1. IEC 61850-9-2 conformance test and the required network bandwidth
Smart Grid Testing department
Woohyun Seo

2. Contents Merging Unit Tripping in Process Bus Conformance test
Introduction, Advantages, Standards
Tripping in Process Bus
Conformance test
Network Bandwidth for Process Bus
Conclusion

3. 1. Merging Unit - Introduction
Busbar
Analog Input Transformers
Analog Measurement
A/D conversion
are moved away from the IEDs and “are placed” into the merging unit
Conventional CTs/VTs
Advantage
. Good saturation curve
Disadvantage
. Signal level output
. Noise influence
Non-Conventional CTs/VTs
Merging Unit
Proprietary Link
Controlled Ethernet Ports
Line protection
PIOC, PTOV, …
Bay controller
CSWI, CSYN, …
Device control interface
Process Bus
Time synch
Configuration

4. 1. Merging Unit - Advantages
Advantage of process bus with MERGING UNIT
Reduce wiring cables and # of CTs/VTs
In conventional scheme, every IED needs CT(s) and/or VT(s) for processing
Improved measuring accuracy
Short distance between CTs/VTs and signal processor
Adopting high-performance eCT/eVT
Small, Light, Broad dynamic range, Isolation between primary & secondary circuits, etc
Unified platform for information sharing
Merging unit broadcast the digitized measured data based on IEC standard

5. 1. Merging Unit - Standards
Signal processing interface
Digital interface
(Communication)
IEC TC38 WG37
IEC TC57 WG10
IEC , ADDITIONAL REQUIREMENTS FOR ELECTRONIC VOLTAGE TRANSFORMERS
IEC , Specific Communication Service Mapping (SCSM) – Sampled values over serial unidirectional multidrop point to point link
IEC , ADDITIONAL REQUIREMENTS FOR ELECTRONIC CURRENT RANSFORMERS
Withdrawn
IEC , Specific communication service mapping (SCSM) – Sampled values over ISO/IEC
IEC , DIGITAL INTERFACE FOR INSTRUMENT TRANSFORMERS
Implementation …
Implementation Guideline for Digital Interface to Instrument Transformers using IEC
IEC , Stand Alone Merging Unit
Conformance test procedure
Test procedures for Sampled Values Publishers according to the "Implementation Guideline for Digital Interface to Instrument Transformers using IEC " (9-2LE)
Not published

6. 2. Tripping in Process Bus
GOOSE OUT

7. 2. Tripping in Process Bus
GOOSE IN
GOOSE OUT
SAMPLED VALUES
Time requirement is more critical!!!

8. 2. Tripping in Process Bus
A/D signal processing time delay
Primary condition for available protection
Guideline : 3 ms (IEC )
Packet jitter and latency control
Part of performance test
Only the total number of packets in 1 sec existed
Standard based syntax
Following IEC and IEC series
Network bandwidth
Lack of bandwidth makes packet loss
Out of range from conformance test

9. 3. Conformance test Conformance test procedure
Documentation : 2 test cases
Configuration : 9 test cases
Communication services : 17 test cases
50/60 Hz, 80/256 samples
According to “Guideline”, Time master is based on “PPS”

10. 3. Conformance test SV conformance test Conformity
Verify conformity and performance
Performance is very important for MU
Accuracy test is not included
Conformity
Connecter and Link layer format verification
100Base-FX full duplex with ST, MT-RJ, LC fibers or Rj45
APDU or ASDU format verification
Quality and Test bit verification

11. 3. Conformance test Performance test
SV maximum delay criterion : ~3 ms(3.3 ms)
Verification # of messages per cycle
PPS pulse
SV with SmpCnt=0
SV delay
Publisher(MU)
Subscriber … … …
PPS pulse
PPS pulse
messages for 80 samples of 60 Hz
Jitter and latency control are required!

12. 3. Conformance test Limitation of SV conformance test
Not verifying focusing on packet treatment
What if MU makes the signal processing delay?
CT/VT or eCT/eVT
Vo, Io
PPS pulse
SV delay
Signal processing delay
SV with SmpCnt=0
Vo, Io
Real tripping time may be delayed

13. 4. Network Bandwidth for Process Bus
Background from IEC
Telegram length : 888bit(packet) + 96bit(interFrame)
BW : 80samples*60Hz*984bits < 5Mbps (per stream)
Reliable?

14. 4. Network Bandwidth for Process Bus
Simple test
Merging Unit
100Mbps, Max 2 streams, 80samples/Hz
Time Synch
1 PPS from GPS
Switch
Separate network only for process bus with MU
Switching latency : 7 micro second
Switching bandwidth : 9.2 Gbps
Testing tool
Smart bit applications
Packet size : 140 bytes(SMV packet : 128 bytes)

15. 4. Network Bandwidth for Process Bus
1 stream
Throughput
Latency
Packet Loss
Passed Rate(%)
(01,01,01) to (01,01,02) (pks/sec)
94.12
73529
Rate Tested(%)
(01,01,01) to (01,01,02) (us)-CT
70.00
18.0
75.00
18.6
80.00
17.4
85.00
17.7
90.00
95.00
100.00
Rate Tested(%)
(01,01,01) to (01,01,02) (%)
70.00
0.000
75.00
80.00
85.00
90.00
95.00
1.080
100.00
5.789
Network load : 5.88 Mbps
Switching bandwidth(9 Gbps) is enough to handle this amount of traffic load
(9,000 / 5.88 = 1,530 ports can be supported)

16. 4. Network Bandwidth for Process Bus
2 streams
Throughput
Latency
Packet Loss
Passed Rate(%)
(01,01,01) to (01,01,02) (pks/sec)
88.40
69061
Rate Tested(%)
(01,01,01) to (01,01,02) (us)-CT
70.00
18.9
75.00
17.0
80.00
19.0
85.00
23.0
90.00
2649.6
95.00
100.00
Rate Tested(%)
(01,01,01) to (01,01,02) (%)
70.00
0.000
75.00
80.00
85.00
90.00
1.906
95.00
7.156
100.00
11.577
Network load : 11.6 Mbps
= 2*5.8 Mbps
Network load for 2 streams is similar to twice one for 1 stream

17. 5. Conclusion Expectation
Network Bandwidth measurement in the real (simulated) process bus network
Theoretically, 100 Mbps based network can handle more than 10 MUs
But, need to check if how many MUs can implemented
For more stable process bus implementation, the critical points will be
Actual A/D signal processing time delay in device
Packet jitter and latency delay from device

18. Thank you for listening
Any Questions?