Category: Industry Trends

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.

Percentage Restraint

A primary concern in differential relay applications is security against high current levels caused by faults

outside the protected zone. Inevitable differences in the saturation characteristics between current

transformers require a compensating decrease in relay sensitivity. It is also necessary to be able to adjust

the sensitivity to compensate for transformer voltage taps or CT mismatches. This is accomplished by

providing a restraint factor proportional to the current flowing through the protected zone (through

current).

BE1-87T relays maintain sensitivity at a specified ratio of trip current to through current. This ratio,

generally referred to as slope, is front-panel adjustable in 5 % increments from 15 to 60 %.

Fifth-Harmonic Restraint

Power transformer overexcitation causes additional exciting current to flow into one set of terminals. This

presents an apparent differential (or operating) current not attributable to an internal fault. Although

potentially damaging, overexcitation is not an internal fault and, therefore, is not an appropriate condition

for transformer differential relay operation. One of the principal components in the complex waveform

produced during overexcitation is the fifth harmonic. BE1-87T relays use fifth-harmonic restraint to inhibit

the differential relay operation.

Control Power (DC+, DC– and AC1. AC2)

Operating power for the Firing Circuit Chassis is applied to the Control Power inputs. If dc operating power

is used, 125 Vdc should be applied to terminals DC+ and DC–. If ac operating power is used, 120 Vac

should be applied to terminals AC1 and AC2. Both inputs may be used if redundant control power is desired.

Bridge Control Voltage (COM, VC+)

This signal determines the firing control angle of the rectifier bridge SCRs. The Bridge Control Voltage

Input accepts a voltage range of –10 to +10 Vdc. The DECS must be programmed to supply the same

range of control voltage. Refer to Basler publication 9369700990 for information about DECS-400

configuration and Basler publication 9597100990 for information about DECS-450 configuration.

Start/Stop (FS+, FS–)

A contact closure at this input initiates sampling of the synchronizing voltage (to determine phase

rotation) and calculation of the pulse generation time delay. Opening this contact input terminates the

firing pulses.

Terminal Voltage Limiter Enable (VTLIM+, VTLIM–)

The terminal voltage limiter is enabled when contact closure is sensed at this input. When enabled, the

terminal limiter will prevent the generator voltage from exceeding the limiter reference level.

Outputs

The following paragraphs describe the function of the IFM-150 outputs.

Firing Pulses

These outputs supply firing pulses to the gate trigger inputs of the Rectifier Chassis. The firing pulse

terminals used depend on the model of IFM-150. Installation illustrates typical firing pulse output

connections for single-phase and three-phase rectifier chassis applications.

Watchdog Relay (WTCHDG1. WTCHDG2)

The Watchdog Relay output closes to indicate a software execution problem within the IFM-150 or a loss

of power supply. This output remains closed for several seconds after the application of control power.

Alarm Relay (ALRM1. ALRM2)

The Alarm Relay output closes when the monitored synchronizing transformer frequency decreases

below the programmable level of the BESTCOMS Safe Mode Frequency setting. The output opens when

the frequency increases to 1 hertz above the Safe Mode Frequency setting. This output is disabled when

the Start/Stop contact input (FS+, FS–) is open.

Terminal Voltage Limiter Active Relay (LIMACTV1. LIMACTV2)

The normally-open Terminal Voltage Limiter Active Relay output closes when the terminal voltage limiter

activates due to high generator voltage. When the generator voltage decreases below the limiter

reference level, the terminal voltage limiter deactivates and the Terminal Voltage Limiter Active Relay

output opens.

Introduction

The Basler Electric IFM-150 Interface Firing Module receives a control signal from a DECS-400 or DECS

450 Digital Excitation Control System and calculates a phase-control firing angle that is synchronized with

the power transformer output. The IFM-150 then generates output pulses to drive the SCRs of an

excitation rectifier chassis.

The IFM-150 is available in two configurations that control either a single-phase rectifier module or a

three-phase rectifier chassis.

Three-phase IFM-150 modules can be user-configured to supply SCR firing pulses to a fully controlled or

half controlled (positive or negative) rectifier bridge. A fully controlled rectifier bridge requires that the IFM

150 supply six sets of firing pulses to drive the SCRs of the bridge. A half controlled rectifier bridge

contains three SCRs and three diodes. Positive control is used when the SCRs are connected to the

positive side (F+) of the field output. Negative control is used when the SCRs are connected to the

negative side (F–) of the field output.

A single-phase IFM-150 provides full control of a single-phase rectifier module. Four sets of firing pulses

are generated by the IFM-150 to drive the rectifier module SCRs.

Second-Harmonic Restraint

Magnetizing inrush current presents another problem unique to transformer differential relays. Relays

must be capable of detecting the small differences in current caused by the shorting of a limited number

of turns, yet remain secure against the occurrence of magnetizing currents many times the transformer

rating (as seen at one set of terminals).

Although magnetizing inrush is usually associated with the energizing of the transformer, any abrupt

change in the energizing voltage may produce this phenomenon. Common causes are the transients

generated during the onset, evolution and removal of external faults. Desensitizing the relay only during

energization is therefore insufficient.

Magnetizing inrush produces an offset sine wave rich in all harmonics. BE1-87T relays use the second

harmonic to restrain operation because it predominates and because it does not occur in significant

magnitude or duration at other times.

Three-phase BE1-87T relays use second-harmonic sharing. The second-harmonic content of all three

phases is summed together to derive the restraint for each phase. As a result, the second-harmonic

inhibit range and the associated factory setting, is higher than on single-phase relays.