in
the flexibility of this kind of test, e.g. resulting from the
delay time of mechanical contacts.
PERFORMANCE AND ITS EVALUATION
GOOSE messaging implementation to achieve
satisfactory performance
It is important to minimize the transmission time of
the GOOSE packet within the IED in order to achieve
the GOOSE performance of class P2/P3 which is defined
15
26
Example of physical
connections for a conventional test
Communi-
Protection Relay
cation
replace hard-
Protection Relay
Binary output
messages
Trip/Autoreclose
GOOSE for Trip/Autoreclose
Binary
input
CB Condition
between a
test device.
Network
traffic simulator
Testing
Tool
Binary
input
wired signals
relay and
Example of physical
connections for GOOSE based test
HUB
GOOSE for CB condition
Binary output
Voltage/Current
Voltage/Current
Dedicated metalic cable (s)
PAC.WINTER.2008
Test Device
A LAN cable
Test Device
Testing
Tool
by Hachidai Ito and Kenichiro Ohashi , Toshiba Corporation, Japan
45
in the standard. One area in which we have been able to
make significant savings in processing time is in the way
in which we process the sending and receipt of GOOSE
messages. Another opportunity was taken to reduce the
time overheads incurred between the GOOSE packet
receiving process, the interpret/response/generate GOOSE
packet process and the sending process. Implementation
of the application software is designed such that the three
processes referred to above are executed in series in a task
activated in a very short period of time together with the
primary protection/measurement etc. functions as shown.
See Figure 8.
Methods for performance evaluation in GOOSE
communication
Figure 9 and table 1 show a test result for the ‘Trip’
GOOSE transfer time in a certified IEC 61850 conformant
numerical distance protection relay as a performance
type test. An IEC 61850 GOOSE enabled test set is used
with 0.1ms resolution. During the performance type test
of an IED, transmission traffic must also be considered.
By calculating the maximum possible traffic on the LAN
to which the IED is intended to be connected, or stating
the maximum traffic value for which the IED can either
publish or subscribe to GOOSE within the specified time,
the performance criteria must be stated by the vendor.
In practical situations, there are many kinds of GOOSE
published by other IEDs and by primary equipment. All of
these frames and also frames of other protocols could be on
the same LAN network simultaneously. This point must,
therefore, be considered when the possible maximum
network traffic is calculated. A performance calculation
example is also included in Appendix I of IEC 61850-5.
Table 1: An example of the test result for GOOSE
transfer time.
27
Example of utilizing GOOSE
for protection testing purpose
28
Simplified sequence model
of procedures in a time crucial proces
GOOSE packet
receive
IED primary
process
GOOSE packet
send
Table 1
Test results for GOOSE transfer time
Network
Traffic
(*1) (*2)
Maximum response time
of GOOSE (*2)
Autoreclose by
GOOSE (*2)
50 Kb/S
100 Kb/S
200 Kb/S
< 0.7 MS
< 0.7 MS
< 0.7 MS
Successful
Successful
Successful
*1 Simulated only by GOOSE which were all captured and processed by
GRZ100 at the same time
*2 Test condition/hardware configuration is same as Figure 6
Table 1 shows an example of the test result
for GOOSE transfer time (‘ta’ in Figure 4) and
of the result of Autoreclose utilizing GOOSE
for all interaction signals in a certified IEC
61850 conformant numerical distance protection relay with simulated network traffic.
29
Trip GOOSE transfer time
measurement results
PAC.WINTER.2008
It is important
to reduce the
time between
the GOOSE
receive and
response.
by Hachidai Ito and Kenichiro Ohashi , Toshiba Corporation, Japan
IEC 61850
protection
46
To obtain
the expected
benefits of
As another aspect of performance evaluation for a single
IED, the GOOSE response time shall be checked since it
directly affects the system performance.
As part of system evaluation, an easy way to test the
response time of an IED could be by the ‘Ping-Pong’
technique as described below. This method is very efficient
because it can check the subscribing time (‘Tc’ of Figure
4) and publishing time (‘Ta’ of Figure 4) at the same time
without other external inputs or triggers.
Set the IED to publish GOOSE (A) when GOOSE (B)
is subscribed.
Arrange external equipment connected to the LAN to
publish GOOSE (B).
Observe the behaviour of GOOSEs with external
equipment connected to the LAN.
Figure 10 shows the test result of an IED, a certified IEC
61850 conformant numerical distance protection relay,
with an IEC 61850 GOOSE enabled test set.
As shown, the response time here is sufficiently fast
to adhere to the requirements defined in the standard
(Figure 10). However, as it is only a single test result then
to actually verify the performance, we must repeat the
same case at least e.g. 100 times and check the maximum
response time under simulated network traffic.
As an extension of these procedures, this ‘Ping-Pong
GOOSE’ can be played continuously between two or
more IEDs without any external equipment. In case of
two IEDs, the same settings as shown above are sufficient
with the exception of exchanging GOOSE (A)/GOOSE
(B) and inverting their logic at one IED. An IEC 61850
network analyzer could observe the continuous ‘Ping-Pong
GOOSE’ rally, and as for evaluation, it is only necessary to
determine how many GOOSEs were issued to the network
in a certain time period, i.e.
10
[ Time period ] / [ Number of GOOSE issued ] =
[ Average response time ]
Here is a test result captured by an IEC 61850 protocol
analyzer, which was carried out between two certified IEC
61850 conformant devices (Figure 11). Furthermore in
this case, once the ‘Ping-Pong’ is set, the IEDs start playing
‘Ping-Pong’ as soon as the IEDs are connected to the
network. Therefore, it could be used also for the purpose
of increasing the network traffic.
Note that cases utilizing GOOSE introduced here can be
basically also applied to all IEC 61850 conformant devices
which support the service for GOOSE.
In order to obtain the expected benefits of IEC 61850
it is of critical importance to apply IEDs which provide
sufficiently high performance of GOOSE messaging.
IEC 61850 GOOSE messaging is now widely used
in substation applications replacing methods using
binary inputs/outputs and wires. GOOSE messaging
performance evaluation for certified IEC 61850 conformant devices is one of the critical issues in achieving required substation functions such as sending
trip commands or exchanging interlock status.
11
Single 'Ping-pong GOOSE'
for performance evalation of an IED
Rally of 'Ping-pong GOOSE'
between two IEDs
Protection Relay
Protection Relay
IEC 61850,it
Test Device with IEC 61850
2. GOOSE (A)
1. GOOSE (B)
is critical to
apply IEDs with
sufficiently high
performance
of GOOSE
messaging.
PAC.WINTER.2008
Protection Relay
GOOSE (A)
GOOSE (B)