GL.22
SEL-421 Relay Date Code 20090715
Glossary
Zero-Sequence Impedance—Zone Time Delay
Zero-Sequence Impedance
Impedance of a device or circuit resulting in current flow when a single
voltage source is applied to all phases.
Zero-Sequence
Mutual Coupling
Zero-sequence current in an unbalanced circuit in close proximity to a second
circuit induces voltage into the second circuit. When not controlled by
protection system design and relay settings, this situation can cause improper
operation of relays in both systems.
Zero-Sequence
Overcurrent Element
Overcurrent protection that operates at conditions exceeding a threshold of
system unbalance.
Zero-Sequence
Voltage-Polarized
Directional Element
An element that provides directionality by the sign, plus or minus, of the
measured zero-sequence impedance.
Z-Number
That portion of the relay FID string that identifies the proper ACSELERATOR
QuickSet software relay driver version and HMI driver version when creating
or editing relay settings files.
Zone Time Delay
Time delay associated with the forward or reverse step distance and zone
protection.
Courtesy of NationalSwitchgear.com
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