Andrew Kasembe

Antonin Popelka

Erick V Mgaya

Jan Svec

Josef Tlusty

Tomas Sykora

Zdenek Muller

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 C I R E D 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 
 
Paper 0681 
 
 
CIRED2009 Session 3 Paper No  0681     
THE MONITORING OF POWER SYSTEM EVENTS ON TRANSMISSION AND 
DISTRIBUTION LEVEL BY THE USE OF PHASOR MEASUREMENT UNITS (PMU) 
 
 
 Josef TLUSTY Andrew KASEMBE       Zdenek MULLER                    
 CTU FEE – Czech Republic CEPS – Czech Republic    CTU FEE – Czech Republic    
 tlusty@fel.cvut.cz kasembe@ceps.cz mullez1@fel.cvut.cz          
  
 Jan SVEC Tomas SYKORA Antonin POPELKA 
 CTU FEE – Czech Republic    CTU FEE – Czech Republic  AIS - Czech Republic 
 svecj3@fel.cvut.cz sykorat1@fel.cvut.cz popelka@ais-brno.cz 
 
 Erick V. MGAYA Oumar DIALLO 
 DIT - Tanzania CTU FEE – Czech Republic    
 emgaya@yahoo.com diallo1@fel.cvut.cz 
 
ABSTRACT 
Large power system disturbances and their consequences, 
represent a challenging problem for the power industry and 
especially for the network system operators, the ones who 
are responsible for the network operation at large, its 
security and reliability. This fact has reinforced interest in 
the new generation of monitoring systems with the aim to 
gain if possible a precise and maximum knowledge about 
those disturbances and their impact. Most of these severe 
events with impact on the entire system typically occur in or 
near the transmission network and are therefore best 
monitored at transmission system level. This puts great 
demands on the equipments and in general restricts the use 
of the data since it becomes property of the transmission 
system operator.  
Synchronized Phasor Measurement System has emerged as 
a powerful tool to improve power systems performance and 
reliability and fault localization possibility. Typical example 
of fault event that occurred in the transmission system and 
which was well registered by Phasor Measurement Units 
(PMU) that are installed in the distribution system will be 
shown in this paper. 
INTRODUCTION 
The deregulation of the electric power industry, the 
demands for better energy quality and restrictions on the 
expansion of the transmission and distribution system have 
increased the complexity of the power system operation [1]. 
While the power system is continuously exposed to 
different disturbances that range from small ones with little 
impact on operation to large ones with severe consequences, 
including blackouts, secure and reliable operation remains 
to be a fundamental requirement for a power network 
system. Only to mention, the following issues from power 
industry deregulation point of view have heighten need for 
more rigorous security assessment: 
• Aging transmission and distribution infrastructures, 
usually means potential components failures 
• Increasing number of small and distributed generators 
brings uncertainty in dispatch patterns 
• Cutbacks in system maintenance that means potential 
for failures such as flashovers to trees 
• Dependence on information technology may leave 
operators blind 
• Expansion of interconnection network system may 
lead to exposure to cascading disturbances. 
• Insufficient and/or improper generation/transmission 
resources which may result from the lack of integrated 
system planning 
In addition to those facts mentioned above (which can be 
classified as long term and development planning factors), 
unpredicted events can stress even the best-planned system 
beyond the acceptable limits. Some of the reasons for less 
than complete system reliability are: 
• Unpredicted changes in power systems, which may 
differ dramatically from the forecasts (one of the fault 
events that will be discussed later happened due this 
reason) 
• A very large number of possible operating 
contingencies  
• A combination of unusual and undesired events (for 
example, human error combined with heavy weather 
or other combination of events that would be 
considered very improbable in the earlier times of 
power system evolution 
• Reliability design philosophy that is pushing the 
system close to the limits, imposed by both economic 
and environmental pressures 
Upon capturing and acquiring a precise knowledge, a power 
system disturbance is mitigated via protection and control 
actions, required to stop the power system degradation, 
restore the normal state and minimize the impact of 
disturbance.  
OVERVIEW OF MONITORING SYSTEMS 
The disturbance aspects mentioned above have required 
better tools for monitoring and control for power system in 
real time operation. Conventional operating guides derived 
by conducting off-line studies have become inadequate 
because number of possible conditions and contingencies 
becomes unmanageable as system complexity increases, 
exact system state is never accurately captured by forecast, 
most study results are never used and some conditions 
 C I R E D 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 
 
Paper 0681 
 
 
CIRED2009 Session 3 Paper No  0681     
which usually cause problems have never studied off-line 
(such as N-1 event evolving into an N-3 event).  
As a promising solution is an On-line security monitoring 
and assessment system which can be based for example on 
measurements from Phasor Measurements Units. This 
system provides a possibility for a network topology and 
operating conditions to be modelled in real time as seen by 
the operator in the control room.  
A variety of methods of monitoring, detecting and locating 
faults on power transmission and distribution system exist. 
Most of these methods utilize measurements from voltage 
and current transformers at substations or switching stations 
to perform their analyses. To gain knowledge about the 
disturbances and their impact, it is necessary to monitor the 
system at sufficiently many geographical locations using 
measurement equipments with sufficient bandwidth. The 
collected data must also be condensed into useful 
information and properly analyzed. 
Monitoring of events in the power system itself provides a 
great deal of insight into the behavior of the system. Due to 
the interconnection and mutual interaction between 
transmission and distribution systems, and in case of 
absence of the monitoring units in the transmission system, 
such monitoring units in the distribution system can be used 
to locate, forecast danger or even fault events in the near 
point of transmission system. Most of these severe events 
with impact on the entire power system typically occur in or 
near the transmission network and are therefore best 
monitored at transmission system substations. This puts 
great demands on equipments and in general restricts the 
use of the data since it becomes property of the transmission 
system operator. An alternative is measurement at lower 
voltage levels.  
This paper documents the close agreement between 
frequency measurements at low and high voltage levels 
during fault in the transmission network. The very high 
quality of the data suggests that valuable information about 
the transmission system can be obtained at lower voltages. 
This aspect is documented by typical example of fault 
events that occurred in the transmission system and were 
well captured by PMU in the distribution system. 
Here, a point can be made that, application of PMUs has 
been rising as one of the new tools to improve the power 
system monitoring and performance. A more complex 
system comprising of PMUs is usually referred as Wide 
Area Measurement System (WAMS). These systems are 
basically composed by PMUs connected to a Phasor Data 
Concentrator (PDC) and applications for monitoring and 
control of power system real time operation [2]. 
Synchronous phasors  
Phasor represents information about the magnitude of 
measured quantity and about its rotation – angle with 
respect to reference vector. Synchronous phasor is 
characterized by position – angle in selected time point. Set 
of synchronous phasors of electric quantities in distribution 
network is denoted as phasor snap of network. 
• All phasors in one snap are obtained exactly in the 
same time 
• Reference vector has zero angle 
• Phasor is complex number associated with the cosine 
wave 
• Time dimension is already contained in the phasor 
snap 
Fundamentals for synchronous measurement and 
communication are described in IEEE Standard C37.118 – 
2005 
 
PMU
GPS
PMU
GPS
Lokální
PDC
Rozvodna 1
PMU
GPS
PMU
GPS
Lokální
PDC
Rozvodna X
PDC
Aplikační
Server
Estimovaná data
Fázory
Konfigurace
Vybraná sada dat
SCADA
DŘS
 
Fig. 1: Typical structure of system WAM 
PHASOR MEASUREMENT  
System for synchronous phasors measurement is used in 
certain distribution regions in Czech Republic. Phasor 
measurements in 128 switching stations with the total of 
475 nodes are available at the end of 2008. The map shows 
location of terminals in distribution network. 
Terminals for the phasor measurement (PMU) are placed in 
switching stations. The terminals measure voltage phasors 
in 10, 22, 35 and 110 kV levels. Selected busbars, lines and 
generator outlets are fitted with PMU. Measured data are 
transferred to the central phasor concentrator (PDC) via 
reserved communication channels. Consequently, the data 
are processed and network phasor snaps are created from 
data measured in the same time point. 
The network phasor snap is presented to the users in 
suitable format and it is also continuously transferred to 
other applications for user processing. Examples of 
consequent applications can be e.g. dispatcher system, state 
estimation and network status calculation programs, 
network stability analysis etc. Archive data for analysis of 
network behavior are also available.   
 C I R E D 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 
 
Paper 0681
 
 
CIRED2009 Session 3 Paper No  0681     
Some data from 110kV was used for presented study. 
ADVANCED FAULT LOCALIZATION 
The data measured in PMUs and transferred to a central unit 
can be processed using advanced methods for fault 
localization. The use of new methods is suitable for 
example in case of a multiple long lines or two long parallel 
lines, where the classical approach always cannot lead to 
the correct determination of the fault distance. 
The description of Z and Y parameters are used for the 
network calculations at present for historical reasons. The 
suggested use of H parameters shows the possibility of 
more accurate fault localization and at the same time it 
works thoroughly with wave description of the line. 
Let’s consider the equivalent diagram of the single-phase 
line section as the T-network. It can be described by means 
of H-matrix (H = hybrid parameters). Its elements are 
known as Blondel constants: 
2 1
2 1
ˆ ˆ
ˆ
ˆ ˆ
U U
H
I I
⎛ ⎞ ⎛ ⎞
=⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟
⎝ ⎠ ⎝ ⎠
 
Advantage of using H description consists in an easy 
describing of cascading elements. For example cascading of 
two sections of the line with the same parameters:  
3 2 12
3 2 1
ˆ ˆ ˆ
ˆ ˆ
ˆ ˆ ˆ
U U U
H H
I I I
⎛ ⎞ ⎛ ⎞ ⎛ ⎞
= =⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎜ ⎟
⎝ ⎠ ⎝ ⎠⎝ ⎠
 
Likewise, the nth power of H-matrix gives the same 
meaning as sorting n circuits of the same sections 
consecutively. Limiting the transition by considering 
partitioning into infinite small differential sections will lead 
the description into the telegraphic equation.  
Now, consider the situation where the line is imaginarily 
divided into n sections, whereas the first m sections is 
unfaulted, (m+1)th section is faulted and the remaining n-
m-1 sections is also unfaulted. Then the system can be 
described by: 
1 11
1 1
ˆ ˆ ˆ
ˆ ˆ ˆ ˆ. . . .
ˆ ˆ ˆ
n m n m
n
U U U
H H H H
I I I
− −
Σ ↓
⎛ ⎞ ⎛ ⎞ ⎛ ⎞
= =⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎜ ⎟
⎝ ⎠ ⎝ ⎠⎝ ⎠
 
Using this method for a known fault character requires the 
use of the method for determination of the function 
minimum.  
Fig. 2 shows the error course for the faulted conductor. The 
error failure values for the non-faulted conductors were 
about hundred times or much higher than for the faulted 
conductor. Therefore the assessment of the right affected 
conductor was simple. Also the assessment of the right 
failure place on the affected conductor was clear because 
the error value in that point is much lower than in the 
neighboring points. 
 
 
Fig. 2: Fault localization 
FAULT EVENT IN THE STUDIED SYSTEM 
This section will be dedicated to the description of the fault 
event that occurred in the transmission network system of 
the Czech Republic (CZ) and were captured by PMUs 
which are installed in some parts of the distribution network 
system. At that time no PMUs were installed in the 
transmission network. 
The fault event on July 25th 2006 
 
Fig. 3: Division of the network into two island areas, blue 
and red respectively 
 
The 25th July 2006 was a very hot day almost with tropical 
temperatures. The actual day energy consumption was much 
higher than its forecasts. This increase of energy 
consumption was registered not only in the CZ but also in 
other parts of Europe. Day energy market, planned energy 
exchange and real-time network operation in most countries 
like CZ found to be in crisis. In the CZ network about 5 of 
its lines were on planned maintenance (i.e. were off-line). A 
combination of unusual events (line disconnections due to 
short circuits together with the decision  of the dispatching 
center to trip the one line because of overload triggered 
other cascading disturbances (see Fig. 3).   
It is assumed that this was related to the oscillation 
phenomenon which was registered at this hour. Because of 
these outages the CZ network system broke into two 
islanding operations (see Fig. 3), blue and red color 
respectively. Part of the system with blue color experienced 
 C I R E D 20th International Conference on Electricity Distribution Prague, 8-11 June 2009 
 
Paper 0681 
 
 
CIRED2009 Session 3 Paper No  0681     
excess power production than its consumption, frequency of 
this part of the system exceeded predefined upper limit, i.e. 
50.2 Hz. In contrary, the red part experienced power 
deficiency of about 1500 MW and frequency went down the 
lower limit 49.8 Hz. The resulted power unbalance affected 
the CZ planned power exchange.  
The described phenomenon which resulted into islanding 
operation was precisely captured by PMUs which at that 
time were only installed in the distribution system. 
Frequency deviation which was computed from the PMU 
measurements located at 110 kV sides (see Fig. 3), of the 
substations of Vitkov (green color) and Chrast (red color) 
indicates how the system frequency gradually changed 
before the whole system broke into islands (see Fig. 4).  
The island occurrences can be also depicted from the 
computed frequency deviation of the mentioned monitored 
substations as can be seen from Fig. 5. 
This picture demonstrates a very good visibility of dynamic 
process in transmission grid from distribution level. The 
graph shows the critical value of relative angle between 
referred nodes. The angle about 54° starts network splitting 
to islands repeatedly in this case. 
 
 
Fig. 4: Case study of PMU application in DS 
CONCLUSION 
The paper deals with two basic tasks: advanced approaches 
to the fault localization and correspondence of phenomena 
in the transmission and distribution systems. 
The big advantage of calculation using H parameters is the 
possibility to describe line like a product of H matrices, 
which enables to include all discreteness of the line in the 
calculation, which must be usually neglected for the reason 
of calculation while using other methods. Consideration of 
all partial special influences and their inclusion in H 
matrices of the system approaches the mathematical model 
more closely to the physical reality.  
This paper suggests that the effect of switching operations 
and fault events in the transmission network will be visible 
in low-voltage measurements in the interacted distribution 
system. Access to measurements from several distribution 
networks makes it straightforward to classify events as 
occurring on transmission or lower levels. 
-1500
-1000
-500
0
500
1000
1500
2000
2500
12
:00
12
:10
12
:20
12
:30
12
:40
12
:50
13
:00
13
:10
13
:20
13
:30
13
:40
13
:50
14
:00
14
:10
14
:20
14
:30
14
:40
14
:50
15
:00
15
:10
15
:20
15
:30
15
:40
15
:50
16
:00
16
:10
16
:20
16
:30
16
:40
16
:50
17
:00
49,85
49,9
49,95
50
50,05
50,1
50,15
50,2
50,25
dP [MW] f [Hz]
Exchange deviation
Frequency
1st  Island incident
2 nd  Island inident
3 rd  Island incident
4 th  Island incident
 
Fig. 5: Frequency deviation and angle computed from 
PMUs at Vitkov and Chrast. 
 
It can also be deducted that the use of PMU data from  
110 kV network provides specific knowledge and 
information about transmission system dynamic behavior 
that can be registered and obtained at lower voltage levels. 
From the case study above only part of information is 
available, it is not for instance obvious the extension of the 
island area, therefore the obtained information is not 
complete and should be used with care but suggests that a 
network of phasor measurement units at a lower voltage 
level may deliver high-quality system-wide data sets, where 
the phase angle information makes it possible to pinpoint 
the location of transmission system events. Information of 
islanding occurrence is provided in our case study. Future 
work can be dedicated at setting up a reasonable PMU 
system at transmission level, collect and analyze data. This 
process has been launched by CEPS. 
ACKNOWLEDGEMENT 
Financial support of the Ministry of Education, Youth and 
Sports, through grant number MSM 6840770017, is highly 
acknowledged. 
REFERENCES 
[1] I.C. Decker, May 2004, "Synchronized Phasor 
Measurement System: Development and 
Applications", IX Symposium of Specialists in Electric 
Operational and Expansion Planning SEPORE, Rio 
de Janeiro, Brazil 
[2] B. Bharat, G. Rodriguez, December 2004, 
"Monitoring the Power Grid", Transmission and 
Distribution World Magazine, pp. 28 - 34 
[3] A. Stankovic, October 2000, "On Model Based 
Estimation of Dynamic Phasors", Proceedings of the 
NAPS, Waterloo, Canada 
[4] V. Böhm, A. Popelka, B. Sadecký, “Synchronous 
Measurement in Electrical Networks”, CIRED 2005 
Torino, Italy 


The monitoring of power system events on transmission and distribution level by the use of phasor measurements units

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The monitoring of power system events on transmission and distribution level by the use of phasor measurements units

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