System and method for restraining differential bias

A method of modifying a trip level of a circuit, the method comprising:

• measuring an induced current from a current transformer to obtain an induced current measurement;
• converting the induced current measurement to a voltage;
• sampling the voltage to obtain voltage samples;
• calculating one or more Fourier values based on the voltage samples;
• calculating a bias current responsive to calculating the one or more Fourier values;
• calculating a differential current responsive to calculating the one or more Fourier values;
• determining if a transformer is experiencing saturation responsive to calculating the bias current and the differential current;
• and
• modifying a trip level of a protection device by a bias value responsive to determining the transformer is experiencing saturation, the bias value being based on a maximum of the differential current, a previously determined bias value, and a multiple of a change in the bias current.

A non-transitory computer-readable medium storing thereon instructions configured to instruct at least one processor to:

• measure an induced current from a current transformer to obtain an induced current measurement;
• convert the induced current measurement to a voltage;
• sample the voltage to obtain voltage samples;
• calculate one or more Fourier values based on the voltage samples;
• calculate a bias current responsive to calculating the one or more Fourier values;
• calculate a differential current responsive to calculating the one or more Fourier values;
• determine if a transformer is experiencing saturation responsive to calculating the bias current and the differential current;
• and
• modify a trip level of a protection device by a bias value responsive to determining that the transformer is experiencing saturation, the bias value being based on a maximum of the differential current, a previously determined bias value, and a multiple of a change in the bias current.