Basler Electric BE1-11g - Manual (Page 143)

9424200994 Rev N 131
Distance (21) Protection
Two distance (21) elements use the calculated impedance of a fault to determine the fault location. The
distance elements provide backup protection for external faults that are not cleared by external protective
relaying due to a failure of the external system protection scheme or equipment.
Element logic connections are made on the BESTlogic
™Plus screen in BESTCOMSPlus® and element
operational settings are configured on the Distance (21) settings screen in BESTCOMSPlus. A summary
of the logic inputs and outputs and operational settings appears at the end of this chapter.
BESTCOMSPlus Navigation Path: Settings Explorer, Protection, Impedance, Distance (21)
HMI Navigation Path: Settings Explorer, Protection, Settings Group x (where x = 0 to 3), Impedance
Protection, Distance 21
Element Operation
The zone of protection for the distance element may be set (using a mho circle) to include the generator-
step-up transformer and the lines that connect the generator to the system. The time delay of the
generator backup distance element must be coordinated with the associated primary zones of protection
to ensure proper operation.
To include the generator in the distance (21) backup zone of protection, use CTs located in the neutral
side of the generator. If neutral CTs are not provided, the BE1-11g may be connected to CTs located at
the generator terminals. With this connection, the generator is not included in the protection system’s
zone of protection, but system backup protection is provided.
Bus CT Configuration
On protection systems equipped with two sets of CTs, the 21 element can monitor CT circuit 1 or CT
circuit 2. The CT source is selected on the Sensing Transformers settings screen in BESTCOMSPlus.
Delta/Wye Compensation
For installations where the generator is connected to the system through a delta/wye step-up transformer,
delta/wye compensation is enabled to provide compensation for the differences in the current
components on the wye and the delta side of the step-up transformer.
Torque Angle
A Torque Angle (or characteristic angle) setting represents the angle between voltage and fault current on
a zero (0) ohm fault. The torque angle is used for impedance calculations.
Pickup and Trip
The Pickup output occurs first, followed by the Trip output.
Pickup
The Pickup output becomes true when the calculated impedance falls within the zone established by the
mho circle. In BESTlogicPlus, the Pickup output can be connected to other logic elements to annunciate
the condition, control other elements in logic, and start the fault recorder (logic element FAULTTRIG).
Assertion of the Pickup output initiates a timer that begins timing to a trip. The duration of the timer is
established by the Time Delay setting. A Time Delay setting of zero (0) makes the 21 element
instantaneous with no intentional time delay.
If the pickup condition subsides before the element delay expires, the timer and Pickup output are reset,
no corrective action is taken, and the element is rearmed for any other fault occurrences.
BE1-11g Distance (21) Protection