(1) In all tests of
watthour meters where comparison of revolutions is made, at least 2 revolutions
of the meter under test shall be taken at light load and at least 9 revolutions
at heavy load. At least 2 checks shall be made at each load. The accuracy of
the meter under test at each load shall be the average accuracy determined from
2 checks taken at the same load which must agree within 0.2 of 1%. However, if
an electro-optical testing device is used, the test procedure may be modified,
provided equal accuracy of the method is maintained.
(2) If the watthour meter has a contact
device which operates a demand mechanism, the disk revolutions when testing
should be multiples of the number of revolutions per contact in order to take
account of the varying friction which may be present during the movement of the
contact cam from one contact to the next.
(3) Polyphase meters shall be tested by one
of the following 4 methods:
(a) Single-phase
test with the potential circuits connected in parallel and all current circuits
connected in series. Three-stator, 4-wire delta meters must have correct values
of current and potential applied to the differently rated circuits. The normal
test loads apply. (See s.
PSC 113.0811(1)
(c).)
(b) Individual stator test with the potential
circuits connected in parallel and each current circuit tested separately. (For
2-stator, 4-wire delta meters, the current circuits of the 3-wire stator should
be connected in series and treated as a single circuit. Three-stator, 4-wire
delta meters must have correct values of potential applied to the differently
rated circuits.) The light load test current shall be one-tenth N times the
reference test current and the heavy load test current shall be between
one-half and one N times the reference test current but not more than twice the
test ampere rating of the meter. (N equals the number of stators in the meter
except for 2-stator, 3-phase, 4-wire wye meters. For the latter, N shall be 4
for the current circuits which are not common to both stators and N shall be 2
for the current circuit common to both stators.)
(c) Individual stator test with the potential
circuits connected to the polyphase circuit in the same manner as in service.
(For 2-stator, 4-wire delta meters the current circuits of the 3-wire stator
shall be connected in series and treated as a single circuit.) The light load
test current shall be one-tenth N times the reference test current and the
heavy load test current shall be between one-half and one N times the reference
test current but not more than twice the test ampere rating of the meter. (N
equals the number of stators in the meter except for 2-stator, 3-phase, 4-wire
meters. For the latter N shall be 3 for each current circuit.)
(d) Polyphase test with the meter connected
to a polyphase circuit in the same manner as in service, with balanced
polyphase currents on the current circuits. This requires the use of a
polyphase standard watt-hour meter or as many single-phase standards as there
are current circuits under test.
(4) Instrument transformers shall be tested
with a burden equivalent to that with which they are to be used or with burdens
from which curves showing the accuracy of the transformer can be derived. Any
approved method may be used for testing instrument transformers. Also see s.
PSC 113.0916.
