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 specific applications. Frequency tracking is used to minimize the sampling
error caused by system frequency fluctuation.
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.
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
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
Two stages of phase overcurrent protection (50/51P)
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)
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, deadbus to live-line or dead-bus to
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
Frequency tracking is provided to accommodate the
frequency shift in power system. Monitoring and Measurement
VT circuit supervision (VTS)
CT circuit supervision (CTS)
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
Counter of circuit breaker operation (single-pole tripping, three-pole
tripping and reclosing)
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 or DNP 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
The relay is based on NR’s 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 a fault 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.