Three Examples of MV Wiring in PV Power Systems

EXAMPLE 1: MV Wiring Used for Long-Distance Inter-connection

This is a single-line diagram of a 300 kW PV system installed at an agricultural site. The array and inverter are located approximately 2,000 feet from the 3-phase 240 Vac premises wiring. Because of the long distance and the low interconnection voltage, MV wiring is used in the inverter output circuit. The inverter produces a 480 Vac output, which is stepped up to 12.47 kV via a pad-mounted distribution transformer. A 12.47 kV feeder is run underground via MV cable to the interconnect point, where it is stepped down via a second pad-mounted distribution transformer to the interconnect voltage of 240 Vac.

EXAMPLE 2: Simple MV AC Collection System

This is a single-line diagram for a 2 MW PV system at a university campus. A pad-mounted transformer is installed adjacent to each of the six inverters to step the inverter output voltage up to 12.47 kV. Two MV collection circuits are used, each with three loop-feed transformers. The feeder circuits are collected at a lineup of 12.47 kV metal-enclosed switchgear that provides fused disconnecting means for the collection circuits and energy metering for the PV power plant. A single PV plant output feeder is routed from the switchgear to the point of common coupling, which in this case is the campus’s primary metered 12.47 kV distribution system.

EXAMPLE 3: Utility-Scale MV AC Collection System

This is a theoretical example of a MV collection system for a 20 MW utility-scale PV power plant. Twenty 1 MW inverter skids are distributed throughout the array field, each with a MV distribution transformer that steps the inverter output voltage up to 34.5 kV. Three ac collection circuits are routed back to the MV metalclad switchgear. A single output feeder is routed to a substation transformer that steps the interconnection voltage up to 69 kV.

resources : SOLAR PRO NOV/DEC 2018 Optimal Design, Installation & Performance