Generators In Thailand

[genset]

i assume that "rectifier load" is the current drawn by the UPS's battery charger. if that is the case why the eff did we make a big hoo-ha about it? wasn't it clear from the beginning that aforesaid load is only a tiny percentage of the total demand?

Hi Naam,

UPS systems and variable speed drives (previously discussed) are both types of SCR based, non-linear loads (rectifier loads).

The big 'hoo-ha' as you have accurately described it, began with post # 81, in which David96 offered the following explanation of the (apparent) low current drawn on startup by your air conditioning systems, raising the question of whether your ACs were non-linear loads:

'Here are the specs for 5 models of Daikin airconditioners available in Thailand. They use inverter technology, in other words they have a variable speed drive and thus reduced voltage starting.'

It was followed up (quite logically...) by Crossy in post # 85 in which he wrote:

I'm wondering what the interesting VI waveforms produced by these VVVF drives will do to the AVR on the Genset. Ref our conversation on UPSs and PC PSUs with active PF correction.

Any A/C load will likely be a significant percentage of the overall consumption along with CFL lighting and switching PSUs.

Based on the floor plan you posted showing the location and size of your AC units, the 'significant percentage' Crossy refers to, would have been way in excess of the 50% (percentage of rectifier load) mentioned in the Australian Defence Dept document (posted by David96).

Although it became clear (following your subsequent post on the subject) that your AC units are not rectifier based loads, we disappeared down the rabbit hole somewhat on the question of non-linear loads from that point.

The degree to which the operation of UPS and other non-linear loads will affect the operation of a generator AVR needs to be observed on site, under working conditions. If a detrimental effect is observed, the previously discussed mitigation techniques should be employed.

Genset

[InterestedObserver]

taking my time and going through all expert opinions again i found:

The designer shall ensure that the generator is suitable for the operation with the UPS load.

When the UPS rectifier load is more than 50% of the total load connected on a generator,

the following special measures shall be considered to ensure stable and reliable operation

of the generator.

i assume that "rectifier load" is the current drawn by the UPS's battery charger. if that is the case why the eff did we make a big hoo-ha about it? wasn't it clear from the beginning that aforesaid load is only a tiny percentage of the total demand?

Most on-line UPS have rectifiers (thyristors) in the input stage to charge the internal DC bus and power the inverter. The rectifiers are therefore required to carry 100% of the UPS load plus charge the backup batteries. Unless on bypass or batteries the on-line UPS will present significant harmonics to the power source. It is common practice to provide some form of power factor mitigation at the input stage.

[Naam]

Most on-line UPS have rectifiers (thyristors) in the input stage to charge the internal DC bus and power the inverter. The rectifiers are therefore required to carry 100% of the UPS load plus charge the backup batteries. Unless on bypass or batteries the on-line UPS will present significant harmonics to the power source. It is common practice to provide some form of power factor mitigation at the input stage.

assuming the inverters are not isolated from the generator the rectifiers do not carry any load as the power from the generator is routed directly (bypassing the rectifiers) to the consuming gadgets. that's the information i received from the manufacturer.

[Crossy]

assuming the inverters are not isolated from the generator the rectifiers do not carry any load as the power from the generator is routed directly (bypassing the rectifiers) to the consuming gadgets. that's the information i received from the manufacturer.

This is quite true in the case of off-line UPSs typically found in SOHO installations.

IO is specifically referring to the case of high-end on-line UPSs typically found in data centres which do not have a bypass, the inverter powers the load at all times even when mains is present and therefore the rectifiers do indeed carry the full load current of the load at all times.

That said, even with an off-line UPS (or no UPS) PC power supplies (particularly those with active power factor correction) present a non-linear load which could upset your genset if it forms a significant portion of the total load.

[InterestedObserver]

When evaluating off-line, the so called SOHO or standby, UPS be sure to get one with a sine wave output if you can. Most of the low end units have a square wave or pseudo sine wave output when running on batteries. Square wave outputs are not suitable for all loads. There will also be a finite delay (milliseconds) while switching to batteries.

[Naam]

When evaluating off-line, the so called SOHO or standby, UPS be sure to get one with a sine wave output if you can. Most of the low end units have a square wave or pseudo sine wave output when running on batteries. Square wave outputs are not suitable for all loads. There will also be a finite delay (milliseconds) while switching to batteries.

i have no idea on what waves my three UPS are surfing what i know is that the computers don't wink an eye, don't realise anything watching TV but one of my former modems (now replaced) minded the switch and started connecting again.

[Deke]

For some reason I can't quote from Genset's first post. Also, apologies for getting into this thread late; it is a good one.

I'd like to point out one thing which is of little practical importance but probably worth noting if you are specifying new equipment.

Since 2007, the standard voltage at the delivery point (low voltage side of the PEA/MEA transformer) is 230/400 V (-10% / +6%).

If you are ordering new equipment, you should take this into account. Particularly if you are buying your own transformer, it should be 22 kV/400 V.

[genset]

For some reason I can't quote from Genset's first post. Also, apologies for getting into this thread late; it is a good one.

I'd like to point out one thing which is of little practical importance but probably worth noting if you are specifying new equipment.

Since 2007, the standard voltage at the delivery point (low voltage side of the PEA/MEA transformer) is 230/400 V (-10% / +6%).

If you are ordering new equipment, you should take this into account. Particularly if you are buying your own transformer, it should be 22 kV/400 V.

Hi Deke,

Welcome to the thread, new blood is welcome it'll prevent us from becoming inbred... I'm hoping the thread will serve as a hub (long term), for questions or comments related to generator installation and operation as they arise, so readers should feel free to pitch in whenever they need feedback or would like to comment. I've been very busy for the past few weeks, but always keep one eye on the thread.

The generators I am promoting (and most AVRs fitted to contemporary generators) feature a potentiometer to enable adjustment of the reference voltage for the alternator. This will allow you to accurately match the voltage requirement of your equipment (+/- 10% of 230/400v) if necessary.

I mentioned in an earlier post, that I would discuss automatic transfer switch systems in more depth and I will do that when time permits; but I would like to briefly address a misconception that seems to exist (based on a number of email enquiries), regarding the role of an automatic transfer switch.

Installing an automatic transfer switch system to control the transfer of power from primary (utility) to secondary (generator) source and back WILL NOT prevent an interruption of electrical supply to your home. An open transition (break, before make) automatic transfer switch system will monitor your utility supply and when needed, automatically start the generator; it will then transfer the supply and carry out the reverse process when the utility supply is restored and stable.

As the system cannot see a power outage coming, there will ALWAYS be an interruption in power during which time the utility contactor is de-energized, the generator is started and self tests are carried out; once a stable supply is being generated, the generator contactor is energized and the power (generator) restored to your home. When the utility supply is restored, the interruption will be much shorter (as both supplies are live), the transfer back to utility power (once the supply is stable) is relatively quick (1 second or so).

If you have critical circuits which you do not want interrupted, you will need to support them with a UPS system of some sort to prevent supply problems, an automatic transfer switch system alone will not prevent an interruption in your supply.

Genset

Edited December 23, 2009 by genset

[david96]

For some reason I can't quote from Genset's first post. Also, apologies for getting into this thread late; it is a good one.

I'd like to point out one thing which is of little practical importance but probably worth noting if you are specifying new equipment.

Since 2007, the standard voltage at the delivery point (low voltage side of the PEA/MEA transformer) is 230/400 V (-10% / +6%).

If you are ordering new equipment, you should take this into account. Particularly if you are buying your own transformer, it should be 22 kV/400 V.

System Voltage. Australia, AS60038 230/400V supply range -6% to +10%.

IEC 60038:1983 (moving from 220/380V) supply range -10% to +6%

The initial introduction of the 230V system has only created an iilusion of a world standard as it has been introduced by tinkering with tolerances. The initial effect in Australia is virtually no change of voltage at the device.

Source NHP Technical News issue 28.

I think you will find that the voltage at the device in Thailand will not change if it adopts

IEC60038. 220 volts falls in between the tolerances of IEC60038.

Calculations should be made on the basis of 230/400V.