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What is UPS?

Uninterrupted Power Supplies are systems which filters impairments (increases, breakdowns, harmonics, frequency deviations, voltage fluctuations) and noises occurring in the networks connected to electrical-electronic devices thus feeding a stable voltage with constant amplitude and continuing to feed during a certain period without making the load evident in blackout conditions.

A condition when source voltage or load current becomes absolutely absent meaning amplitude becomes zero. There are many reasons for occurrence of power blackouts. Blackouts may occur due to various reasons including generator impairments, lightening strike, accidents, natural disasters, network equipment impairments, starting of interrupters.

Decrease in AC voltage is called Voltage Dip. Low voltage waves are seen in network failures or when high take-off currents are depleted. In seasonal regions, when electricity current increases a voltage lower than nominal voltage arrives from the distribution station. It may be encountered when loads with high take-off currents are started (engines, CNC, elevators, compressors etc.)

When a voltage higher than nominal value is encountered in the network this condition is called a Spike. It can be encountered in sudden drops of load, single phase short circuits, incorrect adjustment of voltage staging in power distribution units and in regions where loads decrease seasonally. Major reason for this occurrence is lightening strike which can cause dramatic skips in the voltage.

Network problems can cause interruptions, disruption or cessation in work flow , data loss or creation of incorrect data in computers, high cost hardware failures, production loss and decrease in product quality, incorrect operation of control systems, impairments in semiconductor devices, monetary and time losses. Most comprehensive common solution to all problems is utilization of Uninterrupted Power Supplies before our critical loads. UPS provides protection for almost all network power problems mentioned before thus protecting users from problems created by network.

Decrease in AC voltage is called Voltage Dip. Low voltage waves are seen in network failures or when high take-off currents are depleted. In seasonal regions, when electricity current increases a voltage lower than nominal voltage arrives from the distribution station. It may be encountered when loads with high take-off currents are started (engines, CNC, elevators, compressors etc.)

Failures in any point of the network let it be power plants producing the network voltage or consumer’s home plug connection the impacts the consumers. Short or long duration power blackouts are seen when power transmission line breaks, breakers open the circuit in overload, even lightening strike, step-down and step-up transformers going on and off in the circuit and consumer is not provided with clean power. Furthermore, problems caused by operation characteristics of machinery, switching and sudden start ups in industrial environments impact the consumer negatively. For this reason utilization of Uninterrupted Power Supply becomes a necessity.

Uninterrupted Power Supplies are utilized in every environment where electrical and electronic devices are being used. Main utilization fields are hospitals, telecommunication, airports, control towers, automation, emergency lightening, defense systems, communication centers, shopping malls, banks, offices, elevators, computers, cash registers etc.

Uninterrupted Power Supply are divided into two according to their structure.

Dynamic Uninterrupted Power Supplies; As is evident from their name, these are systems feeding the load with mobile particles in case of network failures.

Static Uninterrupted Power Supplies; These are semiconductor systems consisting of Rectifier, Storage Battery Group and Inverter layer

Static Uninterrupted Power Supplies are divided into three groups consisting of Standby (Off-line), Line-Interactive and On-Line.

When there is network power, entry loads are fed from network and storage batteries are charged. Utilization purpose of Off-Line UPS is the requirement for controlled shutting down of computers in case of blackout rather than operation during blackout. Their simple structure and affordable price make them preferable. They cannot work effectively enough in situations where blackouts are frequent and voltage fluctuations are present. Due to absence of voltage regulation, this product is not suitable for present day conditions. Therefore they are not recommended.

Line-Interactive UPS models regulates the voltage sending it to network output if there is line voltage between a certain range. At the same time it charges its storage batteries in network condition. In network condition, enables output regulation by either adding or subtracting the portion of the network less or more 220 V AC.


  • Personal Computers at homes or offices.
  • Generator supported multiple user computer systems. Utilization purpose in these systems is to enable operation of the system until generator starts working.
  • Low capacity card pass systems and gate control systems. In order to prevent information loss and enable the system to stay in stand-by condition at the least in case of blackout.
  • Since electronic scales and cash registers are low power devices, operation allowance periods are long, product and pass cuts do not cause problems.
  • Emergency lightening units. They can be used in lightening entry gates located in closed areas in case of power blackout or security lightening of building facades.
  • Apart from the above, they can be used in feeding low power systems which do not require network isolation and accept short blackouts..


  • Line-Interactive UPS has better output voltage regulation compared to Off-Line UPS.
  • If there is line voltage, inverter unit consumes power just enough to balance the portion of the network lower or higher than 220 VAC, therefore power loss will be insignificant. This feature is the major superiority of Line – Interactive UPS compared to On-Line UPS.
  • Since it does not use storage battery when operation in network condition, utilization life of storage batteries is increased. When UPS is working in network condition, storage batteries remain in buffer charge.
  • They come in smaller sizes since their charging units are produced in lower power and inverter unit is designed for short term operation.


  • There is no network insulation. Since it regulates line voltage when working in network condition the input is short circuited to the output and voltage increases and decreases occurring in the input are briefly reflected in the output. Regulation units have response periods to voltage variations. Although said response times are brief, they do not suffice to balance high frequency electrical noises and instant voltage variations in the line. In particular, measurement and testing devices for medical purposes (ultrasound, electrocardiograph etc) are extremely sensitive to high frequency electrical noises. These noises cause incorrect operation or failure of the devices. High power electric engines (water pumps, coolers etc) or welding machines operating close to UPS location cause drop or increase in line voltage measured in miliseconds. When these impair ments go above a certain limit they compromise almost all electric devices. Line-Interactive UPS cannot provide adequate protection in these type of situations.
  • A brief interruption occurs when passing from the line to the inverter. Majority of computer systems do not sense this interruption .
  • Regulation limits of Line-Interactive UPS at network condition are not adequate for certain devices.
  • They cannot be produced in high powers. Due to their structure, when they are manufactured at powers higher than 2 kVA, problems arise as a result of their relay pass and wave forms.
  • Charging time is long due to low power of charging unit . They cannot work effectively where power blackouts are frequent.

On-Line UPS provide input voltage by producing it from DC voltage continuously received from storage batteries . . When there is line voltage charging unit balances storage battery voltage (since output voltage is continuously supplied from inverter unit, power loss of the inverter is continuous.) Voltage variations in the line never impacts input voltage. Network insulation is present. On-Line UPS has static by-pass units for protection during failures or overload. Output wave forms are called sine or sinusoidal.


  • They can be used in all fields where Line-Interactive UPS is used.
  • They can be used safely in multiple user computer systems without generator support.
  • They can be used for protection and error-free operation in medical and university laboratory devices requiring fine input regulation, network insulation and stability and all measurement and testing units.
  • They can ensure feed and protection of the machinery in automation systems. requiring three phase voltage.


  • They enable fine input regulation . Since inverter unit is continuously on, response time problems are not present and response to instant load variations is very rapid.
  • It prevents electronic noises being reflected on the device due to full network insulation. On-Line UPS provide crucial protection especially in industrial regions where there is abundant noise and impairment in the line.
  • They can be applied in all electronic devices safely due to fully continuous operation .
  • Suitable for 3 phase operations. (They present an unreplaceable solution especially in automation systems.)
  • Due to presence of static by-pass unit, it can make transition to network condition without causing any interruption in case of failure or overload.


  • More expensive compared to other UPS models, have bigger sizes than other UPS models.
  • Power loss is present since it continuously feeds the loads with the voltage produced by itself.

Power is the energy amount in unit time. When determining output power of uninterrupted power supply, apparent power (unit VA) is used.

Apparent Power = S =U x I

U= source voltage effective value, I = effective value of the current extracted from source

Apparent Power consists of combination of active and reactive power.

Active Power (P): Energy extracted by the load a large portion of which is transformed into work and small amount to loss .Its unit is Watt. (W)

Reactive Power (Q): Energy amount in unit time extracted from the network oscillating between the load and the network however not used actively. Its unit is volt-ampere reactive.

Feature of direct operation from storage batteries when there is no electric energy.

Power Factor = Active Power / Apparent Power = W / VA = cosʟ Ideally 1 is required for this ratio. In this situation since Apparent Power and Active Power will be equal to each other reactive power will be zero. This means that same amount of energy can be obtained by lower current.

It can be done only in same power and feature devices. 2 variations can be done:

1) Power Increase , like (10 + 10) = 20 kVA.

2) Redundant 10 + 10 = 10 kVA.

When used for power increase, if one UPS fails other UPS will shut down automatically. The reason is the fact that 20 kVA power cannot be extracted from a 10 kVA capacity UPS.

When used for redundancy purposes, if one UPS fails other UPS automatically continues to feed its connected load .

Transfer time is the period between the occurrence instant of a problem in case of voltage dip or blackout until the time UPS stars using its battery power. The shorter the transfer time the better. Transfer time in standby and line-interactive UPS vary between 2 ms and 20. Online UPS are specifically designed to have zero transfer time.

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