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The PCS-921 numerical relay provides the protection

of circuit breakers with breaker failure protection, pole

discrepancy protection, dead zone protection, phase/

neutral overcurrent protection, single and/or three-pole

auto-reclosing and synchronism check functions. The PCS-

921 relay employs the programmable logic, configurable I/

O and definable 3-color LEDs to provide flexibility for the

specic applications. Frequency tracking is used to minimize

the sampling error caused by system frequency uctuation.

The PCS-921 relay adopts the advanced multi-processor

platform, providing the interfaces to station bus and process

bus respectively and supporting IEC 61850-8-1 MMS,GOOSE, IEC 61850-9-2 Sampling Value. In addition, RJ-45

faceplate port for testing and setting to make commissioning

and maintenance easier.

PCS-921Circuit Breaker Protection

Functions

Protection and Control

Breaker failure protection (50BF)

Re-tripping the own breaker and tripping the adjacent

breakers will be issued if the external tripping command is

received but the overcurrent element does not drop off. To

improve the sensitivity of generator/transformer protection,

the neutral and negative-sequence overcurrent elements are

provided besides phase overcurrent element.

Pole discrepancy protection (62PD)

The pole discrepancy is detected using the breaker auxiliary

contacts, and the asymmetrical current element could be

selected as an additional criteria.

Dead zone protection (50DZ)

The adjacent breakers will be tripped if the fault between CT

and breaker (dead zone) is detected via the initiating binary

input from external protection, breaker auxiliary contacts and

overcurrent element.

Two stages of phase overcurrent protection (50/51P)

Second harmonic element could be selected to block the

overcurrent element to avoid the maloperation due to

transformer inrush current.

Two stages of neutral overcurrent protection (50/51N)

Second harmonic element could be selected to block the

neutral overcurrent element.

Synchronism check (25)

The criteria could be set as frequency difference, voltage

difference, and phase angle difference. And the checking

condition could be selected as live-bus to dead-line, dead-

bus to live-line or dead-bus to dead-line.

Single and/or three-pole auto-reclosing (79)

Up to 4 shots could be selected for the single-/three- pole

auto-reclosing.

Voltage and current drift auto adjustment

The relay continually and automatically traces the voltage

and current drifts and adjusts the zero point.

Frequency tracking

Frequency tracking is provided to accommodate the

frequency shift in power system.

Monitoring and Measurement

VT circuit supervision (VTS)

CT circuit supervision (CTS)

Self diagnostic

Auxiliary power supervision

Event recorder including 1024 disturbance records, 1024

binary events, 1024 supervision events and 1024 operating

logs

Disturbance recorder including 64 disturbance records

with waveforms (The file format of disturbance recorder is

compatible with international COMTRADE le.)

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Counter of circuit breaker operation (single-pole tripping,

three-pole tripping and reclosing)

Communication

Two 10Base-T/100Base-TX (RJ45) ports and two optional

100Base-FX ports with IEC 61850-8-1 MMS and GOOSE for

non-time-critical message, IEC 60870-5-103 over TCP/IP orDNP 3.0

Two RS-485 rear ports with IEC 60870-5-103

Six or Eight 100Base-FX ports with IEC 61850-9-2 Sampling

Value and GOOSE for time-critical message

One RS-485 rear port for clock synchronization

One RS-232 rear port for printer

One faceplate RJ45 port for testing and setting

Clock synchronization via Pulse-Per-Second, IRIG-B and

SNTP

Features

The relay is based on NRs well established and proven

UAPC hardware platform with multi-processor architecture.

The multi CPU technology supports parallel operating

simultaneously.

The two independent data acquisition paths can prevent any

undesired trip caused by component failure. One works as afault detector and the other is designed for protection and its

logic. Tripping outputs are supervised by the fault detector to

prevent a mal-operation.

The sensitive DPFC fault detector element is integrated to

target on the quick response to short-circuit fault.

The relay is compatible with IEC 61850-8-1 MMS, GOOSE

and IEC 61850-9-2 Sampling Value and provides the

independent interfaces for station bus and process bus

respectively.

Technical data

Power Supply

Standard IEC 60255-11:2008

Voltage Range 88 to 300 Vdc or 88 to 264 Vac

Permissible AC ripple voltage 15% of the nominal auxiliary voltage

Burden

Quiescent condition

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Rated current 1.2mA 1.5mA 2.4mA 1.1mA 1.25mA 2.2mA 2.5mA

Pickup voltage 13V~17V 17V~21V 26V~34V 60.5V~77V 60.5V~77V 121V~154V 121V~154V

Dropout voltage 90% of pickup voltage

Maximum permissive voltage 300Vdc

Withstand 2000VAC, 2800VDC(continuously)

Resolving time for logic input

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Minimum receiving power Min. -20dBm Min. -24dBm

System reserve Min +3dB Min +3dB

- Print Port

Type RS-232

Baud Rate 4.8kbit/s, 9.6kbit/s, 19.2kbit/s, 38.4kbit/s, 57.6kbit/s, 115.2kbit/s

Printer type EPSON 300K printer

Safety level Isolation to ELV level

- Clock Synchronization Port

Type RS-485

Transmission distance 100M@500VDC

- Electromagnetic Compatibility

1MHz burst disturbance test

Per IEC 60255-22-1:2007

Common mode: class III 2.5kV

Differential mode: class III 1.0kV

Electrostatic discharge test

Per IEC60255-22-2:2008 class IV

For contact discharge: 8kV

For air discharge: 15kV

Radio frequency interference tests

Per IEC 60255-22-3:2007 class III

Frequency sweep

Radiated amplitude-modulated

10V/m (rms), f=801000MHz

Spot frequency

Radiated amplitude-modulated

10V/m (rms), f=80MHz/160MHz/450MHz/900MHz

Radiated pulse-modulated

10V/m (rms), f=900MHz

Fast transient disturbance tests

Per IEC 60255-22-4:2008

Power supply, I/O, Earth: class IV, 4kV, 2.5kHz, 5/50ns

Communication terminals: class IV, 2kV, 5kHz, 5/50ns

Surge immunity test

Per IEC 60255-22-5:2008Power supply, AC input, I/O port: class IV, 1.2/50us

Common mode: 4kV

Differential mode: 2kV

Conducted RF Electromagnetic DisturbancePer IEC 60255-22-6:2001

Power supply, AC, I/O, Comm. Terminal: Class III, 10Vrms, 150 kHz~80MHz

Power Frequency Magnetic Field ImmunityPer IEC 61000-4-8:2001

class V, 100A/m for 1min, 1000A/m for 3s

Pulse Magnetic Field ImmunityPer IEC 61000-4-9:2001

class V, 6.4/16s, 1000A/m for 3s

Damped oscillatory magnetic eld immunityIEC 61000-4-10:2001

class V, 100kHz & 1MHz100A/m

Auxiliary power supply performance

IEC60255-11: 2008

Voltage dips: Up to 300ms for dips to 40% of rated voltage without reset

Voltage short interruptions: 100ms for interruption without rebooting