Distribution-connected generators in Ontario can expect to hear from Hydro One shortly about something called LVRT, or “Low Voltage Ride-Through.” Although the term may be unfamiliar to most people, it’s a safe bet that generators are going to hear a lot more about it in the near future.
LVRT is a set of capabilities that allow generators to assist with stabilizing the grid when there are unexpected drops in voltage. As more generators connect to the distribution system, the importance of having LVRT capabilities has grown because distributed generation can be both a source of grid disruptions and assist with mitigating certain kinds of grid problems. In some cases, the offering of LVRT may become marketable commodity, whereas in other cases it may be a reliability or contractual requirement. Larger generators have provided LVRT to varying degrees over the years, but only recently are grid operators starting to look to distribution-connected generators for the same kind of service.
The North American Electric Reliability Corporation (NERC), the body that oversees reliability standards in North America for transmission facilities above 100kV, has been assessing LVRT for several years. Planning Standards (TPL-001-2) requires tripping of generators where simulations show generator bus voltage or high-side of GSU voltages are less than known or assumed generator low voltage ride-through capability. The NERC PRC-024-1 standard, currently under development, is another example of LVRT specifications, albeit designed for transmission-connected generators. Interested parties can find more by Googling “NERC PRC-024-1.”
Jake Brooks of APPrO observed that this development is a concrete indication that Hydro One and other grid operators are carefully assessing such issues. He said, “[T]he provision of these kinds of services by generators can be expected to lead to a more reliable, responsive, flexible and efficient grid.” He cautioned however that generators may need to be careful about unintentionally making statements that could be interpreted at a later point as some kind of assurance that they will provide these kinds of services without specific compensation.
At this time Hydro One is not aware of any jurisdictions that publish LVRT requirements for generators less than 10MW. However, the IEEE 1547.8 working group is currently investigating LVRT requirements for these generators, and if the IEEE standard changes, many people expect that Hydro One, other distributors, and their counterparts in other jurisdictions will adapt to these changes. They are being proactive by collecting information and raising awareness about the issue at this stage.
There is a wide variety of potential LVRT schemes. Any particular LVRT standard might, for example, establish predetermined time periods for which a generator must be able to stay connected during low voltage conditions, the types of conditions and frequency ranges that should be tolerated, and so on.
To collect information that will help it prepare for upcoming discussions involving NERC, IEEE and other bodies, Hydro One has agreed to survey its distribution-connected generators to assess generator capabilities for LVRT. Each connected generator has an account manager at Hydro One who will likely be the primary point of contact for questions about the survey. The following are examples of some of the areas in which Hydro One expects to seek information from generators:
• Is your generation facility capable of any sort of ride-through?
• If so, is it a standard feature or an optional extra?
• Does your facility comply with any specific ride-through requirements (curves) or can they be customized upon request?
• What is the range of options available in terms of what the current configuration of equipment can do during a contingency (fault, low voltage, or low frequency event):
• Do nothing until the grid recovers and then be available to supply power immediately?
• Support the grid with some level of real power?
• Support the grid with some level of reactive power?
• Is continued provision of ride-through capability expensive?
• Would an assured ride-through service interfere with the generator’s anti-islanding protections?
Hydro One is targeting to have the survey in circulation around the end of January, roughly when this issue of IPPSO FACTO is expected to be printed. For more information please contact
Low Voltage Ride-Through
What is it?
Low Voltage Ride-Through is a control strategy that requires generators to remain connected to the grid during certain power system contingencies. In particular, a Low Voltage Ride-Through scheme requires a generator to remain connected for a pre-determined time-period given particular power system voltages and frequencies that are outside of the nominal values.
Why does Hydro One require information?
Hydro One is currently investigating Low Voltage Ride-Through for its transmission and distribution systems. This investigation requires technical study and simulation, and generator capabilities are one of the inputs to this study.
Why is Low Voltage Ride-Through becoming a concern in North America?
Increasing cost and regulatory pressure has made it more difficult to maintain acceptable system power flows during every operating condition. There is a need to investigate the utilization of existing and planned generation that may help maintain or improve system stability during and after certain contingencies.
How would collection of this information eventually benefit the generators, the system and Ontario?
Generators may benefit from Low Voltage Ride-Through because it allows them to remain connected to the power system during certain power system contingencies. The power system, and therefore Ontario benefit because Low Voltage Ride-Through may improve system reliability and stability.