Ambient Temperature Input - GE TRANSFORMER MANAGEMENT RELAY 745 Instruction Manual

8 COMMISSIONING
By injecting a current into Phase A of Winding 1 and Phase A of Winding 2 only, I
an injected current of 1 × CT, the transformed Y-side currents will be:
For the purposes of the differential elements only, the transformation has reduced the current to 0.57 times its original value
into Phase A, and created an apparent current into Phase B, for the described injection condition. If a 1 × CT is now
injected into Winding 1 Phase A, the following values for the differential currents for all three phases should be obtained:
Phase A differential: 0.57 × CT ∠0° Lag
Phase B differential: 0.57 × CT ∠180° Lag
Phase C: 0 × CT.
b) EFFECTS OF ZERO-SEQUENCE COMPENSATION REMOVAL
The transformation used to obtain the 30° phase shift on the Y-side automatically removes the zero-
sequence current from those signals. The 745 always removes the zero-sequence current from the delta
winding currents.
NOTE
If the zero-sequence component is removed from the Delta-side winding currents, the Winding 2 current values will change
under unbalanced conditions. Consider the case described above, with the 1 × CT injected into Phase A of Winding 2.
For the 1 × CT current, the zero-sequence value is 1/3 of 1.0 × CT or 0.333 × CT A. The value for I
0.333) × CT = 0.6667 × CT A. This value must be divided by the CT error correction factor of 0.797 as described above.
Therefore, the value of differential current for Phase A, when injecting 1 × CT in Winding 2 only, is:
The action of removing the zero-sequence current results in a current equal to the zero-sequence value introduced into
phases B and C. Hence, the differential current for these two elements is:
Now, applying 1 × CT into Winding 1 Phase A and the same current into Phase A Winding 2, but 180° out-of- phase to prop-
erly represent CT connections, the total differential current in the Phase A element will be (0.57 – 0.84) × CT = –0.26 × CT.
The injection of currents into Phase A of Windings 1 and 2 in this manner introduces a differential current of (–0.57 × CT +
0.42 × CT) = –0.15 × CT into Phase B and (0.0 × CT + 0.42 × CT) = 0.42 × CT into Phase C.
a) BASIC CALIBRATION OF RTD INPUT
1. Enable ambient temperature sensing with the
setpoint.
2. Connect a thermocouple to the relay terminals B10, B11, and B12 and read through the
TEMP AMBIENT TEMPERATURE
3. Compare the displayed value of temperature against known temperature at the location of the sensor. Use a thermom-
eter or other means of obtaining actual temperature.
An alternative approach is to perform a more detailed calibration per the procedure outlined below.
GE Multilin
Courtesy of NationalSwitchgear.com
8.4 DISPLAY, METERING, COMMUNICATIONS, AND ANALOG OUTPUTS
I I
–
W1a W1c
---------------------------- - ,
I I
=
W1a' W1b'
3
×
1 CT
---------------- - ,
I I
=
W1a' W1b'
3
0.667 CT A
I ---------------------------------- -
=
( )
A differential
I I
=
( ) (
B differential C differential
S2 SYSTEM SETUP
actual value.
745 Transformer Management Relay
I I
I
–
W1b W1a
W1c
---------------------------- - ,
I ---------------------------- -
= =
W1c'
3
W1b
×
×
1 CT
0 CT
–
-------------------- ,
I ---------------- -
= =
W1c'
3
3
×
×
0.84 CT A
=
0.797
×
0.333 CT A
×
---------------------------------- - 0.84 CT A
= =
)
0.797

8.4.5 AMBIENT TEMPERATURE INPUT

AMBIENT TEMP
I
–
W1b
3
= I = 0 A. Therefore, if we assume
W1c
is therefore (1.0 –
W2a'
AMBIENT TEMPERATURE SENSING
A2 METERING
(EQ 8.7)
(EQ 8.8)
(EQ 8.9)
(EQ 8.10)
8
AMBIENT
8-9