GE Multilin 565, Инструкция по эксплуатации

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CURVE INFORMATION AND TABLES
7-1
Overcurrent Protection
The 565/575 Relay continuously monitors the three phase
currents and ground current in the feeder through its CT’s and
initiates an alarm and/or feeder breaker trip if any rise above
the pick-up level. The setting for phase and ground are
independent of each other and the time for either action to be
initiated is based on the chosen time/overcurrent curve and
overload level. Note that smaller overcurrents can be toler-
ated for longer periods than larger ones.
The 565/575 Relay allows the following curves to be chosen:
1. Moderately Inverse.
2. Normal Inverse.
3. Very Inverse.
4. Extremely Inverse.
5. IEC A
6. IEC B
7. IEC C
8. Programmable Curve
Use of Standard Curves
If it is intended to use the standard curves, for overcurrent
protection, then the curve shape and number must be deter-
mined and entered into the 565/575 Relay. For each shape,
there are 32 different curves corresponding to a different time
dial. The selection of protection curve shape, pick-ups and
time dial must be determined from a system co-ordination
study. To determine the curve shape and number most suited
to your system proceed as follows:
Plot the time/overcurrent characteristics of all the related
system equipment to the feeder on a blank log/log sheet.
Alternately only the most critical items may be plotted. This is
called the System Plot.
Now choose an overcurrent value on the system plot, prefer-
ably the one which is most critical to the device being pro-
tected. Next select the standard curve shape which most
closely matches the time/overcurrent characteristics of the
item to be protected. Finally, the curve number must be
selected to position this curve in the correct vertical location.
The standard curves which are programmed into the 565/575
relay are shown in Figure 7.1 through Figure 7.8.
Use of Custom Curve
In addition to the standard curves, the 565/575 Relay also
has a user-programmable curve. This curve can be defined by
the user and thus be closely matched to the needs of the
particular application. This is a vast improvement on conven-
tional feeder protection devices which forced the user to
compromise on protection by using a standard curve which
might not exactly match the protection requirements of the
particular system.
Alternately, the custom curve can be used to match the
system requirements very closely.
CAUTION
Ensure when selecting a curve, either preprogrammed or
custom, and the delays to trip the feeder breaker, that the
maximum current into the relay at the rear terminals of the
565 shall not exceed 100A for more than 3 seconds.
Failure to ensure the maximum current vs. delay can cause
damage to the relay which may result in loss of relay
protection.
Example: Any time a pickup level is selected greater than
100% of CT using the 5A tap, care must be taken to ensure
that current to the relay is limited to 100A for 3 seconds
maximum. If a pickup level of 150% is selected with a maxi-
mum of 20 times pickup then 150A will be flowing into the 565
relay. Therefore, an instantaneous trip must be selected for
any current above 100A. ie. 13.3 × pickup level.