GE G60 Instruction Manual page 509

CHAPTER 5: SETTINGS
The operating characteristic is shaped out of two offset mho circles shifted down along the imaginary axis as shown.
Stage 1 settings
The stage 1 characteristic is typically set to detect a loss of excitation for load conditions of 30% of the nominal or higher.
This is achieved with a mho element with a diameter equal to the base impedance of the machine and an offset equal to
half the machine transient reactance (X'd).
The stage 1 element should be time delayed to allow for blocking by the VT fuse failure element (50 ms).
Stage 2 settings
The stage 2 characteristic is typically set to detect a loss of excitation for all load conditions. This is achieved with a mho
element with a diameter equal to the synchronous reactance of the machine and an offset equal to half the machine
transient reactance (X'd).
During stable power swing conditions, the positive-sequence impedance can momentarily enter the stage 2 characteristic.
For security of the function under such conditions, it is recommended to delay stage 2 by a minimum of 0.5 seconds.
The setting specifies a FlexLogic operand for blocking the feature based on user-programmable
LOSS OF EXCIT BLK
conditions. When the blocking input is asserted, the element resets its timers, de-asserts the
asserted), clears self-reset targets, logs a 'blocked' event if events are enabled, and becomes inactive. When unblocked,
the element starts functioning instantly. If exposed to pickup conditions for an extended period of time and unblocked, the
element picks up and starts timing out at the moment of unblocking.
The element responds to the positive sequence impedance as shown in the logic diagram.
G60 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
LOSS OF EXCIT BLK:

Off
LOSS OF EXCITATION

TARGET: Self-reset
LOSS OF EXCITATION

EVENTS: Disabled
Figure 5-169: Loss of excitation operating characteristics
GROUPED ELEMENTS
Range: FlexLogic operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
and
PKP OP
5
Eq. 5-35
Eq. 5-36
operands (if
5-295