5-240 G60 Generator Protection System GE Multilin5.6 GROUPED ELEMENTS 5 SETTINGS55.6.17 STATOR GROUNDa) MAIN MENUPATH: SETTINGS GROUPED ELEMENTS SETTING GROUP 1(6) STATOR GROUNDThree 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-sequencevoltage of the machine terminals.• Third harmonic neutral undervoltage protection that responds to the third harmonic in the voltage at the machine neu-tral point.• 100% stator ground protection based on sub-harmonic injection.The three protection elements are configured through their individual setting menus. They share the STATOR GROUNDSOURCE setting. This setting specifies a signal source used to provide current and voltage signals for stator ground faultprotection.For the 100% stator ground protection function, the stator ground source shall be configured as follows:• Phase voltages measured at the terminal of the machine shall be configured as phase VT banks. The element extractsthe third harmonic of the zero-sequence voltage from the phase voltages in order to operate. The VTs must be con-nected in wye.• Voltage measured at the neutral of the machine shall be configured as the auxiliary VT bank. The element extracts thethird harmonic of the auxiliary voltage from the source in order to operate.For the third harmonic neutral undervoltage protection function, the stator ground source shall be configured as follows:• Phase voltages measured at the terminal of the machine shall be configured as phase VT banks. The element usesthe voltages to measure the power at the machine terminals for power supervision.• Phase currents measured at the terminal of the machine shall be configured as phase CT banks. The element usesthe currents to measures the power at the machine terminals for power supervision.• Voltage measured at the neutral of the machine shall be configured as the auxiliary VT bank. The element extracts thethird harmonic of the auxiliary voltage from the source in order to operate.For the sub-harmonic injection based 100% stator ground protection, the stator ground source shall be configured as fol-lows:• Voltage measured at the neutral of the machine shall be configured as the auxiliary VT bank. The element extracts the20 Hz component of the auxiliary voltage from the source in order to calculate resistance. The fundamental frequencycomponent from the same input is extracted when the same source is configured for auxiliary overvoltage protectionelement to provide 95% stator ground fault protection. The auxiliary VT connection setting should be chosen as “Vn”for this element.• Current measured at the secondary of the neutral grounding transformer of the machine shall be configured as thesensitive ground CT bank. The element extracts the 20 Hz component of the ground current from the source in order tocalculate resistance.• This source can be independent of any of the other inputs from the generator such as neutral end CTs, terminal endCTs and terminal VTs. Or these auxiliary VT and sensitive ground CT can be combined with either neutral side or ter-minal side inputs within the same source settings. STATOR GROUNDSTATOR GROUNDSOURCE: SRC1Range: SRC 1, SRC 2, SRC 3, SRC 4MESSAGE 100% STATOR GROUND See page 5–241.MESSAGE 3RD HARM NTRL UNDERVOLTAGE See page 5–244.MESSAGE SH STATOR GROUND See page 5–246.
