FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
PROVISIONAL SPECIFICATION
(See section 10 and rule 13)
TITLE OF INVENTION
On-line critical current monitor for Superconductor Transformer
APPLICANTS


Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Ramakichenan Vaithiyanathan, of Product Technology Centre, CG Global R&D Centre, Crompton Greaves Limited, Kanjur (E), Mumbai 400042, Maharashtra, India, an Indian National
PREAMBLE TO THE DESCRIPTION
The following specification describes the invention


The invention relates to an on-line critical current monitor for superconducting transformer.
Prediction of critical current for superconductor is required for estimation of ac losses and controls the temperature rise in the winding. The critical current depends upon the flux penetration and temperature of superconductor winding. The more the decrease in critical current the more the ac losses and more energy required to maintain the temperature of cryogenic fluid which is liquid nitrogen. The temperature of liquid nitrogen is maintained by cryocooler. The cryocooler needs external energy for it operation. Therefore the energy to the cryocooler can be saved efficiently if the critical current and ac losses of the winding is known during the operation of transformer. Prior art in the form of Patent # US5218296 discloses similarities of the proposed invention only to the extent of using microprocessor for measurement of critical current through coil with magnetic core. Whereas in the proposed invention, the superconducting transformer generally comprises a low voltage winding and a high voltage winding made of a superconducting material wire and wound on a non-magnetic material former in coaxial relationship with each other and radially spaced apart. The superconducting windings are immersed in a cryogenic fluid contained in a cryostat and are kept cooled by the cryogenic fluid. The temperature of the cryogenic fluid is maintained by the cryocooler. The temperature rise is a function of ac losses occurs in the winding during the operation of transformer. As we know that the ac loss is a function of critical current and transport current of superconductor tape. The ac losses for different current can be
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calculated and monitored continuously during the operation of transformer. Based on the measurement of ac loss at any given current, the power to the cryocooler can be utilized efficiently and improve the efficiency of superconductor transformer and save cryocooler energy.
It is an object of the invention to provide a magnetic coil in the leakage flux path of superconducting transformer that monitors critical current continuously during the operation of transformer.
It is an object of the invention to provide a magnetic coil in the leakage flux path of superconducting transformer that monitors ac loss continuously during the operation of transformer.
It is an object of the invention to provide a magnetic coil in the leakage flux path of superconducting transformer that monitor ac loss continuously and improve the cooling efficiency of the cryocooler.
It is an object of the invention to provide a digital processor that monitors critical current and ac losses continuously on-line.
It is an object of the invention to provide a magnetic coil in the leakage flux path of superconducting transformer that monitor ac loss continuously and improve the cooling efficiency of the transformer and save cryocooler energy.
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An on-line critical current monitor for superconducting transformer of this invention discloses a small coil of certain diameter is wound on a magnetic core. The coil is placed in the leakage magnetic field path of a transformer winding. When the leakage flux link with the coil an emf is induced across the coil. This emf is proportional to the operating current of the transformer. Then coil measures the operating current of transformer to measure the critical current of the winding, the maximum perpendicular flux penetrating any portion of the winding corresponding to the full load current is predicted by simulation. Using the retention characteristics of the tape due to perpendicular flux, the critical current can be estimated. Since the leakage flux density is linear below the full load current. The perpendicular flux versus current is plotted up to the full load current of transformer and the corresponding critical current can be estimated using the retention characteristics. A graph represent the critical current versus operating current of transformer can be plotted. A digital processor can be used to find the critical current using the graph for different operating current. Hence on-line monitoring of critical current of superconductor tape is possible.
The invention is described in detail herein, a partial cross-sectional view of the winding assembly of a superconducting transformer along with magnetic coil placed at the top of the winding near the high low gap according to an embodiment of the invention. The winding assembly comprises a plurality of layers of low voltage winding and a plurality of layers of high voltage winding made of superconducting material wire and a gap in between high low winding and wound on non-magnetic material formers. The windings
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are in coaxial relationship with each other and radially spaced apart. Dielectric insulation in the gap between the windings and end insulation. A magnetic coil is placed above the high-low gap of the winding which consists of low loss magnetic core and wound with copper wire and the terminals across the coil are taken outside for processing the signal to monitor critical current. The leakage fluxes of the transformer link with this magnetic coil and induces emf across the coil that is proportional to the operating current of the transformer. In order to measure the critical current of the winding, the maximum perpendicular flux penetrating any portion of the winding corresponding to the full load current is predicted by simulation. Using the retention characteristics of the tape due to perpendicular flux, the critical current can be estimated. A graph represent the critical current versus operating current of transformer can be plotted. A digital processor can be used to find the critical current using the graph for different operating current. Hence on¬line monitoring of critical current of superconductor tape is possible. As we know that the ac loss is a function of critical current and transport current of superconductor tape. The ac losses for different current can be calculated and monitored continuously during the operation of transformer. Based on the measurement of ac loss at any given current, the power to the cryocooler can be utilized efficiently and improve the efficiency of superconductor transformer and save cryocooler energy.
In accordance to the present invention an on-line critical current monitor for superconducting transformer comprises magnetic coil, said coil wound on a core, made up of magnetic material, was placed in said transformer winding
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In accordance to the present invention said coil placed in the leakage flux path of the said transformer to measure operating and critical current
In accordance to the present invention said coil placed in the leakage flux path of the said transformer to measure operating and critical current by using retention characteristics of the tape due to perpendicular flux penetration
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In accordance to the present invention a superconducting transformer comprising a coil, a digital processor to monitor critical current of the winding. A superconducting transformer comprising a magnetic coil and a digital processor to monitor critical current and ac losses of the winding to enhance the transformer efficiency.