GE G60 Instruction Manual page 516

GROUPED ELEMENTS
The following three means of stator ground fault protection are provided:
• 100% stator ground protection that uses third harmonic signals at the neutral of the machine and in the zero-
sequence voltage of the machine terminals
• Third harmonic neutral undervoltage protection that responds to the third harmonic in the voltage at the machine
neutral point
• 100% stator ground protection based on sub-harmonic (SH) injection
The three protection elements are configured through their individual setting menus. They share the
setting. This setting specifies a signal source used to provide current and voltage signals for stator ground fault
SOURCE
protection.
For the 100% stator ground protection function, configure the stator ground source as follows:
• Configure phase voltages measured at the terminal of the machine as phase VT banks. The element extracts the third
harmonic of the zero-sequence voltage from the phase voltages in order to operate. The VTs must be connected in
wye.
• Configure voltage measured at the neutral of the machine as the auxiliary VT bank. The element extracts the third
harmonic of the auxiliary voltage from the source in order to operate.
For the third harmonic neutral undervoltage protection function, configure the stator ground source as follows:
• Configure phase voltages measured at the terminal of the machine as phase VT banks. The element uses the voltages
to measure the power at the machine terminals for power supervision.
• Configure phase currents measured at the terminal of the machine as phase CT banks. The element uses the currents
to measures the power at the machine terminals for power supervision.
• Configure voltage measured at the neutral of the machine as the auxiliary VT bank. The element extracts the third
harmonic of the auxiliary voltage from the source in order to operate.
5
For the sub-harmonic injection based 100% stator ground protection, configure the stator ground source as follows:
• Configure voltage measured at the neutral of the machine as the auxiliary VT bank. The element extracts the 20 Hz
component of the auxiliary voltage from the source in order to calculate resistance. The fundamental frequency
component from the same input is extracted when the same source is configured for auxiliary overvoltage protection
element to provide 95% stator ground fault protection. Set the auxiliary VT connection setting as "Vn" for this element.
• Configure current measured at the secondary of the neutral grounding transformer of the machine as the sensitive
ground CT bank. The element extracts the 20 Hz component of the ground current from the source in order to
calculate resistance.
• This source can be independent of any of the other inputs from the generator, such as neutral end CTs, terminal end
CTs and terminal VTs. Or these auxiliary VT and sensitive ground CT can be combined with either neutral side or
terminal side inputs within the same source settings.
• In addition, set the relay with frequency tracking enabled and set the source used as
to the one connected to generator terminal VTs. The tracking frequency, which is essentially the generator
REFERENCE
frequency, is used to block the sub-harmonic stator ground protection and auxiliary over voltage protection in the
frequency range of 15 to 25 Hz.
5.7.17.2 100% stator ground (ANSI 64TN)
SETTINGS  GROUPED ELEMENTS  SETTING GROUP 1(6)  STATOR GROUND  100% STATOR GROUND
 100% STATOR
 GROUND
5-302
100% STATOR GROUND

FUNCTION: Disabled
100% STATOR GND STG1

PICKUP: 0.150 pu
100% STATOR GND STG1

DELAY: 1.00 s
100% STATOR GND STG1

SUPV: 0.0057 pu
FREQUENCY AND PHASE
Range: Disabled, Enabled
Range: 0.000 to 0.900 pu in steps of 0.001
Range: 0.00 to 600.00 s in steps of 0.01
Range: 0.0010 to 0.1000 pu in steps of 0.0001
G60 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
STATOR GROUND