Abstract:
The South African power utility, Eskom, and, in turn, the metropolitan and local
municipalities, have difficulty meeting the country's growing demand for electricity. In this
study, electric water heaters have been identified as the appliances consuming the most
energy in residential buildings.
There are periods when the demand for electricity is very high across the power system,
specifically in the mornings and evenings during winter from May to August, when
consumers’ need for electricity, for lighting, cooking, and heating water, peaks. Methods
are constantly being sought to assist Eskom and municipalities with network constraints
and overloading during periods of high demand, as well as to assist consumers in
reducing their electricity costs. Overloading the power system can result in power outages
and blackouts and damage to equipment. These challenges can be prevented by
introducing load management systems, also known as Demand Side Management, to
balance the supply of electricity on the network. This is a method of controlling the load
to meet the demand, thereby reducing peak loads, and maintaining and protecting power
system stability. Constant upgrading of power plants and primary and secondary
substations is needed to meet the growing peak demand, but, alongside this, measures
to save electricity must constantly be explored.
This dissertation examines ripple control as a load management tool to shift the energy
demand of electric water heaters in residential buildings from periods of high demand for
electricity to off-peak periods. Ripple control enables the power utility to switch off the
electric water heaters of a group of consumers simultaneously, to prevent high demand
during peak hours overloading the power system. This could assist municipalities with
network constraints and provide considerable savings to the consumer. This method has
been successfully used throughout South Africa by Eskom and municipalities.
A dynamic of control load model of ripple controller was used in this research, to obtain
real-time load measurements on the consumption pattern of electric water heaters. The
Rietvlei substation is supplied with 400 kV from Eskom transmission lines and stepped
down to 132 kV. Data to measure the load was collected from the City of Tshwane
Municipality’s Eskom meter connected inside the Rietvlei substation. The ripple control
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telegram was injected into the medium voltage busbars in the substation and propagated
down to the low voltage networks throughout the distribution area, where receivers picked
up the signal and switched loads or tariffs, as indicated in the study conducted. The results
confirmed the effectiveness of the ripple controller for load shifting and load factor
improvement during high peak demand.
A capacity test indicated that Centurion has 8 000 receivers to operate. Based on 8 000
receivers, the annual saving on the municipality’s Eskom account is over R 11 592 000
per year at today’s tariff. This provides evidence that the application of such a system is
essential. The prime objective of a Load Control scheme is to do energy shifting and avoid
demand peaks.
