23-06-2014, 11:05 AM
Key Performance Indicators of a Transmission System
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INTRODUCTION
Electricity transmission companies normally
measure their achievements by using various types of
qualitative and quantitative assessments [1]-[4]. They
measure achievements of their objectives through
monitoring a number of performance indicators [5], [6].
These quantitative indicators are commonly known as
Key Performance Indicators (KPIs). Once company
operating objectives are clearly determined, both
technical and financial KPIs can be used to measure the
degree of achievements.
These selected KPIs were recommended by the
CIGRE Study Committee C2 and JWG B3/C2-14 Task
Force 02, [1]. A customer of a transmission grid is
considered to be each company that has a connection
agreement with the grid. To account for customers with
multi-connection-points to OETC grid, such as
DISCOs, we may use the number of connection points
in place of the number of customers. An alternative way
is to count the number of supply delivery points from
the transmission system to distribution networks and
direct customers.
Results of the main transmission grid in Oman,
over the last 3 years, are presented. The results are
useful in indicating trends of the KPIs and
determination of future targets to improve transmission
system performance.
The goal of presenting the paper at the GCC 09 is
to open a discussion among transmission utilities in the
Gulf region for introducing possible common KPIs to
evaluate system performance. This could provide an
excellent opportunity to establish acceptable
benchmarks of the proposed KPIs.
The next sections of the paper are organized as
follows. Section 2 describes the main transmission
system of Oman including generating stations, grid
stations, transformers and transmission lines. Some
statistical information is summarized in Section 3 to
show technical and financial performances. Section 4
concerns with the definitions and equations of the
performance indicators. Section 5 gives the results of
the recommended KPIs calculated during the last three
years. Section 6 presents three additional KPIs,
including the Customer Average Interruption Duration
Index (CAIDI), Voltage Deviation Index (VDI), and
Frequency Deviation Index (FDI). Finally, Section 7
summarizes main conclusions and recommendations.
MAIN TRANSMISSION SYSTEM
OF OMAN
The existing transmission system extends across
the whole of northern Oman and interconnects bulk
consumers and generators of electricity located in the
Governorate of Muscat and in the regions of Batinah,
Dhahirah, Dakhliyah and Sharquiya. Figure 1 shows a
geo-diagram of the system. It has two operating high
voltages, i.e. 220 kV and 132 kV.
After the electrical sector was unbundled; Oman
Electricity Transmission Company (OETC) has taken
over the operation of transmission system since the 1st
of May 2005. The present OETC transmission system
consists of:
PRESENT OETC PERFORMANCE
INDICATORS
At present a number of performance indicators are
used in Oman Electricity Transmission Company.
Details can be found in the Annual Reports [7]–[9].
Some operational and financial statistics as well as
performance indicators are summarized here.
A. Operational and Safety Performance
Table (I) summarizes some statistical information
on the operational performance of the main
transmission system of Oman. The average annual
increase in the regulated units transmitted is 13.1%. The
peak load increases with a rate of 10.4% per year. Four
new grid stations ware installed in 2007, but no
additional grid stations was introduced during 2008.
More than 20 new grid stations are planned to be build
during the five year plan (2009-2013). In the field of
HSE activities, OETC achieved zero injury lost time in
2008.
Transmission Losses
This KPI gives indirect indication of the
transmission grid efficiency. Transmission losses can
be calculated as the difference between the total
electrical energy received from the generating plants
and the total energy supplied to all transmission
customers. It is usual to express losses as a percentage
value rather than absolute value. The losses are
measured over a definite period (e.g. one year or one
month). The total energy received is the sum of
energies measured at the connection points with
generators. Similarly, the total energy supplied to
customers is the sum of energies measured at grid
supply points to all transmission customers. These
include all DISCOs and all directly connected
customers. Time of measurement and position and
accuracy of the instrumentation used should be
carefully considered.
CONCLUSIONS
The paper has described a number of key
performance indicators for electricity transmission
system. These include a group of six KPIs
recommended by the CIGRE Study Committee C2 and
JWG B3/C2-14 Task Force 02 and results of the
application to Oman electricity transmission system. A
group of three additional selected KPIs have been also
proposed. The two groups cover important practical
performances of electricity transmission systems. These
include availability, reliability, quality and maintenance
cost indicators. The KPIs can be used to measure the
system performance compared to benchmarks and to
illustrate the trends in these indicators. Thus, companies
can set targets and take corrective actions, if necessary,
to improve system performance.
These KPIs may provide a useful tool for
evaluating the operational performance of transmission
systems in the Gulf region. The GCC CIGRE is
encouraged to establish a task force committee from the
countries in the region to further study the possibility of
using these KPIs. Precise definitions, methods of
calculations, procedures, etc, need to be agreed among
all parties.