Differential Trip (Device 87) 4160vac 6 Gen Parallel System
Differential Trip (Device 87) 4160vac 6 Gen Parallel System
(OP)
Six Generator Detroit Diesel(1750Kva units) 4160vac ASCO system carrying building load varying around 6000Kva. One unit trips 86 lockout from 87 device. Flag on 87 fires so it is not control circuit issue. Will stay on bus at lighter loads but right around this level it trips. Swapped Relay, relay case and reactor unit and it still trips. Put same parts in other generator and they work fine. Testing firm tested all CT's, meggered the cable and local disconnect switch, all good. 3ph Current looks correct on ASCO EDGEWISE meters. Also swapped SR voltage regulator, no change. Rotating rectifier is good. I have HIOKI and a Dranetz Power Analyzer (old monster). Any ideas! I have 3 years of BSEE but didn't finish 4th year. Vectors stuff is not my strong suit. Now I will say "HELP". Uses cross-current CT's on B phase aloso.....






RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
Just testing the CTs individually won't find a mistake in connections. Same with the relay.
regards, rasevskii
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
These BBC relays are old analog type, there are no reports.
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
Ideally a 3 phase SC test should be done using the generator as a source to verify all the CT circuits. Probably beyond the capability of the available personnel. A separate excitation of the exciter field from an external DC source needed. Should have been done at the original commissioning but who knows what was done 20 years ago...
IF you disable the relay and actually have a fault, it will get very ugly, with possible severe damage. High Short Circuit power. Some severe Legal and possible Insurance issues.
Get a professional in to survey the situation and advise your organization.
regards, rasevskii
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
And regardless of the control scheme of the other generators, If you can run the governor in manual mode you can control the loading. With the governor in manual mode the load on the machine under test will be determined by the throttle setting. If the building load varies, the other machines will automatically adjust their throttles to compensate leaving the load on the machine under test unchanged.
As long as the building load does not drop below the loading of the machine under test there should be no problems. An easy and safe way to load the machine is to put the governor in droop mode and then adjust the frequency slightly. Then, should the building load drop below the setting of the machine under test, the frequency will rise slightly.
With a building load of 6000KVA available you should not need a load bank to load test a 1750 KVA machine.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
that would be effectively a shorted secondary.
If these are the old BBC mechanical relays, please be kind to them, they are irreplaceable and out of manufacture for years.
Such good things will never be made again. Maybe in India?...
rasevskii
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
Muthu
www.edison.co.in
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
I stock hundreds of these, so they are still replaceable, same goes with the powershields.
A simple test using something like a MS-1A will verify operation.
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
I agree with rasevskii, use the machine as its own primary injection set. 1750kVA won't need even particularly heavy shorting links.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Differential Trip (Device 87) 4160vac 6 Gen Parallel System
Hope that helps,
Mike L.