Systems and methods are provided for monitoring or protecting an electric power distribution system using protective devices that may rely on accurate time signals from a common time source. A first protective device may receive a first time signal deriving from the common time source and a second protective device may receive a second time signal deriving from the common time source. The first time signal and the second time signal may be compared; when a difference between them exceeds a defined threshold, time signal manipulation may be detected. The protective devices may modify their operation in response to or to account for the time signal manipulation.

According an aspect of the present invention, a data receiving apparatus includes a calculator. The calculator (1) stores a date and time indicated by the clock unit in association with a first local date and time in the memory as a reference date and time, when the packet includes first date-and-time data indicating the first local date and time and information indicating that the first date-and-time data can be used for date and time association, and (2) calculates, when the packet includes sensor data and second date-and-time data indicating a second local date and time associated with the sensor data, a third date and time based on a difference between the first local date and time and the second local date and time, and on the reference date and time.

A management apparatus in a time synchronization system includes a time variation information receiving unit configured to acquire time variation information and position information of a time synchronization apparatus, a position information classifying unit configured to classify time synchronization apparatuses into predetermined categories based on the acquired position information, a time variation analysis configured to determine majority based on whether patterns of time variation of the time synchronization apparatuses belonging to an identical category are identical to each other, and to analyze the time variation based on the determined results, and a filtering and delivery unit configured to output an instruction to block the time information received from the positioning satellite, to the time synchronization apparatus having abnormal time variation. A GPS-FW includes a filtering determination unit configured to blocks the time information received from a GPS satellite in a case where a block instruction is received from the management apparatus.

According an aspect of the present invention, a data receiving apparatus includes a calculator. The calculator (1) stores a date and time indicated by the clock unit in association with a first local date and time in the memory as a reference date and time, when the packet includes first date-and-time data indicating the first local date and time and information indicating that the first date-and-time data can be used for date and time association, and (2) calculates, when the packet includes sensor data and second date-and-time data indicating a second local date and time associated with the sensor data, a third date and time based on a difference between the first local date and time and the second local date and time, and on the reference date and time.

Systems and methods are provided for monitoring or protecting an electric power distribution system using protective devices that may rely on accurate time signals from a common time source. A first protective device may receive a first time signal deriving from the common time source and a second protective device may receive a second time signal deriving from the common time source. The first time signal and the second time signal may be compared; when a difference between them exceeds a defined threshold, time signal manipulation may be detected. The protective devices may modify their operation in response to or to account for the time signal manipulation.

An electronic timepiece includes an obtaining circuit, a first processor and a second processor. The obtaining circuit obtains information on current time from outside. The first processor measures time. The second processor is connected to the obtaining circuit. The first processor obtains a synchronization signal corresponding to the current time, obtains the current time, which the second processor obtains from the obtaining circuit, and based on the current time and the synchronization signal, corrects the measuring time, which the first processor is measuring.

A management apparatus in a time synchronization system includes a time variation information receiving unit configured to acquire time variation information and position information of a time synchronization apparatus, a position information classifying unit configured to classify time synchronization apparatuses into predetermined categories based on the acquired position information, a time variation analysis configured to determine majority based on whether patterns of time variation of the time synchronization apparatuses belonging to an identical category are identical to each other, and to analyze the time variation based on the determined results, and a filtering and delivery unit configured to output an instruction to block the time information received from the positioning satellite, to the time synchronization apparatus having abnormal time variation. A GPS-FW includes a filtering determination unit configured to blocks the time information received from a GPS satellite in a case where a block instruction is received from the management apparatus.