Geomagnetic Induced Current (GIC) is the result of CME’s from the sun which interact with the earth’s magnetosphere through a process called electromagnetic induction resulting in geomagnetic disturbances (GMD).
There are two kinds of solar activity that have the potential to disrupt our lives on earth: solar flares and coronal mass ejections (CMEs). Watch this video from NASA to learn the difference.
When CME’s occur, magnetic particles are ejected from the sun’s surface and are carried in the solar winds, generating rapidly changing magnetic fields as they move across the earth’s surface. . Here is a video depicting scientists tracking the journey of a solar eruption.
The magnetic fields interact with the earths conductivity resulting in ground voltage differences. The ground voltage differences result in the flow of GIC current through the neutral conductor of wye connected transformers, interconnected by high voltage transmission lines.
Where do Geomagnetic Disturbances Occur?
- GMD events are just as likely to occur in the southern hemisphere as the northern hemisphere
- Industry studies have identified locations with latitudes above 45-50 degrees may be susceptible to GMD events
- The probability of a GMD event increases based on the sunspot count, but GMD events can occur at any time during the solar cycle.
To better evaluate whether your transformers are at risk, read through the NERC standard TPL-007.
What is the effect of GIC on Transformers?
The flow of GIC in transformers is the root cause of all GMD related power system problems.
- The magnitude of the GIC current and the associated DC offset is superimposed on the excitation current which forces the transformer into part cycle saturation.
- GIC can result in increased reactive power requirements and large harmonic currents during GMD events.
- The harmonics can result in tripping of VAR compensation devices at times when additional VARS are needed most resulting in system disturbances and instability. Large GMD events are often associated with a variety system alarms.
New Standards Relating to Geomagnetic Induced Current
The increase in awareness of geomagnetic disturbance events has led to the creation of new standards in the US including FERC order 830 which resulted included the creation of NERC standard TPL-007. The standard establishes guidelines on planning for geomagnetic disturbances.
All transmission owners and generator owners with grounded wye connected transformers operating with a high side voltage of 200kV or greater are subject to the requirements of TPL-007. The standard requires owners to perform an assessment of their assets and collecting GIC data to validate system modelling of GIC flow during GMD’s.
GIC Monitoring Options
Geomagnetic Induced Current (GIC) Sensors
- Split core design allows easy installation
- Range of the sensor can be easily adjusted
- Hall affect sensor provides excellent response time and is linear over the entire operating range
- Senses pure DC and quasi-DC up to 3Hz
- Bracket design allows for centering the sensor around the conductor and provides conduit support for 4-20mA output
- Core material is stable over a wide temperature range
- Hall effect sensor has excellent response time and is linear over the entire operating range
Harmonics and VAR Loading with the E3 Transformer Monitor
- Measure and calculate current waveform harmonics
- Measure the DC offset in the current waveform during through faults and system disturbances
- Measure the VAR requirements of the transformer
- Operates with the latest industry standards