Solar Power Down Under

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Australia, the land of the sun—in fact, around 3,300 hours of sun­shine are record­ed every year in Perth, West­ern Aus­tralia where the head­quar­ters of net­work oper­a­tor West­ern Pow­er is locat­ed. This is cer­tain­ly a fig­ure that could make West­ern Euro­peans green with envy: By com­par­i­son, MR’s head­quar­ters in Regens­burg, Ger­many reg­is­ter around just 1,600 hours of sun­shine annu­al­ly.

It’s no won­der then that Aus­tralia is cur­rent­ly the world leader when it comes to the amount of ener­gy pro­duced from pho­to­volta­ic (PV) sys­tems. 2.3 mil­lion solar units are cur­rent­ly installed on Aus­tralian roofs, equat­ing to an ener­gy sup­ply of close to 1 gigawatt—a fig­ure which is set to account for an addi­tion­al 150 MVA annu­al­ly in the com­ing years.

GOOD FOR THE CLIMATE, BAD FOR THE GRID

For Mariza But­ler, Senior Engi­neer Grid Trans­for­ma­tion at West­ern Pow­er, this is first and fore­most good news: “We want as many peo­ple as pos­si­ble to use pho­to­voltaics, to sup­ply the ener­gy to the grid, and in doing so to do their bit for cli­mate pro­tec­tion,” she explains. But unfor­tu­nate­ly, there’s a prob­lem: If the pro­por­tion of pow­er flow­ing back into the low­voltage grid from pri­vate pro­sumers increas­es to a point where the pow­er flows exces­sive­ly in the reverse direc­tion, the volt­age in the grid also increas­es.

This is the case dur­ing the Aus­tralian spring and autumn in par­tic­u­lar when mild tem­per­a­tures mean that air­conditioning isn’t required as often, peo­ple spend a lot of time out­doors, and demand for elec­tric­i­ty is low­er. Yet these cir­cum­stances are of lit­tle inter­est to the sun — it con­tin­ues to shine on the solar pan­els unabat­ed. A cer­tain amount of fluc­tu­a­tion in low volt­age (LV) is nor­mal, but there are lim­it val­ues which must be observed. For Euro­pean grid oper­a­tors, there is a lee­way of 58 volts (230 V, +/­10 %) while for West­ern Pow­er, on the oth­er side of the world, the mar­gin is just 29 volts (240 V, +/­6 %).

AUSTRALIA BENEFITS FROM VRDTS

In Ger­many, MR start­ed to focus on this prob­lem back in 2012, as the use of dis­persed sources of ener­gy had meant that the medium­ and low­voltage grids in many indus­tri­al­ized nations increas­ing­ly need­ed some atten­tion. So how could we bring volt­age sta­bil­i­ty to dis­tri­b­u­tion grids faced with volatile ener­gy sup­plies?

MR’s answer: the ECOTAP® VPD® on­load tap­changer. This tap chang­er for volt­age reg­u­la­tion dis­tri­b­u­tion trans­form­ers (VRDTs) is already in its third gen­er­a­tion and enables dis­persed volt­age reg ula­tion in the dis­tri­b­u­tion grid to be achieved. Pre­vi­ous­ly, dis­tri­b­u­tion trans­form­ers couldn’t be reg­u­lat­ed, but this reg­u­la­tion is nec­es­sary to com­pen­sate for volt­age fluc­tu­a­tions in local grids.

“We want as many peo­ple as pos­si­ble to use pho­to­voltaics, to sup­ply the ener­gy to the grid, and in doing so to do their bit for cli­mate pro­tec­tion.”Mariza But­ler, Senior Engi­neer Grid Trans­for­ma­tion at West­ern Pow­er

At a work­ing group meet­ing of Cigre Aus­tralia for dis­persed gen­er­a­tion (C6) back in 2016, Dr.­Ing. Thomas Smol­ka, the Man­ag­ing Direc­tor of Rein­hausen Aus­tralia, gave a pre­sen­ta­tion on this very top­ic. It was from this event that West­ern Pow­er con­sid­ered tri­alling VRDTs as a poten­tial long­term solu­tion and it there­fore agreed to a pilot project with MR which would see eleven select­ed pole­­mounted trans­form­ers equipped with the ECOTAP® VPD®s. Instal­la­tion began in Novem­ber 2019, with field tri­als con­tin­u­ing since then. “Ini­tial results look promis­ing in reg­u­lat­ing the volt­age across the LV feed­ers with­in the pre­scribed lim­its,” says But­ler.

A SET-AND-FORGET SOLUTION

The ECOTAP® VPD® is installed on the high­voltage wind­ing of the trans­former and includes a mea­sur­ing device that mon­i­tors both cur­rent and volt­age on the low­voltage wind­ing and auto­mat­i­cal­ly changes the tap ratio if the volt­age fluc­tu­a­tions move beyond the pre­de­fined lim­its.

“It was impor­tant for us to find a set­and­forget solu­tion to our prob­lem,” explains Butler—in oth­er words, a solu­tion that only needs to be con­fig­ured once and can then be left alone and does not require con­stant drain on tech­ni­cal resources to re­study the issue. The sheer dis­tance across which net­works in Aus­tralia tra­verse means that a cen­tral­ized solu­tion is not pos­si­ble. “With around 1.5 mil­lion dis­tri­b­u­tion trans­form­ers across Aus­tralia, 90 % of which are pole­mounted, this would cause prob­lems,” states Dr. Thomas Smol­ka.

The auto­mat­ic reg­u­la­tion func­tion of Tap­con Dynam­ic Set­point Con­trol (TDSC) par­tic­u­lar­ly appealed to West­ern Pow­er: With the aid of volt­age and cur­rent mea­sure­ments, the mag­ni­tude and direc­tion of real and reac­tive pow­er flows can be deter­mined and the posi­tion of the on-load tap chang­er is then auto­mat­i­cal­ly adjust­ed.

As a result, volt­age drops and the high­er line volt­ages expe­ri­enced when large amounts of PV pow­er are sup­plied can be com­pen­sat­ed. In the first test run, the VRDTs were still linked via the DNP3 com­mu­ni­ca­tion pro­to­col to the con­trol room (CONTROL PRO), which enables the data to be read out and the sys­tem to be con­trolled remote­ly. “We will see whether this will con­tin­ue to be nec­es­sary in the future,” says But­ler.

FIT FOR A MORE SUSTAINABLE FUTURE

The test peri­od is set to run until June 2021 but West­ern Pow­er is hope­ful with the results achieved to date: “With the reg­u­lat­ing ECOTAP® VPD®, we have poten­tial­ly found an effec­tive lever to use in our suite of solu­tions to help us man­age our net­work,” states Mariza But­ler.

So the com­pa­ny can rest easy in the knowl­edge that it is well equipped to deal with a future in which elec­tric cars and home-based ener­gy sup­plies are sure to cre­ate fur­ther new chal­lenges for elec­tric­i­ty grids. “We are total­ly com­mit­ted to doing our bit for cli­mate pro­tec­tion,” states But­ler. “And the VRDTs using MR tech­nol­o­gy make it much eas­i­er for us to achieve this goal.”

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YOUR CONTACT

Want to know more about the ECOTAP® VPD® in Aus­tralia?
Dr.-Ing. Thomas Smol­ka is here to help:
T.Smolka@au.reinhausen.com