Why OLTC Is Critical for 11 Kv Solar Plants PM-Kusum Projects

The PM-KUSUM (Pradhan Mantri Kisan Urja Suraksha evam Utthaan Mahabhiyan) initiative in India has a grand objective of transforming the farming sector energy, by solarising farms to supply less electricity through the grid. An important aspect of a successful implementation of this scheme especially with the decentralised 11kV solar plants is the On-Load Tap Changer (OLTC) version of distribution transformer. Although ignored, the Transformer OLTC is not just an accessory but a vital element of technology that determines the viability of the project, stability of the grid, and financial sustainability of the project in the long term.

UNDERSTANDING THE VOLTAGE CHALLENGE IN RURAL GRIDS

The main role of the 11kV solar plant under PM-KUSUM is to feed solar-generated electricity to the local agricultural feeder to supply the irrigation pumps. Typical plant capacity ranges from 500 kW to 10 MW. Nevertheless, the rural distribution network, in which the plant is integrated, is inherently vulnerable to constant variations in voltage. These changes are due to.

• Long and Weak Distribution Lines: Rural feeders are commonly long and of high impedance and cause large voltage drops and rises.
• Variable Load Profile: Agricultural loads tend to be intermittent and concentrated. As many pumps operate at the same time, the voltage may drop. On the other hand, in times when the pumps are turned off, and the amount of solar generation is high, the voltage may exceed the limits of the statutes.
• Intermittent Solar Production: The output of solar power is volatile, and is determined by the amount of irradiance and weather conditions. This intermittent injection may cause quick and unforeseeable changes in voltage across the grid system.
• Avoiding local hot spots that increase insulation ageing.

These daily and seasonal changes in voltage cannot be met by a standard transformer which has fixed settings of a tap. In this case, the Tansformer OLTC comes in handy.

WHY OLTC IS NON-NEGOTIABLE FOR PM-KUSUM PROJECTS

An Transformer OLTC is an advanced equipment that is installed in a transformer and will provide the opportunity to modify the voltage ratio without disconnection of the transformer to the grid. It automatically controls the output voltage by switching taps on the winding based on actual grid conditions in real time.

For PM-KUSUM 11kV solar plants, the Transformer OLTC is critical for the following reasons:

• Enhances Regulatory Compliance and Eliminates Penalties: An Transformer OLTC equipped transformer will provide continuous compliance with Distribution Companies (DISCOM) limits to prevent solar curtailment, financial penalty, energy payment reduction and even grid disconnection.
• Maximises Energy Export and Revenue: PM-KUSUM plant business model relies solely on the volume of energy input into the grid and the tariff obtained. An Transformer OLTC eliminates avoidable generation curtailment because of overvoltage trips. It achieves this by dynamically controlling the voltage, making it possible to put all potential units of solar generation on export, which has a direct impact of maximising the plants revenue and the income of the farmer.
• Improves Grid Stability and Power Quality: Under PM-KUSUM, Transformer OLTCs improve grid stability by averting voltage excursions, local voltage support, and decreasing the corrective load on DISCOM infrastructure.
• Shields Plant Equipment and Enhances Reliability: Long-term overvoltage may put a strain and wear out the solar inverters, switchgear and the transformer itself. Low voltage may also impact on inverter operation and protection settings. Transformer OLTC ensures a constant voltage profile which increases the life and stability of the whole plant property.
• Future Proofs the investment: During the 25-year lifetime of the plant, an Transformer OLTC offers flexibility to meet increased solar penetration, changing patterns of agricultural loads, and upgrades to grid infrastructure.

HOW IT WORKS IN SOLAR PLANTS

Working with typical + -10 percent variation and 1.25 percent step resolution, the Transformer OLTC automatically increases or decreases the HV tap as the real-time conditions change: during bright daytime it increases the LV voltage by decreasing HV tap, and during evening or in the low-voltage cloudy conditions it decreases the LV voltage by increasing the HV tap, to avoid inverter trip-outs.

ECONOMIC JUSTIFICATION: COST VS. VALUE

While an OLTC transformer carries a higher upfront cost, it is a strategic investment with a compelling return.

• Revenue Protection: Even 1-2 percent loss per year of the generation through voltage-related curtailment can be a major financial loss over 25 years that is far greater than the original premium.
• Risk of the Penalties: It protects the project owner against non compliance fines.
• Less Hassles: Minimises grid tripping and interruption in operation.

In the case of DISCOMs, the extensive use of Transformer OLTCs in PM-KUSUM plants is also profitable because it decentralises the management of voltages, minimises technical losses, and enhances the quality of supply in all rural customers.

COMPARISON: OLTC VS OFF-CIRCUIT TAP CHANGER

Fundamental Characteristics of Insulating Oils:

FINAL WORD

An OLTC is not a luxury in the context of the PM-KUSUM scheme, but a project enabler. It makes a basic solar generator grid-supportive, revenue-maximising, and compliant. The Transformer OLTC guarantees that financial benefits of farmers and developers are preserved, the project technical feasibility is maintained, and the national interests of grid stability and energy security by providing dynamic control of the ongoing voltage issues of the Indian rural network. One of the key conditions of the successful and sustainable implementation of 11kV-decentralised solar plants within PM-KUSUM is, therefore, specification and investment into OLTC-equipped transformers.

Related Link: Future of Solar Inverter Transformers in Sustainable Energy