AUTO SYNCHRONIZING AND AUTO LOAD SHARING OF D. G. SETS.SEQUENCE OF OPERATION

SINGLE LINE DIAGRAM

When mains are healthy, then both the D.G. Sets remain in the standby mode.

• When mains fail, Line Voltage Monitor (L.V.M.) senses it. Starting pulses are given to the Master D.G. Set. (Master D.G.Set is automatically selected by programme.)

• After satisfactory starting of the D.G.Set 1, voltage is sensed by Generator Voltage Monitor (G.V.M.). If voltage is healthy, then closing signal is given to D.G.1 breaker and it is closed.

• Giving corresponding pulses from the Synchronizing Panel can then automatically start load.

• The load is then sensed by KW transducer in the panel & continuously monitored by Programmable Logic Controller ( P.L.C.)

• Engine & Alternator parameters are also continuously monitored by P.L.C. in the Panel. In case of any fault (e.g. Low Lube Oil Pressure, High Cooling Water Temperature etc.), breaker is tripped & engine is stopped.

• If the load reaches & crosses 80 % of the rated capacity of the D.G. 1, then starting pulses are given to the second D.G.set from P.L.C.

• When D.G.2 starts, then again G.V.M. checks the voltage, and if voltage is healthy, then breaker 2 is closed.

• After closing of the second breaker, Auto load sharing function starts sharing the load between the two D.G.Sets. The percentage of sharing is directly proportional to their individual capacities.

• Since sharing is proportional to their respective capacities, even D.G.sets of different capacities can be synchronized successfully.

• D.G.sets continue to run in Synchronization until the load is above 80 % of any one D.G.set.

• When load comes down below 80 % of any one D.G.set, then the automatic signal is given to that D.G. & then it starts taking the full load.

• After transferring the total load to one D.G. (on which 80 % load is to be connected), the breaker of the second D.G.is opened. Now one D.G.is taking the load, which is less than 80 % of its rated capacity.

• The second D.G. is then stopped after its cooling period.

• The programm is repeated automatically for any variation of the load.

• When mains are resumed, then load is transferred to the mains & both the D.G.sets are stopped after their cooling period.

• The percentage setting is programmable which can be set at any value upto say 90 %

• For stable operation even for sudden variations in the load, programmed timers in PLC are used, which take action only after stabilization of the load.

• The total Automatic operation has a manual override. In manual mode, the total operation

can be performed manually.

• Auto load shedding facility can be incorporated by suitable programming of PLC. With this facility, various loads can be brought in or switched off at particular time or for various intervals.

• With the same logic, 3, 4 or 5 sets of equal or different capacities can be Synchronised, with Auto load sharing facility.

ADVANTAGES OF AUTOSYNCHRONISING & AUTOLOAD SHARING

• The total programme is based on load in KW. Hence the actual sharing, starting, stopping & transfers are actual load dependent & not on any other unrealistic parameter like voltage, current. Etc.

• Changing of scheme becomes very easy because of changes are made through software only. There is no changing of wires, adding of components like relays, contactors, which is very time consuming, cumbersome & requiring additional space.

• Along with KW sharing, KVAr sharing & PF sharing is very accurate, because of PLC programming. There is no possibility of any unequal sharing as regards KW, KVAr & PF.

• For any type of load addition or reduction, manual intervention as regards D.G.set operation is not required. However, in case of emergency manual override is possible.

• Special programmers using Real Time Clock (RTC) are possible. With this facility, along with KW dependent programs; day, date & time dependent programmers are possible.

• Because of KW dependent load sharing, optimum utilization of D.G. sets are possible. This increases D.G. sets efficiency & saves lot of fuel.

• D. G.sets are always tried to run with 80 % to 90 % load factor, where we get maximum efficiency of D.G.sets. This is easily possible with our system.

• Because of PLC operation, hardware like relays, contactors, wiring etc is reduced drastically. This reduces fault points & increases the MTBF of the system.

• If any changes are required to be made in future, then there is no need of additional hardware like relays, contactors etc. There is also no need to make new wiring or changes in the wiring. All the changes / modifications can be easily made through software only.

Design &Hosted By:   M.Noman Latif                

EleMech Pakistan (Pvt) Limited

PRODUCT

ELECTRICAL CONTROL PANELSA. M. F. PANELS

•The Automatic Mains Failure Control panel is designed to monitor (& to start Generator automatically) the mains source and upon partial or full failure of the source / Mains supply. •When mains fail, then it is sensed by Line Voltage Monitor (L.V.M.) and three starting pulses are given to Genset. •If Genset does not start within three attempts, then ‘STARTING FAILURE’ alarm is sounded and stop signal is given to Genset to stop it fully & no start signals are given further. •If Genset starts within three attempts, then remaining starting pulses are automatically cut-off. •When Genset starts successfully, it builds up the rated voltage and Genset contactor/breaker is closed automatically. The load then is switched on / transferred to the Genset. •When Mains restores, which is checked by L.V.M. for its healthiness, the generator is then disconnected from the load and automatic transfer back to the mains source takes place, with the generator running on a cool down period and resetting ready for next failure. Load is now connected to the mains. •Genset is then run for about 5 minutes time set, on no load and it is stopped automatically. •The cycle can be repeated if Mains fail again. •Safeties like L.L.O.P., H.W.T. and over speed (optional) are operative when the Genset is •Running. For any of the above faults, Genset stops immediately. •Additional safeties can be added, if it is a specific requirement of the customer. •Automatic function can be totally by-passed and Genset can be started-stopped in manual mode also. •While the load is connected to Mains, the Genset can be tested for its performance in TEST mode also. In TEST mode, the total automatic cycle can be tested, without closing the Genset breaker.Indication for the following :

Shutdown Protections :

  

                                                                                               MANUAL CONTROL PANEL

Technical Specification Manual Start Generator Control panels are designed to operate manually directly on the control panel. The engine control module incorporated as standard is electronic type. The panels are manufactured from 1.5mm sheet steel and painted in stove enamel GRAY textured finish as standard. Set mounting format with integral MCCB or separate breaker panel depending on ratings with an external protection . Operating temperature range: -25ºC to 50ºC

Each panel is complete with the following components as standard :

1 Voltmeter 3- Ammeter 1- Freq. RPM meter Fail to start 1- Battery voltmeter 1-Engine hours run counter 1- Oil press. gauge 1- Engine temp. gauge 3- C.T. above 100 A 1- voltmeter sel. sw 1- Electronic generator control module fully programmable with : Control key switch Off / Run / Start (OPTIONAL) 1- MCB / MCCB 4- AC and DC fuses 1- Control terminals 1- Neutral terminal 1- Set of AV mounts (OPTIONAL) 2- 20/30 amp rated relays for fuel and start solenoids

Indicators for the following:

Low oil pressure High Temp. Over speed Fail to start Under speed Over current V belt failure Blower failure Earth fault (opt.) Control on DG on Shutdown protections: Low oil pressure High room temperature Over speed Fail to start Under speed Over current V belt failure Blower failure Earth fault (opt.)    

Person A (Org A) 17 Feb 01 22:55

I need to know if it is possible to run a 180KVA DG set in parallel with a 500KVA DG set (Synchronising). If yes, what are the precautions to be taken for safe operations?

Person B (Org B) 18 Feb 01 21:55

If properly engineered and designed, one may run the above DG sets in parallel. They have to be properly:

1. System grounded (system ungrounded is possible but to be avoided, if possible)2. Individually protected3. The downstream power distribution must withstand their total short-circuit fault currents

and short-circuit MVAs.4. Designed for the same frequency5. Avoid a short intermittent on-off duty of one of them to keep system stable.6. Loaded according to their permissible loading, kVA vs time curves.

Person C (Org B) 19 Feb 01 9:15

In addition to the general factors mentioned by Person B, you need the following specifics:

1. The governors must be set up for parallel running. This usually means that they must be set for the same percentage droop, so that they can share load in proportion to their ratings. Other control options are available, depending on the type of governor in use.

2. The voltage regulators must also be set up to share reactive load in proportion to rating. This will usually also mean load droop control, or cross-current compensation between the two AVRs.

3. Of course, you will need synchronizing instrumentation & controls to parallel the units in the first place. This can be automatic or manual & can be simple or complex depending on your requirements.

Person A (Org A) 19 Feb 01 14:23

Thanks to Person A and Person B for their helpful hints. The system where I am going to implement this is already running 3 sets of 500 KVA in parallel. The neutral (star point) of each alternator is connected to ground through an isolating contactor, only one of which is on at a time (the rest being floating). The latest set of 180 KVA is being added to take care of peakload requirements.

The paralleling instruments already in place are : Synchroscope (rotating LED type), Check Synchronising Relay (SKE11 Electro-mechanical) and also the dark lamp method!

The other protections are Reverse Power Relay (CCUM21) and Earth Fault Relay (CAG14) for each DG set. Each Alternator is protected by motorised air circuit breakers.

I was wondering if you know any reference book on this subject of synchronising of DG sets.

Person C (Org B) 19 Feb 01 15:10

As far as references are concerned, I suggest that you try the appropriate manufacturer websites. Basler and Woodward governor would be good starting points.

Person B (Org B) 25 Feb 01 16:26

Suggestions:

1. I had to keep my answers in general to avoid any unrelated specifics such as the power management, loading percentages, etc.

2. The original posting calls for safe operation of the additional 180 KVA DG. The power management strategies are considered on safe side.

3. More info on DG units and their controls is available over manufacturers such as http://www.thomasregister.com

  Type Governor under Product / Service that will return Governors: Diesel Engines and 2 companies in addition to the mentioned ones in the previous posting.

 Type Generator Product / Service that will return Generator Sets: Diesel Electric 181 Companies for good selections on more info

4.   References:

Bergen A. R. “Power System Analysis,” Prentice-Hall, Inc., 1986 Page 390 Section 12.5

Special Case: Two Generator Units describes in more detail “power control of two generating units,” including frequency droop characteristics

Person A (Org A) 27 Feb 01 10:56

Even as we were corresponding thru Eng-Tips,I was carrying out the installation work (cabling, control wiring etc.)at the site. Yesterday, I commissioned the set (180 KVA, 415V, 3 phase) by synchronizing it with the existing 3 x 500 KVA sets. I am glad to report that the set ran for over 4 hours in a synchronised state without ever tripping. As the load sharing is being done manually, I tried to load the 180 KVA set but could raise it to only to 90 KW. At this loading, it was drawing a current of 200 Amps. This ampere load remained fairly constant even as I decreased the KW load even to 20kW ! I am still scratching my head over that !

I have asked for the governor to be calibrated afresh ( mainly to give me time to think of a viable load sharing scheme ! ) Well, thanks to Person A & Person B for their interest and without whose prompt replies, I would be still groping in the dark.

Person C (Org B) 27 Feb 01 12:35

Glad to hear that you were successful in commissioning the set. A couple of thoughts regarding your results:

- At 90 kW, 200A, 415V you were operating at 144 kVA and a power factor of 0.63; reducing the real power to 20 kW, you kept at 200A with a power factor of 0.14. How is the control mode of AVR set up?- You may want to try reducing the excitation to increase the power factor up to the rated value (0.80? 0.85?) for this loading. How did the bus voltage respond when the unit came on-line? It should have increased noticeably, so that reducing the unit excitation would bring it back towards nominal.- Assuming that you are not connected to the grid, you may have to back load off of one of the other running sets to get the 180 kVA unit to pick up more load – it all depends on the droop settings. What control mode is the governor set up for? You may also want to verify that the prime mover isn’t limiting the output due to some mechanical problem.

Person B (Org B) 27 Feb 01 13:31

Suggestions:

1. Power flow simulation by suitable software performing power flow analysis/management could help.

2. 180 kVA generator is supplying power to the parallel generators. Please, notice that various regulators, controllers, governors, etc. have their boundary conditions and operating regions. If the current setup does not fit the limiting conditions, there may be a need for their customizations.

neutral connection in generator synchronizing

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01-18-2012 04:39 PM

Hello

I am planning to connect the neutral of the entire three synchronized cat 608 kva similar generator set on the common ground bus bar (the ground will also be connected to the bus bar) without any neutral- grounding contactor (this is because I am using 3 pole contactors for the main synchronization). I have tried to gather information about this idea on the internet and I have seen different ideas posted which contradicts. Will this create problem?

Please advise me from practical point of view.

If it is possible advice me, any ways which could avoids the possible risks without using the neutral contactor

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boopathy86

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Re: neutral connection in generator synchronizing

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01-31-2012 04:36 AM

(81) why a neutral grounding contactor is needed in diseal generator? ■There would not be any current flow in neutral if DG is loaded equally in 3 phases , if there any fault(earth fault or over load) in any one of the phase ,then there will be un balanced load in DG . at that time heavy current flow through the neutral ,it is sensed by CT and trips the DG. so neutral in grounded to give low resistance path to fault current. ■An electrical system consisting of more than two low voltage Diesel Generator sets intended for parallel operation shall meet the following conditions: ■(i) neutral of only one generator needs to be earthed to avoid the flow of zero sequence current. ■(ii) during independent operation, neutrals of both generators are required in low voltage switchboard to obtain three phase, 4 wire system including phase to neutral voltage. ■(iii) required to achieve restricted earth fault protection (REF) for both the generators whilst in operation. Solution: ■Considering the requirement of earthing neutral of only one generator, a

contactor of suitable rating shall be provided in neutral to earth circuit of each generator. This contactor can be termed as “neutral contactor”. ■Neutral contactors shall be interlocked in such a way that only one contactor shall remain closed during parallel operation of generators. During independent operation of any generator its neutral contactor shall be closed. ■Operation of neutral contactors shall be preferably made automatic using breaker auxiliary contacts.

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esantos

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Re: neutral connection in generator synchronizing

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01-31-2012 06:02 AM

Hi nebiyou.

The reason for the use of ground contactor is to avoid circulating high currents among gensets. The high current will depend on lot of things as the kind of load, installation, exciter system, etc. In our projects, we rarely use the ground relay. We have projects with six gensets running for about 3 years without that. I recommend to swap the 3 pole contactor for a breaker with LSIG protection. So the system will be improved in case of a short circuit.

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Re: neutral connection in generator synchronizing

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01-31-2012 07:41 AM

there is problem when you use 3pole contactor in synchronizing system,especially when harmonic/unbalanceload occur there will be no protection.

 

solution :use 4pole contanctor or neutral isollator contactor,

 

 

regards

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see-deif

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01-31-2012 10:28 AM

There are many "rules of thumb" you can listen to, but the only way to know for sure is to do a power system study. Anytime changes are done to a power system, a power system study should be done to find 'hidden' potential problems, to possibly change protective relay settings, etc. I don't do PSS, the company I work for does not do them, so I have no vested interest. Just trying to help.

 

That being said, you did not say if you were going to connect more than 1 neutral - to - ground bonding connection? If you have more than 1 ground connection, you DEFINATELY will have problems. You also did not say how close these gensets would be to each other/how much impedance there might be between them. Last is the type of load: balanced 3 phase (like transformers and motors) or unbalanced single phase (like lighting or single phase transformers.) 

 

It is possible for circulating currents if the generators are not exactly identical. Compare the actual test voltages, not the rated or nameplate values, looking carefully at the winding pitch and voltage balance between phases. AVRs and KVAR/PR regulators will adjust for average voltage differences between machines, but they cannot do anything for voltage balance between phases. Generators are not perfectly identical, but with modern quality control they could be close enough.

 

People parallel generators all the time, so this will probably work. If the voltage balance is not good and there is not much impedance between them, they may not work well unloaded. Expect unstability and higher-than-normal circulating currents. But when you apply some load, the internal voltage drop should reduce/stop the unstability and allow this with no problems. If they are physically far apart or have other sources of system impedances between them, this will be easier. For example, if they have step up or isolation transformers between them or they have many feet of cabling or bus work they will have higher system impedances, which actually helps when running lightly/un-loaded.

 

To fix that, you may need to do 'load-dependent start/stop' of the gensets...only starting as many gensets as needed to supply the actual load KW. Start one gen, load it up to 80%, start the next one, load them both up to 80%, start the next one....you get the idea. Starting and paralleling 3 gens to 1 bus with low system impedances and un-balanced generators will most probably have problems. Unfortunately this is normally the first thing customers want to see!

 

Good luck, write back if you have any more questions,

Steve

why a neutral grounding contactor is needed in diseal generator?

There would not be any current flow in neutral if DG is loaded equally in 3 phases , if there any fault(earth fault or over load) in any one of the phase ,then there will be un balanced load in DG . at that time heavy current flow through the neutral ,it is sensed by CT and trips the DG. so neutral in grounded to give low resistance path to fault current.

An electrical system consisting of more than two low voltage Diesel Generator sets intended for parallel operation shall meet the following conditions:

(i) neutral of only one generator needs to be earthed to avoid the flow of zero sequence current.

(ii) during independent operation, neutrals of both generators are required in low voltage switchboard to obtain three phase, 4 wire system including phase to neutral voltage.

(iii) required to achieve restricted earth fault protection (REF) for both the generators whilst in operation.

Solution:

Considering the requirement of earthing neutral of only one generator, a contactor of suitable rating shall be provided in neutral to earth circuit of each generator. This contactor can be termed as “neutral contactor”.

Neutral contactors shall be interlocked in such a way that only one contactor shall remain closed during parallel operation of generators. During independent operation of any generator its neutral contactor shall be closed.

Operation of neutral contactors shall be preferably made automatic using breaker auxiliary contacts.