A protection apparatus, comprising: a double tuned filter; a high pass filter; an AC bus configured to: connect an input terminal of the double tuned filter and an input terminal of the high pass filter, and transmit AC power supplied from an AC power source to the double tuned filter and the high pass filter a filter protection unit which is configured to: apply a test current to the AC bus to identify a line connection state of an inner circuit of the protection apparatus, when a misconnection does not exist in the inner circuit of the protection apparatus, set a plurality of relay elements for sensing an abnormal state of the protection apparatus, receive an input regarding test information in order to identify whether any one of the plurality of relay elements has a problem, wherein the input regarding test information includes a micro current, compare the level of the micro current inputted into the double tuned filter with the level of a current outputted from the double tuned filter, and identify that an abnormal state is generated when a difference between the micro current inputted into the double tuned filter with the level of the current outputted from the double tuned filter exceeds a preset difference, when at least one of the plurality of relay elements has an abnormal state according to the reception of the input regarding the test information, identify whether the protection apparatus generates an abnormal state sensing signal. a double tuned filter; a high pass filter; an AC bus configured to: connect an input terminal of the double tuned filter and an input terminal of the high pass filter, and transmit AC power supplied from an AC power source to the double tuned filter and the high pass filter connect an input terminal of the double tuned filter and an input terminal of the high pass filter, and transmit AC power supplied from an AC power source to the double tuned filter and the high pass filter a filter protection unit which is configured to: apply a test current to the AC bus to identify a line connection state of an inner circuit of the protection apparatus, when a misconnection does not exist in the inner circuit of the protection apparatus, set a plurality of relay elements for sensing an abnormal state of the protection apparatus, receive an input regarding test information in order to identify whether any one of the plurality of relay elements has a problem, wherein the input regarding test information includes a micro current, compare the level of the micro current inputted into the double tuned filter with the level of a current outputted from the double tuned filter, and identify that an abnormal state is generated when a difference between the micro current inputted into the double tuned filter with the level of the current outputted from the double tuned filter exceeds a preset difference, apply a test current to the AC bus to identify a line connection state of an inner circuit of the protection apparatus, when a misconnection does not exist in the inner circuit of the protection apparatus, set a plurality of relay elements for sensing an abnormal state of the protection apparatus, receive an input regarding test information in order to identify whether any one of the plurality of relay elements has a problem, wherein the input regarding test information includes a micro current, compare the level of the micro current inputted into the double tuned filter with the level of a current outputted from the double tuned filter, and identify that an abnormal state is generated when a difference between the micro current inputted into the double tuned filter with the level of the current outputted from the double tuned filter exceeds a preset difference,