Reliable power supply is one of the key goals of power distribution utilities. The government’s thrust to provide quality power to each village and every household through various schemes like DDUGJY, IPDS and Saubhagya has played a key role in this regard. The government’s increased focus on the segment has increased the demand for new technologies for distribution equipment including cables, substations, switchgear and transformers, among others. A look at the new and emerging technology trends in the key equipment deployed at the distribution level…
Distribution transformers (DTs) constitute one of the largest groups of equipment in the electrical network and, therefore, losses in DTs constitute a major component of the total losses in the network. The most efficient DTs, which are in service continuously, record an electricity loss of approximately 2-4 per cent. Electric utilities and industries are constantly striving for new methods and technologies to reduce transformer losses.
The prime component of losses, that is, no-load loss, can be reduced by better design and by using a core made of superior grades of electrical steel. By using improved/superior grades of cold rolled grain-oriented (CRGO) laminations, the no-load loss can be reduced significantly. Amorphous metal distribution transformers (AMDTs) also reduce core as compared to CRGO core losses.
Amorphous core material offers both reduced hysteresis loss and eddy current loss because this material has a random grain and magnetic domain structure, which results in high permeability giving a narrow hysteresis curve compared to the conventional CRGO material. It is observed that the use of second-hand and impure CRGO results in a higher loss for DTs. Eddy current losses are reduced by the high resistivity of the amorphous material and the reduced thickness of the film. The laminations comprise thin ribbons and the thickness of the sheet is about one-tenth of that of the CRGO, approximately 0.025-0.03 mm. Amorphous core transformers offer a 70-80 per cent reduction in no-load losses compared to transformers using CRGO core material for the same rating of DTs.
Cables and conductors
The voltage profile of electric supply and loss reduction in the system can be improved by using a high voltage distribution system (HVDS) as an alternative to the low voltage distribution system (LVDS). In this, 11 kV lines are extended up to or as near to the load centre as possible, and small-size transformers ranging from 10 kVA to 100 kVA, depending on the load requirement can be installed. The usage of HVDS has the advantage of lower technical losses due to the reduction of low tension (LT) lines. There is also improved voltage regulation at the consumer end due to low voltage/voltage drop resulting from less loading and shorter line length.
HVDS can be single-phase one neutral (continuous neutral from substation), two-phase two-wire (rigidly earthed natural system), or three-phase with small rating transformers. With the single-phase one neutral system, a continuous earth wire is required to be drawn from 33 kV/11 kV substations and the earth wire is to be earthed at all the poles. The neutral of the DT is also earthed on the high and low voltage sides. This conversion does not require the acquisition of additional land and there is no depletion of cultivable or forest land as the conversion to HVDS can be done on the existing poles. Therefore, there is no additional right-of-way requirement for the erection of lines.
Distribution utilities are also focusing on equipment that prevents power theft and ensures greater safety. Underground cables are being increasingly preferred to conventional overhead cables. In underground systems, cross-linked polyethylene (XLPE) cables are most commonly used. XLPE provides insulation to cables to make them withstand the electric field under transient operating conditions. However, these cables require a higher investment and longer restoration time (in case of any fault) as compared to overhead lines.
In the case of an overhead network, utilities rely on aerial bunched cables (ABCs) to prevent power theft and pilferage and ensure reliability, and also increase ease of maintenance. ABCs are overhead power lines consisting of several insulated phase conductors bundled tightly together, with a bare neutral conductor. In contrast, as per traditional practice, uninsulated conductors are separated by air gaps. One of the key benefits of this technology is protection against power theft due to the absence of hooking in distribution lines. The technology also entails negligible losses due to leakage of power. Further, as the ACBs are insulated with a dielectric material, these are less prone to faults caused by high winds, falling trees or birds. ABCs offer benefits such as less inspection and maintenance time, safety to linesmen, low maintenance level, ease of installation and less cluttered appearance.
Substations and switchgear
Substations are an important part of electrical distribution. Conventionally, substations use air for insulation between various live parts and the ground. However, these air-insulated substations (AIS) are directly exposed to the effects of climate change and environmental pollution, owing to their open design. These substations require more space than gas-insulated substations (GIS), in which all the substation equipment such as busbars, circuit breakers, current transformers, potential transformers and other substation equipment are placed inside modules filled with sulphur hexafluoride (SF6) gas.
Over time, GIS has gained popularity as it is suitable for deployment in urban and high density areas that have space constraints. Even though GIS entails higher capital and manpower training costs than AIS, it is relatively safer because of its closed design. Further, the failure rate of circuit breakers and disconnecting switches used in GIS is one-fourth of that in AIS and one-tenth in the case of busbars. Moreover, GIS technology has less environmental impact than AIS as the SF6 leakage rate is less than 1 per cent.
Utilities are also opting for hybrid switchgear-based substations, wherein the air-insulated busbars are integrated with gas-insulated equipment. Hybrid switchgear uses approximately 30 per cent less switchyard area, thereby facilitating quicker installation. The use of GIS technology in a hybrid solution allows rationalisation of switching elements and thus offers more flexibility in bay addition. Utilities have also been deploying digital substations as these are equipped with advanced software that protects systems from potential cyberthreats, thus strengthening system security. Since all the components of the substation are automated, they enable faster implementation of new technological solutions. Further, utilities can track real-time data from these substations, thus ensuring enhanced asset management.
Indian utilities are also undertaking the deployment of smart meters, with the MoP’s directive issued for converting all existing and new meters into smart and prepaid ones within three years starting from April 1, 2019. The implementation of smart metering technologies is expected to enable remote collection and processing of significantly larger volumes of meter data. Further, modifications to the existing systems to support remote meter functionality, management of new asset classes, new billing options and interaction with operational systems such as outage management system will be other capabilities enabled through smart metering systems.
Further, communication technologies for AMI have been one of the most significant developments for utilities in recent years. While there are various communication technology options available for utilities including power line communication, general packet radio service and radio frequency (RF) mesh communication, RF mesh technology scores over its counterparts in terms of scalability and adaptability, and self-healing properties that significantly bring down operating costs.
Broadly, the key considerations for any new technology adoption are expected to be the need to reduce inefficiency and enhance safety; incorporate digitalisation to access more real-time information; and reduce space requirements. Utilities must perform a suitable cost-benefit or feasibility analysis to adopt the right set of technology.