101 Skyline Drive

Warrior, AL 35180



PSStech OPP System

Open phase fault detection (OPFD) has been at the forefront of protection concerns since the January 30, 2012 open phase event at Exelon’s Byron Unit 2.  The cause of this open phase event was the failure of the C-phase insulator stack for the Unit 2 System Auxiliary Transformer (SAT) revenue metering transformer.

On February 28, 2012 another event occurred at the Byron Plant.  A mechanical failure of 345 kV under-hung porcelain insulator on Unit 1 SAT A-frame structure failed due to a manufacturing defect.  The 345kV line fell to the ground causing a phase-to-ground fault which tripped the SAT lockout scheme causing the 6.9 kV busses to fast transfer to the UAT, and the ESF busses to be de-energized and subsequently reenergized by the diesel generators. These failures have highlighted the need for detecting open-phase conditions that can occur in the power delivery system. 

The PSStech OPP System can be used to detect, alarm, and actuate in response to single and double open phase conditions in the offsite power circuit(s). Based on a field-proven system tested in May 2014, the OPP System is specifically designed to detect open phase conditions on industry-recognized types of transformers where an open phase under no-load or lightly-loaded conditions is undetectable by traditional voltage or current measurements.


Allows for a fail-safe and redundant detection design, including neutral overcurrent protection.

Allows for continuous monitoring of all major system components.

Only requires monitoring of a change in signal level. Thus, drastically reducing the system calculations needed.

Combined active/passive protection is the preferred method over passive only protection.

Simple installation requiring minimal outage time and minimal maintenance.

Simple operator interface.


Standard or custom turn-key systems.

Field-proven technology based on EPRI research.

The PSStech OPP System is the only field-proven system without blind spots for any type of open phase condition with or without a ground fault of any impedance.


The PSStech OPP System is based on EPRI Research.

The PSStech OPP System was designed to be capable of detecting, actuating protective features, and alarming locally and remotely under various conditions of open circuit faults on offsite power sources for both loaded and unloaded transfomer conditions.

Open phase element with adjustable definite time delay and 50ND adjustable definite time neutral overcurrent element.

  1. Operating Environment: 

    Ambient Temperature: -10°F to 110°F
    Relative Humidity: 0% to 100%
    Humidity: 0% to 100%

  2. Power Supply Requirement: 208 to 240 Vac, 20 A, 60 Hz, 1F. Other source voltages such as 120 Vac or 480 Vac can be accommodated.

  3. Relay Output Contacts: Five SPDT dry contacts; two tripping relay outputs, system fail alarm output, and two open phase alarm outputs.

  4. Operator Control Interface:

    Three-position control switch with Normal, Alarm, and Off Positions
    Injection Signal Calibrate Pushbutton
    Alarm Reset Pushbutton
    Channel Functional Green Light Indication
    Trip Enabled Amber Light Indication
    Open Phase Alarm Red Light Indication
    Heavy-duty Safety Switch for Obtaining Clearance Point on Transformer