CALCULATIONS / EVALUATIONS

1 HIGH VOLTAGE CALCULATIONS / EVALUATIONS West Virginia Office of Miners Health, Safety & Training Helping You To Work More Safely In The Mining Industry DISCLAIMER The West Virginia Office of Miners Health, Safety and Training publishes this booklet. The material should be used by mine electricians to assist in selecting the proper protective settings for over current, short circuit, and ground fault protection. The material is not all-inclusive and should be used only as an aide in gaining compliance with the regulations.

2 This material is based upon several different publications including West Virginia State Mining Regulations, The National Electrical Code, Title 30 CFR, and the Program Policy Manual. Only two manufacturers of high voltage over current relays are listed; however, products of other manufacturers can easily be cross-referenced to those listed. Nothing herein should be construed as recommending any manufacturer s products. Visit our website West Virginia Office of Miners Health, Safety and Training Doug Conway Director Phillips Deputy Director Gerry Barton Benny Comer Danny Cook Don Crawford Tom Harmon John Scott Kendall Smith Randy Smith Bobby Thornsbury Electrical Inspectors Mine Safety and Health Administration District 4 Larry Cook Supervisor Electrical Engineer Marcus Smith Electrical Engineer National Mine Health and Safety Academy Sandy Neal Graphic Arts INSTANTANEOUS UNIT ADJUSTABLE CORE TAP SELECTOR BLOCK TAP PLUG TIME DIAL CONTROL SPRING ADJUSTING RING INSTANTANEOUSUNIT DISK Direct Relaying.

3 In this method, grounded -phase current is detected directly with a current transformer installed in the grounded neutral conductor. Balance Flux Relaying. In this method, grounded -phase current is detected by a doughnut-type current transformer installed around the three phase conductors. Note: The equipment grounding conductors (including conductor shields) must not be installed through the current transformer. Residual Trip Relaying. In this method, grounded -phase current is detected as the unbalance in the current produced by the phase current transformers.

4 Potential Relaying. In this method, grounded -phase current is detected as the voltage drop across the grounding resistor. An advantage of this method over the three previous methods is that grounded -phase protection is still provided even if the grounding resistor is open. For this reason, potential relaying is often used to provide backup grounded -phase protection for resistance- grounded systems. OVERCURRENT RELAY 4160 volt system phase to phase 2/0 AWG cable 5 KV rating at 90 degree insulation Cable rated for 287 amps X 125% = 359 amps Current transformer ratio 80:1 Tap bar range to 16 80:1 X tap 4 = 320 amps SHORT CIRCUIT Using a breaker, the short circuit is set no greater than 600% X cable ampacity of 287 amps.

5 (287 X 6 = 1722 amps) This setting is achieved by adjusting the instantaneous unit adjustable core screw. GROUND FAULT 4160 volts phase to phase 2400 volts phase to neutral 25 amp grounding resistor 96 ohms Tap bar range to Ground fault current is set at no more than 50% of the amp rating of the resistor Current transformer ratio is 10:1 Current transformer ratio 10:1 set on tap (10 X = 12 amps) which is less than 50% of the 25 amp grounding resistor. 4160 volt system phase to phase 2001 - 8000 VOLTS 8001 - 15000 VOLTS 2/0 AWG cable 5KV volt rating 90c insulationAWG75c85c90cAWG75c85c90c Current Transformer 50.

6 1 ratio21701821882168187194 25 amp grounding resistor rated at 96 ohmsX125% 213228235X125% 210234243 Current tap block 2 - 16 1020 1092 1128X600% 1008 1122 1164 Instantaneous unit adjustable from 20-40 amps11962102171192215221X125% 245263271X125% 240268276 TAPS RATIOX600% 1176 1260 1302X600% 1152 1290 1326A O 1 O51-1BC 10/1 1/0226242249 1/0221247254B O 2 OAB 20/1X125% 283303311X125% 276309318C O 3 OAC 30/1X600% 1356 1452 1494X600% 1326 1482 1524D O 4 ODE 40/1 2/0260278287 2/0253282290E O 5 OCD 50/1X125%325348359X125% 316353363G O 6 OBD 60/1X600%1560 16681722X600% 1518 1692 1740AD80/1 3/0299320329 3/0290324334A O 1 O51-2CE 90/1X125% 374400411X125% 363405418B O 2 OBE 100/1X600% 1794 1920 1974X600% 1740 1944 2004C O 3 OAE 120/1 4/0343367379 4/0333372384D O 4 OX125% 429459474X125% 416465480E O 5 OX600% 2058 2202 2274X600% 1998 2232 2304G O 6 O TIME OVERCURRENT RELAYA O 1 O51-3 MODEL 000000000000 TYPE I A C B O 2 OG INVERSETIME 2 - 16 AMPERES 60 CYCLESC O

7 3 OrINSTRUCTIONS 00000000 PARTS BULLETIND O 4 Oo INSTANTANEOUS UNIT 20 - 40 AMPERESE O 5 OuG O 6 On Current Tap BlockdOOOOOOOOOOO2 3 4 567810121416 Instantaneous Unit Pickup Adjustment 40 MAX ___ 20 MIN. OVERCURRENT & SHORT CIRCUIT PROTECTIONOO Cable ampacity 287 amps X 125% = 359. Set the taps on OO A and D on the multi-tap CT to obtain a 80:1 Which tap on the multi-tap block would be used to obtain the highest allowable setting for the 2/0 AWG cable? 4 What is the actual ampacity set at?

8 320 Set the short circuit instantaneous unit on the maximum allowable 1722amps. Set the instantaneous unit core at amps. ( 1722 Divided by 80:1 CT Ratio - ) Ground Fault Tap Blockoooooooo o oo10:1 Which tap on the multi-tap block would be used to obtain the highest allowable setting? What is the actual setting? 12 Ampacity 287 X 6 = 1722 Divided by 80:1 CT Ratio = Amps Max. CompanyMine I D NumberDate HV Underground Feeder CableFence Gate Shunted & LockedYesCable Size 2/0 Fence: GroundedYesCable Temp.

9 Rating90cDanger HV Signs PostedYesCable KV Rating5 Fence: Height6'Cable Ampacity287 Metal Structures GroundedYesOvercurrent RelaysInsulated Mats YesCable Ampacity287X125%359 Metal Grids GroundedYesRelays 51/1 51/2 51/3 Voltage In12,470CT Ratio 80:1 80:1 80:1 Voltage Out4,160OL Tap Bar Range 2-16 2-16 2-16 Lightning Arrestors PrimaryYesTap Set On444 Lightning Arrestors SecondaryYesSetting Actual Amps320320320 Disconnects: Incoming PowerYesMax. Allow. Tap Disc. 100' Of PortalYesTime Dial Setting111 Primary Fuse Size30 Short CircuitTransformer ConnectionD / YCable Ampacity287X600%1,722 Neutral: Direct or DerivedDirectCT Ratio 80:1 Transformer KVA or Amps5,000 Core Setting Range20 - 40HV OCB / Vac Bkr.

10 IdentifiedYesCore Set Amp Rating600 Setting Actual Amps1,722 OCB Voltage Rating15 KVMax Allow. Core Set. Bkr. Amp RatingN/AGround Fault Relay 51 - GVacuum Bkr. Voltage RatingN/APhase to Neutral Voltage2,400 Grounding Resistor Amps25CT Ratio 50:5 Grounding Resistor Ohms96 Grounding Resistor Amps25 Neutral GND Resistance Ohms250% Resistor Rated GND Resistance Ohms3 Tap Bar Voltage120 Tap Set Amps1 Setting Actual Amps12 Capacitors PrimaryNoMax Allowable Tap SecondaryNoTime Dial I D NumberDate HV Underground Feeder CableFence Gate Shunted & LockedCable SizeFence: GroundedCable Temp.