CURRENT TRANSFORMERS ACCURACY:

Current transformers are devices used to scale down currents that otherwise would be to high to measure. In this page I'll show the results of some performance tests that I did over some current transformers.

TEST PARAMETERS:

When chosing an AC current transformer accuracy is only one of the many parameter of interest. Depending on your application you might consider:

• Nominal currents
• Ratio
• Accuracy/Linearity
• Phase angle error: when measuring energy is important to take in account, and eventually compensate, the phase error of CTs.
• Saturation Voltage / Current: every CT, depending on the burden resistor, will be able to transduce accurately currents up to a maximum point where the error will increase due to saturation.
• DC tolerance: it's known that transformers don't work with DC but, during normal usage, there could be a DC component (coming from single diode rectifier and other electronics). If the transformer is not DC tolerant it will saturate with a consequent reduction in accuracy.
• Nominal frequency
• Openable CT
• Mechanical size
• Maximum cable Section
• Other solutions (Shunt, Hall effect sensors)
• Price
• ...

CTs:

• SCT013-000  Openable 100A CT (New small core version)
• SCT013-000  Openable 100A CT (Old big core version)
• CTKD-10   Openable 75A CT
• ZEMCTK05  Openable 50A CT
• ZMCT103C  PCB Mount 10A CT
• ZMCT102  PCB Mount 20A CT

SCT013-000 Openable 100A CT (New small core version):

Specs: (Datasheet)

I1n	I2n	Ratio	Accuracy	Linearity	Frequency
?? 100 A	50 mA	2000	1 %	?? 0.2 %	50 - 1000 Hz

Popular, low price, CT with mediocre accuracy. These new units are unable to meet their specifications (probably due to the smaller core).

(3 units tested)

• Linearity: Mediocre 0.7 / 1 % Worse than spec!
• Phase angle error: Not good 3° / 4°
• Saturation current: 70A Worse than spec!
• DC tolerance: Mediocre
• Price: 4 / 11 € (Aliexpress, Amazon)

SCT013-000 Openable 100A CT (Old big core version):

Specs: (Datasheet)

I1n	I2n	Ratio	Linearity	Frequency
100 A	50 mA	2000	3 %	50 - 1000 Hz

Popular, low price, CT with mediocre accuracy.

(1 unit tested)

• Linearity: Mediocre 0.7 / 1 %
• Phase angle error: Not good 2.5° / 4° Difficult to compensate since it's not constant.
• DC tolerance: Mediocre
• Price: 4 / 10 €

CTKD-10 Openable 75A CT:

Specs:

I1n	I2n	Linearity	Ratio	Phase angle Error	Frequency
75 A??	37.5 mA	1 %	2000	<1 °	50 - 2000 Hz

Good quality, compact, affordable, and accurate openable CT.<

(1 unit tested)

• Linearity: Ok 0.35 / 1 %
• Phase angle error: Ok 1° / 1.2°
• Saturation Current: <65A Worse than spec.!
• DC tolerance: TBD
• Price: 4 / 10 €

ZEMCTK05 Openable 50A CT:

Specs: (Datasheet)

I1n	I1max	I2n	Linearity	Ratio	Phase angle Error
50 A	70 A	16.67 mA	0.5 %	3000	<1.5 °

Good quality, compact, affordable, and accurate openable CT.

(2 units tested)

• Linearity: Ok 0.35 / 0.5 %
• Phase angle error: Ok 0.8° / 1°
• Saturation Current: 80 / 100 A
• DC tolerance: TBD
• Secondary resistance: 380ohm
• Price: 3 / 8 €

ZMCT103C PCB Mount 10A CT:

Specs: (Datasheet)

I1n	I2n	Linearity	Ratio	Phase angle Error
10 A	10 mA	0.2 %	1000	<0.25 °

Affordable, accurate PCB mount CT.

(over 5 units tested)

• Linearity: Very Good 0.2 %
• Phase angle error: Very Good <0.25°;
• Saturation Current: 10 / 25 A
• DC tolerance: Not good. Due to the small core it saturates easily
• Secondary resistance: 54ohm
• Price: <0.70€

ZMCT102 PCB Mount 20A CT:

Specs: (Datasheet)

I1n	I2n	Linearity	Ratio	Phase angle Error
20 A	10 mA	0.2 %	2000	<0.25°

Affordable, accurate PCB mount CT.

• Linearity: Very Good 0.2 %
• Phase angle error: TBD
• Saturation Current: 30 / 45 A
• DC tolerance: TBD
• Secondary resistance: 140ohm
• Price: <0.70€

Published: 2023-10-00, Last edit: 2024-02-11