Basler Electric BE1-40Q - Manual (Page 17)

SECTION 3
• FUNCTIONAL DESCRIPTION
INTRODUCTION
BE1-40Q Loss of Excitation relays are static devices that respond to the relation of voltage to current
magnitudes of the monitored circuit. As such, they are sensitive to phase rotation. All connections shown
in this manual assume ABC rotation. BE1-40Q relay functions are illustrated in Figure 3-1 and described
in the following paragraphs.
Figure 3-1. Function Block Diagram
VOLTAGE SENSING
The monitored voltage input is derived from a system voltage transformer connected phase-to-phase. An
internal voltage transformer (PT) provides isolation and reduces the nominal value of the voltage sensing
input (i.e., 120, 208, or 240 Vac) to internal circuitry requirements.
PHASE SHIFT
Since the voltage input, V
AB
, leads the sensed input current, I
B
, by an angle of 150
° for a unity power factor
condition, the voltage phasor is internally shifted 68
° in a lagging direction (delayed) to achieve the relay
response characteristics. The resultant I
TRIP
leads the polarizing voltage V
POL
by 8
° (when the system
power factor angle (Ө) is equal to –90° as shown in Figure 3-2.
9171500990 Rev N BE1-40Q Functional Description 3-1