Graded spark gap design for internally gapped surge arrester
An arrester including a metal oxide varistor (MOV) disc and a spark gap assembly electrically connected in series with the MOV disc. The spark gap assembly includes a spark gap and a frequency-dependent grading capacitor electrically connected in parallel with the spark gap.
1 . An arrester comprising:
a metal oxide varistor (MOV) disc; and
a spark gap assembly electrically connected in series with the MOV disc, the spark gap assembly including,
a spark gap; and
a frequency-dependent grading capacitor electrically connected in parallel with the spark gap, wherein a capacitance of the frequency-dependent grading capacitor decreases as a frequency of a voltage across the frequency-dependent grading capacitor increases.
2 . The arrester of claim 1 , wherein the capacitance of the frequency-dependent grading capacitor decreases by at least 40% when the frequency of the voltage across the frequency-dependent capacitor increases from 60 Hertz (Hz) to 500 KHz.
3 . The arrester of claim 1 , wherein the capacitance of the frequency-dependent grading capacitor decreases by at least 75% when the frequency of the voltage across the frequency-dependent capacitor increases from 60 Hertz (Hz) to 500 kHz.
4 . The arrester of claim 1 , wherein the frequency-dependent grading capacitor is constructed from a material including at least one of a donor-doped ferroelectric ceramic, a relaxor ferroelectric ceramic, and an insulator-conductor composite that exhibits enhanced low frequency permittivity due to space charge effects.
5 . The arrester of claim 1 , wherein the frequency-dependent grading capacitor has a dielectric loss tangent that is less than 15% when the frequency of the voltage across the frequency-dependent capacitor is 60 Hz.
6 . The arrester of claim 1 , wherein the frequency-dependent grading capacitor has a dielectric loss tangent that is less than 5% when the frequency of the voltage across the frequency-dependent capacitor is 60 Hz.
7 . The arrester of claim 1 , wherein an impedance of the frequency-dependent grading capacitor is a first percentage of a total series impedance of the arrester when a frequency of a voltage across the frequency-dependent grading capacitor is at a first frequency; and
wherein the impedance of the frequency-dependent grading capacitor increases to a second percentage of the total series impedance of the arrester when the frequency of the voltage across the frequency-dependent grading capacitor increases to a second frequency.
8 . The arrester of claim 1 , wherein an impedance of the frequency-dependent grading capacitor is less than 50% of a total series impedance of the arrester when a frequency of the voltage across the frequency-dependent grading capacitor is 60 Hz; and
wherein the impedance of the frequency-dependent grading capacitor increases to at least 80% of the total series impedance of the arrester when the frequency of the voltage across the frequency-dependent grading capacitor increases to 30 kHz-1 MHz.
9 . The arrester of claim 1 , wherein one or more included MOV disc(s) are constructed from predominantly zinc oxide.
10 . An accessory device electrically connected in series with an arrester, the accessory device comprising:
a spark gap assembly including:
a spark gap; and
a frequency-dependent grading capacitor electrically connected in parallel with the spark gap, wherein a capacitance of frequency-dependent grading capacitor decreases as a frequency of a voltage across the frequency-dependent grading capacitor increases.
11 . The accessory device of claim 10 , wherein the frequency-dependent grading capacitor is constructed from a material including at least one of a donor-doped ferroelectric ceramic, a relaxor ferroelectric ceramic, and a conductor-insulator composite that exhibits enhanced low frequency permittivity due to space charge effects.
12 . The accessory device of claim 10 , wherein the capacitance of the frequency-dependent grading capacitor decreases by at least 40% when the frequency of the voltage across the frequency-dependent capacitor increases from 60 Hertz (Hz) to 500 kHz.
13 . The accessory device of claim 10 , wherein the capacitance of the frequency-dependent grading capacitor decreases by at least 75% when the frequency of the voltage across the frequency-dependent capacitor increases from 60 Hertz (Hz) to 500 KHz.
14 . The accessory device of claim 10 , wherein the frequency-dependent grading capacitor has a dielectric loss tangent that is less than 15% when the frequency of the voltage across the frequency-dependent capacitor is 60 Hz.
15 . The accessory device of claim 10 , wherein the frequency-dependent grading capacitor has a dielectric loss tangent that is less than 5% when the frequency of the voltage across the frequency-dependent capacitor is 60 Hz.
16 . The accessory device of claim 10 , wherein an impedance of the frequency-dependent grading capacitor is a first percentage of a combined series impedance of the frequency-dependent grading capacitor and the arrester when a frequency of a voltage across the frequency-dependent grading capacitor is at a first frequency; and
wherein the impedance of the frequency-dependent grading capacitor increases to a second percentage of the combined series impedance of the frequency-dependent grading capacitor and the arrester when the frequency of the voltage across the frequency-dependent grading capacitor increases to a second frequency.
17 . The accessory device of claim 16 , wherein an impedance of the frequency-dependent grading capacitor is less than 50% of a combined series impedance of the frequency-dependent capacitor and the arrester when a frequency of the voltage across the frequency-dependent capacitor is 60 Hz.
18 . The accessory device of claim 17 , wherein an impedance of the frequency-dependent grading capacitor is at least 80% of a combined series impedance of the frequency-dependent capacitor and the arrester when a frequency of the voltage across the frequency-dependent capacitor is greater than 30 kHz.