Basler BE1-51C, Instruction Manual

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3-1
SECTION 3
FUNCTIONAL DESCRIPTION
GENERAL
The BE1-51C relay is a microprocessor based overcurrent relay that can communicate with a remote
computer. The following text is referenced to Figure 3-1, which is a functional block diagram that illustrates
the overall operation of a fully implemented version of the relay.
CURRENT SENSING
The BE1-51C relay can be configured for single-phase, two-phase-with-neutral, three-phase, or three-phase-
with-neutral current monitoring. The illustrated relay is of the three-phase-with-neutral type.
The internal current sensing transformers are designed to receive their input from the 5 A nominal
secondaries of standard current transformers (CTs). Note the dual primaries of the internal transformers.
One or the other is connected during manufacturing to obtain a LOW or a HIGH current sensing range (0.5
to 5.0 A, or 2.00 to 11.00 A) in accordance with the specified Style Number of the relay.
The outputs of the internal transformers are applied to scaling circuits (one for each of the phases, one for
neutral) that convert each of the input currents to a voltage level that can be utilized within the relay.
A coarse incremental adjustment for the current pickup setting is provided by the TAP switches. These are
front-panel rotary switches
one for the phases, and another for neutral if neutral current is monitored. The
current setting represented by each of the 10 switch positions is given for each range (HIGH and LOW) in
the table printed on the front panel. (Reference Figure 2-1.)
The fine adjustment of the current pickup point is determined by the value (00 to 99) stored in the relay Tap
Cal registers (again, one setting for the phases, one for neutral). When the Tap Cal register contains the
value 00, the pickup setting of the relay is the indicated TAP setting.
The Tap Cal registers provide a means of adjusting the timed trip pickup between the selected position of
the TAP switch and its next higher position. For example, when the TAP switch is set to position A, the Tap
Cal register provides an adjustment from 0.5 to 1.0 A for the LOW range, and from 2.00 to 3.00 A for the
HIGH range. EXCEPTION: At the highest TAP position (i.e., J), the setting of the Tap Cal register is
ignored. Therefore the J values of 5.00 and 11.00 represent the upper limits of the LOW and HIGH ranges,
respectively.
POWER SUPPLY
General
The solid state power supply is a low burden, flyback switching design which delivers a n5 and ±12
Vdc to the relay internal circuits. The power supply also delivers an is5 Vdc for the communications
circuits.
The input terminals of the power supply are not polarity sensitive. A red POWER LED illuminates to indicate
that the power supply is functioning.