2-40 Relay Element Settings
Date Code 20020206 SEL-300G Instruction Manual
OVERCURRENT ELEMENTS
Element Description
Functional Description
The SEL-300G Relay offers an assortment of nondedicated overcurrent elements for protection,
indication, and control functions.
Overcurrent Protection, All Relay Models
All relay models provide the following overcurrent elements:
• Two levels of phase definite-time overcurrent, 50P1 and 50P2
• Two levels of neutral definite-time overcurrent, 50N1 and 50N2
• Two levels of residual ground definite-time overcurrent, 50G1 and 50G2
• One level of neutral inverse-time overcurrent, 51N
• One level of residual inverse-time overcurrent, 51G
Phase overcurrent elements operate using the maximum of the measured phase current
magnitudes. The neutral overcurrent elements operate using the magnitude of the neutral current
input. Residual ground overcurrent elements operate using the sum of the three-phase current
inputs.
Where you use the relay to protect high-impedance grounded or resistance grounded generators,
the neutral overcurrent elements provide stator ground fault detection for faults in the upper area
of the winding when connected to a generator neutral current transformer, as shown in Section 5:
Installation. The 50P, 50N, and 50G elements may be set sensitively and applied for inadvertent
energization protection, as described in Section 4: SEL
OGIC
®
Control Equations.
Where you use the relay to protect solidly grounded generators, the phase, neutral, and residual
overcurrent elements can all respond to stator ground faults in the mid- and upper-winding areas.
Overcurrent Protection, Relay Models With Differential Protection
Relay models with differential protection functions add the following overcurrent elements:
• Two levels of phase definite-time overcurrent, 50H1 and 50H2
• Two levels of negative-sequence definite-time overcurrent, 50Q1 and 50Q2
• Two levels of residual ground definite-time overcurrent, 50R1 and 50R2
The 50H1 phase overcurrent element operates using the maximum of the measured phase current
inputs from the IA87, IB87, and IC87 phase current inputs. The 50Q1 and 50Q2 elements
operate using the magnitude of the negative-sequence current, I
2
, calculated from the IA87, IB87,
and IC87 phase current inputs. The 50R1 and 50R2 residual ground overcurrent elements
operate using the magnitude of the sum of the IA87, IB87, and IC87 phase current inputs. In
applications where the generator is connected directly to a bus, you can use the 50H and 50R
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