SYNCHRONIZING

For what you are trying to do do not worry about cross current compensation.. Put the system in manual and increase the speed on the machine with the less load until the current matches, this in turn will cause whatever synch check feature you are using to allow circuit breaker closure.. You also need to match the voltage on the two machines so the vars (reactive power) do not go crazy..

The cross current CTs must be connected in series, and should be switched in upon circuit breaker closure. If you do not plan on running the machines in parallel for extended periods of time cross current compensation is not necessary..

The 1 amp and 5amp CT connections on the regulator will differ the sensitivity.. The CT you are using more than likely has a five amp secondary if you are in the states. Europe generally uses 1 amp secondary CTs..

From a person who does this for a living, for 34 years and an ex Cat field service person:

1) Speed adjust, once paralleled, balances load (Watts). If you don't have a watt meter, use turbo boost pressure as a rough guess of how much load is on each machine.

2) Once paralleled, voltage levels balance the amps and VARs (indicated in amps).

So depending on the governors you have, your extra amps can be related to one machine carrying more load, or, voltage imbalance and one unit carrying more VARs which show up in the form of amps.

VARs are watt-less, and therefore have no load effect on the engine. Only real power (Watts) load up the engine. VARs are made up of recirculating magnetism between induction loads on the rig and the generator winding. VARs heat up the generator rotor more than normal (more excitation required to drive the VARs), and add heat to the stater windings in the simple form of more amps.

The speed droop (no load to full load speed differential) must be the same on both engines if you have 3% governors (non isochronous). What governors do you have? If one unit has more droop under load, it will carry less load (less amps).

Voltage droop must be the same also, no load to full load. The cross current CTs keeps the regulator excitation current balanced to each unit and the voltage droop in proportion. Use only the 5 amp side of the CT. NEVER NEVER have an open secondary line on the CT as without a draw on the secondary wires, the load going through the CT will build voltage levels inside the CT into the hundreds of thousands of volts and blow it up.

If this doesn't make sense then call a Cat guy to come out and set this up, watch how it's done, and learn. There is a great chance to screw this up if you are not comfy with paralleling concepts. Half a day rig rate will pay for the Cat guy. Reduce risks of loosing hole time by getting an expert out there.

Also, if you are just doing blinkless transfer, who cares if one has 100 A and the other 300 A amps. They'll only run that way for 5 seconds while you open the breaker of the 'hot' unit. A 200 amp block load on the 'cold' unit is no biggie.

hi

i adjust the voltage of the generator on line to 480v and adjust the incoming generator voltage to 475v, when i put the other generator online its breaker trips due to reverse power relay. i mean they should be exactly the same vlotage to keep them running parallel. i use to check the voltage with digital multimeter.

i know that when both generators are not KVR sharing i can adjust the voltage to make them the same. but here if i increase the voltage of generator#1, generator#2 breaker will trip off due to reverse power condition. reverse power relay sitting ''30 amps of reverse current will trips off the main breaker''

is it tripping off because no KvR sharing between the generators? or because of reverse power relay sitting? thats why i am asking about cross current compensation?

You have not indicated about governor control.After synchronization adjust the speed for proper kw sharing,increase the speed of the machine which is taking less load.If there is no load on the system, there should not be any active power transfer ,if there is ,you may have to adjust the speed.

Generally the revers power relays act only when revers power takes place and it will not act on reverse kVAR, therefore I presume you have a problem with governor droop settings.( I do not know what make and type of Reverse power relay is fitted)

You can check the governor droop settings, by operating the sets individually , put different loads (say 25%,40%,60%,80% and 100%) on each machine and note down the speed variation, it should be same for both the machines.If the variations are not same then your governor droops are not matching and you will have problem of in equal load sharing only.

Other members have already given you suggestions.

The variations in currents supplied by the sets are due to speed variations.Governor droop settings for both the sets should be same.

Regarding the QCTs (Quadrature current current compensating CT),I suggest, use the NC contact of the breakers across the CTs.

Generally these QCT1 and QCT2 are to be connected in parallel with each other.To avoid damage to CT connect auxiliary potential free NC contact of DG1 breaker and DG2 breaker in parallel to QCTs.

QCTs will be effective only when both the breakers are ON, thus avoiding damage to the CTS.

caterpillar sr4 600kva generators as the power supply for mechanical drilling rig. they are 2 generators but we use one at time. the maximum load is about 450amps.we need to do synchronizing to change over between the generators. i tried but they are not sharing the load, one of them is carrying 300amps and the other is 100amps. both generators have caterpillar VR6-B voltage regulators. each regulator connected to droop CT and to minimise the circulating currents flow between the generators i have to connect X connection between both droop CTs leads ''cross current compensation'' as per regulator manual. this connection has to be on when both generators are online and off when only one of them is online, so the wire has to pass normaly open contacts in series for both generators main breakers. my question is if i just connect them without passing the contacts ''always connected'' ''two droop CTs on parallel'' is this will effect operation of the generator running alone? also i have another question: droop CT terminals at the regulator are 3 ''one is common and one is for 1amp CT and the third is for 5amp CT'' so it depends on the CT you are using if it is 1amp output or 5amp output. i am using the original CTs came with the generators. my question is: is the droop CT for caterpillar SR4 generators 1amp or 5amp output? i am connecting it as 1amp output CT, and maybe it is not. maybe thats why the generators are not sharing the load. any reply will be appreciated.

Your Message: Help

If you are only paralleling for a few momwnts, you can merely adjust the engine speed up on the unit with less load until the units are carrying equal load. Do not be concerned with the droop. As far as your CT ratio, that can be sometimes answered by having the parts department at the local Cat dealer look up the part using the generator set serial and arrangment numbers. The simpler task is to look at the label on the CT. A 700:5 ct has a 5 amp output at 700 amp load. A 700:1 ct would have a 1 amp output at 700 amp load.

Try adjusting speed to load share while making the changeover and see if this will work for you.