Power Generation: Product Operation and Maintenance

[bashar]

If any body could help out it would be highly appreciated

Our power synchronizing system consist of  four old generators  island group mode   "Caterpillar "  engine model 3516 1303 KVA ,1024KW, 480V ,60HZ ,1200 rpm each is occupied by 2301  electronic speed controller and load sharing with following part & serial numbers

Gen set No 01  type number 9905-68JL ,serial number 2375147

              No 02 type number 9906-061 ,serial number 2603064

               No 03 type number 9905-061 ,serial number 2603059

             No 04  type number 9905-061 ,serial number 2603060

  Due to power demand increasing and bad condition of one of a/m gen sets we decided to replace it,So  we bayed new gen set  Caterpillar Engine model 3512 1418KVA 480V 60HZ 1800 rpm is accommodated by the same speed controller  2301 part No 9905-018 REVH ,Serial No 17618816,by rehabilitation new gen set instead of  old one and made all necessary connection and adjusting  all parameters related to sync & load sharing of the new controller to be same as the existing group  (Load gain ,Speed D droop) ,Then dedicated new set as a first priority and started system  and here is our finding

1- New gen set which has been assign as leader start and run smoothly and individual ACB close to dead bus bar all parameters are OK (volt ,current ,Hz,...etc)

2-Second gen set start ,run,synchronize with line and close circuit breaker for few second and then ACB trip due to reverse power fault hence  the gen set  act as motor and consume power (real power,PF are  minus)  never the less the Syncroscope was running clockwise direction which means clearly that the incoming set speed higher than on line set's speed .

Same scenario  occurred when we tried to exchange  leader set between new gen set and one of old sets 

If more symptoms or information's it may be required for complete analysis please let me know 

Best Regards .

[RM_FNTS]

How much wiring was involved in replacing the 2301 LSM on the new unit?

Two possibilities to start with.

First ensure that the load share lines are connected properly, if the wires are reversed it will cause your issue. One way to verify this is to put one unit on the bus and put some load on it, 25% will work.

At each of the units not on line measure the voltage on the load sharing lines. It should be the same level and polarity as the unit on-line. Do this for each unit.

Make sure all CT and PT wiring is correct and the CT polarity is as specified in the manual.

Have you made the necessary adjustments to the voltage regulator?

[bashar]

Thanks for your interesting and kind reply

Level and frequency at same level and all synchronizing condition are OK since the two generators (old |& new) go through synchronizing and problem appear when load share start even if we start without load where active power switch from on to another and load factor become leading in one and lagging in the other one while volt, frequency and current are same for two generator and synchronize pointer keep steady the difference are only in real power ( one generator acts as generator transfer power to second generator which acts as motor )

[RM_FNTS]

Did you verify the load share line polarity?

You are experiencing circulating currents.

Because two generators are connected together on a low resistance buss, voltage and frequency will be the same on the two machines. Current will be the same because one is generating current and the other is absorbing it, current metering is not directional.

Circulating current in this situation can be caused by two things

1 Incorrect speed bias

2 Incorrect voltage bias

To confirm that the 2301 has control over the speed of the machine you need to turn the "Rated Speed" potentiometer. The machine should follow the adjustment. Turning clockwise should raise speed. Counterclockwise should lower speed.

This MUST be confirmed before proceeding.

Next: as stated in the previous post you need to verify that the load share lines are connected correctly.

If they are reversed it WILL cause your issue.

As far as voltage control goes I assume you are operating in a voltage droop mode.

Have you confirmed that all regulators are correctly set up for droop?

[njc1979]

Move this post to the proper area of the forums- more ppl may comment on this..

[kc]

From what you are describing, I am not certain it is circulating currents.  If your kvar is extremely high it may be a pitch issue with the newer generators windings not matching the existing.  From what you initially discribe I would check your droop settings for speed and voltage.  Matching setting would not give a desirable outcome since your new generator has a greater rating.  You would have to set them up for proportional load sharing vice equal load sharing. 

[see-deif]

All suggestions above are valid. I will summarize and add some:

1. wiring issues.

   a. Load share line polarity.

   b. I would add -- CT/PT wiring / polarity and sync scope wiring, as needed / if changed.

2.  Setup

  a. droop, KW and KVAR. Good ideas, all. I would add Regulator Settings. Due to having 6 pole and 4 pole machines, you will need to tune them up carefully. They should each be tuned into load bank or the same load, step the regulators, measure the responses, tune them the same. (setting the same PID/gain values will NOT be enough) These different machines will have different response times, KW and KVAR, and the regulators SHOULD be able to compensate. You might have to slow everything down considerably to ride-thru load acceptance and load rejection testing. That is, you might get it working for awhile, but sooner or later it will trip due to response times being different during transient conditions. Not sure if the old 2301's have all 3 parameters: P, I, and D.

  b. generator pitch. you are paralleling a 6 pole machine with a 4 pole machine. My first guess would be this. If the pitches are not the same, the same symptoms would result. You can sometimes use a transformer to hide the problem by dissipating the reactive power due to circulating currents, but you never "fix" this problem.

  c. nominal values / regulator settings.  

Do you know it is a reverse power trip and not a reverse var trip? Or an overcurrent trip? What is the configuration of the system? Y or Delta? Solidly grounded or iimpedance grounded? Has there been a power system study?

And remember lightly loaded or no-load running conditions are some of the most difficult. In addition to the tight speed regulation, the generator is inherently unstable in those conditions. Maybe if you could add some load banks during testing, it might settle out some.

Good luck

Steve