Basler Electric BE1-87G - Manual (Page 13)

Variable Restraint Characteristic
At high current levels, the inevitable difference in the saturation characteristics between current
transformers indicates a need for a compensating decrease in relay sensitivity. The design of the BE1-
87G provides a restraint factor that is proportional to input current when the restraining current (I
R
) is
greater than nominal (5 Aac for sensing input range 1 or 1 Aac for sensing input range 2). The BE1-87G
compares the protected zone sensed input and output currents. The lesser of the two sensed current
levels becomes the restraining current. The difference between the two sensed currents (the operating
current) is compared to a reference established by the sensitivity setting, and adjusted by an amount
proportional to the restraining current. This makes the BE1-87G more sensitive to low current internal
faults, and less sensitive to external faults with high levels of through current.
When the restraining current is at nominal (5 Aac for sensing input range 1 or 1 Aac for sensing input
range 2) or less, the relay trips if the differential current exceeds the relay setting (I
S
). But when the
restraining current is greater than nominal, the overall sensitivity is a combination of the front panel setting
and the restraint factor.
Design Highlights
Some of the many advantages of the BE1-87G relay are summarized below:
•
Seven sensitivity levels on each of the two sensing input ranges. The seven levels allow
compensation for CT mismatch and provide the flexibility and adaptability necessary for many special
applications such as split-winding generator protection.
• Stabilizing reactor. Minimizes dissimilar performance of system CTs. Reactor can be located on the
back of the relay or remotely from the BE1-87G for flexibility of system installation.
• Variable restraint. The variable restraint characteristic allows increased sensitivity to low-current,
internal faults while providing increased security against high levels of through-current caused by
external faults.
• Single- or three-phase availability. Either configuration is available in the Basler Electric S1 draw-out
case.
• High-speed operation. The BE1-87G operates in 30 milliseconds for fault levels of 10 times the
sensitivity setting. This high-speed operation minimizes potential damage to the protected equipment.
Response characteristics for sensing input ranges 1 and 2 are shown in Section 5, Testing and
Setting.
MODEL AND STYLE NUMBER
The model number BE1-87G designates the relay as a Basler Electric, Class 100, Variable Percentage
Differential Relay.
The electrical characteristics and operational features of the BE1-87G relay are defined by a combination
of letters and numbers which constitutes the relay style number. The style number describes the features
and options of the BE1-87G relay and appears on the front panel, draw-out cradle, and inside the case
assembly.
Style Number Chart
The BE1-87G style number chart is illustrated in Figure 1-3.
Style Number Example
As an example, if the style number of a BE1-87G were
G1EA1JA0C0F, the relay would have the
following characteristics and features:
G three-phase current sensing
1 switch-selectable sensing input range for 0.1, 0.15, 0.2, 0.4, 0.5, 0.8, or 1.6 Aac
E one normally-open output relay
A1 instantaneous timing
J relay operating power derived from 125 Vdc or 100/120 Vac
A internally operated targets (one per phase)
0 option 1 not available
C push-to-energize outputs (pushbuttons)
0 no auxiliary output contacts
F semi-flush mounting case
9170800990 Rev N
BE1-87G General Information 1-3