The first match was accidentally discovered in 1826 when John Walker scraped a stick with chemicals on the end against a stone floor.
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| Number | Title | Issue Date |
| 7340355 | Compensated current differential relaying method and system for protecting transformer Disclosed is a compensated current differential relaying method and system for protecting a transformer more correctly by calculating and estimating an exciting current including a core-loss current and a magnetizing current, and, in particular, to a compensated cur... | 03/04/2008 |