Current Differential Relay
GARD 8000 SYS RFL Electronics
June 20, 2014 13-59 973.334.3100
Figure 13-39. High Set Trip for an External Fault Condition
Figure 13-40. High Set Trip for an Internal Fault Condition
13.5.1.4.1 Generation of the HST message
As with the current differential routines the HST routines are processed for the positive half-cycle for
the phases and negative half-cycle for the ground. If the relay measures four consecutive samples
(instantaneous current measurements) that exceed the HST setpoint a HST message is sent.
As with the CCD message the HST message includes data indicating how long the delay was between
determining the current exceeded the HST setpoint and the message was actually transmitted.
13.5.1.4.2 Processing received HST messages
When the HST message is received the local currents are compared to a blocking current to avoid
tripping on through faults.
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