E L E C T R I C A L S Y S T E M S Evaluation of Pole Bonding Methods NEETRAC Project No. 08-226 Shashi Patel IEEE ESMOL 2011 WINTER MEETING Las Vegas, Nevada February 14, 2011 GTRC 2011 1
Overall Project Details Tests on a three pole single phase distribution line with 25 kv specifications at Hubbell High Power Laboratory in Centralia, MO. A total of three trips to the site over one year period (2009-2010) Approximately 150 single phase tests (500 measurements) Approximately 500 moisture measurements Three basic wood pole bonding methods: poleband, unstapled or insulated downlead and stapled bare downlead Tests on a simulated three wire or no-neutral system Tests on a simulated steel pole GTRC 2011 2
Basic Characteristics of Wood Pole Bonding Methods Poleband provides bonding simply by wrapping around pole. Unstapled or insulated downlead provides bonding through a ground electrode at the base of the pole. Stapled bare downlead provides bonding through staples in addition to the ground rod at the base of the pole. GTRC 2011 3
Specific Test Scenarios I TPG 1.5 I TPG 2 Pole-1 Aged Penta Pole-2 Aged Creosote Pole-3 Aged CCA Downlead Options -No downlead -Unstapled bare (insulated) -Stapled bare Test Scenarios 1) Without poleband and downlead (no bonding) 2) With poleband 3) With unstapled or insulated downlead 4) With stapled bare downlead 5) With poleband + unstapled downlead 6) With poleband + stapled bare downlead GTRC 2011 4
Measurement Set Up I TPG Fib Optic Trans DAD I PB 14.4 /0.12 kv PTs 200' Remote rod Measured Parameters 1) TPG current (at Generator), I TPG 2) Voltage across 1000 Ohms resistor, V exp(cc) or I exp 3) Phase to remote voltage (with and w/o 1000 Ohms resistor), V ph-r 4) Neutral to remote voltage (with 1000 Ohms resistor), V n-r 5) Nails to remote voltage (w/o 1000 Ohms resistor), V nails-r 6) Current in poleband TPG, I PB GTRC 2011 5
Measurement Setup FO Trans + PS 1000 Ohms V ph R Nails Remote rod I TPG V n R 14.4/0.12 kv PTs I PB GTRC 2011 6
Moisture Measurements GTRC 2011 7
source voltage source impedance I TPG Evaluation of Pole Bonding Methods jumper impedance C1 C2 contact resistance (conductor to hand) body resistance 1000 Ω contact resistance (foot to pole) Thevenin s Equivalent Circuit C 1 neutral impedance (multi-grounded) contact resistance (pole to pole band) pole resistance (one foot) pole ground wire pole resistance (~35 feet) V exp(oc) V exp(oc) or V exp(cc) pole grounds electrode resistance contact resistance (pole to electrode) contact resistance (pole to earth) I exp R b = 1000 Ω Electrical Circuit Representing a Worker Contact between Phase Conductor and Wood Pole through Climbers (Between C1 and C2) Bonding by a Poleband R thev V exp( oc ) I exp R thev R b C 2 GTRC 2011 8
Typical Moisture Data GTRC 2011 9
Test Results (Stand-alone Bonding Methods) V exp(oc) Dry Surface Wet Hardwood I exp or V exp(cc) R thev GTRC 2011 10
Test Results (Combination Bonding Methods) V exp(oc) Dry Surface Wet Hardwood I exp or V exp(cc) R thev GTRC 2011 11
Test Results (Stand-alone Bonding Methods) V exp(oc) Wet Surface Wet Hardwood I exp or V exp(cc) R thev GTRC 2011 12
Test Results (Combination Bonding Methods) V exp(oc) Wet Surface Wet Hardwood I exp or V exp(cc) R thev GTRC 2011 13
Test Results (Comparison of Iexp between Penta and CCA Poles) GTRC 2011 14
Test Results (Influence of Higher Vph-R on Iexp) GTRC 2011 15
Test Results (Influence of Surface Wetness on Iexp) GTRC 2011 16
Test Results (Iexp Measured on Simulated 3-Wire or No Neutral System) 140 Vph-R =5169 Volts, I TPG = 982 A Pole 1 (Penta) I exp (ma) or Vexp(cc) (V) 120 100 80 60 40 20 0 Ph-Rod TPG w/o PB & DL Ph-PB-Rod TPG w PB dry surface 58 35 wet surface 115 6 GTRC 2011 17
Key Conclusions Between three bonding means, the bare downlead provided the best protection with poleband coming next. The insulated downlead provided the least amount of protection. Poleband did not provide any additional protection when the pole was bonded by a bare downlead. However, the worker current reduced significantly when the poleband was installed in addition to the insulated downlead. Due to increase in contact resistance, poleband becomes less and less effective as the surface starts drying. In comparison, stapled bare downlead provides superior protection regardless of surface conditions. GTRC 2011 18