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Customer Success Story

Black Oak

SVC to Increase reliability and reduce congestion over multiple 500 kV lines

A very large Static Var Compensator (SVC) supplied by Hitachi Energy was commissioned at the end of 2007 at Allegheny Power’s Black Oak substation near Rawlings, Maryland. The installation enhances the reliability on Allegheny Power’s 500kV Hatfield-Black Oak-Bedington transmission line – one of the most heavily-loaded lines in the PJM (Pennsylvania, Jersey, Maryland) Interconnection area – by quickly changing reactive power levels to control the line’s voltage. In addition to improving reliability, the SVC will enable increased transmission capacity across the PJM region. Enabling more power to flow on existing lines is an efficient use of resources and an important step in keeping pace with the region’s increased demand for electricity.

The SVC is a midline SVC and constructed to stabilize the voltage at the point of connection during network operation events and contingencies.

The project was initiated as part of PJM’s Regional Transmission Expansion Plan, which identifies upgrades and additions to ensure the reliability of the electric transmission system throughout its multi-state region. 

Main data
System SVC
Controlled voltage 500 kV
SVC rating 145 Mvar inductive to 575 Mvar capacitive
Control system Voltage control by means of a closed loop system with control of the positive-phase sequence voltage around a dead-band and switching control of external MSC
Thyristor valves PCT type thyristors, water cooled, indirect light firing


Single-line diagram, Black Oak