Differential Principle; Biased Differential Characteristic - GE B90 UR Series Instruction Manual

9 THEORY OF OPERATION

9.3DIFFERENTIAL PRINCIPLE

The B90 uses a dual-slope dual-breakpoint operating characteristic as shown in the figure below.
The PICKUP setting is provided to cope with spurious differential signals when the bus carries a light load and there is no
effective restraining signal.
The first breakpoint (
LOW BPNT
vorable conditions such as high residual magnetism left in the magnetic cores or multiple autoreclosure shots. This point
defines the upper limit for the application of the first slope (
The second breakpoint (
HIGH BPNT
tion. This point defines the lower limit for the application of the second slope (
The higher slope used by the B90 acts as an actual percentage bias regardless of the value of the restraining signal. This is
so because the boundary of the operating characteristic in the higher slope region is a straight line intersecting the origin of
the 'differential - restraining' plane. The advantage of having a constant bias specified by the
obstacle of a discontinuity between the first and second slopes. This is overcome by using a smooth approximation (cubic
spline) of the characteristic between the lower and higher breakpoints. Consequently, the characteristic ensures:
• a constant percentage bias of
• a constant percentage bias of
• a smooth transition from the bias of
GE Multilin
) is provided to specify the limit of guaranteed linear operation of the CTs in the most unfa-
LOW SLOPE
) is provided to specify the limits of operation of the CTs without any substantial satura-
OPERATE
PICKUP
Figure 9–2: BIASED OPERATING CHARACTERISTIC
for restraining currents below the lower breakpoint of
LOW SLOPE
for restraining currents above the higher breakpoint of
HIGH SLOPE
to
LOW SLOPE HIGH SLOPE
B90 Low Impedance Bus Differential System
9.3 DIFFERENTIAL PRINCIPLE

9.3.1 BIASED DIFFERENTIAL CHARACTERISTIC

).
).
HIGH SLOPE
HIGH
SLOPE
BLOCK
LOW
SLOPE
restraining
836720A1.CDR
HIGH SLOPE
between the breakpoints.
setting creates an
,
LOW BPNT
, and
HIGH BPNT
9
9-3