Questions about MIG-21Bis electric system

[rocaf2003]

Hello,I saw the manual states that the MIG-21Bis has three inverters (PO750 No.1,2,emergency) and three electrical buses(electrical bus No.1/2/3).Is there a corresponding relationship between these inverters and electrical buses?For example, Does PO750 No.1 inverter correspond to No.1 electrical bus, PO750 No.2 inverter to No.2 electrical bus, and the emergency inverter to No.3 electrical bus?Apperciate for any reply!