Track record

Putting isolation transformers into a UPS system is not innovative. In fact , some technologies relied on the transformer to create the electricity waveform (ferro-resonance). In most cases the need for the transformer was as a result of it’s ability to step up an AC voltage. This made possible an inverter to output a low AC voltage caused by limitations on the voltage capacity on the power electronic pieces. More recently advances in power electronics have enabled often the transformer to be removed and the inverter output connected straight away to the load. This is called a high frequency design and is the basis pertaining to modern online double conversion UPS.

The 1/2V 10V Myth

Some UPS manufacturers include an isolation thermique transformer to allow the Neutral to be bonded to the earth thereby having a new N-E bond and eliminating any Neutral that will Earth Voltage. Claims have been made that common manner voltage (and that means a voltage referenced to a prevalent source – in this case the ground or earth conductor) with over V or normal mode (between live in addition to neutral) of over 10V can cause equipment malfunction.

Still Neutral to Earth voltage does not cause malfunction by using modern electrical equipment. This can be easily demonstrated by going to Saudi arabia and plugging something into the wall socket. You can then disconnect it, turn the Schuko lead around by 180 degrees and plug it in again. Hey presto, what was once survive is now neutral and vice versa and guess what – the exact electrical equipment works just the same without any problems at all, regardless of the odd neutral to earth voltage being 230V. Or you may possibly simply rewire your mains lead to demonstrate.

In the UK, the very neutral and earth are bonded at the consumer component in any case, and any significant N-E voltage is an infra-structure issue that would require addressing by an electrician. These days perhaps such claims were meant for higher frequencies thin use of the isolation transformer is to eliminate noise, after all I heard such claims that the isolation transformer “removes audio from the earth, and since many electronic devices use earth as being a logic reference any noise of over V at this point can cause logic errors”. Noise on the earth is a mistaken phrase. Electrical Noise is simply a high frequency voltage which is certainly measured between two points. You cannot have noise on the world in isolation, it must be between earth and some other issue and in this case the claim is between Neutral plus Earth.

This would mean that for any malfunction to occur with well under 0. 5V of N-E noise, the Neutral caudillo must, in some way be used within the logic of the electronic gadget. Now many years ago this could have been the case, but nothing built over around the last 20 years would have this drawback. Electric powered safety standards require that the Live & Neutral automovilista are separated from the earth with a high degree of muscle group isolation (tested at up to 3000 Volts). To do this they use inside isolation. All computer devices use DC power based in the main from a device known as a switched mode power supply (SMPS). This contains an isolation transformer which operates in the high frequency which allows it to be substantially smaller than a droits frequency equivalent. The output DC logic levels of the SMPS will be completely isolated from the input AC Live and Impartial conductors. Devices that do not utilise SMPS often apply rectifiers from a low level AC source, derived from a step all the way down isolation transformer.

This internal isolation negates the need for another isolation transformer as Neutral to Earth Noise in the input cannot propagate to the DC levels used by the pc logic except in extreme cases.

This is not to say of which noise on the AC power line can not cause challenges, but there are other ways of addressing this such as simple blocking or improved earthing. The isolation transformer also necessitates additional filtering to deal with noise and is effective only being a filter in this scenario. The EMC directive has also demanded equipment to be more robust to the effects of electrical noise.

The exact Schuko Lead. Proof that N-E Voltage isn’t a point.

Voltage Regulation

An issue with transformers is that they have an productivity voltage that is dependent upon the loading on the transformer. That is called Regulation. The output voltage of an isolation transformer less than no-load is higher than the output voltage under full basketfull.

This causes the terminal voltage to vary with switching loads. It also means that there is the potential to have dangerously huge or too low voltages on the output. The input and even output voltages of a transformer are dictated by the relative amount of the number of windings on the primary side to the volume of windings on the secondary side. In order to overcome the legislations issue with transformers operating at close to their capacity will be to slightly step up the voltage. This is so as the transformer becomes loaded, the output voltage falls. So for a 230V input at 0% load, the output may be a few por 100to higher than a nominal, and at 100% load the output would have been a few % lower. How big this % is relies on how good the design of the transformer is. The problem is, if your suggestions voltage is on the high side (the specification with the UK is 230V10%, so that could be 253V) adding one or two % more makes the output voltage dangerously high and may also cause equipment damage. Equally if your mains voltage can be on the low side (207V) then a few % lessen may cause your equipment to stop operating.

Some UPS get this with buck and boost circuits, however I did known for the output voltage from a transformer based UPS, besides a buck function to be at 260V.

RCDs Shouldn’t Trip

It is perhaps one of the most disturbing aspects that many people installing a power protection device containing an isolation transformer are unacquainted that any residual current device that was put into the main infrastructure to provide fast disconnection in the event of a fault is not going to operate. Of course , large fault currents as created for the duration of short circuits will cause other protection measures to operate, nonetheless small fault currents that RCDs are designed to protect against will not likely cause the RCD to trip.

This is because an RCD operates by detecting an imbalance between the Live together with Neutral conductors. Since the isolation transformer isolates the alternative side from the primary, any fault current to globe -no matter how large- causes no deviation with the incoming Live and Neutral current balance as the failing current loop (secondary Live to earth) is was comprised of entirely within the secondary side of the transformer.

This is, actually , why isolation transformers are used for safety, and are also used in significant power applications such as operating theatres, intensive care wards and chemical plants etc ., where an earth wrong doing should not cause disconnection of the supply, and ensures that people are safe from electric shock even with a fault. Nonetheless this is only true if the output conductors are floating regarding earth, that is, there is no Neutral to Earth Bond.