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
Superconductor winding critical current and temperature tnonitor
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 a superconductor winding critical current monitor and temperature monitor.
Prediction of critical current and temperature for superconductor is required for estimation of performance parameters like ac losses and efficiency of transformer and to control, 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 loss of the winding is known during the operation of transformer. Regarding temperature, it is important to predict the abnormality taking place in the winding which can raise the temperature. If there is a sudden breakdown in cryocooler, the temperature of the cryogenic fluid increases and temperature monitor immediately predicts such happenings and trip the transformer. The Patent application W09737238A1 describes a process for determining the critical current Ic of superconductors and measuring instrument. The prior art discloses a process of measuring local critical current of superconductor and thereby providing an economical way to assess the working property of the superconductors. Determining critical current of superconductors - involves measuring voltage or voltage drop continuously over entire superconductor for constant current or at discrete points depending on current, with magnetic field penetrating superconductor. However, the said invention is novel in devising a relation between operating current and

critical current of a superconductor transformer and utilizing a digital processor to find the critical current using the graph for different operating currents, thereby, making it possible for the monitoring of critical current of superconductor transformer. Further, the AC loss measurement is a function of critical current and that makes it possible to continuously monitor the ac losses for different currents during the operation of a transformer. As mentioned in the Invention disclosure and understood from the description, the said invention as per analysis is still further distinct in measuring differential voltage between the superconductor tape present at the top and bottom terminal of the winding which is not the case with the prior art. The prior art determines voltage at discrete fixed points. Further, as per our understanding of the invention, the temperature control and monitoring in superconductor transformer is done by utilizing the operating current and critical current relation which is inventive. The relation of critical current to magnetic field with temperature as reference is well known. The prior art does not mention anything related to temperature control by utilizing operating current. The Patent application US 5134360 describes an apparatus and method for critical current measurements. The prior art discloses an apparatus and method for critical current measurement by monitoring the reactance of the superconductive coil with a phase detector, the point where a component of the impedance deviates is measured as the critical current. However, the said invention is novel in devising an online monitoring system based on relation between operating current of the transformer and critical current of the winding. Further, the said invention utilizes a digital processor to find the critical current using graph of operating current. Since, AC loss is a function of critical current, the AC loss of a transformer can be continuously monitored during its operation. Further,

the said invention is distinct in measuring differential voltage between superconductor tape present at the top and bottom terminal of the winding and is kept equidistant from the top and bottom end of winding as understood from the Invention disclosure. As per our understanding, the temperature control and monitoring in superconductor transformer by utilizing operating current is distinct in the said invention. The prior art utilizes cooling to maintain temperature to a fixed preselected value by monitoring it but there is no control mechanism relating to operating current in the prior art. The Patent application WO/2001/004646 describes an apparatus for measurement of critical current in superconductive tapes. The prior art relates to an apparatus for measurement of critical current in superconductive tapes and to a method of identifying areas of superconductive tapes with lower critical current properties. The prior art discloses a measurement technique of applying localized magnetic field to specific fixed potions of the tape and then measuring the critical current across that section and thereby providing critical current mapping of multiple portions of the superconductive tape. However, the said invention is distinct in devising a relation between the operating current and critical current of the superconductor tape, thereby making it possible for monitoring of critical current for different operating current. Further, the said invention is distinct in measuring differential voltage between superconductor tape present at the top and bottom terminal of the winding and is kept equidistant from the top and bottom end of winding as understood from the Invention disclosure. As per our understanding of the invention, the temperature control and monitoring in superconductor transformer is done by utilizing the operating current and critical current relation. The relation of critical current to magnetic field with temperature as reference is well known. The prior art does not

disclose any such temperature control and monitoring mechanism as utilized in the said invention. The Patent application ES2293759AA describes a measurement device for critical current in superconducting rings by using continuous monitoring source, it consist of ferromagnetic nucleus, primary coil, secondary coil and superconducting ring. The prior art discloses a device for critical current measurement by utilizing ammeter and voltage measurement across the tape by using voltmeter. The device consists of ferromagnetic nucleus, primary coil, secondary coil and superconducting ring. The said invention is similar in measuring critical current value but the system of the said invention is distinct from the prior art. The invention devises a measurement technique of finding critical current for various operating current by plotting a graph and utilizing digital processor for the purpose. The said invention is also distinct in measuring voltage across any portion of the tape of the superconductor winding of a transformer inside the cryostat. As per our understanding of the invention, the temperature control and monitoring in superconductor transformer is done by utilizing the operating current and critical current relation. The relation of critical current to magnetic field with temperature as reference is well known. The prior art does not disclose any such temperature control and monitoring mechanism as utilized in the said invention.
It is an object of the invention to provide a superconductor link at the start and end terminal connection of the transformer winding at equidistant from the top and bottom end of the winding in the leakage flux path of superconducting transformer that monitors temperature and critical current continuously during the operation of transformer.

It is an object of the invention to provide a superconductor link at the start and end terminal connection of the transformer winding at equidistant from the top and bottom end of the winding in the leakage flux path of superconducting transformer that monitors cryogenic fluid and winding temperature continuously during the operation of transformer.
It is an object of the invention to provide a superconductor link at equidistant from the top and bottom end of the winding 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.
It is an object of the invention to provide a digital processor that monitors critical current, temperature and ac losses continuously on-line.
A differential voltage across the superconductor tape is measured to monitor temperature as well as critical current of superconductor winding. The voltage is measured at the start and end terminal connection wire otherwise called as superconductor link at the source side of the superconductor transformer. This superconductor link is placed equidistant from the top and bottom portion of the winding. When the leakage flux penetrates the superconductor link, the critical current decreases and emf across the link increases equally at the top and bottom link which are placed at equidistant from the winding end. Therefore the differential voltage across the between the two link will be zero. Hence the voltage cancels each other due to flux penetration in the superconductor link. As we


know that the critical current is a functional of temperature apart from flux density penetration as per the retention curve of superconductor tape. As we know that due to convection effect, the top winding temperature is higher than the bottom winding temperature. The bottom winding temperature will be constant all the time. Therefore there will be a differential voltage which is due to temperature difference between the top and bottom link which is independent of flux penetration of the tape. The differential voltage changes with operating current as per the retention characteristics of the superconductor tape. The change in differential voltage for a given operating current is a indication of top winding temperature of superconductor winding. A threshold or reference voltage can be set for a top winding temperature for a given current by means of digital processor outside the transformer. Hence the status of the top winding temperature can be ■ monitored. When the voltage across the superconductor link is monitored separately, then the critical current of the winding can be monitored. Because the flux penetration of the tape dominates and that decreases the critical current as per the retention curve and an emf is induced across the tape. This emf is calibrated for a given flux density corresponding to an operating current. By using the retention characteristics the critical current can be estimated.
The invention is described in detail herein, a partial cross-sectional view of the winding assembly of a superconducting transformer along with superconductor link placed at the top and bottom end of the winding near start and end terminals of the winding respectively 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 are in coaxial relationship with each other and radially spaced apart. Dielectric insulation in the gap between the windings and end insulation. A superconductor links are placed at the top end and bottom end of the winding at the start and end terminal connection of the superconductor terminals of the superconductor winding. The induced voltage due to flux density and temperature is measured across the terminals at the top and bottom end of the winding and sent to the digital processor for analysis and to monitor critical current, temperature and ac losses continuously online during the operation of the transformer. The leakage fluxes of the transformer link with this superconductor link at the top and bottom end of the winding 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. the differential voltage is measured which gives the temperature gradient between top and bottom of the winding. As we know that the temperature of cryogenic fluid is almost constant at the bottom side and hence the differential voltage is an indication of the top cryogenic fluid temperature and hence the winding temperature can be estimated.
In accordance to the invention, Superconductor winding critical current and temperature monitor for superconducting transformer comprises superconductor link at the start and end terminal of the winding, the said superconductor link is placed at equidistant from the top and bottom end of the winding.
In accordance to the invention, said superconductor link at the start and end terminal of the winding placed in the leakage flux path of the said transformer to measure operating and critical current,
In accordance to the invention, said superconductor link placed in the leakage flux path at the top and bottom of the said transformer to measure differential voltage to monitor temperature by using retention characteristics of the tape due to perpendicular flux penetration at different temperature.
In accordance to the invention a superconducting transformer comprising a superconductor link. a digital processor to monitor critical current and temperature of the winding. A superconducting transformer comprising a superconductor link at the top and

bottom end of the winding and a digital processor to monitor critical current of the winding and temperature to protect the transformer from abnormal operation and enhance the transformer efficiency.

*th
Dated this 19th day of March 2009


10

(Ivan Bernard Fuller)
of Khaitan&Co
Agent for the Applicants