Evaluating noise and excess current on a power line

1. A method comprising:

measuring peak amplitudes of spectral components of partial discharge (PD) pulses sensed on an electrical cable over a plurality of phases of a cycle of a power signal on said electrical cable;

subtracting a background noise level from said peak amplitudes, thus yielding resultant amplitudes;

summing said resultant amplitudes, thus yielding a first PD sum that indicates a magnitude of PD activity on said electrical cable at a first time;

repeating said measuring, subtracting and summing after a passage of time, thus yielding a second PD sum at a second time; and,

issuing an alarm if a difference between said second PD sum and said first PD sum is greater than a threshold value.

2. A method comprising:

measuring, at a first location on a power cable, a first magnitude of a first power current that exceeds a threshold;

measuring, at a second location on said power cable, a second magnitude of a second power current that does not exceed said threshold;

determining a location of a fault on said power cable, based on a relationship between said first magnitude and said second magnitude, and,

wherein said first power current and said second power current are transient power currents with durations in a range of about 1 millisecond to about 500 milliseconds.

3. A system comprising:

a switch that when closed passes noise from a power line, and when opened does not pass said noise;

an amplifier downstream of said switch, that produces an amplified output;

a channel having:

a filter that passes a spectral component of said amplified output within a particular frequency band, thus yielding a filtered output; and

a detector that detects values of said filtered output at a plurality of times, thus yielding a series of values; and

a processor that:

(a) determines a lowest value of said series of values while said switch is opened, thus obtaining a first baseline value;

(b) determines a lowest value of said series of values while said switch is closed, thus obtaining a second baseline value; and

(c) determines a difference between said second baseline value and said first baseline value, thus yielding an excess value that indicates an excess of power line noise above amplifier noise.

4. The system of claim 3 , wherein said processor also:

(d) disqualifies said channel as a partial discharge detector if said excess value exceeds a predetermined threshold.

5. A system comprising:

a processor; and

a memory that stores instructions that are readable by said processor, and when read by said processor, cause said processor to:

measure peak amplitudes of spectral components of partial discharge (PD) pulses sensed on an electrical cable over a plurality of phases of a cycle of a power signal on said electrical cable;

subtract a background noise level from said peak amplitudes, thus yielding resultant amplitudes;

sum said resultant amplitudes, thus yielding a first PD sum that indicates a magnitude of PD activity on said electrical cable at a first time;

repeat said measurement, subtraction and summation after a passage of time, thus yielding a second PD sum at a second time; and,

issue an alarm if said second PD sum is greater than said first PD sum by more than a threshold value.

6. A system comprising:

a processor; and

a memory that stores instructions that are readable by said processor, and when read by said processor, cause said processor to perform actions of:

measuring, at a first location on a power cable, a first magnitude of a first power current that exceeds a threshold;

measuring, at a second location on said power cable, a second magnitude of a second power current that does not exceed said threshold; and

determining a location of a fault on said power cable, based on a relationship between said first magnitude and said second magnitude, and

wherein said first power current and said second power current are transient power currents with durations in a range of about 1 millisecond to about 500 milliseconds.

7. A non-transitory storage medium that contains instructions that are readable by a processor, and when read by said processor, cause said processor to:

measure peak amplitudes of spectral components of partial discharge (PD) pulses sensed on an electrical cable over a plurality of phases of a cycle of a power signal on said electrical cable;

subtract a background noise level from said peak amplitudes, thus yielding resultant amplitudes;

sum said resultant amplitudes thus yielding a first PD sum that indicates a magnitude of PD activity on said electrical cable at a first time;

repeat said measurement, subtraction and summation after a passage of time, thus yielding a second PD sum at a second time; and,

issue an alarm if said second PD sum is greater than said first PD sum by more than a threshold value.

8. A non-transitory storage medium that contains instructions that are readable by a processor, and when read by said processor, cause said processor to perform actions of:

measuring, at a first location on a power cable, a first magnitude of a first power current that exceeds a threshold;

measuring, at a second location on said power cable, a second magnitude of a second power current that does not exceed said threshold;

determining a location of a fault on said power cable, based on a relationship between said first magnitude and said second magnitude, and,

wherein said first power current and said second power current are transient power currents with durations in a range of about 1 millisecond to about 500 milliseconds.