Voltage Management in Electricity Distribution
Managers of electricity distribution networks strive for the best levels of system reliability consistent with best practice benchmark standards. An important part of system reliability is power quality, and an important part of power quality is maintaining the steady state voltage limits of 230 ±6% defined in the NZ Electricity Safety Regulations. The regulations mandate compliance at electricity consumers “point of supply”, which for most sites is on the low voltage (LV) network.
There are several industry changes that are presenting challenges for maintaining good power quality, namely:
· Introduction of distributed energy resources or DER. DER systems both create higher voltages on the LV and are very sensitive to existing high voltage issues.
· Increasing load, from the normal new network growth and from electrification of transport and process heat. Increasing load can cause the connection voltage to fall below the required limit.
With both the over-voltage and under-voltage limits being tested, it is a prudent time for EDB’s to review their voltage management processes and standards and to explore innovative planning solutions. Smart meters offer the opportunity to increase the visibility of the LV network and provide new control methods.
Managing voltage levels across a network involves many aspects, however, it is useful to group the tasks into, identifying non-compliance and designing solutions.
1. Identifying non-compliance (constraint identification)
The focus of this activity is identifying and prioritizing non-compliant voltage. Non-compliance generally occurs due to a deviation from the original design, normally due to new connections or other network load increases. A voltage will only be non-compliant if it breaches and EDB’s power quality service levels which are based on the applicable New Zealand standards. Voltage breaching the planning limits is not a non-compliance.
Traditionally, non-complaint voltage was identified by power quality complaints or HV network studies. Smart meters and other network data loggers now offer a far greater visibility. Constraints can be prioritized by creating cost risk models representing the relative extent and severity of the problem. Constraint identification can be further broken down to:
· Existing constraints: these are existing voltage issues currently being experienced by energy consumers.
· Constraint forecasting: involves forecasting of over-voltage and under-voltage issues based on load growth, introduction of DER and network reconfiguration.
2. Designing solutions
When voltage compliance issues are discovered and prioritized for remediation, a network planner will look at options to remedy the constraint. With the preferred option selected the project will progress to design and if network solutions are needed this new network is built according to a standard. Customer-initiated and renewal projects are also designed to this same standard.
Designed solutions should consider not only the existing load and configuration but also account for a likely future state. This is because retrospective upgrades are often an order of magnitude more costly than adding more capacity at install. Two of the ways of achieving this are planning limits and demand estimations.