RESTRAINT CHARACTERISTICS

At high current levels, the inevitable difference in the

saturation characteristics between current transform

ers requires a compensating decrease in relay

sensitivity. The design of the BE1-87G provides a

restraint factor that is proportional to input current.

Specifically, the BE1-87G compares the two sensed

currents (in and out) to determine which is less. This

lower current level becomes the restraining current.

The difference between the two sensed currents (I0

) is compared to a reference established by the sensitivity

setting and adjusted by an amount proportional to the

restraining current. (The typical ratio is given in the

formula on page 3.) This makes the BE1-87G more

sensitive to low current internal faults, for which the

relay should operate, and less sensitive to external

faults with high levels of through current for which the

relay should not operate.

Dual Zero Sequence Current and Voltage

Dual polarization is preferred where ground source impedance varies, or to provide redundant

polarization. Dual polarization is achieved using a polarizing signal that is the phasor sum of the current

and voltage polarizing signals.

OUTPUT CONTACTS

BE1-67N relays have the following output contacts: relay status alarm (relay fail), tripping, and auxiliary

(optional).

Relay Status Alarm

A relay status alarm output contact (relay fail) indicates that proper voltages are not being supplied to the

internal relay circuitry or that the microprocessor self-diagnostics has detected an error. This alarm output

contact is normally closed.

Tripping

Normally open or normally closed tripping contacts are included for each function within the relay.

Configuration of these contacts is defined by the relay style number. These output contacts are used with

optionally selected target indicator circuits.

Auxiliary

Normally open, normally closed, or single pole double throw (SPDT) auxiliary contact configurations are

provided to act in parallel with the tripping function(s) of the relay. Configuration of the auxiliary output

contacts are also defined by the relay style chart.

An auxiliary contact can be configured (via internal switches) to operate in parallel with any combination

of tripping outputs. Configurable auxiliary outputs permit use of the BE1-67N relay in various carrier

schemes.

PURPOSE

BE1-67N Ground Directional Overcurrent Relays provide ground fault protection for transmission and

distribution lines by sensing the flow of ground (zero sequence) current into or out of protected zones.

Zero sequence quantities provide a secure reference for the directional element because these quantities

are defined by the total source impedance of the power system.

APPLICATION

BE1-67N Ground Directional Overcurrent Relays are recommended for multi-grounded systems to

provide coordination necessary to selectively trip the faulted line. A directional overcurrent relay operates

by comparing the measured current to a reference quantity to determine whether current is flowing into or

out of the protected zone. Reference quantity is also referred to as polarizing quantity.

BE1-67N relays use one of the following quantities for polarization:

• Zero sequence current

• Zero sequence voltage

• Dual zero sequence current and voltage

The polarizing quantity is field selectable using a switch mounted on the analog circuit board. When the

selected polarizing quantities are less than the minimum threshold, relay operation will be inhibited. When

using dual polarization, the relay will operate if either polarizing quantity is above minimum threshold.

APPLICATION

BASIC PRINCIPLES

Differential relaying is the most selective form of fault

protection that may be applied to the individual

elements, or zones, of ac power systems. Various

types of differential relays and relaying systems have

evolved to take advantage of the differential principle.

The BE1-87G is a single or three-phase solid-state

variable percentage differential relay designed to

provide selective, high-speed differential protection

for generators, motors, and shunt reactors.

The selectivity of differential relaying is based on the

ability of the relay to distinguish between an internal

fault (within the protected zone) and an external fault.

Under normal operating conditions the current into

the protected zone equals the current out of the

protected zone with a net operating current equal to

zero. Internal faults upset this balance and result in a

difference between the input and output currents.

External faults have relatively little effect on the

balance, because the current in still equals the

current out of the protected zone. Therefore, by

comparing the currents on both sides of the protected

element or zone and detecting when these currents

are not equal, a differential relay acts to isolate the

element or zone from the system.

The BE1-87G typically trips a lockout relay (86), which

in turn trips the generator breaker and, when present,

the field and/or neutral breakers.

The BE1-87G is a single or three-phase solid-state variable percentage

differential relay designed to provide selective, high-speed, differential

protection for generators, motors, and shunt reactors.

ADVANTAGES

• Single or three-phase relays available.

• Variable percentage characteristic.

• Low operating burden.

• Balancing impedance in CT inputs provides excellent security

during external faults or other transients.

• High speed operation.

• Seven sensitivity settings cover the range of 0.1 to 1.6A

or 0.02 to 0.32A.

• Pickup accuracy within ±5% of the operate characteristic.

• Qualified to the requirements of- IEEE C37.90.2 for Radio Frequency

Interference (RFI)- IEEE C37.90.1-1989 for Fast Transient and Surge Withstand

Capability- IEC 255-5 and ANSI/IEEE C37.90 for Impulse and Dielectric tests.

• UL recognized per Standard 508. UL File #E97033.

• Gost R certified per the relevant standards of Gosstandart of Russia.

• Five year warranty.

Synchronization Voltage

Voltage is applied to this input and passed through the synchronizing transformer. These voltage signals

are used to define the time reference for the rectifier chassis SCR control pulses. The voltages are also

used for generator voltage metering in applications where the rectifier chassis operating power is supplied

from the generator output (if the Internal mode of the generator voltage sensing is selected (for three

phase applications only)).

Terminal labeling for the synchronization voltage input varies according to the model of IFM-150 (single

phase or three-phase control).

The single-phase IFM-150 accepts synchronization voltage at terminals A1 and B or A2 and B. Terminals

A1 and B are used for synchronization voltage in the 240 Vac or 480 Vac range. Terminals A2 and B are

used for synchronization voltage in the 120 Vac range.

The three-phase IFM-150 accepts synchronization voltage at terminals A, B, and C.

Generator Voltage (B2. B3)

The dc output from the transducer, used to sense the generator voltage, is applied to this input. This

signal is used for generator voltage metering if the external generator voltage sensing mode is selected.

Gate Drive Block (BL+, BL–)

When a contact closure is sensed at this input, SCR firing is blocked and the IFM-150 output is disabled.

Full Invert (INV+, INV–)

The pulse outputs are forced to their maximum delay when a contact closure is sensed at this input. This

results in maximum negative voltage at the exciter output until the field current decays to nearly zero. The

Full Invert contact input is used only on full-control bridges.

Functional Description

Introduction

The IFM-150 Interface Firing Module receives a control signal from the DECS-400 or DECS-450 Digital

Excitation Control System and then calculates a time delay based on the zero crossing of each phase of

voltage from the synchronizing transformer. At the end of the time delay, the IFM-150 produces the

properly synchronized sets of pulses to drive the SCRs of the excitation system rectifier chassis. As the

DECS control signal increases (or decreases), the time interval between the zero crossing of each phase

voltage and the start of its next output pulse will decrease (or increase). This results in an increase (or

decrease) in the rectifier chassis output voltage.

A terminal voltage limiter within the IFM-150 can be enabled to monitor the generator voltage through the

synchronizing transformer or external voltage transducer and compare the measurement with a user

adjustable reference level. If the generator voltage exceeds the reference level for a user-adjustable

amount of time, the IFM-150 will modify the SCR firing pulses and limit the generator voltage.

Inputs

The function of each IFM-150 input is described in the following paragraphs.