SEL-251 Relay - Link to SPSU`s main Web page.

ECET 4904
Special Topics Course
Power System Protection
&
Protective Relaying
SEL-251
Phase Overcurrent Relay
1
SEL-251 Relay
The SEL-251 Distribution Relay is designed to protect,
control, and monitors distribution feeders.
It contains both phase and negative-sequence overcurrent
elements to detect phase faults, and ground/residual
overcurrent elements to detect ground faults.
Negative-sequence overcurrent elements reject three-phase
load to provide more sensitive coverage of phase-to-phase
faults, while the phase overcurrent elements provide
protection for three-phase faults where negative-sequence
quantities are not produced.
SEL-251 Relay
The SEL-251’s Phase Overcurrent Elements for phase and
three-phase faults include:
• 51T – Phase Time-Overcurrent Element
Time dial: 0.5 to 15.00 in 0.01 steps
Pickup (51P): 1 to 12 A
Curve families: moderately inverse, inverse,
very inverse, extremely inverse
Time delay or one-cycle reset time
2
SEL-251 Relay
The SEL-251’s Phase Overcurrent Elements for phase and
three-phase faults include:
• 50LT – Phase Definite-Time Overcurrent Element
Time delay: 0 to 16,000 cycles in 1-cycle steps
Pickup (50L): 0.5 to 100 A
• 50H – Phase Instantaneous Overcurrent Element
Pickup: 0.5 to 100 A
• 50C – Phase Instantaneous Overcurrent Element
Pickup: 0.5 to 100 A
SEL-251 Relay
The SEL-251’s Negative-Sequence Overcurrent Elements for
phase-to-phase faults include:
• 51QT – Negative-Sequence Time-Overcurrent Element
Element measures 3xI2 negative-sequence current
Time dial: 0.5 to 15.00 in 0.01 steps
Pickup (51QP): 1 to 12 A
Curve families: moderately inverse, inverse,
very inverse, extremely inverse
• 50QT – Negative-Sequence Definite-Time OC Element
Time delay: 0 to 16,000 cycles in 1-cycle steps
Pickup (50Q): 0.5 to 100 A
3
SEL-251 Relay
The SEL-251’s Ground/Residual Overcurrent Elements for
ground faults include:
• 51NT – Ground/Residual Time-Overcurrent Element
Settings similar to 51QT, except 51NT pickup
(51NP) 0.25 to 12 A secondary
• 50NLT – Ground/Residual Definite Time-OC Element
Pickup based on 51NP setting
Time delay: 0 to 16,000 cycles in 1-cycle steps
• 50NH – Ground/Residual Instantaneous OC Element
Pickup: same range as 50NLT
SEL-251 Relay
The SEL-251 also includes a multiple-shot Reclosing Relay:
• The reclosing relay allows up to four reclosing shots
• Separate open interval timers from 0-16000 cycles
• Reset interval timer from 0-16000 cycles
Additionally, the SEL-251 includes time-delayed trip functions
(52A pickup and 52B dropout) to handle fuse-saving and
inrush current situations.
4
SEL-251 Relay
Along with is protection functions, the SEL-251 relay provides
complete voltage and current metering.
• It determines real and reactive power values, demand values,
peak demand values, and negative- and zero-sequence
components of both the voltages and currents.
The relay also provides statistics relating to the circuit
breaker’s operation for maintenance purposes, including:
• A count of the circuit breaker’s trip operations
• A running sum of the current interrupted by each circuit
breaker pole
SEL-251 Front and Rear Panels
The Front and Rear Panels of the SEL-251 Relay are Shown Above
5
AC Connections
The above figure shows the SEL-251 Relay’s AC connections to its
monitored distribution line via a set of CTs and PTs
DC Connections
The above figure shows the SEL-251 Relay’s AC connections to its
monitored distribution line via a set of CTs and PTs
6
Serial Port Setup
Serial Connection:
Connect 9-pin, serial, cross-over cable
from Port 2R on rear panel of SEL-251
to COM2 port on rear of PC.
PC Serial Port Configuration:
Baud Rate
Data
Parity
Stop
Flow Ctrl.
– 9600 bps
– 8 bits
– None
– 2 bits
– None
Relay Access Levels
Level 0 – Level 0 is the base command-prompt access level for
the relay when a serial-port connection is initiated.
Level 1 – The level 1 command prompt provides access to the
majority of the relay’s commands excluding those
that can be used either to change the relay’s settings
or to directly control (trip/close) the circuit breaker.
Level 2 – The level 2 command prompt provides complete
access to all of the relay’s commands.
Command Prompts:
Level 0
=
Level 1
=>
Level 2
=>>
7
Selected Commands
Level 0:
ACCESS – Command to access level 1. Requires a
password response if enabled.
(Password = “SPSU”)
Level 1:
2ACCESS – Command to access level 1. Requires a
password response if enabled.
(Password = “SPSU”)
BREAKER – Displays the running sum of the circuit
breaker trips and the total current
interrupted by each pole.
EVENT n – Shows the record for event “n” in the History.
Selected Commands
Level 1:
HISTORY – Shows the Date, Time, Event, Location, Shot,
Targets and maximum fault Current for the
last 12 events.
METER – Displays the phase, residual and negative-sequence
currents, the real and reactive powers, and the
line-to-neutral, line-to-line, zero-sequence and
negative-sequence voltages.
QUIT – Returns control to access Level 0.
SHOWSET n – Displays the relay settings stored in group
“n” along with the relay’s global settings
without affecting them.
8
Selected Commands
Level 2:
CLOSE – Closes the circuit breaker.
OPEN – Opens the circuit breaker.
SET n p – Initiates the setting procedure to set/change the
relay settings stored in group “n”. If a setting is
entered for option “p” (i.e. – if p = “P51”), then
the setting procedure will begin at setting “p”,
bypassing all of the previous group settings.
SET g p – Initiates the setting procedure to set/change the
relay’s global settings. If a setting is entered for
option “p”, then the setting procedure will begin
at setting “p”, bypassing all of the previous
global settings.
Sample Command Results
=>METER – Displays the phase/residual/negative-sequence currents,
the real/reactive powers, and the line-to-neutral/
line-to-line/zero-sequence/negative-sequence voltages.
Negative-Sequence (3I2)
Current, Real (P) and
Reactive (Q) Powers
Line (AB BC CA) and
Negative-Sequence (3V2)
Voltages
Phase (IA B C)
and Residual (R)
Currents
Phase (VA VB VC)
and Zero-Sequence (3V0)
Voltages
9
Sample Command Results
=>HISTORY – Shows the Date, Time, Event, Location, Shot, Targets
and maximum fault Current for the last 12 events.
Most Recent
Event in History
Instantaneous
Overcurrent
Element
Last Event
In History
Phase A to Ground Fault
Trip Initiated
Reclose
Shot #
Maximum
Fault
Current
Sample Command Results
=>SHOWSET n – Displays the relay settings stored in group “n” along
with the relay’s global settings without affecting them.
(Page 1)
CT and PT
Ratios
Ammeter
Demand
Settings
Line Impedance
Values
Reclosing Relay
Settings
Instantaneous and
Time Overcurrent
Element Settings
10
Sample Command Results
=>SHOWSET n – Displays the relay settings stored in group “n” along
with the relay’s global settings without affecting them.
(Page 2)
Programmable
Trip Conditions
Programmable
Event Report
Trigger Conditions
Programmable
Reclose Cancel
Conditions
Sample Event Report
=>
11