LESS THAN STANDARD SEPARATION BETWEEN 2 ACR. OPERATIONAL ERROR.

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I WAS WORKING THE ZID HI RADAR SECTOR (FL240/310). ACR X WAS TURNED OVER TO MY FREQ AT FL330 APPROX 5 MI NE OF VHP; VIA VHP; FWA; DTW. OUR LETTER OF AGREEMENT WITH ZAU REQUIRES THAT DTW LANDERS BE LEVEL AT FL290 25 MI SW OF FWA. FWA VOR WAS OUT OF COMMISSION. I WAS ALSO WORKING ACR Y WBOUND VIA ROD; CAP; MCI; AT FL310. ACR Y WAS APPROX 30 MI NE OF VHP; WBOUND. I OVERLOOKED ACR Y WBOUND AT FL310 AND DSNDED X TO FL290. ABOUT 50 SECS LATER I RECOGNIZED MY ERROR AND INSTRUCTED X TO TURN 30 DEGS LEFT AND STOP HIS DSCNT. HE ACKNOWLEDGED. I THEN INSTRUCTED Y TO TURN IMMEDIATELY LEFT TO A HDG OF 180 DEGS. NO RESPONSE. I AGAIN INSTRUCTED Y TO TURN IMMEDIATELY LEFT TO HDG OF 180 DEGS AND DSND TO FL290. HE ACKNOWLEDGED. I WAS TALKING TO 7 ACFT ON FREQ. 4 WERE ON RADAR VECTORS; 4 WERE DSNDING AND 1 WAS ON SPD CONTROL. THERE WERE 15 DATA BLOCKS ON MY RADAR. TFC HAD BEEN BUILDING JUST PRIOR TO THE INCIDENT AND WAS BEGINNING TO TAPER OFF. THE ANGLE AND CLOSURE RATE OF THE ACFT PREVENTED ME FROM KEEPING 5 MI SEP. THE THING THAT I WOULD HAVE DONE DIFFERENTLY OTHER THAN RECOGNIZING THE TFC OF COURSE WOULD BE TO HAVE CALLED FOR A TRACKER (AN EXTRA PERSON) FOR HELP (OR ANOTHER PAIR OF EYES TO HELP MONITOR THE SITUATION). CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR GAVE TYPES OF ACFT. THEN WE HAD A LONG CONVERSATION REF THE PROBS IN THE NAS TODAY. HE CITED THE MANY TYPES OF COMS PROBS THAT HE ENCOUNTERS DAILY. THINKS PLT EXPERIENCE LEVEL IS MAJOR FACTOR IN POOR COMS. HIS FAC HAS RECEIVED AND IS DISSEMINATING INFO REF FAA/INDUSTRY COM AWARENESS INITIATIVE.