RFL 9300 RFL Electronics Inc.
January 30, 2002 6-66 (973) 334-3100
The TOC status will be supplied to the phase controllers using the Phase Time Overcurrent Status Message
(63H) and to the 3I0 controller using the 3I0 Time Overcurrent Status Message (64H) .
Each curve has a reference time dial setting stored in a lookup table. The reference dial setting for each USA
curve (USA1-USA4) is the 0.5 setting. The reference setting for each IEC curve (IEC1-IEC4) is the 0.05 set-
ting. The remaining dial settings are calculated from the reference settings. Each point on these curves repre-
sents a multiple of pickup (M) that has a trip delay time constant associated with it. The following multiples of
pickup, M, are used for each dial setting:
1.5 , 2 through 30 ( integer values only)
The time constant selected from a lookup table is a 16 bit value with each bit representing 2 milliseconds. The
maximum time constant allowed for any dial setting is 65530 * 2 ms = 131.06 seconds. Any dial setting /M
combination that exceeds this will be truncated at the maximum value of 131.06 seconds. Refer to the TOC
Curves shown in Figures 6-33 through 6-40.
The contents of a 16 bit register will be used to determine if the input current has exceeded the pickup value.
This register holds the integral sum of the input current samples over the previous 8 ms. The value represents
a running 8 ms average of the input current. If the input current exceeds the pickup point the TOC timer will be
started.
From this point on the TOC timer will be updated at 2 ms intervals. Using the true integral value, buffers the
overcurrent algorithms from the effects of current spikes and glitches, but does not eliminate the DC offset
present in fault current waveforms. However this is alleviated to some degree as the M value integer is recal-
culated on a 16 ms basis for as long as the TOC timer remains active. This will insure the time delay is
adjusted to the fault current changes. Once this calculation is completed, the time delay is obtained from the
selected dial setting curve and stored in a 16 bit TOC delay timer register.
If 1<M<1.5 the TOC timer updates will stop but the timer will not reset. If M calculates to a value < 1.0 the
function will terminate and the TOC timer will instantaneously reset to 0 (reset function).
If the fault current continues to be detected until the time recorded by the TOC timer exceeds the delay time
stored in the delay timer, a trip signal will be issued.
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