Voltage fluctuations and flicker - Assessment and mitigation (part 1)

The quality of the voltage distributed to electricity-using installations is a concern shared by both industrial companies, whose equipment can be sensitive to non-quality, and electricity distributors, who are concerned about customer satisfaction.

It should be noted that deregulation of the electricity market is complicating the task of electricity carriers and distributors in terms of quality. In addition, the proliferation of increasingly sophisticated and powerful applications is having an impact on voltage quality. If we also note that the average situation on European networks is currently better than that described by the European "voltage quality" standard (EN 50160), then it is to be feared that this favorable situation will be difficult to maintain.

We therefore need to provide the means to compensate for any nuisance resulting from the use of electrical energy. This is the role of technology. If the means exist, the debate on their implementation can begin, a debate which, by its very nature, lies outside the scope of this article. On the other hand, it is essential to agree on the way in which we apprehend the phenomena. Where there is an element of subjectivity, we need to agree on the assessments required for knowledge. Where the complexity of phenomena can no longer be tracked analytically, but can be examined statistically, we need to agree on methods. These are the reasons why international standardization, whose vocation is to establish consensus, is essential for defining nuisances, the way to deal with them, the methods for measuring them and, finally, the rules for limiting them.

Among the nuisances we have long noted are voltage drops which, if repeated at certain rates, have particularly annoying effects on one of electricity's main applications: lighting. It was also identified early on that voltage drops are all the more significant the higher the power demand and the higher the impedance of the distribution network. While impedance is a constructive characteristic of the network that can only be changed by adapting it to the power it intends to distribute, power calls can be compensated for by appropriate equipment.

In alternating current, reactive power fluctuations are the main source of voltage fluctuations, especially on medium-voltage (MV) and high-voltage (HV) networks, whose internal impedance is mainly inductive. Compensation therefore consists in smoothing reactive power fluctuations by means of devices that modulate consumption in addition to that of the load to be smoothed. Relatively similar techniques can be used to compensate for voltage imbalances introduced by high-power single-phase loads.

Today, these devices are typically based on thyristors,...