GE Multilin
745 Transformer Management Relay
8-7
8 COMMISSIONING
8.4 DISPLAY, METERING, COMMUNICATIONS, AND ANALOG OUTPUTS
8
8.4DISPLAY, METERING, COMMUNICATIONS, AND ANALOG OUTPUTS
8.4.1 DESCRIPTION
Accuracy of readings taken in this section should be compared with the specified accuracies in Section 1.2: Specifications
on page 1–4. If the measurements obtained during this commissioning procedure are “out-of-specification” verify your
instrumentation accuracy. If the errors are truly in the relay, advise the company representative.
8.4.2 CURRENT INPUTS
The general approach used to verify the AC current inputs is to supply rated currents in all the input CTs. Displayed read-
ings 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 values, 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 disabled!
2.
With the above current signals ON, read the actual values displayed under
ACTUAL VALUES
ÖØ
A2 METERING
Ö
CUR-
RENT
. The actual values can be quickly read using the 745PC software.
3.
Read the rms magnitude and the phase of the current signal in each phase of each winding.
Note that the Winding 1
Phase A current is used as the reference for all angle measurements.
I
phase rms displayed
=
I
phase input
x CT ratio for that winding
The phase angle will be 0° for all phase currents if the same current is injected in all phase input CTs. Sequence com-
ponents will be:
(EQ 8.1)
4.
Since the transformer load is calculated using the Phase A current, the displayed load should be:
,
where
(EQ 8.2)
5.
Verify the harmonic content display in
A2 METERING
ÖØ
HARMONIC CONTENT
ÖØ
THD
ÖØ
W1...W2...W3
. It should be
zero or equal to distortion of input current.
6.
Verify frequency shown in
A2 METERING
ÖØ
FREQUENCY
ÖØ
SYSTEM FREQUENCY
. It should be 60 or 50 Hz, as per fre-
quency of input current on Phase A.
7.
To verify the positive and negative sequence component values, apply the current signal to Phase A of each winding in
series. Read the values of positive and negative sequence current displayed by the relay.
, where a = 1
∠
120°
(EQ 8.3)
(EQ 8.4)
All angles will be 0°. These values are displayed in the
A2 METERING
Ö
CURRENT
ÖØ
POSITIVE SEQUENCE
ÖØ
W1...W2...W3
and
A2 METERING
Ö
CURRENT
ÖØ
NEGATIVE SEQUENCE
ÖØ
W1...W2...W3
actual values menus.
8.
Now, lower the current amplitude while displaying the system frequency. Verify that the frequency is displayed correctly
with current levels down to approximately 50 mA rms input. Decrease current to 0 A.
I
1
CT Ratio
I
a
aI
b
a
2
I
c
+
+
3
-----------------------------------
×
0, since all three currents are in phase, where
a
120°
∠
=
=
=
I
2
CT Ratio
I
a
aI
b
a
2
I
c
+
+
3
-----------------------------------
×
0, since the three currents in phase
=
=
I
zero-sequence
CT Ratio input current
×
=
I
neutral
3 CT Ratio input current
×
×
=
I
ground
Ground CT Ratio input current into Ground CT
×
=
% Loading
Actual Current
Rated MVA Current
----------------------------------------------------
100%
×
=
Rated MVA Current
MVA
3
kV
L L
–
-------------------------
=
I
1
1
3
---
CT Ratio
×
I
a
aI
b
a
2
I
c
+
+
(
)
×
1
3
---
CT Ratio
×
I
a
×
since
I
b
I
c
0
=
=
=
=
I
2
1
3
---
CT Ratio
×
I
a
a
2
I
b
aI
c
+
+
(
)
×
1
3
---
CT Ratio
×
I
a
×
since
I
b
I
c
0
=
=
=
=