Interfacing Power System Simulators with Geomagnetically Induced Currents (GIC) Simulation Programs. Luis Marti Hydro One, Canada

Transcription

1 1 Interfacing Power System Simulators with Geomagnetically Induced Currents (GIC) Simulation Programs Luis Marti Hydro One, Canada

2 2 GMD 101 Background. What is a GMD event. Effects on the power system Complexities: earth models, unpredictable forcing functions. Geoelectric field is time varying not spatially uniform and coupling between geomagnetic and geoelectric fields is spatially and frequency dependent.. GIC steady state and time domain simulations. Frequency assumptions. Role of load flow simulations: assessment of the effects of var absorption. GIC solvers Use of scripts and iteration with load flow software. Convergence rates. Advantages and disadvantages. Commercially available software and their approach to modelling issues For instance: PowerWorld PSS E and PSLF, EMTP. Final observations

3 3 Geomagnetic Disturbance (GMD) earth Sun magnetosphere Coronal Mass Ejection source:

4 4 Geomagnetic Disturbance (GMD) Electrojet CME Source: Scientific American Electrojet currents are typically millions of Amperes and are located km above the earth s surface

5 Mutual Coupling on a Planetary Scale 5

6 6 Geomagnetically Induced Current (GIC) V induced GIC V E dl V induced Rest of System V induced Geoelectric Field

7 7 GIC and half cycle saturation Xsc/2 1:1 Xsc/2 Xmag Vo Saturated flux B Time I Unsaturated flux Normal currents Half-cycle saturation currents Time

8 As saturation increases so does the magnitude and distortion of magnetizing currents 8 20 A 33 A 47 A

9 Effects of GIC on Power System Apparatus

10 Transformer reactive power absorption Magnetizing currents during half cycle saturation can be visualized as placing a small shunt reactive branch during half the 60 Hz cycle. The power system sees this as effective reactive power absorption This causes RMS voltages to drop The time constant difference between GIC changes and the system response, allows the assumption that transformer reactive power absorption is nearly instantaneous and final steady state values for var loss can be modelled in a load flow program as a constant var source. Reactive power absorption assumes undistorted system voltages Q = V 60 I 60, where subscript 60 indicates the fundamental of voltage and current

11 Reactive power absorption and core type

12 For instance GMD event July 26 27, Spike at 22:44 July 26, 2004, EST ESSA GIC :24 19:12 0:00 A Neutral currents 4:48 9:36 14: Time

13 500kV voltage responses July 26, CWD HNM Bruce :52 21:21 21:50 22:19 22:48 23:16 23:45 0:14 kv Time

14 230kV voltage responses July 26, ESSA CLV 21:21 21:36 21:50 22:04 22:19 22:33 22:48 23:02 23:16 23:31 23:45 0:00 kv Time

15 The Earth Model GIC frequency is very low (0.1 mhz to 100 mhz). High depth of penetration. Higher resistivity larger induced geoelectric field. Typically modelled as laterally uniform: indicates that the earth consists of horizontal uniform layers

16 Five major regions in parts of Ontario. Induced geoelectric field depends on the relative orientation of the geomagnetic field and the transmission circuits, is frequency dependent and spatially dependent.

17 Real time vs. Steady state Study purpose Real time Situational awareness in the control room Alarms Triggers for pre planned mitigation measures Event playback Steady state Planning Impact assessment Determination of mitigating measures and their effectiveness

18 Real time vs. Steady state GIC Modelling Real time dc network GIC and var absorption E field from db/dt Single or multiple earth models GIC and harmonics GIC and transformer thermal response Steady state dc network GIC and var absorption Usually uniform B field Different orientation Single or multiple earth models Single frequency (0.1mHz 100 mhz)

19 Storm orientation matters N W Zone 1 E S

20 N Zone 2 W E S

21 N Zone 3 W E S

22 N Zone 4 W E S

23 N Zone 5 W E S

24 N Zone 6 W E S

25 GIC solvers Probably since the early 1980 s for geophysical simulations. NRCan s real time GIC simulator was a GIC solver designed to provide a service to power system operators produced around the mid 2000 s. Focused on displaying GIC flows is a power network Graphical display Situational awareness. In the late 2000 s Hydro One s real time simulator development started. Focused on real time assessment of var absorption and transformer hot spot heating. Arbitrary simulation time step (no FFT inversion) In service in 2012.

26 Integration of GIC distribution and load flow The interface point between a GIC and a load flow simulation is transformer var absorption (assuming that netwotk topology is consistent) If GIC in every transformer is known for a given system configuration then the effects of var loss can be modelled in a load flow program by connecting a constant var source to the transformer terminals (constant I or constant Q). Some commercial software do this transparently using lookup tables or var/gic characteristics (or linear K factor) Different construction means a different lookup table or K factor Lookup tables are often obtained from published calculations but can also be generated with EMTP or equivalent simulations that take into consideration the distribution of flux according to construction. Lookup tables always assume an infinite system source. In other words, harmonic currents do not cause harmonic voltage distortion. o Voltage/flux is assumed to be sinusoidal

27 Integration of GIC distribution and load flow Commercially available software that include GIC and load flow calculations is relatively young and evolving. Before GIC modules/options were available, integration was done with scripts running both applications: Calculate var absorption with GIC modeller Include var loss into load flow Obtain system voltage profile Iterate

28 Integration of GIC distribution and load flow In a sense separate programs are a more powerful option since GIC simulators have more advanced features such as thermal transformer modelling, harmonics and complex earth models. In the case of 3 limb core type transformers, the need to iterate between load flow and GIC solutions is important.

29 Integration of GIC distribution and load flow Commercially available load flow programs use different approaches to integration. In the case of PSS E GIC and load flow are different modules that communicate through files. Not much different than using GIC simulators with Python scripts Arguably time domain software such as the EMTP could be used Unfamiliar to most planning engineers that carry out load flow system studies Practical difficulties with large systems and matching base case load flow models Not designed to carry out automated contingency analysis. Niche is probably the simulation of harmonics.

30 Final observations Since circa 2010 when NERC s GMD Task Force started, commercial software developers appreciated the need to account for GIC modelling in their tools. Complexities of GIC modelling are being introduced into commercial tools with varying approaches and simplifications. Different earth models Non uniform B field The right way to carry out system simulations is not quite there yet. Proposed NERC Standard TPL 007 has been a powerful motivator.