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September 22, 2016, the Federal Energy Regulatory Commission (FERC) approved the National Energy Reliablity Council’s (NERC’s) Reliability Standard TPL-007-1 (Transmission System Planned Performance for Geomagnetic Disturbance Events). The new standard, establishes for the first time, mandatory requirements for transmission owners and other entities to assess the vulnerability of transmission systems to Geomagnetic Disturbance events (“GMDs”).
GMDs occur when the sun ejects charged particles that interact with the earth’s magnetic field. The particles are accelerated by Earth’s magnetic field and high speed collisions with gas molecules in the upper atmosphere displace electrons and ionize the gas. The resulting ionic currents in the earth’s upper atmosphere can induce quasi-direct currents in long transmission lines and buried metallic structures.
Power transformers with grounded neutral windings are vulnerable to core saturation due to the dc offset imposed on the ac waveform, as these Geomagnetic Induced Currents (GICs) flow into the windings. Depending on the specifics of its design, a transformer may exhibit winding overheating, stray flux heating of end-frames and Flitch plates, anomalous gas generation, and in extreme cases, bubble formation and catastrophic failure.
Utility planning coordinators, transmission planners, transmission owners, and generation owners have new mandatory responsibilities under the standard. Transmission-owning utilities are now required to analyze and assess the performance of their transmission systems, including transformers under a GMD benchmark planning event.
In particular, the standard stipulates that utility operators provide “Documented evaluation of potential susceptibility to voltage collapse, cascading, or localized damage of equipment due to geomagnetic disturbances”.
Who is Affected?
All systems that include power transformer(s) with a high side, wye-grounded winding with terminal voltage greater than 200 kV.
Kinectrics Can Help:
Kinectrics’ power system engineers can analyze your network, perform grounding studies, and determine the system’s response to the flow of GICs.
Our team of transformer experts can assess the specific designs of transformers on your utility system that might present significant operational risk due to GMDs. We can provide comprehensive reports that fulfil the requirements of NERC TPL-007 from a transformer perspective.
Typical vulnerability studies include a determination of peak and average magnetizing current, harmonic content of magnetizing current, reactive power draw, winding hottest spot; top/clamping plate and Flitch plate temperatures; and thermal capability curves all for up to five (5) GIC dc current magnitudes.