GE G30 Instruction Manual page 306

SYSTEM SETUP
5.5.4.3 Windings
SETTINGS  SYSTEM SETUP  TRANSFORMER  WINDING 1(2)
 WINDING 1

The G30 is provided with this optional feature, specified as an option at the time of ordering. Using the order
code for your device, see the order codes in chapter 2 for details.
The settings specific to each winding are shown in the table.
The following discussion applies to a G30 device protecting the generator step-up (GSU) transformer, assuming that the LV
winding CTs are on the neutral side of the generator and the HV winding CTs are on the system side of the step-up delta-
5
wye transformer. It is also assumed that CTs are differentially connected as per regular transformer differential
applications, as shown in the Typical Wiring, VT on the LV Side of the Transformer diagram in the Applications of Settings
chapter.
The flexibility of G30 phase compensation allows the wiring of CTs to have polarities looking inside the protected zone or
looking into the system. This can be needed to provide correct forward metered power at both sides of the GSU. When CTs
are differentially connected (wired with polarities both pointing inside the zone), the angle between winding currents
should be 0° plus an additional phase shift caused by the wye-delta connection of the transformer. When CTs are wired to
point into the system, the angle between winding currents should be 180° plus an additional phase shift caused by the
wye-delta connection of the transformer. Therefore, the adopted CTs polarities must be taken into account in the
SETUP  TRANSFORMER
transformer differential protection with different CT polarity options.
Transformer differential protection uses the following calculated quantities (per phase): fundamental, second harmonic,
and fifth harmonic differential current phasors, and restraint current phasors. This information is extracted from the
current transformers (CTs) connected to the relay by correcting the magnitude and phase relationships of the currents for
each winding, so as to obtain zero (or near zero) differential currents under normal operating conditions. Traditionally,
these corrections were accomplished by interposing CTs and tapped relay windings with some combination of CT
connections.
The G30 simplifies these configuration issues. All CTs at the transformer are connected wye (polarity markings pointing
away from the transformer). User-entered settings in the relay characterizing the transformer being protected and allow
the relay to automatically perform all necessary magnitude, phase angle, and zero-sequence compensation.
This section describes the algorithms in the relay that perform this compensation and produce the required calculated
quantities for transformer differential protection, by means of the following example of a delta-wye (Δ-Y) connected power
transformer with the following data:
5-132
WINDING 1 SOURCE:

SRC 1
WINDING 1 RATED MVA:

100.000 MVA
WINDING 1 NOM φ-φ

VOLTAGE: 220.000 kV
WINDING 1

CONNECTION: Wye
WINDING 1 GROUNDING:

Not within zone
WINDING ~ ANGLE WRT

WINDING 1: 0.0°
settings menu. See the Applications of Settings chapter for examples of setting up G30
Range: SRC 1, SRC 2, SRC 3, SRC 4
(or the user-defined name)
Range: 0.001 to 2000.000 MVA in steps of 0.001
Range: 0.001 to 2000.000 kV in steps of 0.001
Range: Wye, Delta, Zig-zag
Range: Not within zone, Within zone
Range: –359.9 to 0.0° in steps of 0.1, ('~' > 1)
(shown when viewed Winding is not Winding 1)
G30 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
SYSTEM