13.40
SEL-311C Relay Instruction Manual Date Code 20060320
Testing and Troubleshooting
Test Procedures
ohms. The angle of maximum reach of the ground distance elements is
defined by the Z1ANG setting and the zero-sequence current compensation
factor for the zone under test.
Each zone has an instantaneous indication. For example, the Z3G element
asserts without intentional time delay for A-G, B-G, and C-G faults within the
Zone 3 mho or quadrilateral characteristic. All zones include time-delayed
indication through elements Z1GT, Z2GT, Z3GT, and Z4GT. In addition, each
individual phase-ground distance element provides an instantaneous
indication for each zone. For example, the MAG1, MAG2, MAG3, and MAG4
elements provide instantaneous indication of A-G ground faults in each zone.
For general testing, use the instantaneous and time-delayed elements that
respond to any phase-ground fault within a given zone such as Z1G, Z2G, etc.
You can record more detailed and specific test results through use of the
instantaneous element associated with the faulted phase and zone under test.
There are a number of supervisory conditions that must be fulfilled before the
relay allows a ground distance element to pick up. These supervisory
conditions are described below.
Ground Distance Element Supervisory Conditions
Phase and Ground Nondirectional Overcurrent Elements, 50Ln and
50GZn
Each zone ground distance element is supervised by two nondirectional
overcurrent elements, 50GZn and 50Ln, where n indicates the zone associated
with the overcurrent element. For example, the relay may assert the Zone 3
A-ground distance element only if the A-phase current is greater than the
50L3 setting and the residual current is greater than the 50GZ3 setting.
Ground Directional Element. The ground distance protection function is
supervised by the ground directional element to provide improved directional
security. Forward-reaching distance elements may not assert unless the 32GF
element is asserted. Reverse-reaching distance elements may not assert unless
the 32GR element is asserted. See Directional Control for Ground Distance
and Residual Ground Overcurrent Elements on page 4.9 for a complete
description of ground directional elements.
Loss-of-Potential Logic
If ELOP = Y or Y1, the relay supervises the ground distance element logic
through use of the Internal Loss-of-Potential condition (ILOP). When ELOP =
Y or Y1, the relay disables the ground distance elements when a loss-of-
potential is detected, regardless of other signals applied to the relay. If you use
low-voltage signals to test the ground distance elements, set ELOP = N to
simplify the test.
Pole Open Logic
If significant pole-scatter occurs when a circuit breaker closes, sensitive
ground distance elements may operate undesirably because of the unbalanced
signals applied. The SEL-311C disables the ground distance elements during
Three-Pole Open conditions and for a short, settable time after the breaker
closes. The time is set by the 3POD time delay settings. To simplify distance
element tests, apply control voltage to any inputs assigned to perform the 52
auxiliary functions.
NOTE: Unless otherwise indicated,
all of the supervisory conditions listed
below apply to the ground mho and
ground quadrilateral distance
elements.
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