Triangle shaped with lights moving slowly, no sound

I was watching what I thought was a helicopter hovering over an electrical substation above one mile or less from my front yard. I watched and watched and it didn't move but stayed where it was for approximately 20 minutes, then moved very slowly to the northwest. It was triangle shaped with lights all around, white, red and green lights, it was not a helicopter nor was it an airplane. It went straight over the top of me standing in my front yard, thee was zero sound. It moved slowly until it disappeared over the hills. I had heard before of aircraft-like visitors hovering above the substations but that was first one I had seen.
Date is uncertain.