Application Analysis of ICT Isolation current transformer in Photovoltaic Systems

The article deals in depth with an analysis of the ICT series isolation current transformer plug-in current transformers from the company HEYI Electric, their role within the photovoltaic system, the usage methods, advantages, and practical applications.

HEYI Electric’s ICT Isolation current transformer

In other words, the ICT or Isolation current transformer acts like a “current adapter” or “current matching device” in a power system. Normally, it would be installed between the main current transformer and the load-a relay or meter, for example-and would have two major functions:

1.Current ratio adjustment

when the main current transformer current output-such as 1 A or 5 A-is not equal to the required current to the equipment, the ICT can make the conversion.

2.Phase difference correction

During transformer differential protection, it can correct the phase offset caused by the transformer wiring method for the purpose of assuring the accuracy of operation of the protection system.

Key technical characteristics of ICT

Accuracy class: 0.5 or 1.0, meeting high standards for measurement and protection.

Insulation and protection: Totally encapsulated in flame-retardant resin for the most demanding protection requirements outdoors or in harsh conditions.

Operating Voltage: 720V suitable for medium and low voltage systems.

• Standards compliant: It conforms to international standards such as IEC 185 and BS 3938.

Operating temperature: -20℃ to 70℃, able to work in most climatic conditions.

Why would a photovoltaic system need it

A complete PV system typically consists of a PV array on the DC side, an inverter for converting DC to AC, a step-up transformer for grid connection, and protection and monitoring equipment such as relays and meters. On the AC side, particularly at the point of grid connection, accurate current measurement and phase synchronization are called for. ICT Current Transformer can help in the following:

1.Current ratio adjustment

When the primary CT output is 1A and the protection device requires an input of 5A, plug-in CT can do the conversion, thereby avoiding the losses and troubles caused by replacing the main CT or transmitting large current over long distances.

2.Transformer Differential Protection

When a step-up transformer in a photovoltaic power station adopts a non-standard wiring connection method, such as Δ-Y, a phase difference will appear between the high- and low-voltage sides of the current. Insertion current transformers correct this phase difference, enabling differential protection to act correctly without malfunction or failure to operate.

3.Eliminate the influence of zero-sequence current

With the help of delta connection, the insertion CT can filter out the zero-sequence current in the circuit and improve the stability of the system operation by preventing malfunction to the protection device.

4.Optimize long-distance signal transmission

In a large-scale photovoltaic power plant, the distance of CT signal transmission may be as long as tens or hundreds of meters. Inserting a current-matching CT near the source of the signal can reduce line loss and electromagnetic interference, ensuring signal quality for monitoring purposes.

5.Recommendations for Practical Application of Photovoltaic Systems

In the actual deployment process, there are several places that need special attention:

Grid connection monitoring:

Insertion CTs can be installed directly when the main CT output is incompatible with either the electricity meter or protection equipment. Adaptation of CT: An insertion CT provides adaptation.

Step-up transformer protection:

If there is a malfunction of the differential protection due to phase difference, an input CT can be used for phase correction.

Power line monitoring

Over long distances, the signal will be attenuated, although for enhanced signal quality, local CT scanners can be used.

Several points to note

Additional burden:

Insertion CT will add extra load to the main CT. The total load has to be calculated at the design stage to make sure it is within the allowable range.

Cost considerations:

If it is a simple matching ratio, the adjustment of the main CT ratio or direct selection of a CT with a suitable ratio may cost less.

Environmental adaptability:

Most of the photovoltaic power plants are outdoors, and the protection level and the temperature range of the ICT can meet the needs of most environments; however, evaluation for those in extreme climate areas is still essential.

ICT plug-in current transformers are really great: flexible, reliable, masters of current matching, and phase correction. They are especially suitable for:

– When the proportional conversion of current is needed;

– When phase correction in transformer differential protection needs to be performed;

– When current signals need to be transmitted over long distances. Used in low-voltage grid connection and transformer protection of photovoltaic systems, they make current monitoring clear and the measurement of the system more accurate, and the protection more stable.

If you work on protection and monitoring systems for a photovoltaic power station and are facing current mismatch or phase discrepancies, try the ICT series plug-in CTs; they will no doubt be of immense help. For detailed selection instructions or wiring diagrams, please refer to the circuit diagram section of the product manual or directly consult HEYI Electric; their technical support is very good. Hope this analysis is helpful! Welcome to discuss with us if you have specific experience in photovoltaic projects.

Compay：HEYI Electrical Co., Ltd.

Brand: HEYI/ASCT

Contact: Bethy

E-mail: heyi@heyiele.com             

Tel: 86-13968747975

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