Basler BE1-67, Instruction Manual, Page: 8 / 73

1-2 General Information BE1-67
Figure 1-2. Trip Direction Defined
Twelve standard time-current characteristic curves are available to aid in the coordination of this relay with
other protective devices in the system. These include seven characteristic curves that are standard in North
America and five that are compatible with British or IEC standards requirements. In addition, an option allows
the relay to be supplied with all of these curves any of which may be switch selected to suit requirements at
the time of installation.
Table 1-1. Selection Considerations For Characteristic Curves
Style
Designation
Characteristic
Shape Special Characteristics
B1 Short Inverse Relatively short time, desirable where
preserving system stability is a critical
factor.
B2, E2 Long Inverse Provides protection for starting motors and
overloads of short duration.
B3 Definite Time Definite Time Fixed time delay according to
the time dial setting. Useful for sequential
tripping schemes.
B4, E4 Moderately Inverse Accommodates moderate load changes as
may occur on parallel lines where one line
may occasionally have to carry both loads.
B5, E5 Inverse Provide additional variations of the inverse
characteristic, thereby allowing flexibility in
meeting load variations, or in coordinating
with other relays.
B6. E6 Very Inverse
B7, E7 Extremely Inverse
If the supply to the protected portion of the system is constant, and if the magnitude of the fault current is
determined primarily by the location of the fault on the line, the selection of a more inverse time characteristic
is more desirable to provide selective coordination with adjacent line protection. However, if the capacity of
the supply varies significantly over a period (such as a day), a less inverse time or even the definite time
characteristic, may be preferred to provide smoother coordination.
LIMITED REGION OF OPERATION
A limited region-of-operation option is available to
provide additional protection against false tripping
on mutually coupled lines. Faults on adjacent lines
that share the same poles, towers or right-of-way
may induce currents on the protected line which
appear as fault currents in the tripping direction.
The limited region of operation mode provides
discrimination between faults on the protected line
and faults on the adjacent line. To order this option,
specify option 3-5 or 3-6.
One consideration in applying a phase directional
overcurrent relay is the definition of trip direction.
For most applications, the setting of the relay
directional element is based upon the impedance
characteristics of a given circuit. This angle is then
used as the maximum torque angle and any current
flowing in the half-plane defined by this angle is
considered to be in the trip direction.