Why Isolation Transformer is must in Online UPS

The isolation transformers are transformers that transfer electrical power from the source to the load by galvanically isolating the load from the power, thus completely segregating the connected load from the incoming supply. They are capable of preventing the noise, harmonics, and other power surges from being getting transferred from supply to the load.

The On-Line UPS provides uninterrupted power supply to the connected loads and thus protect them from power outages and make connected loads keep working continuously without fail. The On-Line UPS provides clean power at the output to let the load perform properly without malfunctioning.

There are different types of On-Line transformers. Few On-Line UPS are provided with transformer while few others are without any transformer in their system. Some other types of On-Line UPS are provided with a normal step-up or step-down transformers while others are provided with isolation transformers.

The UPS provided with normal transformers are different from those provided with the isolation transformers. The isolation transformers provide the galvanic isolation to the load from the incoming supply while the other UPS with regular step-up and step-down transformers don’t provide this protection. They cannot prevent the flaws in the incoming power and the faults generated in the bust from being getting transferred to the load.


Why isolation transformers are required in UPS?

The isolation transformers though not mandatory, are still provided in the UPS for more than one reason. The UPS comes with the isolation transformers as well as without them and both of them have their applications depending upon the type of the load and the type of safety, we are interested in for the connected load across it.

Isolation transformers are typically provided in the UPS for several reasons to provide different benefits depending upon the connected load. The few of the significant reasons are-

      1. Grounding – The UPS supplies are commonly on a high resistance grounding system, but the loads require solid grounding for their proper functioning, safety, and, performance. In the absence of a solid grounding, the sensitive load may not perform the way they are expected to. Their output may not be to the mark as desired and for what they are connected for.For instance, if the sensitive equipment such as heart monitors or other measuring systems are not provided with a solid grounding, no doubt they would function and provide the output but which could not be accurate thus defeating the purpose for what exactly they are installed. A small error in the reading would result in wrong medication costing many people their lives. Thus, it becomes important to provide a solid grounding to all the sensitive equipment, and a UPS with a good isolation transformer could smartly serve this purpose without fail in addition to protecting the equipment because of other faults that may emerge in the system due to improper grounding.
      2. Voltage conversion – At most of the times, the connected load is at a different voltage than the incoming voltage. In such cases, a transformer is required to step or step down the voltage before feeding to the load. Though the transformers are provided to step up or step down the voltage in many UPS, they have not isolated transformers and don’t provide the protection that an isolation transformer could provide.Such UPS misguides the users of having the benefits of galvanically isolation of the load from the poor quality incoming supplies and other generated faults which may arise because of generated faults in the neighbourhood connected loads, which transfer the fault currents or the spikes and surges in the entire bus leading to their transferring the fault to all the equipment connected on the bus. This will either damage or completely burnt out all the equipment connected on the bus.Thus, to protect your gadgets and equipment, it is a must to install an isolation transformer before UPS.
      3. Limiting the fault current to down-stream equipment -The isolation transformers provide protection from upstream faults to the downstream equipment as well as from the downstream fault to other equipment connected on the bus. If a fault occurs at the connected load to the UPS and the UPS doesn’t have an isolation transformer in the system, then there is a high probability of the fault current to get transferred to the entire bus feeding the fault current to all the connected loads on the bus. Therefore, in case the UPS is with an isolation transformer, then there is no chance of this fault current being transferred to the bus and disturb other connected loads.
      4. Easy maintenance – An isolation transformer in the system provides safe and easy maintenance of the entire system as it isolates the incoming supply from the load side thus prevents fault currents from being transferring in the system during maintenance, thus securing the life of the maintenance personnel. Otherwise, the generated fault current could become fatal for the maintenance person.
      5. Noise Protection from the grid – The sensitive equipment requires protection from the noise on the grid for smooth and normal functioning of the equipment. The noise is the disturbances created on the grid because of the electrical and magnetic effects, and prevent the connected equipment from behaving normally. The equipment does run, but not in the way they are expected to run. The equipment malfunction and provide incorrect readings which cannot be realized unless the power quality is monitored properly. The incorrect readings misguide the further action taken on behalf of them as is in the case of the health monitors or research equipment. As the isolation transformers prevent the noise and the power surge reduction; thus, it’s essential to install them with UPS. The isolated transformers use Faraday shields to eliminate the noise and the leakage currents.
      6. Restraining harmonics – The Low-frequency 3n-order harmonics can be restrained only by connecting an isolation transformer to the UPS. These harmonics cannot be restricted without galvanically isolating the system from the incoming supply.
      7. Protection from Grid noise – Most of the UPS are ‘buck and boost’ type and thus have the battery floating in parallel to the rectifier inverter connection. It is not connected between the rectifier and the inverter in series, and therefore the UPS grounding cannot protect the system from harmonics generated in the system. Therefore, separate earth is required to protect the system from the harmonics.


What are the Drawbacks of On-Line UPS with Isolation transformers?

Every coin has two sides and so have the On-Line UPS with isolated transformers. They do have many advantages but have few drawbacks also.

  1. Larger Size – These On-Line UPS with isolated transformers are obviously larger in size as they house the isolated transformers in their housing.
  2. Costlier – These UPS are expensive than the other On-Line UPS which are without isolation transformers owing to the additional isolation transformer provided in the system. They are even costlier than the other On-Line UPS which are fitted with the regular step-up or step-down transformers as these transformers are cheaper than the isolation transformers.
  3. Occupies larger space – The On-Line UPS occupies larger space than their counterparts of the same rating, thus further adds to the cost of the space where space is already at a premium such as in data centers, research centers, hospitals and at other areas of their application.
  4. Heavier and bulky – The On-Line UPS with isolation transformers are much heavier and bulkier than the other types of UPS with same ratings. These UPS thus need rugged and tough shelves to house them in comparison to the other UPS which are without isolation transformers.

However, the advantages of the On-Line UPS with isolated transformers outweigh the limitations or drawbacks they carry.

So, where are these On-Line UPS with isolated transformers used?

These UPS are broadly used at all places where the noise-free quality input power is a must, and even an iota of deviation from the required quality of the power is not acceptable They are used in controlling all mission-critical power backup applications such as medical equipment, life-saving monitors, and other sensitive equipment or critical research centres, spacecraft laboratories, and other medical, and IT applications.


An isolation transformer is a must on the On-Line system to not only protect the connected load but to also protect the other loads connected on the same bus besides providing safety and secured life to the maintenance persons. The isolation transformers provide galvanic isolation to the connected loads to the UPS from the other faults and loads connected on the system in addition to providing a solid grounding to the connected load. As the isolation transformers prevent the noise and the power surge reduction; thus, it’s essential to install them with UPS. The isolation transformers provide the precision, reliability, and safety to sensitive equipment such as medical devices, measuring instruments, research equipment, and much more.

We, Servostar Servo Voltage Stabilizers are an established renowned manufacturer based out of India and are catering to entire pan India in power equipment like Servo Stabilizers and all type of transformers including isolation transformers for domestic households and other industrial applications. We have a proven track record of supplying quality transformers and voltage stabilizers to various industries, commercial setups, residences, and the utility. We do provide consultancies services and customized transformers too.