1.3.1.3.2: Systems
Even though most of the underlined processes involved in
operations management cited above are carried out manually, there exist
nevertheless some operations management systems/technologies to aid in their
management.
1.3.1.3.2.1: Existing SCADA
system
Supervision and control of all the operations on the southern
transmission network is done in the control room at the grid dispatch center in
Edea using two SCADA systems deployed on the southern transmission network, the
SKAN4 since 2008 and the LS 2000 since 1979 running in parallel and by a team
of 10 grid dispatch operators working on a shift of 8 hours per day. These two
systems are depicted in the figure below where components of the SKAN4 system
are colored in red
Figure 5: SCADA systems
on the southern grid [1]
This control room depicted in the figure below is made up of a
control desk with two operator stations, each with also two MMI color 21"
Displays, corresponding keyboards and event printers available for display,
printing, control and monitoring of limited parts of the 225 kV/90 kV network
substations and power stations of the southern grid.
The SCADA system supplied by «Landys & Gyr«
consist of redundant (main and back-up) master computers of type LS 2000 to
process information acquired and transmitted from the Substations and Power
stations through the installed RTUs, 7 from type Telegyr 709 as Master RTUs and
12 from type Telegyr 065 as slave RTUs [1]. The information to be processed
includes
§ Critical and non critical alarm signals (AN and AC)
§ Single indications (TS)
§ Double indications (IM and IR)
§ Telecontrols (TC)
§ Measurements (TM)
§ Query signals (QG)
Figure 6: Control room
at dispatch center, Magombe, Edea, Cameroon.
All data from and to the substations and power stations RTUs
are transmitted with 200 Baud Power Line Carrier (PLC) links using the 225 kV
and 90 kV overhead line conductors.
A mimic board is also installed at the control room in front
of the operator desk. Only few information (status indications, alarms and
measurements) acquired directly from the Mangombe Substation are still
available at the mimic board [1]. At the control center the mimic board is
presently used mainly as a passive network single line information board and as
the conventional back up local control panel for the Mangombe 225/90 kV
Substation.
The SKAN4 system supplied by `Siemens' and which runs in
parallel with the LS 2000 system has a similar configuration with the LS 2000
system but consist of 15 TG 805 and 2 TG 065 RTU/data concentrators sending
signals (status, measurements, alarms and control signals) back to a redundant
(master and back-up) set of MMIs for processing through a PLC communication
link. The one operator station with the computers for monitoring, supervision
and control has one keyboard, a mouse and a separate printer for event
printing.
1.3.1.3.2.2: Existing
telecommunication system
The existing telecommunication systems in use for SCADA in
Cameroon (in the southern grid) comprise mainly Power Line Carrier (PLC),
UHF/VHF and Microwave radio links, some Fiber Optic (FO) links installed in
recent time. The telecommunication network is used for transmission of SCADA
data (from some 20 substations and power stations in the 90kV and 225kV
network) and operational voice communication. Except for some links in the
Southern grid, redundant telecommunication paths do not exist.
There are another 5 stations in the north of the country, connected via PLC to
the 90/110kV grid. The PLC links in the northern grid are only used for voice
communication [1]. At present there is no hierarchical structure with regional
control centers i.e. the RTUs send their telegrams directly to the SCC, which
is the high level control center.
The following bullets show the basic SCADA communication
concerns:
· Only some 20 RTUs (out of approx. 30 stations that will
be situated in the 90/225kV southern grid in the future) are connected to the
control center today.
· SCADA data transmission between the RTUs and the
control center is using data channels with transmission speed of 200 bit/s.
For operational voice communication besides the PLC network;
GSM, Cisco IP phones and VHF radio based telephone system are installed for
connection of the SCC and the power stations and substations and other
administrative offices for AESS all over the country. AES SONEL is also using
public telephone lines for the operational voice communication [1].
Besides the usage of PLC, GSM, Cisco IP phones, VHF and
Microwave links, connections to the public telephone services are partly being
used for administrational voice communication from AES SONEL main office with
offices all over the country. Data communication is mostly being done through
emails using an intranet system.
1) PLC (Power Line Carrier) system
Most of the existing PLC terminals are manufactured by AREVA
(former CEGELEC-ALSPA), some by ABB (former BBC). For PLC communication AES
SONEL, is utilizing the frequency range from 40 kHz-500 kHz. The coupling
method used is phase-to-ground coupling [1]. The PLC terminals have a 4 kHz or
2X4 kHz bandwidth respectively, which is used to transmit voice and data
information. Between the substations Logbaba and Koumassi (8.3 km) and between
BRGM and Oyomabang (4 km), each one PLC link is interconnected through coaxial
cables (50 ohm), which are integrated inside the 90 kV overhead line ground
wire. The last part of ground wire between Logbaba and Koumassi is embedded in
the earth with the 90 kV cable. The age of the PLC installations ranges from
some years to over 25 years. Spare parts for the older types of PLC terminals
are expensive or not available any more [1]. Especially for larger stations and
for the interconnection of the power stations to the SCC, the SCADA data
transmission speed of 200 bits/s is insufficient compared to state of the art
SCADA systems. Most of the installed PLC terminals are not operational while in
some cases only voice communication is possible, and the status of some links
is such that they do not provide a reliable transmission medium for the
transmission of SCADA data. Especially with the implementation of standard
protocols (IEC 60870-5-101 and -104) for connection of RTUs to the Control
Center, it is a vital requirement to install reliable data links providing
sufficient data rates.
2) Radio systems
AES SONEL uses UHF/VHF and Microwave equipment in their radio
system. The radio links are used for voice communication to substations, power
stations and to AES SONEL offices (for administrative purposes) [1].Presently,
12 VHF relay stations, with 8 for the south and 4 for the north, cover the
essential routes of HV, MV and LV AES-SONEL electrical
network. Each relay station is corresponds to an independent
sub network and the sub-networks are not interconnected between each other [1].
The majority of the installed radio equipment is manufactured by Motorola of
which some those especially the microwave equipments are non-functional while
some have been abandoned.
3) Fiber optic system
AES SONEL's fiber optic system is presently made up of some fiber
optic cables installed by AES SONEL in the southern grid with the total length
of these fiber optic links summing up to approximately 288 km [1].
4) Telephone system
For operational voice communication within the AES SONEL; PAX
based telephone, GSM and IP telephone systems are connecting the Control
Centers, power stations, substations and administrative offices [1].
For voice communication between the SCC, substations and power
stations in the southern grid of AES SONEL, PAX based telephone systems of
various types and status are installed. The transmission is mainly using the
existing speech channels (4 kHz) of the interconnected PLC equipments between
the substations and power stations. PAX telephone systems are also installed in
the substations and power stations of the northern grid [1].
Operational communication is using not only using the existing
AES SONEL owned telecommunication network, communication with many substations
is also through the Public Telephone Network [1].AES SONEL offices are using
various communication paths for voice and data communication for administrative
purposes (AES SONEL owned as well as Public Telephone Network) such as Cisco IP
phones over the fiber optic links, MTN GSM mobile phones and an intranet system
for data communication over the fiber optic link
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