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10.5 DISPLAY, METERING, COMMUNICATIONS, ANALOG OUTPUTS
10.5 DISPLAY, METERING, COMMUNICATIONS, ANALOG OUTPUTS
Accuracy of readings taken in this section should be compared with the specified relay accuracies, chapter 1. If
the measurements obtained during this commissioning procedure are "out-of-specification" verify your instru-
mentation accuracy. If the errors are truly in the relay, advise the company representative.
The general approach used to verify the AC current inputs is to supply rated currents in all the input CTs. Dis-
played readings will then confirm that the relay is correctly measuring all the inputs and performing the correct
calculations to derive sequence components, loading values, etc. Since the displayed values are high-side val-
ues, you can use this test to verify that the CT ratios have been correctly entered.
1. If you are using a single phase current supply, connect this current signal to all the input CTs in series,
winding 1, 2 and 3, if using a 3-winding configuration, and the ground CT input(s). Adjust the current level
to 1 A for 1-amp-rated relays and to 5 A for 5-amp-rated relays.
Some elements may operate under these conditions unless all elements have been dis-
abled.
NOTE
2. With the above current signals ON, read the Actual Values displayed under:
ACTUAL VALUES/A2 METERING/CURRENT
The actual values can be quickly read using the 745PC program.
3. Read the rms magnitude and the phase of the current signal in each phase of each winding. Note that
phase A, winding #1 current is used as the reference for all angle measurements.
I
phase rms displayed
The phase angle will be 0° for all phase currents if the same current is injected in all phase input CTs.
Sequence components will be:
I
=
CT Ratio
1
where a = 1∠120°
I
=
CT Ratio
2
I
zero sequence
= 3 × Phase CT ratio × input current
I
neutral
= Ground CT ratio × input current into ground CT
I
Ground
4. Since the transformer load is calculated using the A-phase current, the displayed load should be:
% Loading
where
Rated MVA Current
5. Verify the harmonic content display: should be zero, or equal to distortion of input current.
10
ACTUAL VALUES/A2 METERING/HARMONIC CONTENT/THD/W1...W2...W3
10-8
= I
x CT ratio for that winding
phase input
2
I
aI
a
I
+
+
×
a
b
c
---------------------------------- -
=
0
since the three currents are in phase.
3
2
I
a
I
aI
+
+
×
a
b
c
---------------------------------- -
=
0
since the three currents are in phase.
3
= CT ratio × input current
Actual Current
×
100%
=
--------------------------------------------------- -
Rated MVA Current
MVA
=
------------------------
3 kV
L L
–
745 Transformer Management Relay
10 COMMISSIONING
10.5.1 DESCRIPTION
10.5.2 CURRENT INPUTS
GE Power Management
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