The question pertains to the limitations of Buchholz relay protection in power systems. The Buchholz relay is a safety device used in oil-filled transformers for detecting faults. Here, we evaluate why only one of the given options constitutes a limitation of Buchholz relay protection.

1. Understanding Buchholz Relay: This relay is specifically designed for transformers that have a conservator tank. It is installed in the pipe connecting the main tank to the conservator to detect gas produced by faults within the transformer.
2. Evaluation of Options:
   • Automatic detection of gas accumulation inside transformer oil systems: This is a function rather than a limitation. The Buchholz relay excels at detecting gas accumulation due to internal faults.
   • Detection of incipient faults inside oil immersed transformers effectively: This is one of the primary functions of a Buchholz relay, making it an advantage rather than a limitation.
   • Fast isolation of internal transformer faults during abnormal conditions: This is also a feature, as the relay aids in rapidly identifying and isolating faults.
   • Operation possible only in transformers provided with conservator tanks: This is indeed a limitation, as Buchholz relays cannot be used in transformers without conservator tanks, which limits their applicability.
3. Conclusion: The correct answer is "Operation possible only in transformers provided with conservator tanks," as this is a genuine limitation that restricts the deployment of Buchholz relays to specific transformer designs.