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Multi-Winding Current Differential Protection Protection
Protect power transformers with as many as four windings using
a combination of single- or dual-slope percentage differential
characteristics, overcurrent protection, and restricted earth fault
protection. Control
Locally control relay operation, and initiate or block automation
sequences from remote sites or control systems. Monitoring
Simplify fault and system disturbance analysis with event reports
and sequential events recorder. Use breaker contact wear and
substation battery voltage monitors to efficiently dispatch
maintenance resources.
Specify optional thermal modeling per IEEE C57.91:1995 for mineral-
oil immersed transformers. Use the thermal element to activate a
control action, or issue an alarm when your transformer is in danger
of excessive insulation aging or loss of life. Automation
Reduce total project costs through remote communications
capabilities and elimination of external control switches and
indicating lamps. Use remote communications capabilities for
control, monitoring, and alarm purposes.
Making Electric Power Safer, More Reliable, and More Economical
®
Multi-Winding Current
Differential Protection
SEL-387 Current Differential and Overcurrent Relay
Apply the SEL-387 Relay for protection
of two-, three-, or four-winding power
transformers. Use overcurrent
elements from combined CT inputs
for backup protection.
Features and Benefits Each of the four, three-phase current input terminals has a total of
eleven overcurrent elements, nine of which are torque controlled.
For backup overcurrent protection in ring-bus or breaker-and-a-half
configurations, two combined overcurrent elements operate on the
sum of the currents from Windings 1 and 2 and/or Windings 3 and 4. The
combined currents from two separate breaker CTs emulate the current
as if from a single bushing CT applied on the power transformer.
The SEL-387 Relay has three differential elements. These elements
use operate and restraint quantities calculated from the two, three,
or fourwinding input currents. Set the differential elements with
either a single- or dual-slope percentage differential characteristic,
as shown below.
Functional Overview
Differential Protection
Overcurrent Protection
52
Time-Overcurrent
Phase
Ground
Neg. Seq.
Combined
Time-Overcurrent
Phase
Ground

Overcurrent
Phase
Ground
Neg. Seq.
52
Time-Overcurrent
Phase
Ground
Neg. Seq.
Overcurrent
Phase
Ground
Neg. Seq.
52
Time-Overcurrent
Phase
Ground
Neg. Seq.
Overcurrent
Phase
Ground
Neg. Seq.
52
Time-Overcurrent
Phase
Ground
Neg. Seq.
Overcurrent
Phase
Ground
Neg. Seq.
(If the fourth winding
is not used in 87)
Three-Phase
Current
Differential
Restricted Earth
Fault (REF)
SEL
OGIC®
Control Equations
Event Reports
Sequential Events Recorder
Breaker Wear Monitor
Station Battery Monitor
ASCII, Binary, and Distributed
Port Switch Communications
Remote and Local Control
Switches
Phase, Ground, Neg. Seq.,
Differential, and Harmonic
Metering
Restrained and Unrestrained
Differential Elements
Second- and Fourth-Harmonic
Blocking or Restraint
Fifth-Harmonic and DC Blocking
CT and Transformer Connection
Compensation
Through-Fault Monitoring
Thermal Monitoring*
Additional I/O*
DNP3 Level 2 Slave Protocol*
SEL-387 Relay

* Optional Functions
50
P
G
Q
51
P
G
Q
50
P
G
Q
51
P
G
Q
50
P
G
Q
51
P
G
Q
50
P
G
Q
51
P
G
Q
67G
87
51
P
G 3
3
1
3
3
Autotransformer
Min

I
op
Slope 2
Restraining Region
Operating Region
Slope 1
I
Restraint
I
O
p
e
r
a
t
e
60%
25%
The SEL-387-5 and SEL-387-6 provide security against conditions
resulting from both system and transformer events that can cause
relay misoperation. Use the fifth-harmonic element to prevent
relay misoperation during allowable overexcitation conditions. Even
harmonic elements (the second and fourth harmonics) provide
security against inrush currents during transformer energization,
complemented by the dc element, which measures the dc offset. The
even harmonic elements offer the choice between harmonic blocking
and harmonic restraint. In the blocking mode, select either blocking on
an independent phase basis or on a common basis, as per application
and philosophy. The second-, fourth-, and fifth-harmonic thresholds
are set independently, and the dc blocking and harmonic restraint
features are independently enabled. Through-fault currents can cause transformer winding displacement
leading to mechanical damage and increased transformer thermal
wear. SEL-387-5 and SEL-387-6 through-fault event monitors gather
current level, duration, and date/time for each through fault.
A convenient set of automation features reduces the need for external
metering and control devices. Automation components include 16 each
of the following:
Local control switch elements provide the functionality of
separately mounted switches without the cost burden of installing
and documenting physical devices.
Remote control switch elements are set, cleared, and/or pulsed
via serial port commands from remote systems or human-
machine interfaces.
Latch control switch elements retain the status of logical element
conditions, such as supervisory on/off selector switch positions.
Display points provide 16 programmable messages for the front-
panel liquid crystal display (LCD). Use SEL
OGIC
®
control equations
to drive the LCD with any logical point in the relay.
Advanced SEL
OGIC
control equations put relay logic in the hands of
the protection engineer. Assign relay inputs to suit the application.
Logically combine selected relay elements for various control functions,
and assign outputs to logic functions. In addition to Boolean-type logic,
16 general-purpose SEL
OGIC
control equation timers eliminate external
timers for custom protection or control schemes. Each timer has
independent time-delay pickup and dropout settings.
Primary Current: IA, IB, IC, IR, 3I2
Instantaneous
Demand
Peak Demand
Harmonic Spectrum (fundamental to fifteenth harmonic)
Secondary Current: IA, IB, IC, IR, 3I1, 3I2
Instantaneous, with magnitude and angle
Differential Quantities: IOP, IRT, IF2, IF5
Operate
Restraint
Second and fifth harmonics
Time-delayed alarm threshold for fifth harmonic
Use
AC
SEL
ERATOR
QuickSet SEL-5030 Software in the SEL-387-5
and SEL-387-6 to customize your protection. Set and edit relay
configuration, settings, and logic.
View the HMI screens in
AC
SEL
ERATOR
QuickSet to check wiring
polarity and connections.
The Restricted Earth Fault (REF) function compares the directions of
neutral current and winding residual current for sensitive ground fault
detection in groundedwye or autotransformerconnected windings.
Restricted Earth Fault Protection
Metering Functions
Advanced SEL
OGIC
Control Equations
Transformer Thermal Monitoring
Simplified Setup and Troubleshooting
Through-Fault Monitoring
SEL-387-6
SEL-2600A
Power
Transformer
SEL-2600A
or PLC
Asset
Management System
Temperature
Inputs
Modbus
®
SEL
Fast Messaging
or ASCII Protocol
Typical functional diagram for collection of temperature data.
Specify the SEL-387-6 Relay to provide thermal modeling for monitoring
and protection of a single three-phase transformer or three indepen-
dent single-phase transformers.
AC
SEL
ERATOR
QuickSet HMI simplifies configuration and troubleshooting.
Enhanced Automation Elements AC Current Inputs (twelve total)
5 A nominal
15 A continuous, 500 A for 1 second, linear to 100 A symmetrical
Burden
0.27 VA @ 5 A
1 A nominal
3 A continuous, 100 A for 1 second, linear to 20 A symmetrical
Burden
0.13 VA @ 1 A
Frequency and Phase Rotation
60/50 Hz system frequency and ABC/ACB phase rotation are
user-settable
Output Contact Ratings (eight total, standard model)
30 A make per IEEE C37.90-1989 paragraph 6.7.2; 6 A continuous
carry; MOV protected
Optoisolated Input Ratings (six total, standard model)
24, 48, 110, 125, 220, or 250 Vdc, level-sensitive (specify voltage
when ordering)
Serial Communication
Two rear-panel and one front-panel EIA-232 serial ports
One rear-panel EIA-485 serial port with 2.1 kVdc isolation
Baud selection 300, 1200, 2400, 4800, 9600, 19200 (per port)
Time-Code Input
Demodulated IRIG-B accepted at EIA-232 Port 2 and the EIA-485 port
For each terminal, the SEL-387 Relay keeps track of the number of
breaker operations, total interrupted current by pole, and contact wear
by pole. Schedule timely breaker maintenance based on actual breaker
wear that is related to the breaker manufacturers maintenance curves.
Schweitzer Engineering Laboratories, Inc. is committed to
quality. Our certification to the ISO 9001 quality standard
and our worldwide, ten-year product warranty are exam-
ples of this commitment. We encourage and appreciate
your feedback about the use of SEL equipment, and we
will use this information to continually improve our
products and services.
2350 NE Hopkins Court Pullman, WA 99163-5603 USA
Tel: 509.332.1890 Fax: 509.332.7990 Email: info@selinc.com
www.selinc.com www.selindustrial.com
SEL-387 Current Differential and Overcurrent Relay
Intelligent Breaker Monitor
Commitment to Quality
Making Electri