A voltage dip management program for Swaziland
Abstract
The importance of Power Quality (PQ) is recognised by governments internationally to such an extent that in non-competitive electricity markets such as Southern Africa, it is required by law that the supplier of electricity must comply with a technical minimum standard. It is achieved in mostly, a similar approach in these countries by stipulating these requirements in the license agreement between the supplier of electricity and the energy regulator. The energy regulator normally operates under a government mandate to protect the economy, not only by price regulation, but also by protecting the needs of users in ensuring that the electricity is served at a minimum level in PQ and supply reliability. The above requires that PQ parameters are continuously recorded and monitored for compliance to the minimum technical standards. A PQ monitoring system only presents the visibility on the performance level of the utility. It is the first step to what the energy regulator requires, namely the management of PQ. Data analysis is then needed for the assessment of recorded data. The information resulting is used for deployment in network operation. The latter is the ultimate goal, namely a voltage dip management program. Voltage dips are generally the main focus of PQ. One major reason is that every voltage dip can represent a local outage to a user. A production process can shut down when voltage is reduced for a period within the technical definition of a voltage dip. This voltage dip is only recorded as a dip by the utility and not an outage. It can be that a utility reports high reliability but that the customer experiences a loss of production during every voltage dip. Voltage dips will in general occur much more frequently than interruption events as most of the root-causes (e.g. lightning and birds) are not within the direct control of the utility. Voltage dips constitutes 50% of all PQ problems to be investigated by a utility [6]. Investigation requires finding the root-cause of each dip, the impact on the load, the penetration into the network and finally, the possibilities to mitigation. Most of the voltage dips correlate to an interruption as a voltage dip is mostly the result of a short-circuit condition somewhere in the network. A fault current will normally be interrupted after a period dictated by the trip setting of protection equipment. During the time that the fault current flows, voltage drops over the impedances towards the location of the fault, dictated as the loss of voltage at the point of measurement. A lesser number of voltage dips are expected to be due to three phase - phase load action such as the energisation of transformers and the online starting of rotating loads. These types of voltage dips are expected to be due to a balanced loss of voltage between phases. Most of the voltage dips are therefore unbalanced between the phases. At present, more than 70% of Power Quality customer complaints received by Swaziland Electricity Company are dip related hence the need to develop a voltage dip management program. In this dissertation, the root-causes of the dips, ownership, its impact on customer loads and dip mitigation measures will be discussed in order to formulate an effect voltage dip management program for SEC.
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