SCADA application in Kenyan National Power Grid

220kV and 132kV network voltages

The entire 220 and 132 kV transmission system is supervised from the National Control Centre (NCC). At 220/132 kV, 220/66 kV and 132/66kV substations the NCC also controls the 66kV busbar voltage. In the case of SCADA system disturbances, the 220kV and 132kV substations can also be controlled from the RCCs.

The National Control Centre (NCC) located at Juja road in Nairobi is responsible for operation of the Kenyan power system as a whole.

Specifically it is responsible for:

• Long, medium and short term planning of the future operation of the power system
• Proper function and administration of the power system
• Control and monitoring of the entire transmission and distribution networks
• Voltage control in the 220kV, 132kV network and the voltages at the in-feed points to the 66kV and 33kV networks (bus voltages)
• Security analysis of the overall network and applying control actions that achieve the goal of the system security and economy
• Supervision and monitoring of system and frequency and initiating corrective measures as necessary
• Determination of spinning reserve for large and medium size power system
• Monitoring the 132kV DC tie line and control of the power purchase from Uganda
• Analysis of outages affecting the power system and equipment
• Preparation of system operation statistics

The case study for the SCADA system was undertaken on the Kenya National Grid which is shown in Figure 1.

Data Acquisition and RTUs

The functions to be performed by the SCADA system are described in detail in this section. Real time data is collected from the following sources for use by the SCADA system. 23 existing RTUs communicate with the SCADA system through dedicated data channels.

1 new contractor supplied local RTU and 1 re-used RTU at the NCC are located at the computer room for training, maintenance and testing purposes. Spare RTUs are provided and installed with simulation tools to simulate process inputs and outputs.

Calculated data – These are generated by programs that periodically calculate database values. The calculated data may be generated by programs that are part of the data acquisition function or other application functions. It may be analog or discrete in nature.

Non-telemetered data entered by operator – These data may be analog or discrete in nature and are similar in all aspects to data collected from RTUs.

RTU data

Any RTU data may collect data from more than one substation or a substation may have more than one RTU. All alarm and events messages generated by the SCADA system provide the name of the substation and bay from which the data originated.

• Periodic scans: it is possible to assign each telemetered point to one or more scan groups. Data is collected from the RTU by specifying the scan group.
• Demand scans: the SCADA system is able to collect any and all status and analog values from any RTU on a non-periodic basic.
• Calibration, maintenance and test: the operator is able to declare any RTU in the test mode for purposes of calibration, maintenance or testing.
• Telemetry failure and delete from scan: if valid data are not received from an RTU in response to a scan command, another scan request for data from that source is issued.