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SECTION 3 - HIGH VOLTAGE INSTALLATIONS High voltage installations are a special case. In this area the CEC goes further and becomes more complex in order to deal with the increased possibility for harm. Section 36 addresses some special hazards by limiting ground potential rise (GPR) and step and touch voltages in outdoor substations and transformer stations Ground potential rise (GPR) is the voltage rise in a substation grounding system during a ground fault. It may be calculated as the product of measured substation ground resistance and the maximum available ground fault current. Step voltage is the potential difference on the substation or transformer station surface, a distance of one pace in the direction of a ground fault. Touch voltage is the potential difference between any metal object and a point on the substation or transformer station surface one arm’s length away. GRP, step and touch voltages must be maintained within the limits specified in the Code. Rules 36 – 304 and 36 – 306 specify that outdoor stations above 7,500 volts phase-to-phase must have a GPR no higher than 5,000 volts. Table 52 limits step and touch voltages under various station surface conditions for ground faults of either 1.0 or 0.5 second. For example, in an outdoor station, with a crushed stone surface, where the electrical utility’s ground fault protection operates in 0.5 second or less, Table 52 restricts the permissible step and touch voltages to 3,143 volts and 885 volts. In this example, the station ground electrode must be designed to satisfy these voltage limits. Section 36: STATION GROUNDING and BONDING 36 – 300 Material and Minimum Size of Grounding Conductor and Ground Grid and Connections: |
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(1) |
Bare copper conductors shall be used for grounding purposes. | |
| (2) |
Notwithstanding (1), a galvanized steel, copper-weld, or other conductor shall be permitted, provided that |
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(a) |
its current-carrying rating is equal to or greater than that of the copper conductor specified . |
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| (b) |
consideration is given to galvanic corrosion . |
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| (c) |
the method of bolting or connecting such conductors to each other and to other surfaces is such as to maintain the required current-carrying capacity for the life of the electrode design. |
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36 – 302 STATION GROUND ELECTRODE |
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(1) |
Every outdoor station shall be grounded by means of a station ground electrode and shall: |
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(a) |
consist of a minimum of four driven ground rods located adjacent to the equipment to be grounded. |
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| (b) |
have the ground rods interconnected by conductors not less than 2/0 AWG bare copper. |
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| (c) |
have the station ground grid conductors in (b) connected to all non-current-carrying metal parts of equipment and structures and shall form a loop around the equipment to be grounded. |
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