10-04-2017, 09:20 PM
ABSTRACT
The electric distribution network in Nigeria is beset with anomalies in the form of frequent fluctuations, sub-standard voltage and outages that damage both distribution as well as consumer equipment. Residential Consumers have evolved responses to most of these problems by proactively changing the phase to which they are connected. The method used is to bring all three phases to an accessible point and manually select the perceived best phase. This paper presents a model that can help in doing this and effecting load balancing in the system. Issues of transients and overall system stability is considered and it is concluded that if supply authority should allow for such a system, the consumer and the distributing authority will be better for it.
INTRODUCTION
Power distribution in Nigeria is done predominantly at 415V phase phase on 3 phase, 4 wire system. Usually, transformers rated between 50 and 500kVA are used at substations to supply groups of residential and commercial consumers in a radial manner. The high demand for electricity has resulted in overloading at most substations which leads to frequent outage and other anomalies. For the 3 phase system to function with minimum power loss, the leads on the phase must be balanced or as close to balanced as possible. This amongst other requires that the load be balanced. Load balancing is the process whereby loads/consumers are shared amongst the phases in such a manner that the total load at any time on each phase will be approximately equal [1]. [2 and 3] presented phase switching algorithms that can be used for optimal phase balancing switching sets of loads. There are three possible methods of achieving this as highlighted below.
LOAD ESTIMATION BEFORE CONNECTION
In the first method, estimates of the load are used as the basis for allocating the phase to which a consumer is connected in the first instance when being first energized. Unfortunately this estimate often depend on factors that may change such as diversity factor which means the deviation from balance could be quite marked. In a system which is running well within its capacity, this technique can be applied and the deviation from balance may be no more than 20% of the rated current. Unfortunately in Nigeria, except at the inception of a new feeder or in isolated and well-managed loads, the distribution lines are overloaded. This situation coupled with widely changing loading patterns by the consumers can in many instances lead to differences in phase current in the excess of 100%. Automatically losses are very high, and balancing will be required.
In the Nigerian system, maintenance procedures do not include regular and periodic assessment and balancing of the phases. As elsewhere, the largest number of consumers is residential consumers who by regulation must be connected with a single phase meter, usually with maximum amperage of 100A.
Due to the very rapid growth of electric power distribution occasioned by consumer demand, new connections are often done without being recorded. It is further exacerbated by the fact that the lines are substantially overloaded before hand. The resource needed to carry out an authority-supervised balancing operation is very high and may not even be achievable given the dynamic nature of many loads. As a result, no positive actions have been taken in recent times.
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