The AMSC D-VAR® VVO STATCOM is a dynamically adjustable resource for injecting or absorbing reactive current on distribution feeders. This provides a new tool for distribution planners to meet a variety of objectives related to feeder optimization:
1) Voltage Management:
- Maintain a flat voltage profile across the feeder
- Avoid rapid voltage changes
- Stay within appropriate voltage range
2) Maximize the useful life of existing assets:
- Reduce LTC/Regulator operations
- Reduce Switched capacitor operations
- Defer or avoid large capital projects for voltage management
- VVO in lieu of reconductoring long circuits
- VVO in lieu of Substation relocation
3) Meet efficiency, power quality and renewable energy objectives:
- Reduce reactive demand at distribution substations
- Enable Conservation Voltage Reduction Schemes
- Enable use of circuit ties constrained by voltage stiffness
- Replace harmonically resonating capacitors
- Increase Distributed Energy Resource (DER) hosting capacity
In general, feeders that are not meeting voltage management objectives are candidates for the VVO. The following are some identifiers:
- 11kV Distribution circuits supplied from weak 22kV or 33kV sub-transmission or small power transformers
- Long feeders, particularly those with more than two stages of regulation or low ampacity conductor
- Feeders with load growth concentrated near the end of the main line
- Feeders with high penetration of variable renewables like wind and solar
- Regulators experiencing maximum boost or boost or excessive tap changes
- Problems managing average power factor on the circuit using only discrete capacitor sizes
The VVO placement strategies can be summarized as follows:
1) Consider placing a VVO approximately 2/3rds of the way into a regulator’s regulation zone (replacing or supplementing capacitors located nearby)
2) If more than two regulators are in series, consider replacing any additional downstream regulators with VVOs.
3) Rather than focusing on conductor types, evaluate fault power to identify VVO locations. In general, VVOs can have a meaningful impact on voltage where fault power is below 50 MVA (refer to Figure 3).
4) Design the total capacitor and VVO capacity to roughly equal the maximum reactive power demand on the circuit. For instance, a circuit that peaks at 12,000 kVA @ 94% PF will require approximately 4,000 kVAR in compensation which can be provided from two 900 kVAR capacitors and two three-phase VVO units distributed across the feeder.
5) Consider placing a VVO near any variable generation that is causing increased regulator or capacitor switching or persistent high voltage.