LOST OF SENSING ISSUE DECS-200 1

[brunogt5]

HI THERE, OUR BEST REGARD;

FIRST, SORRY FOR OUR BAD ENGLISH, WE ARE A TROUBLE WITH OUR DECS-200. WE HAVE A 4.6 MW GENERATOR, WHEN WE GIVE THE STOP COMMAND, 3 SECONDS LATER OPENS THE GENERATOR'S SWITCH THEN APPEAR ON SCREEN VOLTAGE MATCHING,OF COURSE, THE GENERATOR VOLTAGE DECREASE AND 2 SECONDS LATER APPEAR "LOST VOLTAGE SENSING" ALARM AND TRIP 86E TROUGH RELAY 3 BECAUSE WE SET SO. OUR QUESTION IS WHY APPEAR THAT ALARM WHILE GENERATOR IS STOPPING, AS SOON AS STOP, WE RESET AND EVERYTHING TURN INTO NORMAL, IN NORMAL OPERATION THE DECS-200 WORKS ON PF CONTROL AND DOESNT TURN TO FCR IF LOST OF SENSIG OCURRS. PLEASE HELP US

 

[catserveng]

Sounds like you may be going back into START mode after STOP command is given then removed. It also sounds like you have the box checked in the programming that pushes the DECs into FCR mode when it sees a loss of sensing. Most likely it is something with the sequencing of the digital control inputs.

Probably your best bet is to setup your datalog to watch the control inputs, and then review it to see what is coming back in. The DECS is a very capable regulator, but with all of its features, sometimes is hard to get it setup to meet your needs.

Is this a new unit startup? Or an existing unit that worked ok before and now appears to have a problem?

Hope that helps, Mike L.

 

[brunogt5]

Thanks Mike for your fast reply, Our unit is an existing unit, and this problem is a new problem too, we are going to setup our datalog to see what's going on if were loosed wire we should have trouble during operation (FCR mode)and only appear during stopping, we command this unit remotely and we have to reset 86E everytime gen stop. I first tough that the stop command is not given (False contact) thats why DECS keep running and detects low voltage and trip the unit, we really appreaciatte your help and if you have more information that's great before put hand on our DECS.

 

[brunogt5]

HI Mike I would like to give you more information that I justo found, when alarma shows up, 6 seconds later the DEC turn to AVR (auto) mode,I notice that appear and desappear these alarmas too: "Under frequency" and "sistem below 10 Hz", When Unit stop completely, shows unit is off, by then, those alarms are gone but LOST VOLTAGE SENSING is staying until reset.

 

[catserveng]

Based on what you're describing, it sounds like you are shutting off the DECS after the unit is stopped. Ideally, as soon as you issue a STOP command to the generator, you should also issue a STOP command to the DECS, and not assert the Start command until the unit is above the cutoff frequency. Since this is a new problem on an in service unit, was something done to change how the start/stop sequence operates?

On many units I work on, we only issue a stop command to the DECS when we have a fault, usually tied to the 86 lockout. This is mainly on smaller (1-2MW) standby units and we don't program the DECS to do any protection, we let the protective relaying handle it. Otherwise it stays in START all the time and when unit speed gets above the cutoff frequency it ramps to rated and builds voltage quickly. You may or may not consider this depending on how well your protective relaying is setup.

Hope that helps, Mike L.

 

[squeeky]

Dear Brunoqt5,

We have a policy to run the generator into reverse power mode and trip on our protection relay which is set at 2%. This ensures that the reverse power is operational and opens the contacts at minimal current. This would disable the alternator in line with your protection policy.

I am assuming you are refering to the DECS 200 from Basler.I agree with the above comments that it is a very good and veritile unit. There are two sets of contacts; A33 and A34 (Parallel) and A35 and A36 (VAR)

Using combinations you can get different control modes.

In my manual it is on page 5-31.

If you are running with other generator you should be in droop mode. 52L/M open and 52J/K closed. If you are running with the utility, 52L/M open and 52J/K open. If you are running as a single unit, 52 L/M Closed and 52J/K closed. The status comes from the breaker auxilieries and feed into the contacts.

Your 86E is a lock out which should have a requirement for human intervention to reset.

Good luck

 

[brunogt5]

Dear catserveng and squeeky,

I really appreaciatte your help, you gave me tons of ideas of what the problem could be, let me tell you that i got it fixed, the DECS it was not receiving stop command trough a N.C. contact when we were stopping, a contact that is supposed to close when the main switch is oppened it was not doing so, the contacts A23 and A24 (STOP) kept opened, we cleaned the contacts, test and since now on, everything turned to normal.