Loss Of Excitation - Impedance Based (40Z) Protection; Element Operation - Basler BE1-11g Instruction Manual

9424200994 Rev U 147
Loss of Excitation - Impedance Based
(40Z) Protection
The loss of excitation - impedance based (40Z) element implements a two zone offset mho characteristic
to protect against varying load conditions. The small inner diameter (Z1) protects for loss of field
conditions while the large outer diameter (Z2) provides protection at or near no load conditions. The 40Z
characteristic is illustrated in Figure 93.
Element logic connections are made on the BESTlogic™Plus screen in BESTCOMSPlus® and element
operational settings are configured on the Loss of Excitation - Impedance Based (40Z) 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, Loss of Excitation -
Impedance Based (40Z)
HMI Navigation Path: Settings Explorer, Protection, Settings Group x (where x = 0 to 3), Impedance
Protection, Impedance Based 40Z

Element Operation

The 40Z element monitors three-phase voltage and current and determines the impedance as viewed
from the BE1-11g terminals outward towards the power system.
The 40Z element has two mho characteristics offset below the R axis by a settable amount, and centered
on the X axis. The offset of each mho circle is defined as the most negative point where the circle crosses
the R axis. The size of the mho circles is defined by their diameter.
Modes of Protection
Three modes of protection are available: Non-Voltage Control, Voltage Control, or Both.
Directional Supervision
The Directional Supervision Angle setting modifies the effective tripping area of the mho circle. Directional
supervision is disabled when the angle is set to zero (0). When the directional supervision angle is used,
tripping is blocked when the measured impedance is above the directional supervision angle, and
enabled when below.
Bus CT Configuration
On protection systems equipped with two sets of CTs, the 40Z element can monitor CT circuit 1 or CT
circuit 2. The CT source is selected on the Sensing Transformers settings screen in BESTCOMSPlus.
Pickup and Trip
The Pickup output occurs first, followed by the Trip output.
Pickup
The Pickup output becomes true when the offset increases above the threshold established by the Offset
setting. In BESTlogicPlus, the Pickup and 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 40Z 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 occurrences of loss of excitation.
BE1-11g

Loss of Excitation - Impedance Based (40Z) Protection