How To Install A Single-Phase Voltage Of 208 Volts?

Project designers who want to use an UPS, or uninterruptible power supply, that requires 208V single-phase power should be familiar with the characteristics of 208V electricity and how they interact with various UPS types.

Because it varies depending on the kind of UPS, because it is something that you may not run across on every project, and because it has the potential to be a pricey oversight if it is disregarded, this is one of the topics that generates the most inquiries.

As was said before, this circumstance does not always present a problem. Even though SEPS has designed the standard component numbers to eliminate any possible problems, there are still queries that need to be answered.

The Structure of the Problem

Simply expressed, there is the possibility of a mismatch occurring with certain combinations of UPS model, bypass switch type, and input voltage depending on the specifics of the setup. All of this is due to the characteristics of 208V electricity and the way that transformers have an effect on it.

Power at 120/208 Volts, Single Phase

208-volt three-phase electricity is converted into 120/208-volt single-phase power.

When seen on an oscilloscope, the three voltage waveforms that are present on the three conductors that are considered to be “hot” all peak at different times; more specifically, each one is 120 degrees behind the one that came before it.

When working with a single-phase voltage of 120/208 volts, you may utilize any two of those same three hot conductors, but the peaks of the two waveforms must be offset by 120 degrees from one another.

Due to the fact that the peaks of the two waveforms occur at separate times, the total power that you obtain from them is less than the sum of their numerical values.

The voltage measured by one waveform is at its highest point when it is 120V, whereas the voltage measured by the second waveform is just 88V when it is only halfway through its cycle

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. The total combined voltage is 208V. If the two waveforms were coincidental, meaning that their maxima occurred at the same moment, then you would, as you would anticipate, be able to achieve 240V by adding the two 120V peaks together.

Make-Before-Break Switches Are Used as A Maintenance Bypass.

In the case that the UPS has to be serviced or replaced, this device will open up a way for the protected equipment to be powered by the utility power in the event that this channel is needed.

It totally disconnects the UPS from the power supply, which eliminates the risk of the service personnel receiving an electric shock while they are working inside the UPS.

This switch is required by Motorola for all hardwired uninterruptible power supply (UPS) systems because it enables the UPS cabinet to be entirely removed and changed without requiring the protected equipment to be powered down.

The Make-Before-Break (MBB) switch overlaps the power on the “UPS” line with the utility power on the “Bypass” line whenever the switch handle is moved.

This brief overlap does not create a problem since it lasts for such a short period of time; yet, it is essential because it allows the switch-to-switch sources without disrupting the operation of the equipment that is being safeguarded.

Transformer for removing Signals

This device, which may be an integral part of the UPS or an entirely distinct unit, transforms the electricity from the utility company into power that has been cleaned and conditioned.

In situations in which the power from the utility company is described as “dirty” or “harsh,” you should make use of an uninterruptible power supply (UPS) that has isolation in order to provide your equipment the highest level of protection possible.

According to Motorola’s R56 Standards, uninterruptible power supply (UPS) systems that contain isolation are regarded as independently derived power sources.

(The page titled “Isolation Explained” in this section provides a more in-depth description of isolation transformers; please refer to it for further information.)

According to Kirchhoff’s Law, the amount of power that goes into a circuit must be equal to the amount of power that comes out of it. This includes transformers, in which the power on the primary side (which is the input side) must match the power on the secondary side (which is the output side).

Transformers are only able to manipulate the power that is already there; they cannot “create” new power. If you put 120 volts in, you will get 120 volts out; if you put 208 volts in, you will get 208 volts out; if you put 240 volts in, you will get 240 volts out; and so on.

Putting Everything into Perspective

When electricity with a single-phase voltage of 120/208 volts is fed into an isolation transformer, the two distinct hot conductors of 120 volts are merged into a single waveform of 208 volts.

We need to divide the 208V back into two 120V conductors so that we can power the majority of the Motorola equipment, but this cannot be done since the voltage is too high.

As was said before, the amount of power that is put in must be equal to the amount of power that is taken out without producing anything brand new. Only 208 volts of total voltage are available when the single 208-volt waveform that is coming out of the transformer is divided into two conductors.

Additionally, the peaks of both conductors occur simultaneously. It is impossible for any piece of machinery to make use of the remaining 88 volts of power once one 120-volt wire has been generated.

Because 240V can be divided equally between two 120V conductors, this problem may be solved by setting the output of the UPS to 240V, which is the obvious approach. If there wasn’t a maintenance bypass option for the Make-Before-Break feature, this would be successful.

The electricity from the utility (120/208V) and the power from the output of the UPS (120/240V) are superimposed on one another whenever that switch is activated.

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A magnetic “crash” will occur as a direct consequence of the disparity in phase angles between the two voltages, which will cause the circuit breaker that supplies power to the UPS to trip.

Solutions

Since 120/208V input is not possible in isolated UPS systems and the UPS output must be 120/240V to prevent the “88V leg,” the input voltage must be 120/240V. If this is already present at the location, then there is really no need to worry about anything in this regard.

On the other hand, if the voltage at the site that feeds the UPS is 120/208V, you will have to modify it to 120/240V. Both the FERRUPS and the 9170+ UPS systems are capable of achieving this goal in their own unique ways.

FERRUPS

Because the FERRUPS incorporates a ferro resonant transformer as the primary component of its construction, every single model comes included with an internal isolation system.

This indicates that any and all FERRUPS models that might potentially be powered by a 120/208V circuit would be impacted by this issue.

When searching for a FERRUPS model number, it is important to keep in mind that models 3,000W and above may be set up as either 208V or 240V source systems, and you will need to choose the one that is most suited for your needs.

The main difference between the two lies in the fact that the 208V source systems use an external transformer, which brings the input voltage up to 120/240V.

You have the option of using the Break-Before-Make (BBM) maintenance bypass switch rather of the step-up transformer. When the switch is activated, the BBM switch does not overlap the output feeds coming from the utility and the UPS, which results in a power interruption.

Because the electricity will be cut off and any equipment that is still running will be destroyed, it is imperative that any equipment that is protected be turned off first.

Because Motorola maintains the position that the protected equipment should never be turned off, not even for maintenance on the UPS, the BBM is not available in any regular model configurations.

If the external transformer is not a solution that can be implemented, SEPS can provide you with an estimate for a customized configuration.

 9170+

For all versions that have a “ISO” appended to its name, the 9170+ comes standard with an external isolation transformer. The output of this external transformer is set to 120/240V, and it may accept electricity at either 120/208V or 120/240V via its various input taps.

Because this transformer supplies the isolation and outputs 120/240V to the bypass switch, none of the two difficulties discussed before is relevant.

Power may be provided to the 9170+ at either 120/208V or 120/240V, depending on whether or not it is fitted with an isolation transformer. All of the problems that were discussed before are resolved when the transformer is not there.

If the location where the UPS will be installed has electricity that is 1220/240V, then you have the option of going with an internal isolation transformer rather than going with an external isolation transformer (for more information, see the component number listings for the Power ware 9170+).

Using this feature makes the 9170+ extremely similar to the FERRUPS, including the 88V leg and phase angle mismatch, therefore it is only accessible with a 240V supply.

SEPS suggests that you do not choose for the internal transformer in order to err on the side of caution if there is uncertainty about the site voltage.