Nace CP 1, Руководство по эксплуатации

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RP0177-2000
14 NACE International
potentials and currents under normal conditions, fault
conditions, and lightning surges. Because significant
AC potentials may be encountered during field
surveys, all personnel shall follow proper electrical
safety procedures and treat the structure as a live
electrical conductor until proven otherwise.
6.2.2 Tests and investigations to estimate the extent
of AC influence should include the following:
(a) Meeting with electric utility personnel to
determine peak load conditions and maximum
fault currents and to discuss test procedures to
be used in the survey.
(b) Electrical measurement of induced AC
potentials between the affected structure and
ground.
(c) Electrical measurement of induced AC
current on the structure.
(d) Calculations of the potentials and currents
to which the structure may be subjected under
normal and fault conditions.
8
6.2.3 A survey should be conducted over those
portions of the affected structure where AC exposure
has been noted or is suspected. The location and
time that each measurement was taken should be
recorded.
6.2.3.1 The potential survey should be
conducted using a suitable AC voltmeter of
proper range. Contact resistance of connections
should be sufficiently low to preclude
measurement errors because of the relationship
between external circuit impedance and meter
impedance. Suitable references for measure-
ments are:
(a) A metal rod.
(5)
(b) Bare pipeline casings, if adequately
isolated from the carrier pipe.
(c) Tower legs or power system neutrals, if
in close proximity to the affected structure.
(Meter connections made to tower legs or
power system neutrals may present a
hazard during switching surges, lightning
strikes, or fault conditions.)
6.2.3.2 The presence of AC on a structure may
be determined using a suitable AC voltmeter to
measure voltage (IR) drop at the line current test
stations. This method, however, provides only
an indication of current flow, and cannot be
readily converted to amperes because of the AC
impedance characteristics of ferromagnetic
materials. A clamp-on AC ammeter may be
used to measure current in temporary or
permanent bond connections.
6.2.3.3 Indications of AC power levels on
affected structures may be obtained by
temporarily bonding the structure to an adequate
ground and measuring the resulting current flow
with a clamp-on AC ammeter while measuring
the AC potential. Suitable temporary grounds
may be obtained by bonding to tower legs,
power system neutral, bare pipeline casings, or
across an isolating joint to a well-grounded
system. DC drainage bonds existing on the
structure under investigation should also be
checked for AC power levels.
6.2.3.4 Locations indicating maximum AC
potential and current flow values during the
survey discussed in Paragraphs 6.2.3 through
6.2.3.2 should be surveyed with recording
instruments for a period of 24 hours or until the
variation with power-line load levels has been
established.
(6)
6.2.4 In designing mitigative measures, the following
power system parameters should be determined:
(a) Maximum operating and emergency load
conditions.
(b) Maximum single line-to-ground fault current
and duration.
(c) Maximum phase-to-phase fault current and
duration.
(d) Type of grounding system used.
6.3 Special Considerations in Cathodic Protection Design
6.3.1 AC influence on the affected structure and its
associated cathodic protection system should be
considered.
6.3.2 Cathodic protection survey instruments should
have sufficient AC rejection to provide accurate DC
data.
____________________________
(5)
Following meter hookup, the reference rod should be inserted deeper into the earth until no further potential increase is noted. This reduces the
possibility of high-resistance contact errors in the measurement.
(6)
Survey data gathered in accordance with Paragraphs 6.2.3 through 6.2.3.4 should be reviewed with electric utility personnel for the purpose of
correlating with the power-line operating conditions at the time of the survey.