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Measuring current transformers manufacturer VIKODEK

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Low-Voltage Measuring Current Transformers

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Catalogue of low-voltage measuring current transformers VIKODEK

Current transformers catalog VIKODEK

What current transformers’ parameters say?

Below you can find main current transformers’ parameters that are essential for both high-voltage and low-voltage current transformers as well as voltage transformers.

1. Nominal primary current is the value of nominal current of primary winding of current transformer when given current transformer works in the best way. This is optimal value of primary current under which the transformer error is minimal and degree of efficiency is the highest, this determines the best productivity under condition of optimal heating of current transformer.


2. Nominal secondary current The same as nominal primary current is the value of current of secondary winding when transformer errors are minimal. In the other words nominal current of current transformers’ secondary winding is such a current value under which is obtained maximal productivity of the device.


3. Secondary load of current transformer is a total circuit resistance of its external secondary winding (amperemeters, windings of electric meters, current relays of protective relay, different current converters). Its value is calculated in Ohms (Ohm). It is also possible to express secondary load of current transformer in terms of full output that is measured in volt-amperes (VA) under certain power factor and nominal secondary current.


4. Nominal loading of current transformers. This parameter reflects maximum output value, connected to the secondary winding of current transformer. In the other words it is nominal power of the given device. Usually it is expressed in Ohms (Ohm) or as a product of current by voltage (V*A).


5. Nominal frequency of current transformer Is such value of system frequency under which measuring current transformer is working. Usually it is 50-60 Hz.


6. Accuracy class of current transformer. This parameter reflects the highest total acceptable error in percentage under nominal current. Standard accuracy classes are 0.1, 0.2, 0.5, 1, 3 and 5. For example, if the accuracy class or simply the class of measuring current transformers is 0.1, then it means that maximal acceptable error is 0.1%. That is to say if to measure 100A with current transformer with the accuracy class of 0.1, then measured value can be either 100.1 or 99.9 or any other value within this range. For specific goals are used current transformers with different accuracy classes: e.g. for commercial electric counters – 0.5; for electrical measuring instruments – 1; for current protection relay - 3; for laboratory instruments – 0.2.


7. Nominal short-term thermal current or electro-dynamic endurance. For current transformer nominal short-term thermal current is function of mean square value of primary current, which current transformer can resist within certain amount of time with closed secondary winding without any harmful damages that influence the stability of its work. This characteristic determines how long current transformer can endure the regime of short circuit. The longer time and correspondingly the bigger short circuit current transformer can endure the better device it is. This parameter is very important when choosing current transformer for automatic relaying schemes. Because of its construction current transformers of company VIKODEK are notable for advanced reliability and endurance to off-normal operational modes that make them irreplaceable candidate for providing electrical equipment protection in both household and on an industrial scale from uncontrolled problems, forced by power supply system overloads or sudden short circuit.


8. Instrument security factor (overcurrent number). This parameter is defined as the ratio of maximum primary current to nominal primary current. The limit of current transformer is main value after which it becomes saturable. In details this characteristics can be described as follows. If maximal nominal current of given current transformer is 20A, transformation ratio is 20/2. Then in this case security factor (overcurrent number) is 10. It means that under condition of short circuit of primary winding the load current become saturated and the value of current in secondary winding will not surpass 20A and as a consequence current transformer will not burn off.


9. Nominal voltage of current transformer. Such voltage value is used to indicate concrete the highest voltage of operation of current transformer. For example current transformers of company VIKODEK are built to be used with currents up to 720 Volts.

Such current is used in electrical networks of the majority of industrial and household consumers what makes our current transformers the most in-demand on the market. In our catalogue you will find current transformers devices for one-phase as well as three-phase that is suitable for protection of any equipment.


10. Transformation ratio or Transformation Coefficient is one of the main parameter of current transformers. Transformation coefficient is primary-to-secondary current ratio. In the calculation differentiate real and nominal transformation ratio. Real transformation ratio – is real primary current to real secondary current ratio. Nominal transformation ratio is nominal primary current to nominal secondary current ratio. In fact this indicator shows what fold the value of current is decreasing or increasing in comparison to the input current. Transformation ratio usually is indicated as nominal primary current to nominal secondary current, for example: 1000/1 (when primary winding current is 1000A and secondary winding current 1A)



Main characteristics of current transformers VIKODEK:

Nominal Current

0.72 kV

Nominal primary current In

1-3000 A

Nominal secondaru current

1А or 5А

Accuracy class

0.2; 0.2s; 0.5; 0.5s; 1; 3

Nominal loading (output)

1; 1,5; 2,5; 3,5; 5; 7,5; 10; 12,5; 15; 20; 30; 45; 60 VA

Nominal permanent current

1.2× In

Nominal short-term thermal current Іth

60× In

Nominal dynamic current Іdyn

2.5× Ith

Nominal frequency

50-60 Hz

Overcurrent number

5; 10

Class of insulation


Operating temperature

from -20 °C to + 45 °C

Storage temperature

from -50 °C to + 80 °C

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