Constant Voltage Transformer (CVT)

Constant Voltage Transformer

Constant Voltage Transformer (CVT) or Ferro resonant Transformer (Ferro) is a non-linear transformer, which passively provides a regulated voltage output through an electromagnetic phenomenon called ferro resonance (where the term ferro resonant transformer was derived). Ferro resonance is associated with the behavior of iron cores while operating near a point of magnetic saturation, wherein the core is so strongly magnetized that further variation in the input voltage results in little or no increase in magnetic flux. Basically, the ferro resonant action is a flux limiter rather than a voltage regulator. Nonetheless, with a fairly constant supply frequency, the CVT can maintain an almost constant output voltage even as the input voltage varies widely. In fact, the output voltage of the ferro varies about 1.2% for every 1% change in supply frequency, such that even with a considerable generator frequency change (2-Hertz), results in an output voltage change of only 4%.

In short, CVTs are basically 1:1 transformer that are excited high on their saturation curves, thereby providing an output voltage which is not significantly affected by input voltage variations. This special characteristic is the foundation of the application of ferroresonant transformers as power conditioners.

Product Description

The portion of the magnetic core over which the secondary winding is wound is saturated, while the portion over which the primary is wound is not saturated. A capacitor is connected across the secondary winding to tune out the output at a fre¬quency very close to 50 Hz.

This capacitor also makes the current in the secondary winding to increase which helps in the saturation of the secondary flux. Since the secondary ac flux is restricted to a saturated value for a large range of the input voltage (170-270 V), a constant voltage is available across the secondary winding. The output voltage will not be of a pure sinusoidal waveform but will be an approximate sinewave with the peaks flat¬tened approaching a square wave. Output voltage waveform of a CVT is shown in figure. In figure, a compensating winding is shown connected in series to the secondary to improve the CVT performance.

Technical Specification

OUTPUT VOLTAGE 220 V - (+/-)1%
LINE FREQUENCY 50 Hz - (+/-)5%
OUTPUT REGULATION 1% at no load to full load
WAVEFORM DISTORTION 5% (approx. under full load)
LOAD FACTOR 0.75% lag to 0.9% lead


  • Electronic equipment’s
  • Telecom equipment’s
  • Electronic type writer
  • Bio medical equipment’s
  • Micro / mini computer
  • TV / DVD recorder and player
  • CNC system
  • X – ray machine


  • No moving parts used, hence very high reliability
  • Faster voltage correction almost instantaneous
  • Intrinsic current limiting and short circuit protection
  • Short term over load capability
  • Very high line transient/spike rejection capability and excellent input to output isolation characteristics


  • What is Constant Voltage Transformer (CVT)?

    The very best power protection comes from a special type of transformer known as a Constant Voltage Transformer (CVT). Providing unparalleled reliability and conditioning performance, spikes and electrical noise are neutralized with attenuation as high as 75dB.

    In addition, the input (or primary) and output (or secondary) transformer windings are physically separated. Known as Galvanic isolation this separation ensures that there is no direct connection between the mains supply and load.

    A CVT therefore provides an impenetrable barrier to spikes and high frequency electrical noise. This barrier also works in reverse mode to prevent a 'noisy' load from polluting the mains supply itself.

  • Features Of Constant Voltage Transformer(CVT)
    • It does not have any moving parts or semiconductor and hence highly dependable.
    • Input control is not used
    • Comes with output amendment within ½ cycle for specific load
    • Competent overburden for short term
    • Output costing
    • Spike dismissal or overdrive line transient
  • Common Features Of Constant Voltage Transformer(CVT)
    • Space saving design
    • Quick installation
    • Easy transportation
    • Superior efficiency
    • Low maintenance hassles
    • Good voltage control and power regulation
  • Benefits of Constant Voltage Transformer(CVT)
    • It offers better voltage regulation despite the variation in voltage regulation from 1 to 4%.
    • It can be customized to meet the constant current output Vs. the voltage supplied to normal devices.
    • Controlling the current is the major advantage of CVT
    • It is highly durable and does not come with any moving part facilitating easy maintenance allowing them to work longer hours without any sags.
    • It can regulate output voltage of upto 60% for a particular period during voltage drop. Though, it does not offer good resistance when there is temporary voltage interruption or during very intense voltage drops.
    • CVT is preferred over sag-mitigation gadgets as it is maintenance free and there is no need for batteries to run the device
    • It comes with special features and with tank circuit design. It is a combination of an inverter and UPS application. Moreover, it offers uninterrupted transfer to secondary source.
    • In case of an overload or fault it comes handy. Even during complete inverter failure, it helps to maintain the power load.
    • It helps to supply constant current output instead of constant voltage.
    • Current limiting is an inlaid benefit in ferro resonant transformer
    • During load current going over 150% of the rated region, there is a collapse in the output voltage in a limited value thereby limiting the current.v
    • There is no surges, noise or harmonics occurring during the circuit design
    • It is long lasting and sturdy and comes with warranties touching 10 years too
  • Disadvantages Of Constant Voltage Transformer(CVT)

    At full load and ideal conditions, its efficiency can reach up to only 93% and substantially drops at light load. Meaning, as the ferro resonant transformer's loading decreases, its efficiency also reduces significantly. Typically, at half load, CVT efficiency ranges from 75% to 85% only as compared to a regular transformer that has an efficiency of more than 95% for the same loading percentage. humming audible sound and relatively high cost

    • The efficiency of Ferro – resonance transformer is lower than conventional transformer.
    • The efficiency of CVT is approximately 93% for its full load range and it decreases as the load decreases.
    • The efficiency of CVT at half load is lies in the range of 75% to 85% whereas the efficiency of power transformer is approximately above 95% for that load.
    • The design of CVT is done by considering overload or inrush current.
    • When the size of CVT increases 2 to 3 times for rated current, its efficiency drastically reduces and it also produces humming sound.
  • Special Features Of Constant Voltage Transformer(CVT)
    • It is highly reliable and comes with zero moving parts
    • Feedback control is not used
    • Comes with short circuit protection
    • Restricted inbuilt current
    • Protection from line loss
    • Short term overcharge capacity
    • Prominent input voltage
    • Highly isolation between input and output
    • Quick corrections
    • Low maintenance cost
    • Quick voltage regulation

    It has unique configuration that offer isolation from load equipment. Moreover, the device is free from surges and line noise. The product is highly reliable and long lasting supported by warranties. There is a huge demand for CVT in the market and the device can be customized to meet the client needs.

  • How to get superior output voltage using CVT?
    • In the CVT the primary and secondary windings are separated with a broad air gap impacted by magnetic field. This results in a striking decrease of capacitive and inductive loadings. Regular power transients are taken care of by this exclusive design.
    • In between the output voltage and the input voltage there exist phase difference giving rise to superior output sound reduction.
    • The windings in a CVT is isolated the noise is cut off from the high frequency module.
    • Ferro resonance is a phenomenon in the CVT that keeps the balance from any type of variation that occurs in the AC voltage. In this case the secondary output inductor forces to vibrate making use of a greater degree of capacitor performance giving rise to this occurrence.
    • The features stated above indicate that CVT is unique and superior to other type of voltage stabilizers and SMPSs. The CVT allows consistent power output saving the appliances during power surge.