Electrical Generator For Domestic Supply?

KevinBloodyWilson · August 22, 2009

I have a house in Isaan where the power supply is very erratic - often it is more on than off. At present it has a 15A circuit - the usual thing with no earth circuit.

I am tempted to see if a diesel generator can be attached to start up when the mains supply is cut (usually some hoon crashing into a power pole somewhere upstream). From my high school days I guess I would need to generate about 3.5KWH.

Anyone got any idea:

Is it legal?

is it feasible?

How much would it cost?

What would I need to put in to the house circuitry to get it working?

I know the square root of bugger all about electrics apart from not being a good idea to mess with it.

Crossy · August 24, 2009

There are a few genset threads about, have a look here and come back with questions

http://www.thaivisa.com/forum/Electricity-...se-t274684.html

http://www.thaivisa.com/forum/Automatic-Ma...ng-t260624.html

http://www.thaivisa.com/forum/Backup-Gener...Plz-t69591.html

Yes, it's legal if done correctly (no having a lead with a plug on each end).

Yes, it's practical

No, it's not something you can do yourself if you "know the square root of bugger all about electrics", you need a man who can

Crossy · August 24, 2009

Just noticed that we have a forum sponsor "Generator Solutions" http://www.generatorsolutions.org/ should be the man who can

You could PM 'genset' who is their online persona

genset · August 25, 2009

I have a house in Isaan where the power supply is very erratic - often it is more on than off. At present it has a 15A circuit - the usual thing with no earth circuit.
I am tempted to see if a diesel generator can be attached to start up when the mains supply is cut (usually some hoon crashing into a power pole somewhere upstream). From my high school days I guess I would need to generate about 3.5KWH.

Anyone got any idea:

Is it legal?

is it feasible?

How much would it cost?

What would I need to put in to the house circuitry to get it working?

I know the square root of bugger all about electrics apart from not being a good idea to mess with it.

Hi Kev,

I would echo Crossys comments regarding the legality and practicality of fitting an automatic mains failure system with a standby generator.

It is possible to purchase gasoline driven, electric start generators in the size you are contemplating from one or two of the larger DIY stores in Thailand, but they are not manufactured specifically for use with an Automatic Transfer Switch (this is the panel you place in your house) and a little creative wiring is required to enable remote starting. To my knowledge, the best option available in Thailand is a small (5Kw) diesel generator in a soundproof canopy. This set has been designed for use with ATS, it also features an automatic voltage regulator. If you would like to contact me at [email protected] I will send you a picture of the genset along with a full spec sheet and answer any other questions you may have.

Genset John.

KevinBloodyWilson · August 25, 2009

I have a house in Isaan where the power supply is very erratic - often it is more on than off. At present it has a 15A circuit - the usual thing with no earth circuit.
I am tempted to see if a diesel generator can be attached to start up when the mains supply is cut (usually some hoon crashing into a power pole somewhere upstream). From my high school days I guess I would need to generate about 3.5KWH.

Anyone got any idea:

Is it legal?

is it feasible?

How much would it cost?

What would I need to put in to the house circuitry to get it working?

I know the square root of bugger all about electrics apart from not being a good idea to mess with it.

Hi Kev,

I would echo Crossys comments regarding the legality and practicality of fitting an automatic mains failure system with a standby generator.

It is possible to purchase gasoline driven, electric start generators in the size you are contemplating from one or two of the larger DIY stores in Thailand, but they are not manufactured specifically for use with an Automatic Transfer Switch (this is the panel you place in your house) and a little creative wiring is required to enable remote starting. To my knowledge, the best option available in Thailand is a small (5Kw) diesel generator in a soundproof canopy. This set has been designed for use with ATS, it also features an automatic voltage regulator. If you would like to contact me at [email protected] I will send you a picture of the genset along with a full spec sheet and answer any other questions you may have.

Genset John.

Thanks guys, I really appreciate the replies. John, I will write to you today.

Kev

elkangorito · August 28, 2009

About ATS units.

The problem with ATS's (automatic transfer switches) is about "FAULT CURRENT".

I have designed many switchboards with ATS units, usually for commercial or industrial applications. On almost every occcasion, the "generator" people have insisted upon "contactors" to be used. I have always opposed this concept, to a degree. BTW, the same applies for domestic situations.

Contactors are purely designed to switch a load (turn it on or off). They generally have a low Fault Current tolerance. Circuit Breakers are also designed to switch loads but can withstand greater Fault Currents.

For an ATS, a contactor is acceptable "on the generator side" (very low prospective fault current). The only way a contactor can be SAFELY used on the SUPPLY side is if the supply contactor is adequately protected by HRC fuses (minimum BS88), which can make this scenario prone to "nuisance trips". Therefore, the only solution is to use a circuit breaker for the supply protection (cheaper than a contactor) & to also make sure that adequate seperation between the generator supply & the incoming supply, is adequate. This is done to prevent magnetic affects from affecting the contactor under "fault" conditions.

In summary, do not use contactors as part of an ATS (even though they are commonly used)

Use circuit breakers in the ATS. Speed is not important...reliability & safety is important.

Using circuit breakers is initially more expensive (shunt trips, more wiring etc) but the equipment will not be affected by high fault currents (if properly selected) & will last significantly longer than contactors. Any reputable switchboard manufacturer will endorse this.

genset · August 30, 2009

About ATS units.
The problem with ATS's (automatic transfer switches) is about "FAULT CURRENT".

I have designed many switchboards with ATS units, usually for commercial or industrial applications. On almost every occcasion, the "generator" people have insisted upon "contactors" to be used. I have always opposed this concept, to a degree. BTW, the same applies for domestic situations.

Contactors are purely designed to switch a load (turn it on or off). They generally have a low Fault Current tolerance. Circuit Breakers are also designed to switch loads but can withstand greater Fault Currents.

For an ATS, a contactor is acceptable "on the generator side" (very low prospective fault current). The only way a contactor can be SAFELY used on the SUPPLY side is if the supply contactor is adequately protected by HRC fuses (minimum BS88), which can make this scenario prone to "nuisance trips". Therefore, the only solution is to use a circuit breaker for the supply protection (cheaper than a contactor) & to also make sure that adequate seperation between the generator supply & the incoming supply, is adequate. This is done to prevent magnetic affects from affecting the contactor under "fault" conditions.

In summary, do not use contactors as part of an ATS (even though they are commonly used)

Use circuit breakers in the ATS. Speed is not important...reliability & safety is important.

Using circuit breakers is initially more expensive (shunt trips, more wiring etc) but the equipment will not be affected by high fault currents (if properly selected) & will last significantly longer than contactors. Any reputable switchboard manufacturer will endorse this.

Hi Elkangorito,

I appreciate your comments. I have been reading this forum since I began building my house a few years ago and am firmly of the opinion that you and Crossy have played a significant and commendable role in highlighting electrical safety issues for expats in Thailand. I certainly wouldnt want my posts to detract from that.

'Speed is not important... reliablity and safety is...' I couldnt agree more with your statement. As you would seem to recognize, from top to bottom in our industry (generator manufacture and installation), contactors are routinely used in domestic and smaller industrial ATS panels to switch the load from mains to generator supply, we also use them to a limited degree for synchronised (g59) parallell systems.

I am glad that you raised this issue, as the safety of my installations is paramount to me and I would like to think it will be one of the defining characteristics of the service I will provide in Thailand. As you have stated (and I have commented on previously also..) contactors are only used to switch the loads and are NOT a substitute for a circuit breaker. The generator supply is always fed through a circuit breaker located in a panel on the generator itself, the utility supply to the ATS is always fused and the supply from the ATS panel passes through a circuit breaker prior to feeding the circuits in the distribution board/consumer unit. Neither the electrical engineers with whom I work, nor the local utility company who are occasionally present during installation and commissioning of our synchronised systems, have ever raised the issue of prospective fault current and our use of contactors, but that doesnt mean that such an issue is not a valid concern and that an amendment/upgrade to the design of our ATS panels to ensure every possible safety concern is addressed, is not warranted.

I will discuss this further with our engineers and look at the cost of replacing contactors with shunt trip circuit breakers as a possible solution. I do have one question for you (I'll find out myself on Monday, but as I'm typing this I might as well ask). Using contactors allows me to interlock the contactors electrically AND mechanically. Using auxilliary contacts would allow me to electrically interlock the circuit breaker coils, but do you know if there is a model of circuit breaker with shunt trip out there that supports a mechanical interlock also? I like the safety net of a mechanical interlock to prevent the possibility of simultaneous connection of generator and utility supply.

Gary A · August 30, 2009

I can tell you that a nine HP Kubota diesel will put out 5,000 watts day after day using less than a liter of diesel per hour. One of our sparkies will have to tell you what kind of battery bank could be charged with this to supply your house. I worked it out some time back but can't find my numbers. These single cylinder water cooled Kubota diesels are available up to fourteen HP.

elkangorito · August 30, 2009

Hi Elkangorito,
I appreciate your comments. I have been reading this forum since I began building my house a few years ago and am firmly of the opinion that you and Crossy have played a significant and commendable role in highlighting electrical safety issues for expats in Thailand. I certainly wouldnt want my posts to detract from that.

'Speed is not important... reliablity and safety is...' I couldnt agree more with your statement. As you would seem to recognize, from top to bottom in our industry (generator manufacture and installation), contactors are routinely used in domestic and smaller industrial ATS panels to switch the load from mains to generator supply, we also use them to a limited degree for synchronised (g59) parallell systems.

I am glad that you raised this issue, as the safety of my installations is paramount to me and I would like to think it will be one of the defining characteristics of the service I will provide in Thailand. As you have stated (and I have commented on previously also..) contactors are only used to switch the loads and are NOT a substitute for a circuit breaker. The generator supply is always fed through a circuit breaker located in a panel on the generator itself, the utility supply to the ATS is always fused and the supply from the ATS panel passes through a circuit breaker prior to feeding the circuits in the distribution board/consumer unit. Neither the electrical engineers with whom I work, nor the local utility company who are occasionally present during installation and commissioning of our synchronised systems, have ever raised the issue of prospective fault current and our use of contactors, but that doesnt mean that such an issue is not a valid concern and that an amendment/upgrade to the design of our ATS panels to ensure every possible safety concern is addressed, is not warranted.

I will discuss this further with our engineers and look at the cost of replacing contactors with shunt trip circuit breakers as a possible solution. I do have one question for you (I'll find out myself on Monday, but as I'm typing this I might as well ask). Using contactors allows me to interlock the contactors electrically AND mechanically. Using auxilliary contacts would allow me to electrically interlock the circuit breaker coils, but do you know if there is a model of circuit breaker with shunt trip out there that supports a mechanical interlock also? I like the safety net of a mechanical interlock to prevent the possibility of simultaneous connection of generator and utility supply.

Hi genset.

As you may be well aware, contactors are quite hardy but are very sensitive to temperature & fault current.

It's fine using contactors for a domestic installation providing that the Prospective Fault Current of the installation does not exceed about 5kA. Most small contactors (30 amps AC-1) have a Shortime Withstand of between 150 to 180 amps for about 10 seconds (60 degrees C) & cannot be subject to a Shortcircuit Fault of any more than 5kA for any length of time.

Most domestic installations have a Prospective Fault Current of between 5kA & 10kA. This may not be the case if the residence is fed from a large transformer.

In our "home" countries, the supply Prospective Fault Current is easily obtainable via the energy supplier. I don't think that this is the case in Thailand.

As a result, the Prospective Fault Current needs to be found & appropriate protection needs to be placed in order to prevent contact welding & destruction. Circuit breakers may not perform this job adequately if they are too slow. HRC fuses will do the job properly & if "cordinated" correctly, should not trip unnecessarily.

I have personally seen a switchboard (25kA) that had been almost completely destroyed. It contained two 400 amp contactors (ATS), both of which were melted. Circuit breakers were used as the "protection" (perhaps the wrong type of CB). The cause was that a partial fault occured, which meant that there was not enough current to quickly trip the circuit breakers. The contactors "pulsated" (opened & closed) due to the magnetic forces of the fault, which didn't allow the CB's to trip. Under these conditions, the magnetic forces exceeded the spring force in the contactor, which with AC meant that the contactor opened & closed rather quickly...almost like relay chatter.

The same situation could occur at lower Prospective Fault Currents. The answers are;

1] Find the Prospective Fault Current of the installation.

2] Coordinate the protection of the contactors according to time/current curves of protective devices & according to the temperature characteristics/short circuit characteristics of the contactors.

Cable selection is another matter along with switchboard design.

With regard to mechanically interlocking circuit breakers, this is normally available on larger CB's (by cable usually). http://www.abb.com/product/seitp329/2deffb...d.aspx?tabKey=7

Electrical interlocks are ok for smaller CB's.

My usual scenario is as follows;

1] Normal supply fails.

2] Normal Supply CB opens. Start signal to generator.

3] After a generator start, wait at least 5 minutes before closing Generator CB (warm up).

4] Close generator CB. Allow generator to supply load for at least 15 minutes disregrading if Normal Supply has returned or not.

5] Upon return of Normal Supply (after minimum 15 minutes), open Generator CB & allow a "rundown time" according to the size of generator, before shutting down generator. Close the Normal Supply CB.

I can tell you that a nine HP Kubota diesel will put out 5,000 watts day after day using less than a liter of diesel per hour. One of our sparkies will have to tell you what kind of battery bank could be charged with this to supply your house. I worked it out some time back but can't find my numbers. These single cylinder water cooled Kubota diesels are available up to fourteen HP.

Gary, is the HP Kubota diesel a "portable" generator or a "stand-by" generator?

genset · August 30, 2009

Hi Elkangorito,

I will look at both options. If HRC fuses correctly selected for the characteristics of the contactors installed will stand repeated operation without nuisance tripping that may be an acceptable solution, I will set up a test unit and let you know how I get on. I will also look at the alternate option of using circuit breakers with shunt trips.

We have a Fluke 1653 installation tester we use for checking phase rotation etc, I just had a look at the specs and it will test both prospective short circuit and prospective earth fault current also. Where an installation has MEN am I disconnecting earth and neutral before testing live to earth? (again, I will consult with my engineers, but would appreciate your input).

On Garys Kubota Diesel genset, it may look something like the photograph I have attached. This is the same type of Kubota engine used in walk behind tractors and is commonly configured in this manner to belt drive an alternator. I found this one on sale at a hardware store in Khon Kaen, they were asking 90,000 baht for it...! They are a sturdy workhorse as Gary suggested, and a fairly common sight, but in my opinion there are far better options available circa this price.

elkangorito · August 31, 2009

Hi Elkangorito,
I will look at both options. If HRC fuses correctly selected for the characteristics of the contactors installed will stand repeated operation without nuisance tripping that may be an acceptable solution, I will set up a test unit and let you know how I get on. I will also look at the alternate option of using circuit breakers with shunt trips.

We have a Fluke 1653 installation tester we use for checking phase rotation etc, I just had a look at the specs and it will test both prospective short circuit and prospective earth fault current also. Where an installation has MEN am I disconnecting earth and neutral before testing live to earth? (again, I will consult with my engineers, but would appreciate your input).

On Garys Kubota Diesel genset, it may look something like the photograph I have attached. This is the same type of Kubota engine used in walk behind tractors and is commonly configured in this manner to belt drive an alternator. I found this one on sale at a hardware store in Khon Kaen, they were asking 90,000 baht for it...! They are a sturdy workhorse as Gary suggested, and a fairly common sight, but in my opinion there are far better options available circa this price.

Hi again Genset.

There is a simple solution to all of this. It's called "Type 2 Coordination". If this method of protection is used, the contactors must have an overload fitted. This type of protection will prevent damage to the switchgear under high fault conditions, which also means that the operator is safe. It must be used STRICTLY within the test parameters (voltage, Max PFC etc). Make sure of any differences between RMS PFC & Peak PFC.

You will find that most notable switchgear manufacturers have Type 1 & Type 2 coordination tables. I know for sure that "S & S" & Telemecanique have these types of coordination fully tested & approved (IEC Standards). In some cases, circuit breakers can be used for the upstream protection but fuses are preferable.

Of course, in order to be fully compliant to the standard, the exact equipment listed for Type 2 Coordination MUST be used.

Also, Type 2 Coordination is used to protect motor starters. In a way, an ATS is a kind of "starter", the only difference being the load. Domestic house loads are not sinusoidal due to harmonics. A motor (non-vfd) will not introduce any harmonics (it's a sinusoidal load). This difference may have an affect on the effectiveness of Type 2 Coordinated switchgear...you'd need to check this out.

I've never heard of a Fluke 1653 installation tester. How can it find PFC? To effectively find out the PFC, the characteristics of the supply (transformer) must first be known & then the impedance from the point of supply to the load be calculated. Or are you refering to Earth Fault Loop Current?

There are a few methods used to calculate the Earth Fault Loop impedance (& thence the current) & the method can vary between the types of devices used in the test. The test should be carried out according to the requirements & limitations of the device used in the test.

Cheers.

Crossy · August 31, 2009

Seems someone ran out of tape

It would be interesting to know what the measured Prospective Fault Current is on various locations and types of installation in Thailand. Since Genset has the test kit.......

Details of the Fluke here http://www.pat-services.co.uk/fluke-1653-230.htm It calculates PFC by measuring Zs (using voltage droop between no-load and a 12A test-load) and multiplying by the supply voltage. It's not particularly accurate (resolution is 0.1kA) but is certainly good enough to verify your CPDs are adequate.

It also measures:-

Voltage and Frequency

Wiring Polarity Checker

Insulation resistance 50,100,250,500 and 1000v

Loop and Line resistance

PFC/PSC (fault/ short circuit current)

Continuity

Loop Impedence

RCD Tripping time

RCD Tripping Current level (ramp test)

Automatic RCD Test sequence

Tests DC Sensitive RCD's

Earth Resistance

Phase sequence indicator

Self Test

EN 61577* VDE 0413 Compliant

Illuminated Display

Live Voltage Indicator

Battery Indicator and Battery Test Function

Memory - 500 measurements

Computer Interface

Time Stamp (with Flukeview forms)

Dead handy little beast, well worth the 750 Quid it costs.

elkangorito · August 31, 2009

Seems someone ran out of tape

It would be interesting to know what the measured Prospective Fault Current is on various locations and types of installation in Thailand. Since Genset has the test kit.......

I can't quite make out the picture...looks like some safety pins or something .

About PFC, the usual size txer I've seen is no larger than about 150kVA. Given that the impedance will be somewhere between 4% & 6%, the PFC will be between about 4kA & 6kA respectively, at the txer terminals.

Having said this, the small resort up the road is supplied by an 800kVA txer. This txer also feeds smaller buildings. I wonder if anybody took into account the PFC?

I have some more (new) info for Genset & I'll give it to him if & when he replies.

genset · August 31, 2009

Seems someone ran out of tape

It would be interesting to know what the measured Prospective Fault Current is on various locations and types of installation in Thailand. Since Genset has the test kit.......

Details of the Fluke here http://www.pat-services.co.uk/fluke-1653-230.htm It calculates PFC by measuring Zs (using voltage droop between no-load and a 12A test-load) and multiplying by the supply voltage. It's not particularly accurate (resolution is 0.1kA) but is certainly good enough to verify your CPDs are adequate.

It also measures:-

Voltage and Frequency

Wiring Polarity Checker

Insulation resistance 50,100,250,500 and 1000v

Loop and Line resistance

PFC/PSC (fault/ short circuit current)

Continuity

Loop Impedence

RCD Tripping time

RCD Tripping Current level (ramp test)

Automatic RCD Test sequence

Tests DC Sensitive RCD's

Earth Resistance

Phase sequence indicator

Self Test

EN 61577* VDE 0413 Compliant

Illuminated Display

Live Voltage Indicator

Battery Indicator and Battery Test Function

Memory - 500 measurements

Computer Interface

Time Stamp (with Flukeview forms)

Dead handy little beast, well worth the 750 Quid it costs.

Yes...Thailand wouldnt quite be the same place if there wasnt some aspect of locally manufactured and/or assembled equipment that made your jaw drop and (perhaps in this particular case) your hair stand on end...

When I bought the installation tester I didnt anticipate making use of all the functions, but never say never I guess and in this particular instance, I'm glad I went the whole hog instead of skimping on the cheaper version. I paid £660 for mine, I'll bring it back with me when I return and I would be happy to test and report back PFC values on various installations and locations as the opportunity presents itself.

genset · August 31, 2009

Seems someone ran out of tape

It would be interesting to know what the measured Prospective Fault Current is on various locations and types of installation in Thailand. Since Genset has the test kit.......

I can't quite make out the picture...looks like some safety pins or something .

About PFC, the usual size txer I've seen is no larger than about 150kVA. Given that the impedance will be somewhere between 4% & 6%, the PFC will be between about 4kA & 6kA respectively, at the txer terminals.

Having said this, the small resort up the road is supplied by an 800kVA txer. This txer also feeds smaller buildings. I wonder if anybody took into account the PFC?

I have some more (new) info for Genset & I'll give it to him if & when he replies.

Hi Elkangorito,

Apologies for the delay in responding, I have been back in the UK for just over a month now. It's approaching our busy time of the year, the 3 phase tariff for commercial properties goes up in Nov and we are becoming inundated with enquiries for maintenance calls, replacement alternators and new generators. It's good for business, but here's hoping this will be my final winter here (UK).

Thank you for the information regarding Type 2 Co-ordination, you've given me much to think about, I'm very grateful. It may take me a little while to chew this all over (for the reasons given above) and I hope you don't mind if I have some follow up questions but it will be worth the time and effort if the result is enhanced safety of my installations and my customers peace of mind.

Genset

elkangorito · August 31, 2009

More information (for Genset).

Is a contactor ATS really a contactor?
True (NEMA) contactors are electrical devices designed to make or break current. They are most often designed for motor starting and lighting control, are electrically or mechanically held and have mechanical endurance ratings that can number in the millions of operations. Contactor type transfer switches do not use contactors that are designed for lighting or motor control and do not provide the same certified endurance ratings.

What is the difference between an open contact design ATS and an enclosed contact design?

Contactor type transfer switches use an Open Contact circuit breaker design that incorporates breaker contacts, arcing horns and arc chutes. Some of these types of switches were developed with circuit breaker manufacturers at the time of their original design. This Open Contact design is then tested and certified in accordance with the applicable automatic transfer switch standards, UL #1008, CSA #178 in North America and IEC 947-6 in Europe.

Automatic transfer switch certification requires that all automatic transfer switches pass the endurance ratings as per UL standard UL #1008 table 30.2 and CSA standard #178 table 10 as a minimum. The endurance tests listed in the UL #1008 and CSA #178 standards are the only endurance tests that are certified by Underwriters Labatories and the Canadian Standards Association for automatic transfer switches. No other claims related to endurance should be given consideration unless recognized by the appropriate certifying bodies.

Enclosed Contact transfer switch designs take advantage of the technology in switching, contact, arc chute and arcing horn designs that continue to be developed in molded case circuit breakers. Just as the original designers of Open Contact transfer switches saw the advantages in circuit breaker switching and contact technology available at the time, Enclosed Contact manufacturers take advantage of the technical advances of today.

Enclosed Contact designs utilize devices that are specifically tested and certified (UL #1008 and CSA #178) for automatic transfer switch applications. In addition to being certified to the applicable automatic transfer switch standards, devices used in enclosed contact designs have often been certified to other more demanding certification tests such as; UL 489, UL 1089, CSA 5.1, CSA5.2. These certified test results are recognized by the appropriate certifying bodies and should be considered when comparing automatic transfer switch designs.

It appears as though contactors can now be safely used in ATS's providing that the standards are adhered to.

Link to the above quote;

http://www.kraftpower.com/pdfs/KPC_02_ATS_...rsus_series.pdf

What may also be of interest is info on contactors;

http://www.nhp.com.au/sprecherandschuh/catalogues.asp

I might also add that larger ATS units are still predominantly circuit breaker switched (>500A).

PLEASE DISREGARD INFO ABOUT TYPE 2 COORDINATION (I've done some quick research).

I believe that Type 2 Coordination is not applicable for ATS applications for the following reasons;

1] the load is not balanced.

2] the type of load may not present a sinusoidal value (harmonics = heating. RMS & Peak values of Fault Current will not cause the protective device to trip in the time anticipated).

3] Power Factor will constantly vary.

Sorry for the initial misinformation.

Gary A · September 1, 2009

Hi Elkangorito,
I appreciate your comments. I have been reading this forum since I began building my house a few years ago and am firmly of the opinion that you and Crossy have played a significant and commendable role in highlighting electrical safety issues for expats in Thailand. I certainly wouldnt want my posts to detract from that.

'Speed is not important... reliablity and safety is...' I couldnt agree more with your statement. As you would seem to recognize, from top to bottom in our industry (generator manufacture and installation), contactors are routinely used in domestic and smaller industrial ATS panels to switch the load from mains to generator supply, we also use them to a limited degree for synchronised (g59) parallell systems.

I am glad that you raised this issue, as the safety of my installations is paramount to me and I would like to think it will be one of the defining characteristics of the service I will provide in Thailand. As you have stated (and I have commented on previously also..) contactors are only used to switch the loads and are NOT a substitute for a circuit breaker. The generator supply is always fed through a circuit breaker located in a panel on the generator itself, the utility supply to the ATS is always fused and the supply from the ATS panel passes through a circuit breaker prior to feeding the circuits in the distribution board/consumer unit. Neither the electrical engineers with whom I work, nor the local utility company who are occasionally present during installation and commissioning of our synchronised systems, have ever raised the issue of prospective fault current and our use of contactors, but that doesnt mean that such an issue is not a valid concern and that an amendment/upgrade to the design of our ATS panels to ensure every possible safety concern is addressed, is not warranted.

I will discuss this further with our engineers and look at the cost of replacing contactors with shunt trip circuit breakers as a possible solution. I do have one question for you (I'll find out myself on Monday, but as I'm typing this I might as well ask). Using contactors allows me to interlock the contactors electrically AND mechanically. Using auxilliary contacts would allow me to electrically interlock the circuit breaker coils, but do you know if there is a model of circuit breaker with shunt trip out there that supports a mechanical interlock also? I like the safety net of a mechanical interlock to prevent the possibility of simultaneous connection of generator and utility supply.

Hi genset.

As you may be well aware, contactors are quite hardy but are very sensitive to temperature & fault current.

It's fine using contactors for a domestic installation providing that the Prospective Fault Current of the installation does not exceed about 5kA. Most small contactors (30 amps AC-1) have a Shortime Withstand of between 150 to 180 amps for about 10 seconds (60 degrees C) & cannot be subject to a Shortcircuit Fault of any more than 5kA for any length of time.

Most domestic installations have a Prospective Fault Current of between 5kA & 10kA. This may not be the case if the residence is fed from a large transformer.

In our "home" countries, the supply Prospective Fault Current is easily obtainable via the energy supplier. I don't think that this is the case in Thailand.

As a result, the Prospective Fault Current needs to be found & appropriate protection needs to be placed in order to prevent contact welding & destruction. Circuit breakers may not perform this job adequately if they are too slow. HRC fuses will do the job properly & if "cordinated" correctly, should not trip unnecessarily.

I have personally seen a switchboard (25kA) that had been almost completely destroyed. It contained two 400 amp contactors (ATS), both of which were melted. Circuit breakers were used as the "protection" (perhaps the wrong type of CB). The cause was that a partial fault occured, which meant that there was not enough current to quickly trip the circuit breakers. The contactors "pulsated" (opened & closed) due to the magnetic forces of the fault, which didn't allow the CB's to trip. Under these conditions, the magnetic forces exceeded the spring force in the contactor, which with AC meant that the contactor opened & closed rather quickly...almost like relay chatter.

The same situation could occur at lower Prospective Fault Currents. The answers are;

1] Find the Prospective Fault Current of the installation.

2] Coordinate the protection of the contactors according to time/current curves of protective devices & according to the temperature characteristics/short circuit characteristics of the contactors.

Cable selection is another matter along with switchboard design.

With regard to mechanically interlocking circuit breakers, this is normally available on larger CB's (by cable usually). http://www.abb.com/product/seitp329/2deffb...d.aspx?tabKey=7

Electrical interlocks are ok for smaller CB's.

My usual scenario is as follows;

1] Normal supply fails.

2] Normal Supply CB opens. Start signal to generator.

3] After a generator start, wait at least 5 minutes before closing Generator CB (warm up).

4] Close generator CB. Allow generator to supply load for at least 15 minutes disregrading if Normal Supply has returned or not.

5] Upon return of Normal Supply (after minimum 15 minutes), open Generator CB & allow a "rundown time" according to the size of generator, before shutting down generator. Close the Normal Supply CB.

I can tell you that a nine HP Kubota diesel will put out 5,000 watts day after day using less than a liter of diesel per hour. One of our sparkies will have to tell you what kind of battery bank could be charged with this to supply your house. I worked it out some time back but can't find my numbers. These single cylinder water cooled Kubota diesels are available up to fourteen HP.

Gary, is the HP Kubota diesel a "portable" generator or a "stand-by" generator?

I have a mechanical buffalo with an eleven HP Kubota. The Kubota has extra pulleys on the flywheel side to run whatever you want to run so I guess you could call the power plant portable. I have not found a generator yet but the plan is to mount the generator on wheels and spot it where necessary before putting the belt on it. I have a steel trailer that would haul a large battery bank. I have backed off because where I needed the power is too isolated to put a weekend house. As you may know the Thais will steal whatever they can carry off. I now have a very small gasoline generator that will run my computer, a light and a fan. I do plan to buy a 6,000 to 7,000 watt generator if I can find a good one.

genset · September 1, 2009

Hi Elkangorito,

So using contactors manufactured to meet the UL1008 standard for specific use in an ATS configuration puts the contactor issue to bed. It would seem to do no harm to continue with the idea of using HRC fuses for the mains supply?

Interesting PDF document, thank you for that. Have you ever come across the type of single solenoid contactor detailed in the document?

Genset

Crossy · September 1, 2009

Interesting PDF document, thank you for that. Have you ever come across the type of single solenoid contactor detailed in the document?

I've not actually seen one of those, but if you look on the (mostly American) websites of ATS manufacturers they seem very common.

Looks like they only need a pulse to the solenoid to switch to the other position, energy saving and they can be manually switched

elkangorito · September 2, 2009

Firstly, I would like to make some amendments to my initial statements. Please refer to the bolded & underlined text in my below quote. My comments are in blue.

About ATS units.
The problem with ATS's (automatic transfer switches) is about "FAULT CURRENT".

I have designed many switchboards with ATS units, usually for commercial or industrial applications. On almost every occcasion, the "generator" people have insisted upon "contactors" to be used. I have always opposed this concept, to a degree. BTW, the same applies for domestic situations.

Contactors are purely designed to switch a load (turn it on or off). They generally have a low Fault Current tolerance. Circuit Breakers are also designed to switch loads but can withstand greater Fault Currents.

For an ATS, a contactor is acceptable "on the generator side" (very low prospective fault current). The only way a contactor can be SAFELY used on the SUPPLY side is if the supply contactor is adequately protected by HRC fuses (minimum BS88), which can make this scenario prone to "nuisance trips". Therefore, the only solution is to use a circuit breaker for the supply protection (cheaper than a contactor) & to also make sure that adequate seperation between the generator supply & the incoming supply, is adequate. This is done to prevent magnetic affects from affecting the contactor under "fault" conditions.

In summary, do not use contactors unapproved contactors as part of an ATS (even though they are commonly used)

If the complete ATS unit complies with UL1008, CSA178 and IEC 947-6, it can be safely used.

I can tell you that a nine HP Kubota diesel will put out 5,000 watts day after day using less than a liter of diesel per hour. One of our sparkies will have to tell you what kind of battery bank could be charged with this to supply your house. I worked it out some time back but can't find my numbers. These single cylinder water cooled Kubota diesels are available up to fourteen HP.

Hi Gary,

The difference between a "portable" generator & a "standby" generator is significant. It has little to do with the motor (mechanical) & much more to do with the generator (electrical).

The fundamental differences are as follows:

Portable Generators ("brushless");

1] If not "inverter" controlled, will give poor quality electricity (poor sine wave control).

2] Will have poor voltage regulation if not inverter controlled (>5%).

3] Cannot run 24 hours a day without reducing generator life. Can only run for its "duty cycle" time before greatly affecting the life of the generator (not motor).

Standby Generators (have brushes);

1] "Inverter" control not needed to provide "clean" power. Good quality sine wave is produced "naturally".

2] Has good voltage regulation (<5%...usually between 1% & 3%).

3] Is designed to run 24 hours a day without reducing the life of any equipment by doing so.

As you may now see, your Kubota is not the issue...the generator you attach to it may be an issue.

Hi Elkangorito,
So using contactors manufactured to meet the UL1008 standard for specific use in an ATS configuration puts the contactor issue to bed. It would seem to do no harm to continue with the idea of using HRC fuses for the mains supply?

Interesting PDF document, thank you for that. Have you ever come across the type of single solenoid contactor detailed in the document?

Genset

Using an ATS that incorporates magnetically held contactors (single coil) is perfectly ok if the installation complies with UL1008, CSA178 and IEC 947-6. IMHO, HRC fuses are always preferable as a means of Short Circuit protection. The initial cost is cheaper, they act very quickly & take up less space in a switchboard. The alternative is to use Fault Current Limiting circuit breakers, which are very expensive. Normal circuit breakers may be used but this may require an increase in cable size & contactor size.

Using "mechanically held" contactors (latching contactors) is certainly more economical than using standard contactors (less energy used). On any occasion that I've been asked to design a control circuit, which uses contactors that are held in all the time, I choose DC coils. DC coils are designed to do this (AC coils are not really designed for continuous duty). The only problem then is that a DC source must be provided (more expense).

"Latched" contactor coils obviously are not worried about "duty", since they are momentary. Most "latched" contactors are dual coil.

Gary A · September 3, 2009

I have the same problem with the local electric supply as many others in Thailand. The voltage is up and down, frequent disconnects of just a few seconds and maybe once every three weeks or so, a disconnect lasting several hours. I'm not interested in having enough backup power for the entire house. I have separate breakers for the air, water heater and water pump. The lighting circuit is only 10 Amp. My computer, TV and all the house lights are on that circuit. I'd guess that if everything were turned on at once, the 10 Amp breaker would pop. In my case, it has never popped out.

I don't want to have to run the generator all the time. Just long enough to charge the batteries. I would like to use batteries and an inverter for continuos power to to my 10 Amp circuit. this would eliminate voltage variation and the frequent very short time interruptions. The batteries would normally stay charged with the mains power and with an extended outage, start the generator. Does my intended usage of the generator mean that I could use the brushless model?

genset · September 3, 2009

Now might be a good time to offer a few words of advice on generator selection and a little on how a generator works.

Generators are rated according to the capacity of differing alternator (the power generating portion of a generator) and engine (drive-train) combinations, to convert mechanical energy into electrical energy at a given rate, for a given period of time. Ratings are divided into four categories.

Emergency Standby Power

Standby Power

Prime Power

Continuous Power

The categories differ according to the duration and frequency of use and the amount of power generated by the alternator as a percentage of the maximum alternator output. The typical operation for an Emergency Standby Generator is to supply 70% of its rated output for around 50hrs a year (less than one hour a week) with a maximum expected usage of 200hrs, for a Standby Generator, typical use is 70% for 200hrs (approx 4 hrs a week) with 500hr maximum expected. Standby generators are rated to provide power for the duration of a power outage but little more; they are not rated to run 24 hours a day. Prime Power Generators may operate with varying loads for an unlimited amount of time, typical peak demand for Continuous Power Generators can be as high as 100% of the continuous power rating for 100% of its operating hours. As the requirement to operate with a heavy load for extended periods of time increases, so too must the manufacturing specs, quality and capabilities of the engine and alternator.

To accurately size a generator you need to know the load requirement of your home or business (calculate using the starting wattage of any reactive loads) and what role the generator will be expected to play; standby (in the event of power outage) or prime power (if no reliable, alternate power source is available) as this will affect the choice of alternator and engine combination. If a generator is to supply 70% of its maximum rated output for the best part of 24 hours a day, it is absolutely essential that your engine is correctly selected to produce consistent, reliable, mechanical energy to the alternator.

Smaller, lighter duty engines, are often air cooled, petrol driven and operate at 3000rpm driving a two pole (number of magnet poles on the rotor) alternator. If available, a water cooled, diesel driven engine operating at 1500rpm and turning a 4 pole alternator will reduce the likelihood of overheating, reduce your fuel costs, reduce the noise signature of the generator and increase its life expectancy (4 pole alternators are widely available in sizes from 10Kva up).

Whether an alternator incorporates brushes or not in its design, relates to the manner in which DC excitation current is transferred to the field windings (rotor) which rotate inside the stationary outer casing containing the output windings (stator). In the majority of alternators, the magnets on the rotor are not permanent magnets, they are electro magnets which are activated when a DC current (excitation current) passes through the windings around them. The exciter current is generated by a static or rotating exciter then transferred to the rotor windings by one of two methods. DC voltage from an automatic voltage regulator, (or alternate source) via stationary carbon brushes to slip rings on the rotor shaft, or AC current from a separate exciter winding passing through a rotating rectifier arrangement and converting the AC current into DC current. Whichever method is used, the DC current passes through the rotor field wirings creating an electro magnet. As the electro magnets rotate, they induce an AC current in the stator windings, Et voila.

Electronic voltage regulation is finding its way into smaller and smaller generator sets these days. It is still common for the voltage of portable generators to be regulated by a capacitor for example, but an AVR (automatic voltage regulator) is a far better option. It works by converting a small amount of the generator AC voltage to DC current (once the generator is at full voltage), this current is inversely proportional to the generators output voltage (the higher the voltage output of the generator, the less DC current the voltage regulator produces). AVRs are normally adjustable allowing voltage to be accurately set when the generator is running at full speed with no load. When a load is added to the generator, the output voltage will drop a little. The AVR instantly compensates by increasing the amount of DC current raising the voltage back to its proper level, this is especially useful for motors requiring a surge of power on start up, such as those found in fridge/freezers, air conditioning units etc. With a non changing load on the generator, the voltage regulator produces just enough DC current to keep the generator producing the correct output voltage.

A correctly sized and regularly maintained generator should give you years of reliable service. Periodical (annually or bi-annually, depending on use) changing of the oil, oil filter, fuel filter, cleaning or replacing the air filter, correct use of coolant in the case of a water cooled generator (as important in hot climates as cold) and checking the fan belt tension will all add to the life expectancy of a generator.

More information about generators can be found on my site at http://www.generatorsolutions.org

Cheers, Genset

Gary A · September 3, 2009

So, an AVR would compensate for the RPM changes in the kubota due to increase or decrease of the load? I have no idea how much the rpm's would change.

The little diesel is 11HP water cooled.

Any idea what a dependable AVR generator suitable for 11 HP would cost?

genset · September 3, 2009

So, an AVR would compensate for the RPM changes in the kubota due to increase or decrease of the load? I have no idea how much the rpm's would change.
The little diesel is 11HP water cooled.

Any idea what a dependable AVR generator suitable for 11 HP would cost?

As long as you have selected an engine and alternator sized to handle your maximum load requirement at approx 70-80% of the maximum standby generator output rating, the rpm's should change very little (unless you're starting a motor with a hefty start up wattage). If it is really struggling you may just have a generator which is under sized for your specific needs.

Is it your intention to purchase another alternator with an AVR and belt drive it from your Kubota? If so you will need a double bearing alternator with pulley (single bearings are for direct drive alternators, coupled directly to the flywheel of an engine). Belt driven alternators are less efficient (as a result of being belt driven) direct drive are more efficient. If you are considering this, I would recommend you re-calculate your load requirement in the first instance so that you can accurately size the alternator you need ,then address whether your 11hp Kubota is a sufficient size to belt drive it.

Genset

Gary A · September 3, 2009

Having 6,000 watts available is plenty for my house provided I don't use the air con or hot water shower. I don't have a generator for it now so can buy whatever some knowledgeable person recommends. As far as driving the generator, it would likely be driven with a jackshaft with universal joints to ease any stress on the generator bearings. The generators available locally are cheapies and I wouldn't buy one of those even though the genset would be used very little. 11 HP @2400 RPM converts to 8,200 watts so I should have plenty of HP.

I looked at a 5,000 baht 5000 watt generator but it was made in China.

genset · September 3, 2009

Having 6,000 watts available is plenty for my house provided I don't use the air con or hot water shower. I don't have a generator for it now so can buy whatever some knowledgeable person recommends. As far as driving the generator, it would likely be driven with a jackshaft with universal joints to ease any stress on the generator bearings. The generators available locally are cheapies and I wouldn't buy one of those even though the genset would be used very little. 11 HP @2400 RPM converts to 8,200 watts so I should have plenty of HP.
I looked at a 5,000 baht 5000 watt generator but it was made in China.

Your calculation is correct; 1Hp = 0.746 Kw, therefore 11Hp = 8.2Kw... but heres the caveat... this calculation assumes 100% efficiency in the transfer of mechanical energy from the engine into electrical energy at the alternator. Given that your engine will not directly drive an alternator, your efficiency will be much lower than 100%, possibly as low as 60%. A simple rule of thumb with engines of this type is to work on a calculation of 1Hp = 0.500 Kw, using this calculation, your engine should be able to drive an alternator with a maximum standby rating of 5.5 Kw.

China has something of a bad rap on the generator front. There ARE good generators being manufactured in China, the trick is finding a company who manufactures the engines and alternators to an internationally recognised standard. Either way, 5,000 baht is a ridiculously low and unrealistic figure to pay for a 5Kw genset even if it's a very basic portable model. Quality and reliability cost money I'm afraid and they are two areas you don't want to skimp on when purchasing a standby generator.

To produce 220v at 50hz, your engine will need to drive a two pole alternator at 3000rpm (1500rpm if you have a four pole alternator), not the 2400rpm you mentioned. You should ensure that you can adjust the idle on your machine to run at these speeds without operator input or the frequency of your supply will be incorrect.

Genset

genset · September 7, 2009

Interesting PDF document, thank you for that. Have you ever come across the type of single solenoid contactor detailed in the document?

I've not actually seen one of those, but if you look on the (mostly American) websites of ATS manufacturers they seem very common.

Looks like they only need a pulse to the solenoid to switch to the other position, energy saving and they can be manually switched

Attached is a PDF document for another version of this type of switch. It would seem to be an automatic double throw switch, but according to the PDF document, when managing the changeover from mains to generator supply (or gen to mains), it attempts to briefly synchronize the two supplies before handing over.

I have to admit that I dont like this aspect of the switch. As it cannot 'see' the accurate RPM of the generator (no magnetic pick up sensor) and has no ability to govern the engine throttle (two essential aspects of engine control when setting up a synchronized system), it relies on the natural frequency drift of the mains and generator supply. Waiting until the phase shift is as 'in sync' as possible before activating the changeover.

If the sensitivity of electrical equipment being powered is such that a soft (synchronized) power transfer is preferred, then a genuine 'single genset parallel to mains synchronization controller' should be used. I can think of no reason that this should be the case for a domestic installation. A break before make transfer should always be the default installation for domestic panels.

Genset

GTX_O_M_EN_Rev7.pdf

Crossy · September 7, 2009

I don't think there is any active attempt to sync. the genset to the mains, merely to time the operation of the switch so that disturbances that could affect the load are minimised.

To be honest, unless the frequencies are very close I would think that things would drift out of sync. before the mecanical switch had time to operate.

elkangorito · September 7, 2009

I'm inclined to agree with you Crossy.

To me, this function is superfluous under typical conditions.

genset · September 7, 2009

I don't think there is any active attempt to sync. the genset to the mains, merely to time the operation of the switch so that disturbances that could affect the load are minimised.
To be honest, unless the frequencies are very close I would think that things would drift out of sync. before the mecanical switch had time to operate.

Yes, I tend to agree with you also on this. There cannot be an 'active' attempt to sync as the transfer switch electronics have no way of controlling the generator frequency. I also thought that a double throw switch could only connect the load to one supply or the other (but not both simultaneously). It is the terminology used in the document that leaves me in some doubt, the phrase 'In-Phase monitor tracks the frequency of both the Utility and Generator sources allowing a smooth, synchronous transfer of the load', I find a little misleading.

When tranferring back to mains supply after a power outage for example. Precisely measuring and comparing the frequency and phase angle of both the mains and generator supplies prior to simultaneous connection of both supplies to the load, then the disconnection of the generator supply is my experience of 'synchronous transfer'. If they are simply looking at the frequency of both the mains and generator supply before switching from one to the other at a point in time at which they are most closely matched (sync'd), but without the two sources ever being connected simultaneously then this is a moot point (my initial impression was that this is what they are attempting to do... ) and poses no real hazard. However, if there is at anytime a simultaneous connection of mains and generator supplies, there is potential for the alternator to be damaged (amongst other things) as a result of an unsynchronized connection.

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