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Density Monitoring and Control System

IP.com Disclosure Number: IPCOM000222159D
Publication Date: 2012-Sep-21
Document File: 11 page(s) / 79K

Publishing Venue

The IP.com Prior Art Database

Related People

Julio Danin (JD) Lobo Neto: INVENTOR

Abstract

A density monitoring and control system for monitoring and controlling a density of a gas-phase in a two-phase insulation fluid for a medium- or high-voltage power transmission network is disclosed. The monitoring and control system derives the density ρgas of the gaseous phase of the insulation fluid and – by means of adding heat Q to the insulation fluid – keeps this density over a critical threshold ρcrit. Furthermore, redundant sensors and fault scenario detection are implemented in the density monitoring and control system.

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Density Monitoring and Control System

Technical Field


The present invention relates to a method and

device for monitoring and controlling a density of a gas- phase in a fluid, in particular an insulation fluid in an electrical apparatus in a medium or high-voltage power transmission network.

Introduction and Background Art

          Dielectric insulation media in liquid and/or gaseous states (i.e. fluids) are widely applied to insu- late an electrically active part in a variety of electri- cal apparatuses such as switchgears or transformers. For example, the electrically active part in medium or high voltage metal-encapsulated switchgears is arranged in a gas-tight compartment which encloses an insulation fluid with a pressure of several bars which electrically sepa- rates the compartment of the apparatus from the electri- cally active part. In other words, the insulation fluid does not allow the passage of electrical current from the electrically active part to the compartment. The density ȡgas of the gaseous phase of the insulation fluid is a critical parameter for electrical insulation, however. In other words, a dielectric breakdown strength Ebd of the insulation fluid depends on the gas phase density ȡgas of the insulation fluid.

          A commonly used dielectric insulation gas is sulfur hexafluoride SF6 which exhibits excellent insula- tion and electric arc extinguishing capabilities. In this case, since the boiling point for SF6 is at -63.9 °C (sublimation point), there is no or at least no consider- able condensation of the gas at temperatures within the operating range of the device. This leads to a more or less constant gas phase density ȡgas, provided that no leakage or other fault situations are present. However, SF6 is a strong contributor to the green-house effect and

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thus has a high global warming potential. Therefore, al- ternative insulation fluids should be found. Several al- ternative insulation fluids have been identified.

          Some of these alternatives are multi-phase fluids at normal operating conditions (e.g., tempera- tures), e.g., they comprise coexisting liquid and gaseous phases of the insulation fluid. If, however, an insula- tion fluid is chosen for which the operating conditions may reach, e.g., below the boiling point Tboil of the in- sulation fluid, then the gas phase density ȡgas of the insulation fluid needs to be critically monitored and controlled to keep the gas phase density ȡgas above a minimum critical density ȡcrit. In other words, when the operating temperature range of the insulation fluid goes below the boiling temperature Tboil of the insulation fluid, it is necessary to control the system to ensure that the minimum required gas phase density ȡcrit for proper insulation is not underrun. At temperatures T be- low the boiling temperature Tboil the insulation fluid gas phase density ȡgas follows the va...