Basler Electric BE1-46N Negative Sequence Overcurrent Relay

Description

BE1-46N Negative Sequence Overcurrent Relays are three-phase solid

state relays designed to provide protection for generators and motors

from unbalanced loading or power system faults. These relays protect

the machinery from damage when the protective scheme or other

equipment, external to the generator, fails to eliminate the unbalanced

condition.

BE1-46N Negative Sequence Overcurrent Relays accurately monitor the

magnitude and control the duration of the negative sequence current

component. These relays incorporate a time delay that replicates the

machinery heating and cooling characteristics.

An alarm element in the relays may be used to provide time to locate

and isolate the fault. Doing this avoids damage to the machinery, prevents

an undesired trip, and precludes a potentially prolonged outage of the

machinery.

BE1-46N relays are designed for use with any poly-phase generating

system having known (I2)2t limits between 1 and 99. Relays that operate

using phase currents to determine the negative sequence component are

phase rotation sensitive. BE1-46N relays are phase rotation sensitive.

Principles of Symmetrical Components

Principles of symmetrical components allow an unbalanced system to be

considered as three separate, balanced subsystems. These balanced

subsystems may then be analyzed as single phase quantities.

These quantities are the positive, negative, and zero sequence components

of current and voltage.

The positive sequence component of current (I1) represents the portion of

the total current which has normal phase rotation and produces no adverse

effect on the system. An ideally balanced system contains only positive

sequence phase currents and voltages.

The zero sequence component of current (I0) also has no adverse effect

on a three-phase, three-wire (no neutral connection) power system because

it produces no appreciable magnetic flux and causes no excessive heating

in the generator rotor or windings.

The negative sequence component of current (I2) produces a magnetic flux

in the stator that has the same rotational speed as the rotor flux, but in the

opposite direction. This causes the stator magnetic flux to rotate at twice

the system frequency and induce eddy currents into the rotor. These eddy

currents create excessive heat in the rotor iron and windings, and, if allowed

to persist, could result in severe damage to the system.

Model and Style Number

Electrical characteristics and operational features included in a specific relay

are defined by a combination of letters and numbers that make up the style

number. Model number BE1-46N designates the relay as a Basler Electric

Negative Sequence Overcurrent Relay. The model number, together with

the style number, describes the options included in a specific device and

appears on the front panel, draw-out cradle, and inside the case assembly.