Program Policy Manual - VOLUME V - Mine Safety and Health ...

More documents

Recommendations

Info

MSHA PROGRAM POLICY MANUAL VOLUME V the phase-to-neutral voltage for potential relaying. Where an ungrounded high-voltage circuit is accepted for use underground under the provisions of Section 75.802(b), the circuit must be provided with grounded-phase protection. Grounded-phase indicating lights that do not trip the circuit breaker upon the occurrence of a phase-to-ground fault are not acceptable as compliance with this Section. Short-circuit protection can be provided by using the instantaneous units of overcurrent relays or by using inverse-time overcurrent relays with minimal time dial settings. The pickup of the instantaneous unit of an overcurrent relay is independent of the pickup of the inverse-time unit and is determined by the position of the top of the screw on the instantaneous unit. Overcurrent devices are required in at least two phases of threephase high-voltage underground distribution circuits. 75.800-3 Testing, Examination, and Maintenance of Circuit Breakers; Procedures If the circuit breaker located on the surface provides overload, short-circuit, undervoltage, and grounded-phase protection for the entire underground circuit, only that circuit breaker is required to be tested by this Section. Circuit breakers installed underground for coordination purposes in such circuits are not required to be tested; however, each independent ground- check circuit must be tested in accordance with this Section. The tests required by paragraph (b)(2) of this Section may be conducted one of three ways: 1. Primary injection test. This test method involves sufficient current to cause the circuit breaker to trip through at least two current transformers associated with the circuit breaker. Since this method requires that test connections be made on high-voltage conductors or terminals, stringent safety procedures must be followed. This method simultaneously tests the current transformer ratio, the current transformer secondary wiring, the operation and calibration of the relays, and the operation of the circuit breaker tripping circuit. February 2003 (Release V-33) 75
MSHA PROGRAM POLICY MANUAL VOLUME V 2. Secondary injection test. This test method involves passing sufficient current to cause the circuit breaker to trip through at least two of the protective relays associated with the circuit breaker. This method simultaneously tests the operation and calibration of relays and the operation of the circuit breaker trip circuit. 3. Mechanical activation test. This test method involves mechanically activating at least two of the protective relays associated with the circuit breaker with a non- conductive probe. This method tests the operation of the circuit breaker trip circuit. 75.801 Grounding Resistors Grounding resistors that are manufactured to meet the extended time rating as set forth in IEEE Standard 32-1972, formerly AIEE Standard 32, are acceptable as compliance with this Section. Resistors that are not manufactured in compliance with IEEE Standard 32-1972 shall be "rated for maximum fault current continuously." 75.802 Protection of High-Voltage Circuits Extending Underground Grounding transformers must be sized to carry the rated groundfault current of the system continuously. Consequently, the kVA rating of a zigzag grounding transformer or a wye-delta grounding transformer bank shall not be less than the rated phase-to-neutral voltage of the system (VON) in kV times the rated ground-fault current of the system (I) in amperes. If other loads are supplied from a wye-delta grounding transformer bank, the rating of the transformer bank must be adequate to supply the additional loads plus the rated ground-fault current. Transformer banks connected wye on the primary side and supplied power from a resistance-grounded circuit shall not have the primary neutral grounded. When used, grounding transformers shall be connected on the line side of circuit breakers so that the system will always be grounded and must be located in/or adjacent to the same substation as the power source transformers. This Section requires that the grounding resistor be located at the source transformers. As used in this Section, the term "source transformer" means the transformer that supplies power to the electric circuit. JULY 2006 (Release V-38) 76
Page 1 and 2:
MSHA PROGRAM POLICY MANUAL VOLUME V
Page 3 and 4:
Page 5 and 6:
Page 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40: MSHA PROGRAM POLICY MANUAL VOLUME V
Page 89: MSHA PROGRAM POLICY MANUAL VOLUME V
Page 127 and 128: MSHA PROGRAM POLICY MANAUL VOLUME V
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
Page 213 and 214:
Page 215 and 216:
Page 217 and 218:
Page 219 and 220:
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
MSHA PROGRAM POLICY MANAUL VOLUME V
Page 235 and 236:
MSHA PROGRAM POLICY MANAUL VOLUME V
show all

Program Policy Manual - VOLUME V - Mine Safety and Health ...

Create successful ePaper yourself

Delete template?

Save as template?