GE 745 Instruction Manual page 133

CHAPTER 5: SETPOINTS
Note
NOTE
Note
NOTE
5.4.4 Onload Tap Changer

ONLOAD TAP
CHANGER
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
This setting is visible only for a 3W transformer.
Whenever transformer type is changed (particularly from 2 W to 3 W) "ground input
selection" setting should be cross-checked.
• WINDING 1(3) GROUND CT PRIMARY: Enter the ground CT primary current rating of
the current transformers connected in the winding 1(3) neutral to ground path. The CT
secondary current rating must match the relay ground current input rating indicated.
• WINDING 1(3) SERIES 3-Φ RESISTANCE: Enter the series three-phase resistance of the
winding (that is, the sum of the resistance of each of the three phases for the winding).
This value is normally only available from the transformer manufacturer's test report,
and is used in the 745 for calculation of harmonic derating factor.
PATH: SETPOINTS S2 SYSTEM SETUP


[ ] WINDING WITH TAP
CHANGER: None
NUMBER OF TAP
MESSAGE
POSITIONS: 33
MINIMUM TAP POSITION
MESSAGE
VOLTAGE: 61.0 kV
VOLTAGE INCREMENT
MESSAGE
PER TAP: 0.50 kV
RESISTANCE INCREMENT
MESSAGE
PER TAP: 33 Ω
This section contains the settings to configure the tap position input. The 745 accepts a
resistive input from the tap changer control circuitry, which is used in the 745 to
dynamically correct for CT ratio mismatch based on the dynamically changing voltage
ratio of the transformer. Thus, the percent differential function of the device can be set for
greater sensitivity. See Dynamic CT Ratio Mismatch Correction on page 5–6 for more details
on the tap position input.
• WINDING WITH TAP CHANGER: Enter the winding with the tap changer. Enter 'None'
for a transformer with no onload tap changer, or to disable this feature.
• NUMBER OF TAP POSITIONS: Enter the number of tap positions here.
• MINIMUM TAP POSITION VOLTAGE: Enter the voltage at the lowest tap position. This is
an auto-ranging setpoint dependent on
VOLTAGE WINDING RATING
• VOLTAGE INCREMENT PER TAP: Enter the voltage increment for each tap. The range is
affected by the setpoint. This is an auto-ranging setpoint dependent on the
SETUP TRANSFORMER

following table:
Setting
MINIMUM TAP POSITION
VOLTAGE
ONLOAD TAP CHANGER

S2 SYSTEM SETUP
; see ranges in the table below.
LOW VOLTAGE WINDING RATING

Low voltage winding rating value
above 5 kV
0.1 to 2000.0 kV in 0.01 to 200.00 kV in
steps of 0.1 steps of 0.01
S2 SYSTEM SETUP
Range: None, Winding 1, Winding 2,
Winding 3
Range: 2 to 50 in steps of 1
Range: Dependent on LOW VOLTAGE
WINDING RATING; see below.
Range: Dependent on LOW VOLTAGE
WINDING RATING; see below.
Range: 10 to 500 Ω in steps of 1
TRANSFORMER
 
S2 SYSTEM
value; see ranges in the
1 kV to 5 kV below 1 kV
0.001 to 20.000 kV
in steps of 0.001
LOW
5–37