My church constructed one of the last PV solar projects in Indiana to receive net metering certification before the legislative door closed on December 31st, 2017. As the lone, gray-haired circuit board designer in this technology-averse congregation, I got tapped to work with the church's solar contractor. I'm a great single phase switch mode power supply designer but my knowledge of upstream AC power distribution is limited.
The church's project was a 33kW array with three phase 208V outputs from three string inverters.
At the 11th hour the local utility asked that our contractor install a grounding transformer and reactor between their 3 phase 120/208V pole drop and our solar inverters. Our contractor, who was not as technically adept as we had assumed at the time the purchase order was issued, asked why. The utility basically answered "do it...it's not our job to educate solar contractors on matters they are required to understand...".
Some political wrangling ensued, with the result that the church (and I) accepted on faith that a grounding transformer was technically necessary and that the utility's request for one was not a ploy to run out the net metering clock.
Can readers in this forum steer me to reading materials on the internet that talk about isolation requirements for PV arrays? Why is our neighborhood 208V 3 phase grid threatened by 11kw inverters injecting their power in delta configuration rather than the utility's preferred wye configuration? What is the role of the reactor used in conjunction with the isolation transformer?
The array is now up and running and we are harvesting 200kWH+ of energy each day. Thanks in advance for your advice on this topic.
The church's project was a 33kW array with three phase 208V outputs from three string inverters.
At the 11th hour the local utility asked that our contractor install a grounding transformer and reactor between their 3 phase 120/208V pole drop and our solar inverters. Our contractor, who was not as technically adept as we had assumed at the time the purchase order was issued, asked why. The utility basically answered "do it...it's not our job to educate solar contractors on matters they are required to understand...".
Some political wrangling ensued, with the result that the church (and I) accepted on faith that a grounding transformer was technically necessary and that the utility's request for one was not a ploy to run out the net metering clock.
Can readers in this forum steer me to reading materials on the internet that talk about isolation requirements for PV arrays? Why is our neighborhood 208V 3 phase grid threatened by 11kw inverters injecting their power in delta configuration rather than the utility's preferred wye configuration? What is the role of the reactor used in conjunction with the isolation transformer?
The array is now up and running and we are harvesting 200kWH+ of energy each day. Thanks in advance for your advice on this topic.
