• Two-Winding Current Differential, Overcurrent and Breaker Failure Protection
  Apply two-winding dual-slope differential protection with harmonic blocking and restraint as well as phase, negative sequence, residual, and neutral overcurrent elements for backup protection. Use breaker failure protection for two three-pole breakers.
• Transformer Monitoring
  Record and accumulate through-fault duty for use in SELOGIC^® control equations or manual monitoring. Monitor ambient, load tap-changer (LTC) tank and transformer oil temperature with optional 4–20 mA analog inputs or RTD thermal inputs to extend the life of your transformers.

• Operator Control
  Use four programmable front-panel pushbuttons each with two programmable LEDs for a wide variety of applications, including easy trip-and-close control and status indications for a breaker. Implement local and remote operator control schemes with 32 local and 32 remote control bits.
• Metering and Reporting
  Eliminate separately mounted metering devices with built-in metering functions. Analyze Sequential Events Recorder (SER) reports and oscillographic event reports for rapid commissioning, testing, and post-fault diagnostics. Unsolicited SER protocol allows station-wide collection of binary SER messages. SEL-787 metered quantities include harmonics, power, frequency, and energy; phase voltages and currents; neutral currents; sequence voltages and currents; and maximum/minimum logging of selected quantities.
• ACSELERATOR^® QuickSet^® SEL-5030 Software
  Develop relay settings offline, program SELOGIC control equations, and analyze post-fault event reports.
• Rugged Design
  Trust the industry’s widest ambient operating temperature range, –40° to +85°C
  (–40° to +185°F).

• Retrofit Replacement Kits and Mounting Accessories
  Replace existing transformer protection with SEL-787 direct replacement kits.

Enlarged View

Projection mounting collars are available in 45 and 90 mm.

Projection Mounting Collars Instruction Sheet

Find other mounting options with
the SEL Mounting SELECTOR

Advanced Protection
Protect grounded-wye transformers with sensitive restricted earth fault (REF) elements. Provide volts/hertz protection with frequency tracking from 20 to 70 Hz for generator step-up and other variable frequency applications. Implement load shedding and other control schemes with over- and underfrequency and over- and undervoltage elements.

Flexible and Easy Communications

Apply copper or fiber, single or dual fiber Ethernet (DNP3, IEC 61850, Modbus), and up to 4 serial ports.

Flexible I/O for Local Control and System Applications
The base unit includes three digital outputs and two digital inputs. There are three card slots for optional SELECT I/O cards including the following:

• 3 digital inputs / 4 digital outputs / 1 analog input (3 DI / 4 DO / 1 AI)
• 4 digital inputs / 4 digital outputs (4 DI / 4 DO)
• 4 analog inputs / 4 analog outputs (4 AI / 4 AO)
• 8 digital inputs (8 DI)
• Serial communication (EIA-232 / EIA-485)
• DeviceNet™ communication
• 10 internal RTD inputs (or add 12 external RTD inputs with an SEL-2600 RTD Module)
• Neutral ac current input with three-phase ac voltage inputs (1 ACI / 3 AVI)
• Neutral ac current input (1 ACI)

• Provide differential and overcurrent protection for two-winding:
  • power transformers
  • generator step-up transformers
  • autotransformers
• Apply the optional single-phase CT channel along with the RTD thermal elements to provide fan bank control and protection.
• Implement additional RTD thermal elements to monitor load tap changer (LTC) tank temperatures and SELOGIC programming to indicate temperature differential alarms between transformer and LTC tank temperatures.
• Monitor the number of through-faults, accumulated I2t, and fault duration times to determine the frequency (through-fault events per day, week, month, or year) and impact of external faults on the transformer.
• Apply SEL-787 comprehensive reporting to diagnose events, schedule knowledge-based maintenance, detect unfavorable temperature trends, and satisfy information requirements of supervisory systems.
• Select the external RTD module (SEL-2600A or SEL-2600D) to eliminate expensive wire pulls and reduce wiring terminations at the relay by as much as 40 percent, while acquiring clean RTD signals and an additional contact input.
• Use ACSELERATOR QuickSet SEL-5030 or SEL-5010 Relay Assistant Software to manage your relay settings.

Budgetary Retail, Quantity 1: $2,950
Fully Optioned Price: $5,900
(Prices displayed are for planning purposes and are subject to change. Contact your SEL sales representative today for a quote on configurations and quantities to meet your needs.)

SEL-787 Transformer Protection Relay (preliminary)
SELECT I/O Cards (preliminary)

SEL-787 Data Sheet

SEL-787 Transformer Protection Relay