Supply Interruptions

HT and industrial consumers worst hit by voltage variations

Power quality (PQ) is a major concern for most end-users. The most vulnerable to power quality issues are industrial consumers since interruption in power supply results in equipment failure, production loss and negative impact on profitability. This is a key reason why industries today have invested in backup generating units to meet their partial or full demand for power. Such a situation results in not only increased energy costs to the industry but also increased emissions, which would adversely affect the local environment, particularly in urban centres where most of these industries are located. In order to overcome these issues and costs, operating the distribution system in a more reliable manner becomes a priority.

Impact of PQ issues on industrial consumers

Interruptions in power supply affect industries in different ways, depending on the nature of output, electricity intensity and output capacity. Further, losses are influenced by customers’ load compositions and process layout at the plant site.

One of the key problems that high tension (HT) consumers often face is voltage variation, which is a frequent issue in the distribution network at the points of supply. As per an independent industry survey, HT consumers who receive supply at 33 kV and 22 kV voltage levels were observed to suffer from variation in the range of 1 per cent to 3 per cent. Another common issue faced by the industry includes voltage swells. These particularly impact consumers in the steel segment, followed by the automobile, petrochemicals, transportation and precision equipment sectors.

At the individual industry level, these interruptions can lead to the closure of some installations, that do not have the benefit of standby generation facilities. In addition, installations where production costs become non-competitive because of self-generation could be faced with a closure of their businesses. Many small and medium-scale industries fall into this category.

In a typical continuous manufacturing sector (such as an integrated steel plant), large financial losses are incurred by the lost work-in-progress (WIP) due to power quality problems. WIP includes the cost of raw material involved in production, which is inevitably lost, and the labour costs involved in the production, as extra labour is needed to make up for the lost production. In public service sectors like hotels and retail, PQ impact is measured as slowing down their business activities in terms of the revenue lost. Further, harmonic voltages and harmonic currents can both cause failure or abnormal operation of a customer’s devices, which can lead to financial consequences for the customer.

Most states impose nominal penalty to the distribution licensee for not maintaining the voltage level at the point of supply. This, however, is generally not sufficient compensation for the production loss or equipment failure occuring due to voltage variations.

PQ costs to discoms

It is not just consumers who are impacted by PQ problems. Various studies and surveys indicate that network operators too experience additional losses in networks because of harmonic currents, mostly originated by various customers’ devices. When large harmonic currents flow in a distribution network, network operators can often notice its impact immediately as the network components get overloaded. In an extreme situation, these can cause tripping of the protection device. Also, the costs of unwanted tripping of protective devices or control equipment in the network can be significant as it can lead to unplanned supply interruption.

Currently, only a few states have specified provisions and mechanisms for penalising consumers defaulting on harmonics injection limits as specified by the Central Electricity Authority. For instance, in Tamil Nadu, HT-I and HT-II category consumers are liable to pay compensation at the rate of 15 per cent for dumping harmonics into the licensees’ network. Even though in place, the set compensation is not with respect to the intensity of dumped harmonics and also excludes consumers in other HT categories such as irrigation, agricultural townships, residential colonies and green power in the state.

Conclusion

According to industry experts, there is  lack of a structured approach to understand, estimate and evaluate the impact of organisations that may be affected due to compromised power quality. The hidden impact of power quality parameters and related issues are yet to gain the attention of distribution companies and consumers. At the same time, it is important to address the PQ problems in the network that are contributed by customers’ non-linear devices. To fast-track improvements in this scenario, there is  need for coordinated actions and interventions from consumers, utilities and regulatory bodies.

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