Generators In Thailand

[Crossy]

it should be possible to have the (single phase) generator switch to any of the phases in my house as needed. i had a similar but very simple setup in a house (in another "high-tech" country) decades ago. the house was wired single phase but we had a 3-phase incoming supply and used whatever phase was "on" or delivering the correct voltage.

Do you have any 3-phase equipment? If so forget trying to feed one phase off a non-synchronised genset, 3-phase motors would get more than somewhat upset

Otherwise, if you've actually got what amounts to 3 single-phase installations I see no reason why (with appropriate interlocks and safety devices) you shouldn't feed one or more phases from your genset, leaving the 'good' phase powering the remaining kit. How legal this would be in Oz or the UK I don't know, not very I would suspect.

[Naam]

i have two 3-phase sets, my attic exhaust fan and my "whole-house" fan. but both are switched manually only by myself and their RPMs can be adjusted by frequency converters. otherwise each and every consumer is single phase. the once in a while lack of one phase was the reason why i selected the 36k btu aircon single phase.

"legally in Oz or UK". i wish i had photos of the setup i described (using whatever phase was convenient). people like you and Crossy would have slight heart attacks

[genset]

To show the effect of having a reduced voltage starter (soft starter) on the size of a genset.

David96...

At last count, I think this is four attempts you have now made to force an explanation of this issue... I have stopped banging my head against the wall for 5 minutes to ask you AGAIN... to please drop this now

As Naam has stated, on more than one occasion, "the question i asked has nothing to do with any soft starter. anyway, the question is academic and not really relevant for the problems which have to be solved"

Further, you proceeded offer the following advice;

To show the effect of having a reduced voltage starter (soft starter) on the size of a genset.

and...

Advantages of soft starter.

Low starting currents , smooth starting, full motor protection, reduction in genset capacity.

Costs. Cost of a soft starter against the cost of a larger genset. And if you have a larger genset you have spare capacity in kVA for other purposes.

The point you have missed by dragging out this subject and thrashing it to within an inch of its life... is the reason why the question of whether Naams AC units contained soft starter motors, was raised to begin with.... namely the possible effect of non-linear loads on the operation of a generator/avr and why they may present a problem for anybody considering the installation of a generator... You've gone round full circle and ignored the original reason for this subject being raised.

For any reader who may be confused by this string of posts regarding soft starters (I'm sure they're lined up around the block..) please begin by reading Crossys post #85, Naams response #86 and my post #87, that should (I hope), clear up any confusion.

Although I do appreciate your efforts to pitch in with detailed information, I'm afriad your obsession with this subject will have readers chewing through their own arms to get away from the thread, so please, please, please.... enough...!

Genset

Edited November 18, 2009 by genset

[genset]

David,

thanks to your explanations i am well aware what the function of a soft starter is. but the question i asked has nothing to do with any soft starter. anyway, the question is academic and not really relevant for the problems which have to be solved and "Genset" was kind enough to answer it.

I decided to answer Naam, directly by email, in an effort to pour cold water on the discussion of soft starters within the thread.

i also want to keep my installation as simple as possible that in case of a problem either myself or a qualified electrician can lay a hand on. anything that contains chips or is computerised should in my view be avoided when living in the technical wilderness of Thailand. member "Genset" has sent to me by mail the description of a most beautiful gadget which would handle automatic/remote start-up in case of brownouts or phase failures.

I have attached a copy of the data sheet for the 'gadget' to which Naam refers. Manufactured by ComAp, this is an Automatic Transfer Switch controller (True RMS sensing), I use a variety of ComAP controllers including IntelliAMF (Automatic Mains Failure with Generator controls) and IntelliGen (Single Genset Parallel to Mains operation (Synchronized operation)). The IntelliATS is the most basic controller with a simple remote start command to start the generator (monitors under/over voltage and frequency for single and three phase applications), but still very, very reliable. If you have an existing, manual start (electric start) generator, this unit can be retrofitted (to any generator with remote start ability) to enable automatic transfer switching.

additional second thoughts have also come up as far as a 3-phase generator is concerned. i normally face a brownout or complete loss of a single phase only and have still two phases with normal voltage. therefore i think it's an economical nonsense to switch off the "good" phases too and serve all three phases with a 3-phase generator.

It should be possible to have the (single phase) generator switch to any of the phases in my house as needed. i had a similar but very simple setup in a house (in another "high-tech" country) decades ago. the house was wired single phase but we had a 3-phase incoming supply and used whatever phase was "on" or delivering the correct voltage.

opinions please and thanks in advance.

Reasonable comment...

and from your next post...

"legally in Oz or UK". i wish i had photos of the setup i described (using whatever phase was convenient). people like you and Crossy would have slight heart attacks

If you decide to use a single phase genset, configured to address the problem you have cited, I would ask you to consider asking either Crossy or Elkangorito (if they dont mind...) to assist you in designing a method of achieving this safely prior to genset installation.

Genset

InteliATS_NT_Datasheet_2009_02_CPLEIANT.pdf

[Naam]

What size / rating circuit breaker do you have on that circuit naam, that 160+ amps being drawn doesn't trip?

a freaking normal Siemens 'lazy' 25 amp breaker which has never tripped and that is the reason why i doubt all these starting factors 3 and 4

In my photo studio we used the big Bowens capacitor power packs which claimed to have a peak draw rated at 15amps. We would run two of these plugged into a 13amp extension lead protected by a 13 amp fuse, and a total of six or seven on a 30amp ring main. Never a problem. I know it's not motors which is what we're talking about in this thread, but this Quoted Max/Peak drawn current business baffles me too.

it IS motors we are talking about Marvo! and these motors, the compressors in the aircons, have to deal with a heavier load than a normal motor.

[Marvo]

What size / rating circuit breaker do you have on that circuit naam, that 160+ amps being drawn doesn't trip?

a freaking normal Siemens 'lazy' 25 amp breaker which has never tripped and that is the reason why i doubt all these starting factors 3 and 4

In my photo studio we used the big Bowens capacitor power packs which claimed to have a peak draw rated at 15amps. We would run two of these plugged into a 13amp extension lead protected by a 13 amp fuse, and a total of six or seven on a 30amp ring main. Never a problem. I know it's not motors which is what we're talking about in this thread, but this Quoted Max/Peak drawn current business baffles me too.

it IS motors we are talking about Marvo! and these motors, the compressors in the aircons, have to deal with a heavier load than a normal motor.

Yes, yes, yes, I know it's motors we're talking about .

OK, semantics and grammar (naam's favourite topic)!!! I missed a comma in my punctuation . Sorry.

I intended to write "I know it's not motors, which is what we're talking about in this thread, but this........"

and more correctly I should have written "I know it's not motors (I am writing about above), which is what [the subject] we're talking about in this thread, but this........"

This missing comma disorientated you naam, but if you had attended Mrs naam's English classes all these years you'd have subconsciously realised my error and inserted a comma in your mind . To arrive at your interpretation you imagined that I was trying to write;

a ) "I know it's not motors which we're talking about in this thread, but this........" or

b ) "I know it's not motors what we're talking about in this thread, but this........" or

c ) "I know it's not motors that we're talking about in this thread, but this........"

I know what a stickler for detail you are naam, but it was only a comma... .

Back to topic .

Edited November 18, 2009 by Marvo

[genset]

In my photo studio we used the big Bowens capacitor power packs which claimed to have a peak draw rated at 15amps. We would run two of these plugged into a 13amp extension lead protected by a 13 amp fuse, and a total of six or seven on a 30amp ring main. Never a problem. I know it's not motors which is what we're talking about in this thread, but this Quoted Max/Peak drawn current business baffles me too.

Hi Marvo,

I'm not sure your explanation has really clarified what I think you were trying to say... I had to read it myself a couple of times to get my head around it... how about this..

"I understand that my example refers to the load drawn by a capacitor power pack and not the peak load drawn by motors, which is the current focus of this thread..."

Hopefully this will avoid a string of posts from readers tearing their hair out in response to your last missive...

Genset...

Edited November 18, 2009 by genset

[Naam]

This missing comma disorientated you naam, but if you had attended Mrs naam's English classes all these years you'd have subconsciously realised my error and inserted a comma in your mind...

CONSPIRACY! engineered without any doubt by Mrs. Naam. conspiring with Marvo behind my back. expect severe repercussions! both of you!

[Naam]

If you decide to use a single phase genset, configured to address the problem you have cited, I would ask you to consider asking either Crossy or Elkangorito (if they dont mind...) to assist you in designing a method of achieving this safely prior to genset installation.

Genset,

can it route the generator to the phase which is gone? if yes, why using electronics which nobody can service in Thailand within a short time if something goes wrong instead of using good old manual switches?

[genset]

Genset,

can it route the generator to the phase which is gone? if yes, why using electronics which nobody can service in Thailand within a short time if something goes wrong instead of using good old manual switches?

Hi Naam,

I have never before been asked to configure a generator in the manner you are suggesting but I see no reason why it could not be done.

As it is your wish (in the event of a dropped phase) to substitute one of your utility phases (either/or L1, L2, L3) with a single phase standby generator supply, the main issue (as Crossy mentioned with his comment on interlock and safety devices), is ensuring that the single phase generator supply and the phase/s in question are never connected simultaneously.

In my opinion, the safest form of manual transfer switch, is a 3 position 'break before make' rotary switch. The utility supply is fed into one side of the switch, the generator supply is fed into the other, the output from the switch then carries the supply from whichever feed is selected, to the distribution board. In position one, the utility supply is fed to the distribution board. The second position 'breaks' the connection between both the uility supply and the generator supply (this ensures that both the utility supply and the generator supply are isolated from each other and from the distribution board during transfer), and in the third position the generator supply is fed to the distribution board.

To achieve the effect you are suggesting, you would need 3 separate, 3 position 'break before make', single phase rotary transfer switches (imagine them side by side in a line if you will...). The first of your three utility supply phases (L1) would be fed into the utility supply side of the first transfer switch, the second utility phase (L2) into the utility supply side of the second switch and the third utility phase (L3) into the the utility supply side of the third switch. The single phase standby generator supply, would be fed into the secondary supply side of the first rotary switch, it would then be looped to the secondary supply side of the second and third switches. The output from each of the three transfer switches are fed into your 3 phase distribution board MCB to be distributed between your circuits, as per your normal three phase utility supply.

In the event that you drop a utility phase (L3 for example), after starting the generator and checking that you have a stable suppply, you would then manually switch the third rotary transfer switch from position one (utility) to position two, this breaks the utility connection and no power (utility or generator) is available to the circuits on your L3 phase. Selecting position 3 (generator) restores power to your L3 circuits from the generator. When the L3 utility supply phase is restored and stable, you may then move the selector from position 3 (generator) to position 2 breaking the supply to your L3 circuits once more, then select position 1 (utility) restoring the utility supply phase to your L3 circuits, you may then shut down the generator.

Because the generator supply is looped between each rotary transfer switch, the generator supply is able to replace whichever phase has dropped out... you may even (as long as the generator is sized appropriately), use the generator to supply two, or even all three phases should a complete power outage occur (this is only appropriate if you are not running any three phase appliances in your home, under no circumstances should you attempt to operate any three phase appliances using a single phase generator supply).

Just a quick word on your comment regarding the servicability of electronics in Thailand (specifically in regard to the ComAp Automatic Transfer Switch Controllers I use when manufacturing auto transfer switch panels). The authorised distributor of ComAp products in Thailand is a small family company (40 years in business) in Bangkok called Daven Company. I spent some considerable time with the owner (a very engaging 70 year old man) and his technicians this year, they are a very friendy and knowledgable bunch. They speak good English and offer great support for these products (replacement and/or repair if necessary).

I should mention the advantages of an automatic transfer switch, just for the record. I know you mentioned the economic viability of using a three phase generator as a secondary supply when only one phase has dropped out. The advantages are that the entire procedure is carried out automatically (obviously), not only in the event of a dropped phase (voltage asymmetry) but also utility supply under/over voltage, under/over frequency, and over current. It also negates the need for you to get up and start the generator and carry out a manual transfer should this occur in the middle of the night (or other inconvenient times), or if you are not available (away from home) and the task falls to your wife or staff. Also, regular start up and running of the generator on load (in the event of a dropped phase) is a good thing for the generator; if not used in this manner, you should still exercise the generator regularly (once a week, on load if possible) to keep the generator in peak condition.

Hope this helps, if anybody has an alternative solution to Naams requirement, I'd be interested to hear it.

Genset.

Edited November 18, 2009 by genset

[Naam]

Genset,

without going into too many details i admit that some of your logic can't be questioned. but the problem of starting amps using a 3-phase generator including the autosensing/autoswitching and generator start still remains and can't be solved with soft starters only.

correct me if i am wrong in my thinking that only a huge overdimensioned generator could handle the starting amps of the consumers on all three phases EXCEPT if the big consumers (aircons) are handled with timers and other gadgets which switch -before generator start- all of them first OFF and then ON one by one.

[david96]

We should have asked the following questions concerning Naams existing electrical installation.

1 Single phase 220V 2 wire supply or 3 phase 380/220 4 wire supply.

2 Are there any 3 phase motors connected and type of starting eg DOL.

3 Are all airconditioners and other motors single phase.

4 Are all loads balanced across 3 phases if a 3 phase supply.

5 The FL Amps of each motor.

6 Other load, lighting and general power on each phase in amps (approx).

It would appear that he has a 3 phase supply. But no 3 phase motors.

Most of his motors he wishes to run on a genset are connected on one phase only.

In this case one would first balance the loading across the 3 phases as far as practicable and use a 3ph. 380/220V 4 wire genset.

Change over with a 3 pole ATS of suitable rating with control unit.

or, a 3 pole manual change over switch 1- OFF- 2.

However if he wishes to use a single phase 220V generator one would balance the loading

across the existing 3 phases.

Change over with an 3 pole ATS but in this case the 1 phase from the single phase genset

is connected to one of the common terminals of the ATS and bridged out to the other two.

Change over with a manual switch the same principle applies.

Eg. ATS 1, 2, 3. incoming mains supply. 4, 5, 6.to the genset. 7, 8, 9. to the existing load.

Switching - Mains supply Position 1. Terminals 1 to 7. 2 to 8. and 3 to 9.

Generator supply Position 2. Terminals 4 to 7, 5 to 8, and 6 to 9.

With a single phase connection terminals 4, 5, and 6 are bridged and the single phase conductor

from the generator is connected to these terminals.

The neutral conductor is not switched.

You can make a working drawing from this information

There was confusion with the term "consumer" there is only one consumer that is Naam, the "consumers" referred to are actually electrical loads within his installation.

[InterestedObserver]

It would appear that he has a 3 phase supply. But no 3 phase motors.

Naam says:

i have two 3-phase sets, my attic exhaust fan and my "whole-house" fan. but both are switched manually only by myself and their RPMs can be adjusted by frequency converters. otherwise each and every consumer is single phase. the once in a while lack of one phase was the reason why i selected the 36k btu aircon single phase.

[Crossy]

1.

We also have to take in to account that Naam wants to have a partial switch over to generator power. Whereby he can replace any one or more of his incoming phases with the output of a single-phase genset, for use in the event that one phase dies whilst the other two are satisfactory.

2.

Would the simple solution to his start-current issues be simply to use the motor contactors with red and green buttons? These drop out when the power goes off and only re-energise when the green button is pushed, a manual process of course and is still does not address the possibility of the on-off cycle of two or more aircons becoming synchonised over time during a long power outage.

IMHO trying to develop a system that inhibits starting of all other aircons whilst one unit is in the process of starting would become over complex and difficult to maintain, the cost of such a system may exceed the additional cost of a larger genset capable of starting two A/C units.

[Naam]

We should have asked the following questions concerning Naams existing electrical installation.

1 Single phase 220V 2 wire supply or 3 phase 380/220 4 wire supply.

yes

2 Are there any 3 phase motors connected and type of starting eg DOL.

yes two, but switched on manually by the master of the house only (see and read above)

3 Are all airconditioners and other motors single phase.

yes

4 Are all loads balanced across 3 phases if a 3 phase supply.

you bet your sweet arse on it that they are

5 The FL Amps of each motor.

6 Other load, lighting and general power on each phase in amps (approx).

will find out

It would appear that he has a 3 phase supply. yes But no 3 phase motors. have!

Most of his motors he wishes to run on a genset are connected on one phase only.

that depends

In this case one would first balance the loading across the 3 phases as far as practicable and use a 3ph. 380/220V 4 wire genset.

Change over with a 3 pole ATS of suitable rating with control unit.

or, a 3 pole manual change over switch 1- OFF- 2.

???

However if he wishes to use a single phase 220V generator one would balance the loading

across the existing 3 phases.

???

Change over with an 3 pole ATS but in this case the 1 phase from the single phase genset

is connected to one of the common terminals of the ATS and bridged out to the other two.

???

Change over with a manual switch the same principle applies.

???

Eg. ATS 1, 2, 3. incoming mains supply. 4, 5, 6.to the genset. 7, 8, 9. to the existing load.

???

Switching - Mains supply Position 1. Terminals 1 to 7. 2 to 8. and 3 to 9.

???

Generator supply Position 2. Terminals 4 to 7, 5 to 8, and 6 to 9.

???

With a single phase connection terminals 4, 5, and 6 are bridged and the single phase conductor

from the generator is connected to these terminals.

???

The neutral conductor is not switched.

???

You can make a working drawing from this information

you can?

There was confusion with the term "consumer" there is only one consumer that is Naam, the "consumers" referred to are actually electrical loads within his installation.

vhat der fock else? Naam is NOT a consumer of electric energy. Naam, his wife, his two dogs and his two domestic employees USE for various purposes electric energy but they do NOT CONSUME it.

[Naam]

We also have to take in to account that Naam wants to have a partial switch over to generator power. Whereby he can replace any one or more of his incoming phases with the output of a single-phase genset, for use in the event that one phase dies whilst the other two are satisfactory.

i have changed my mind Crossy. Genset and his logical argumentation has convinced me BUT ONLY IF the starting amp problem (see above) can be solved.

[Naam]

Genset sent me a pdf-file from a renowned manufacturer of alternators. it says:

"When a motor is started, a large surge of current is drawn by the motor. This starting current is equivalent to the motors

locked rotor or stall current and is 5 to 10 times normal full load current."

i have two options now:

1. forget about the installation of a generator

or

2. consider all expert opinions on starting amps as bullshit² by referring to my experience in the african bush more than a quarter century ago when

quote my post #79: "going back in history. in ancient times (Nigeria 1982-1983) a 70kva single phase generator was my primary energy source for 1½ years which served 4 houses. if i recall correctly the total number of 1ton aircons was 12 plus 4 2ton units. these were the old rattlers built in the wall, had piston compressors, were drawing more than double the wattage of modern units and ran 24 hours seven days a week. a rough calculation results in a total load 45 kilowatts (~200 amps). engine oil of the generator, plus whatever my chief engineer deemed necessary was checked every day; the service lasted about 10 minutes and then the set was started again. these 10 minutes did definitely exceed the time of the relays which prevents an aircon compressor to start before pressure in suction and pressure pipe was equal.

my question is "how could the diesel and the generator cope with starting amps of 600 (using factor 3)?"

[genset]

correct me if i am wrong in my thinking that only a huge overdimensioned generator could handle the starting amps of the consumers on all three phases EXCEPT if the big consumers (aircons) are handled with timers and other gadgets which switch -before generator start- all of them first OFF and then ON one by one.

Hi Naam,

The short answer to your question is yes... Although the generator would seem to be oversized, calculating your load requirement based on the starting current of all the motors served by your existing 3 phase distribution board (if a whole house solution is required) is the normal method for sizing the generator.

Although in reality, the peak load requirement (of every motor starting simultaneously) may never actually be realized; sods law unfortunately states, that if you select an undersized generator, it would...

If a system designed to inhibit the simultaneous starting of all air conditioner motors, or a generator sized to accommodate the combined peak load requirement of all your appliances, are discounted; linking your critical (comfort) circuits to a separate distribution board (single phase would work as long as these circuits do not include any 3 phase motors), supplied via an automatic transfer switch by a single phase generator and sized to meet the peak load requirement of the aforementioned critical (comfort) circuits, would represent a simple and effective solution. If configured in this way, the transfer switch design would differ slightly from normal, in that the utility supply would feed your existing 3 phase distribution board and the generator supply would feed the secondary (comfort circuits) distribution board via interlocked contactors. This configuration would ensure that both supplies could not be connected simultaneously.

Genset sent me a pdf-file from a renowned manufacturer of alternators. it says:

"When a motor is started, a large surge of current is drawn by the motor. This starting current is equivalent to the motors

locked rotor or stall current and is 5 to 10 times normal full load current."

Naam.... dont panic... the document refers to an alternator sized in the 300 to 400Kva range (not the 30 to 40Kva alternators we are discussing for your application) and as such would be used to power large, 3 phase motors for commercial applications and not small motors such as the type found in your home. The paragraph quoted should not be taken literally, I sent it to you to reinforce the idea that a calculation based on a multiple of 3 (for startup current) was realistic based on your earlier comments, doubting the veracity of 'expert' opinions regarding the rough calculation of startup current for motors posted in the thread.

The best way to solve this conundrum, is to purchase that tong tester (clamp on ammeter with peak hold function) we discussed earlier and take a simple reading of each of your AC 'comfort' circuits on startup, that should put this baby to bed once and for all....

Genset

Edited November 19, 2009 by genset

[Naam]

The best way to solve this conundrum, is to purchase that tong tester (clamp on ammeter with peak hold function) we discussed earlier and take a simple reading of each of your AC 'comfort' circuits on startup, that should put this baby to bed once and for all....

i have been phoning around already. result: "clam testa no habb"

[genset]

i have been phoning around already. result: "clam testa no habb"

... try an electrical supply store instead of a fishmongers... lol...

If you can make it to Bkk, I can give you the address of a place you can buy one...

Genset

Edited November 19, 2009 by genset

[genset]

The best way to solve this conundrum, is to purchase that tong tester (clamp on ammeter with peak hold function) we discussed earlier and take a simple reading of each of your AC 'comfort' circuits on startup, that should put this baby to bed once and for all....

i have been phoning around already. result: "clam testa no habb"

For anybody in need of electrical components or test equipment... attached is a list of electrical distributors in Bangkok.

Genset.

Merlin_Gerin_Square_D_Telemecanique_Distributors_Bangkok.xls

[david96]

Naam, the term "consumer" is the person or entity that has an electricity account in their name. A supply authority (eg the PEA) will have a number of consumers connected to their system. The consumer is the one who is responsible for paying the electricity account.

You have 2 x 3 phase motors, manually switched for starting. If you use the single phase configuration you can not run these two motors, but you can isolate them.

I would willing supply a drawing of the switching if one can find a way of pasting a drawing

using MS Word into a post. I will give it a try.

If you want to run on a partial supply , 220V on one phase only use a single pole changeover switch 1 - 0 - 2 and connect this Mains to term 1, load to term 3 and the common term 2 to the generator. Make sure that your 3 phase motors are isolated first before changing to genset power. In this case your genset will be 220V single phase.

You should look at the cause of these "brownouts" that appear only this one phase. One cause is the loss of a HV fuse at the distribution transformer which will give severe voltage unbalance on one phase. Your motor protection should disconect your 3 phase motors.

Fluoro. lights will go out and any voltage sensitive equipment will be affected on that particular phase. But it might be a different phase next time.

[Naam]

Naam, the term "consumer" is the person or entity that has an electricity account in their name. A supply authority (eg the PEA) will have a number of consumers connected to their system. The consumer is the one who is responsible for paying the electricity account.

i beg to differ but it does not matter

You have 2 x 3 phase motors, manually switched for starting. If you use the single phase configuration you can not run these two motors, but you can isolate them.

of course i can't run them. no need to isolate them as they are switched manually on/off by 3-ph breakers.

I would willing supply a drawing of the switching if one can find a way of pasting a drawing

using MS Word into a post. I will give it a try.

let us wait. i am sending now my wife's driver around with this printout:

Make sure that your 3 phase motors are isolated first before changing to genset power. In this case your genset will be 220V single phase.

see above

You should look at the cause of these "brownouts" that appear only this one phase. One cause is the loss of a HV fuse at the distribution transformer which will give severe voltage unbalance on one phase.

phases with brownouts vary. i have a gadget installed which switches off any phase if voltage drops below 220v.

Your motor protection should disconect your 3 phase motors.

Fluoro. lights will go out and any voltage sensitive equipment will be affected on that particular phase.

i don't have sh*t like fluoresent lights in my house. anyway see "phase off" above. and thanks for your input.

[InterestedObserver]

quote my post #79: "going back in history. in ancient times (Nigeria 1982-1983) a 70kva single phase generator was my primary energy source for 1½ years which served 4 houses. if i recall correctly the total number of 1ton aircons was 12 plus 4 2ton units. these were the old rattlers built in the wall, had piston compressors, were drawing more than double the wattage of modern units and ran 24 hours seven days a week. a rough calculation results in a total load 45 kilowatts (~200 amps). engine oil of the generator, plus whatever my chief engineer deemed necessary was checked every day; the service lasted about 10 minutes and then the set was started again. these 10 minutes did definitely exceed the time of the relays which prevents an aircon compressor to start before pressure in suction and pressure pipe was equal.

my question is "how could the diesel and the generator cope with starting amps of 600 (using factor 3)?"

The diesel engine only had to cope with the real power (kW) portion of the load, while the generator only had to cope with the reactive power (kVAr) portion. The division of kW vs kVAr is determined by the power factor (PF) of the load at any given instant. So the answer is, neither the diesel nor the generator had to cope with the full starting current, 600 amps in this case, it was split up between them in a proportion determined by the PF and the power triangle..

Edited November 20, 2009 by InterestedObserver

[InterestedObserver]

quote my post #79: "going back in history. in ancient times (Nigeria 1982-1983) a 70kva single phase generator was my primary energy source for 1½ years which served 4 houses. if i recall correctly the total number of 1ton aircons was 12 plus 4 2ton units. these were the old rattlers built in the wall, had piston compressors, were drawing more than double the wattage of modern units and ran 24 hours seven days a week. a rough calculation results in a total load 45 kilowatts (~200 amps). engine oil of the generator, plus whatever my chief engineer deemed necessary was checked every day; the service lasted about 10 minutes and then the set was started again. these 10 minutes did definitely exceed the time of the relays which prevents an aircon compressor to start before pressure in suction and pressure pipe was equal.

my question is "how could the diesel and the generator cope with starting amps of 600 (using factor 3)?"

The diesel engine only had to cope with the real power (kW) portion of the load, while the generator only had to cope with the reactive power (kVAr) portion. The division of kW vs kVAr is determined by the power factor (PF) of the load at any given instant. So the answer is, neither the diesel nor the generator had to cope with the full starting current, 600 amps in this case, it was split up between them in a proportion determined by the PF and the power triangle..

Or another way: Most synchronous generators are designed to support 300% of their rated kVA for 10 seconds. From the OP, [(600 amps starting current)(230 volts single phase)]/1000 = 138 starting kVA. The generator was rated at 70kVA, so 300% x 70kVA = 210kVA available to support starting current for 10 seconds. We can see that the generator had more than enough capacity to start the specified loads.

Edited November 20, 2009 by InterestedObserver

[genset]

Or another way: Most synchronous generators are designed to support 300% of their rated kVA for 10 seconds. From the OP, [(600 amps starting current)(230 volts single phase)]/1000 = 138 starting kVA. The generator was rated at 70kVA, so 300% x 70kVA = 210kVA available to support starting current for 10 seconds. We can see that the generator had more than enough capacity to start the specified loads.

Thank you Interested Observer...

I have been so busy over the past few days that some of these questions, deserving of specific answers have slipped through the net so to speak, thank you for picking this up in more detail.

I did respond to this question directly to Naam by email on 17/11 and gave the following (and, as I dont know if I'm coming or going at the moment, woefully brief answer); 'a generator with the correct insulation class (H), may also handle high overcurrent for short periods (such as that mentioned in Naams question), but the potential for alternator insulation failure is high', I followed this up more recently with the comment that 'things just arent made the way they used to be...'

Genset

Edited November 20, 2009 by genset

[Naam]

Observer: "Most synchronous generators are designed to support 300% of their rated kVA for 10 seconds. From the OP, [(600 amps starting current)(230 volts single phase)]/1000 = 138 starting kVA"

Genset:"a generator with the correct insulation class (H), may also handle high overcurrent for short periods (such as that mentioned in Naams question), but the potential for alternator insulation failure is high', I followed this up more recently with the comment that things just arent made the way they used to be..."

Gentlemen, assuming both claims are valid it is beyond my comprehension that the supplier of generators (main parts engine and alternator) would try to save cost by being stingy as far as insulation class of the alternator wiring is concerned. in Nigeria i bought the generator together with his twin second hand from a german construction company which withdrew from the country. that was end of 1981, both units were most probably 2-3 years old. and now i am told that after THIRTY years of technical and manufacturing development the products are inferior?

[david96]

And Naam,here is your drawing of the switching using a manual rotary changeover switch. 1-0-2.

[genset]

Observer: "Most synchronous generators are designed to support 300% of their rated kVA for 10 seconds. From the OP, [(600 amps starting current)(230 volts single phase)]/1000 = 138 starting kVA"

Genset:"a generator with the correct insulation class (H), may also handle high overcurrent for short periods (such as that mentioned in Naams question), but the potential for alternator insulation failure is high', I followed this up more recently with the comment that things just arent made the way they used to be..."

Gentlemen, assuming both claims are valid it is beyond my comprehension that the supplier of generators (main parts engine and alternator) would try to save cost by being stingy as far as insulation class of the alternator wiring is concerned. in Nigeria i bought the generator together with his twin second hand from a german construction company which withdrew from the country. that was end of 1981, both units were most probably 2-3 years old. and now i am told that after THIRTY years of technical and manufacturing development the products are inferior?

Naam,

No, contemporary alternators are not inferior, far from it, but 300% of rated Kva for 10 seconds equates to an enormous amount of heat being generated in the alternator windings. These recommendations exist to extend the life of an alternator at the end of the day Naam... the manufacturer doesnt want you to burn your alternator out through misuse.

Having said that, competition is rife and the bottom line does lead to cost cutting in some areas which irritate me to be honest. Mecc Alte exciter coils is one such gripe... they need to spend a little more money on improving the insulation of their exciter coils in my opinion, far too many of them short out in only moderate damp conditons and can be a real pain to change sometimes. I have taken to disassembling every Mecc Alte alternator that I fit and spraying additional insualtion on the exciter coil to reduce the frequency of these specific faults.

Let me qualify the remark I made, if I may... I regularly see alternators (belt driven PTO Tractor sets mostly), which are thirty + years old. These belong to old farmers who work the things hard, constantly (and dont like to spend money...!). I see them when the belts need changing, these things are overwound and heavily insulated, I have no doubt that they will be providing power to the milking parlours of future farming generations for years to come... 'They just dont build them like they used to...' (is the term I should have used), is a reference to the fact that these generators take a lot of stick and last for years because they were overbuilt and not because they were technically superior.

Genset.

Edited November 23, 2009 by genset

[genset]

The neutral conductor is not switched.

You can make a working drawing from this information

Hi David96,

You went on to add, (a note at the end of the drawing you subsequently posted), that;

'main neutral and generator neutral are connected to the neutral bar of the switchboard directly, they are not switched'

With respect, I disagree with you on the issue of a permanent neutral connection to a secondary power source (generator) for domestic use.

It is my preference to always treat a standby generator for domestic use (and not designed to sync and run parallel with the utility supply), as a separately derived source of power. As such the star point of the alternator is connected to earth via a grounding electrode at the site of installation and the alternator neutral is bonded to the body of the alternator.

When configured in this manner, the neutrals (utility and generator) should be switched and not permanently connected, if ground fault protection devices are in use.

If the utility supply neutral and the generator supply neutral are both, separately grounded and the neutrals of both sources are permanently connected at the transfer switch; should a ground fault occur, any ground fault current would be split along the neutral into two parallel paths to earth. If the amount of sensed ground fault current does not exceed the settings of any ground fault protection devices fitted (now or in the future) to the faulty circuit, they will be rendered ineffective, quite an important point to bear in mind.

The two main ways to solve this problem are to remove the neutral/earth bond from the alternator, or to switch the neutrals at the transfer switch (both of which would return the full ground fault current through the protection device). In my opinion, switching the neutral is a must.

I understand that MEN (PME) is a consideration, but as it is still not implemented country wide throughout Thailand, I prefer to focus on the viability of the local grounding system and proceed as if MEN is not in place (even if it is).

Genset

...Not sure what happened to the formating of this post, I wrote it in Msoft Word and pasted it into the window... the spacing is a little tight but I cant amend it... sorry.

The attached document explains this problem in more detail and quite clearly...

Gen_earth_grounding_and_4_pole_neutral_switching_Cummins_part_2.pdf

Edited November 22, 2009 by genset