CHAPTER 7: COMMISSIONING PROTECTION SCHEMES
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL 7–43
LATCHED a: W1 Neg Seq Inst OC or OPERATED a: W1 Neg Seq
Inst OC
Reduce the current until the element resets.
The reset level should be 97% of the operate level. When the element
resets, the Trip and Message LEDs should remain on if the
W1 NEG SEQ
INST OC TARGET
was selected as Latched. Otherwise, only the Trip
LED should remain on.
Reset indicators and clear messages.
7.5.16.4 Operating Time
Using the setup in General test setup on page 7–25 with the Interval
Timer enabled, set the current level to 1.5 times the operate level of the
element and apply suddenly by closing the double-pole switch.
Record the operate time and compare to the
S4 ELEMENTS NEG SEQ
OC W1 NEG SEQ INST OC W1 NEG SEQ INST OC DELAY setting.
7.5.16.5 Winding 2 and 3 Elements
Because the winding 2 and 3 elements can be set with completely different parameters
than the element for winding 1,
Repeat the full set of tests described for the winding 1 element in this
section.
Connect the current supply to terminals X = H4 and Y = G4 to test the
Winding 2 element. Use X = H7 and Y = G7 for the Winding 3 element.
Note
The blocking from logic input, if enabled, can be tested as described in earlier tests for
other elements.
7.5.17 Frequency
7.5.17.1 Setup
The power system frequency is measured from the voltage input if it has been enabled. If
there is no voltage input, it is measured from the winding 1 phase A current signal. These
tests require a variable-frequency current source for relays without a voltage input and a
variable-frequency voltage and current source for relays with a voltage input. Connections
are shown in the figure below. Only perform tests specific to the relay model.
Note
The underfrequency, overfrequency, and frequency decay elements are all supervised by
optional adjustable minimum current and minimum voltage level detectors. When testing
the performance of these elements on a 745 with the voltage input enabled, it may be
necessary to inject a current signal into winding 1 phase A if the current supervision is
enabled, or else the detectors will not operate.
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