Thesis (Masters Diploma(Technology) - Cape Technikon, Cape Town, 1996 / ESKOM control a massive power grid in a vast geographical area in the R.S.A.. This
power originates at the power stations, from where it is distributed to the users. All
the power generated is pumped into a National Power Grid. The backbone of the
network consists of the following supply voltages:
• 765 kV
• 400 kV
• 132 kV
These voltages are stepped down locally at substations to lower voltages for the
customers. Bigger customers (e.g. Municipalities, Mines, etc.) are bulk users and use
high voltages. Lower voltages range from 220V up to 66kV.
In order to ensure a good service to all power user customers ESKOM must be able to
identify power failures and other abnormal conditions as quickly as possible and react
fast to restore power again.
When supervising a power grid good communication systems are essential.
Communications systems serve as links between the following functional systems:
• Contacting personnel with radio (Mobile or Handheld)
• Contacting personnel \\ith pagers (Digital or Analogue)
• Receiving up to date information on the SCADA network
• Protection on power lines and transformers (Fault conditions)
Without good telecommunication ESKOM will not be able to control the national grid
efficiently. The Telecommunication Department fulfil a vital role ensuring that the
National Grid functions at its optimum.
It is normally impossible to do an accurate measurement of the power level in dBm or
dBv on a communication line while an RTU is communicating to the MASTER.
This is mainly because the duration of the data burst on the communication line is less
than the sample time required by the level meters available. The time duration on a
TELKOR PUTU general poll is 250ms. With the available digital meters (e.g. W & G
SPM33A) it is totally impossible to get a power level reading because the sampling
time of the instrument is I second. With the analogue meters available (e.g. W&G
SPM09, SPM31) it is possible to get a reading, but this normally between 2 dBm and
4 dBm Iow, because of the dynamic behaviour of the moving coil. Thus before the
pointer of the meter has reached the correct level, the burst of data has stopped This
is characterised by three quantities:
1. The inertia (1) of the moving coil about its axis of rotation.
2. The opposing torque (S) developed by the coil suspension
3. The damping constant (D)
A solution is to sample the receive and transmit levels during polling with an
electronic circuit and feed it into an ADC connected to a Microcontroller (e.g. 8031
family). The Microcontroller will do all the converting and mathematical functions
and will output a value through a DAC. This output value will be a current (mA)
value directly proportional to the input level (e.g. -20dBm to OdBm = 0 to 5mA).
These RX and IX level values can be fed into analogue inputs of the RTU. This realtime
measurement of the levels on communication lines will be available at the
SCADA master. These values can then be trended and if a downward trend is
observed, maintenance can be done on the line before a failure. This should result in
higher availability of the SCADA network.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/1104 |
| Date | January 1996 |
| Creators | Delport, Pierre |
| Publisher | Cape Technikon |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/za/ |
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