S4 Elements
745
Transformer Management Relay
Se
tpoints
http://www.GEindustrial.com/multilin
5–50
GE Multilin
b) Time Overcurrent Curves
The inverse time overcurrent curves used by the TOC (time overcurrent) elements
are the ANSI, IEC, and GE Type IAC curve shapes. This allows for simplified
coordination with downstream devices. If however, none of these curve shapes is
adequate, FlexCurves™ may be used to customize the inverse time curve
characteristics. The Definite Time curve is also an option that may be appropriate if
only simple protection is required.
The following overcurrent curve types are available:
•
ANSI Curves
: ANSI Extremely Inverse; ANSI Very Inverse; ANSI Normally
Inverse; ANSI Moderately Inverse
•
IEC Curves
: IEC Curves A, B, and C (BS142); IEC Short Inverse
•
GE Type IAC Curves
: IAC Extremely Inverse; IAC Very Inverse; IAC Inverse;
IAC Short Inverse
•
Other Curves
: FlexCurves™ A, B, and C; Definite Time Curve
A time dial multiplier setting allows selection of a multiple of the base curve shape
(where the time dial multiplier = 1) with the curve shape (
SHAPE
) setting. Unlike the
electromechanical time dial equivalent, operate times are directly proportional to
the time multiplier (
TIME OC MULTIPLIER
) setting value. For example, all times for a
multiplier of 10 are 10 times the multiplier 1 or base curve values. Setting the
multiplier to zero results in an instantaneous response to all current levels above
pickup.
Graphs of standard time-current curves on 11”
×
17” log-log graph paper
are available upon request from the GE Multilin literature department. The
original files are also available in PDF format on the UR Software
Installation CD and the GE Multilin Web Page.
FlexCurves™:
The custom FlexCurve™ is described in
shapes for the FlexCurves™ are derived from the formula:
(EQ 5.6)
where:
T
= Operate Time (sec.),
M
= Multiplier Setting,
I
= Input Current, and
I
pickup
= Pickup Current setpoint
Definite Time Curve:
The Definite Time curve shape operates as soon as the pickup level is exceeded for
a specified period of time. The base definite time curve delay is 0.1 seconds. The
curve multiplier makes this delay adjustable from 0.000 (instantaneous) to 10.000
seconds.
NOTE
T
M
FlexcurveTime at
I
I
pickup
-------------------
×
when
I
I
pickup
-------------------
1.00
≥
=
Summary of Contents for Multilin 745
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