A method for monitoring condition of a vacuum interrupter of an electric device, comprising: receiving a first voltage signal indicating a first voltage at a first contact of a switch inside the electric device, the first contact of the switch coupled to a source line; receiving a second voltage signal indicating a second voltage at a second contact of the switch, the second contact of the switch coupled to a reactive; receiving a current signal indicating a current at the second contact of the switch; determining occurrence of a restrike in response to determining increasing amplitudes of the first voltage signal, the second voltage signal and the current signal in a time slot; and determining the condition of the vacuum interrupter condition based on the determined occurrence of the restrike, and wherein determining the condition of the vacuum interrupter based on the determined occurrence of the restrike comprises: counting switching operation of the switch in a time period; counting the determined restrikes in the time period; computing a ratio of the counted number of the determined restrikes to the counted number of the switching operation; and determining an unacceptable vacuum condition in response to determining that the computed ratio exceeds a predetermined threshold, or wherein determining the condition of the vacuum interrupter based on the determined occurrence of the restrike comprises: counting switching operation of the switch in response to determining the restrike; calculating a number of the switching operation between the restrike and a subsequent determined restrike; and determining an unacceptable vacuum interrupter's condition in response to the number of the switching operation being below a predetermine number. receiving a first voltage signal indicating a first voltage at a first contact of a switch inside the electric device, the first contact of the switch coupled to a source line; receiving a second voltage signal indicating a second voltage at a second contact of the switch, the second contact of the switch coupled to a reactive; receiving a current signal indicating a current at the second contact of the switch; determining occurrence of a restrike in response to determining increasing amplitudes of the first voltage signal, the second voltage signal and the current signal in a time slot; and determining the condition of the vacuum interrupter condition based on the determined occurrence of the restrike, and wherein determining the condition of the vacuum interrupter based on the determined occurrence of the restrike comprises: counting switching operation of the switch in a time period; counting the determined restrikes in the time period; computing a ratio of the counted number of the determined restrikes to the counted number of the switching operation; and determining an unacceptable vacuum condition in response to determining that the computed ratio exceeds a predetermined threshold, or wherein determining the condition of the vacuum interrupter based on the determined occurrence of the restrike comprises: counting switching operation of the switch in response to determining the restrike; calculating a number of the switching operation between the restrike and a subsequent determined restrike; and determining an unacceptable vacuum interrupter's condition in response to the number of the switching operation being below a predetermine number. counting switching operation of the switch in a time period; counting the determined restrikes in the time period; computing a ratio of the counted number of the determined restrikes to the counted number of the switching operation; and determining an unacceptable vacuum condition in response to determining that the computed ratio exceeds a predetermined threshold, or wherein determining the condition of the vacuum interrupter based on the determined occurrence of the restrike comprises: counting switching operation of the switch in response to determining the restrike; calculating a number of the switching operation between the restrike and a subsequent determined restrike; and determining an unacceptable vacuum interrupter's condition in response to the number of the switching operation being below a predetermine number. counting switching operation of the switch in response to determining the restrike; calculating a number of the switching operation between the restrike and a subsequent determined restrike; and determining an unacceptable vacuum interrupter's condition in response to the number of the switching operation being below a predetermine number.