Relay Element Settings
2-71
SEL-300G Instruction Manual
Date Code 20060731
Loss-of-Potential Supervision
When 64G2 is configured as a third-harmonic voltage differential element, the relay must have
information about the level of third-harmonic voltage at the generator terminal. If the potential
transformers are lost, the 64G2 element will operate and cause an unnecessary trip unless the
element is supervised by the loss-of-potential detection logic of the SEL-300G relay. This
supervision can be implemented as shown below.
Modify equations using 64G2T as shown in this example:
SV3 = … + (64G2T*52A*!60LOP) + …
Or,
SV3 = … + (64G2T*!27PP1*!60LOP) + …
Note:
Use of the torque control equation for loss-of-potential supervision (e.g.,
64GTC = !60LOP) is not recommended because it will unnecessarily block 64G1 as
well as 64G2 for loss-of-potential condition.
Relay Word Bits
Relay Word Bit Function
Description Typical
Applications
64G1
Zone 1 Stator Ground Pickup
Indication, Event Triggering,
SER Triggering, Testing
64G1T
Zone 1 Stator Ground Time-Delayed Trip
Tripping, SER Triggering
64G2
Zone 2 Stator Ground Pickup
Testing
64G2T
Zone 2 Stator Ground Time-Delayed Trip
Tripping, SER Triggering
T64G
Zone 2 Pickup for Ground Near Generator
Terminals
Indication, Testing
N64G
Zone 2 Pickup for Ground Near Neutral
Indication, Testing
100% Stator Ground Protection Setting Calculation
Information Needed
•
Generator nominal voltage, VNOM
•
Generator grounding transformer ratio to 1 (use 1 if machine is resistance grounded)
•
Generator neutral voltage transformer ratio to 1 (use 1 if relay is connected directly
to grounding transformer secondary winding)
•
Generator neutral voltage during system ground fault
(This voltage is caused by capacitive coupling in the generator step-up transformer.
If this voltage is not known, coordination can be made on a time basis.)
•
Relay settings PTR, PTRN, and DELTA_Y
Summary of Contents for SEL-300G
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