by Stephen Kishewitsch
A collaboration between faculty from two of Ontario’s universities, Ontario Centres of Excellence (OCE) and OPA, Hydro One, First Solar, London Hydro and Bluewater Power, promises to allow more renewables to connect to the grid, improve power transmission limits, and provide a low-cost way of improving grid stability. It is also an example of how Ontario’s burgeoning innovation network is creating technological solutions and higher value to Ontario’s economy. The $6 million project, titled “Large-Scale Photovoltaic Solar Power Integration in Transmission and Distribution Networks,” is a year into its three-year term. The universities involved are the Universities of Western Ontario and Waterloo.
Ontario’s power system faces two pressures, one a more or less permanent condition and one recent: ever-increasing demand (though held in abeyance in the last couple of years by financial conditions); and a policy direction away from centralized, polluting and carbon-intensive forms of generation and toward more dispersed, cleaner, renewable-source generation. Both of those have far-reaching implications for the operation of the grid: the need to deliver more power over existing corridors, and more recently the need to move it in two opposite directions on the same line. This latter can affect power stability on a distribution grid, as for example when a solar or wind farm on a distribution line wants to send more power into the line than the load on the line can use.
The traditional way to deal with increased or changing demand on the grid is to build new lines – expensive, administratively complicated and time-consuming. Newer, smarter technologies are finding ways of driving more power over the same lines – much cheaper, simpler, and faster. The flexible alternating current transmission system, FACTS, is the umbrella term for such devices. FACTS itself is not terribly new – the Electric Power Research Institute published a manual on it in 1994 – but FACTS devices are still relatively few in number worldwide. Ontario has begun installing one type, the static VAR compensator (SVC), on a few of its lines, to maintain voltage and improve reliability (see the February issue of IPPSO FACTO, page 20), but such devices, at the transmission scale, cost in the low millions. This is still a bargain, compared with the roughly $2 million per kilometre for a new line, but a research collaboration in Ontario is proposing a much simpler and cheaper solution: implementing new technology on the inverters on each of the solar farms that are being built in increasing numbers under Ontario’s Green Energy Act and Feed-in Tariff. Individually they’re too small to control the fluctuations on a transmission line, but there are lots of them, and they have spare capacity to condition power on the line, including power that isn’t being produced at the installation itself.
The issue, and the opportunity, arise when power from a wind farm on a distribution line exceeds demand on the line. This is especially likely at night, when load drops but the wind can pick up. This can create substantial voltage fluctuations, not only on that line but also on all the others connected to the same substation. Indeed, it’s that possibility, identified in the required Connection Impact Assessment, that can often result in a project being rejected. What Dr. Rajiv Varma’s research team at the University of Western Ontario has proposed is that when new technology is implemented with the inverters already installed at a solar farm, for example, in addition to conditioning their output to the grid, the technology can also provide power conditioning to the line they’re on – even if the power isn’t coming from that particular farm. In fact, the surplus generation can be on another distribution line entirely, as long as both are connected to the same substation.
Dr. Varma explains: each FACTS device uses an inverter, with an associated controller, a circuit board about the size of a computer motherboard, plus software. Their project is developing a new form of paired hardware and control programs that will allow the PV farm inverter to regulate power on the line, at much lower cost – thousands, rather than millions, he says – than devices currently in use.
London Hydro has offered to showcase the technology on one of its lines. Bluewater Power in Sarnia is also interested in hosting a trial. Hydro One, as the largest distribution service in the province, is obviously interested. London Hydro and Bluewater Power have agreed to supply the inverter. The Western research team led by Dr. Varma will develop the new control circuit and software within the next six months. Monitoring and testing will follow shortly thereafter.
The novel device will have two related effects: voltage regulation on the line, and as a side effect, improving transmission capacity. However, the team is also designing a second controller to be added to the first that will directly improve transmission limits. The group’s simulations find that for a typical transmission system, a 100 MW solar farm located in the middle of the line could improve transmission capacity at night by at least 150 MW. The group has applied for two US patents, to cover the two innovations. The next step will be commercialization (see “Take your idea to MaRS,” page 26).
Further work will augment the controller on a windfarm to the same purpose, of providing the line with voltage control and a transmission limit increase.
The savings in avoided new construction promise to be considerable. The new control system for the inverter – which a commercial solar farm must have anyway – should cost about $ 50,000, Dr. Varma estimates. That’s compared to a cost at least in the low millions for a purpose-built SVC or STATCOM, or $50 million or more for a Unified Power Flow Controller, which combines voltage control and transmission augmentation in one package.
While they are beginning with the distribution system, the partners expect the larger benefits to be applied directly to the transmission system. Currently solar farms are allowed to control voltage on a distribution line, but not a transmission line. The partners have requested the IESO and Hydro One look at relaxing that code to allow the technique to be tested on a selected transmission feeder or two as well. Then a 20MW solar farm could provide voltage regulation service for a large windfarm in the 100 MW range, both connected directly to a transmission line. Similar wind turbine generator technologies for protection against faults are underway in Germany as well.
The research is being fostered by a burgeoning network to support and commercialize innovation like this in Ontario. See “Ontario’s innovation network ,” in the online version of IPPSO FACTO.
Pushing the limits
The electricity grid faces several limits on the power it can carry, each one more constraining than the last. Professor Rajiv Varma, an expert on transmission technologies at the University of Western Ontario, lists four constraints: the thermal limit, a steady-state and then a transient stability limit, and an electrical damping limit. Each further limits the power that could potentially be sent over the grid without driving it outside the reliability limits that Ontario has committed to.
As Dr. Varma explains it, there are two related technological routes for dealing with such constraints – one will increase the amount of power the line can handle, while at the same time containing the increased oscillations that would arise, while the other does the same thing, but in reverse: it offers direct control of the potential voltage fluctuations, with the added benefit of increasing the linepower transfer limit. Series-connected devices, like Thyristor Controlled Series Capacitors (TCSC) and Static Synchronous Series Compensators (SSSC) fall into the former family, parallel-connected Static Var Compensators (SVC) and Static Synchronous Compensators (STATCOM, aka D-VAR) into the latter. Hydro One has begun installing SVCs on some of its lines. For further background, please see the February issue of IPPSO FACTO, pages 20 and 26, on the Static VAR compensator. There is also the Unified Power Flow Controller (UPFC), which incorporates both types, but at a hefty cost – over $50 million, says Dr. Varma, and there are only three in the world.
At the moment the industry is moving mostly to using SVCs, and to a lesser extent the STATCOM, which operates even faster but costs a bit more. There are no STATCOM devices on transmission lines in Canada. However, on a smaller scale there is one regulating the output of a windfarm in Goderich. More frequently, windfarms use SVCs to connect to the grid – already there are at least thirty in the world, by Dr. Varma’s count. Either will do.
For other articles in this feature, see the following related stories:
• Ontario research companies taking on the world
• Feature interview with Tom Corr, the new President of OCE
• Ontario Centres of Excellence - ready to respond
• Ontario’s burgeoning research infrastructure
• Stories on the MaRS centre , Making the grid even smarter and biomass work at Atikokan