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The current required to close the time overcurrent unit contacts will be within five
percent of the tap screw setting.
RESET (TIME OVERCURRENT UNIT)
time overcurrent units reset at 90 percent of the minimum pickup current,
Inverse
very inverse time units at 80 percent, and extremely inverse time units at 85 percent.
When the relay is de-energized, the time required for the disk to canpletely reset
to the number ID time dial position is approximately six seconds for inverse time
relays, and 60 seconds for very inverse time and extremely inverse time relays.
OPERATING TIME
The time curve for the directional unit is shown in Fig. 14.
The time curves of the time overcurrent unit are shown in Figs. 15, 16 and 17,
respectively for inverse, very inverse and extremely inverse time relays. For the same
operating conditions, the relay will operate repeatedly within one or two percent of
the same time.
The time-current characteristic of the Hi-Seismic instantaneous unit is shown by
Fig. 18 and its transient overreach characteristic is shown by Fig.
l
BURDENS
The capacitive burden of the potential polarizing circuit of the directional unit at
60 cycles and 120 volts is ten volt amperes at 0.86 power factor. Table 8 gives the
current circuit burdens of the directional unit.
DIRECTIONAL UNIT CURRENT
Circuit
Operating
Polarizing
Table 9 gives the current circuit burdens of time overcurrent units.
Ordinarily the potential circuit is in the open corner of broken delta potential
transformers and the current circuits are in
transformers.
The burden is, therefore, only imposed for the duration of the ground
fault and need be considered only for this brief period. Table 10 gives the burden of
the instantaneous unit. i
Revision
*Indicates
TABLE 8
CIRCUIT
Z (Ohms)
VA
12.0
0.46
0.24
6.0
BURDEN AT 60 CYLES AND 5 AMPERES
P.F
0.52
0.95
the residual circuits of current
9
19.
Watts
6.24
5.27
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