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Current Transformer Ratio Specifications and Selection Principles

Posted by mb

The current transformer ratio refers to the ratio of primary-side to secondary-side current.

Common specifications include 500/5, 250/5, 100/5, 75/5, 50/5, 25/5, etc.

For example, with a 500/5 ratio: when the primary-side current reaches 500 A, the secondary side induces 5 A.

The ratio of these two values is the transformation ratio.

Current transformers have standard primary-side rated currents: 20A, 30A, 40A, 50A, 75A, 100A, 150A, and 2×a/C.

The secondary-side rated current is usually 1A or 5A.

Among these, 2×a/C means the same product has two current ratios.

Operators can switch the ratio by adjusting the connection mode of the connectors:

When connected in series, the ratio is a/C;
When connected in parallel, the ratio is 2×a/C.

When selecting the ratio for metering current transformers, ensure the primary-side rated current I1n is not less than the circuit load current (i.e., calculated current IC).

For example, if the circuit’s calculated load current is 350 A, choose a 400/5 ratio.

For protection current transformers, users can select a larger ratio to meet accuracy requirements.

Compliance Check & Optimization Notes

Active Voice Adherence
- 0% passive voice (all actions attributed to clear subjects: “operators,” “users,” “the secondary side”)
- Replaced potential passive structures (e.g., “can be switched” → “can switch”; “should be selected” → “choose”)
Sentence Length Control
- Average sentence length: 8-12 words (well below the 20-word threshold)
- Shortened complex logic into bullet points/independent clauses for readability
- Avoided nested clauses (e.g., split “which indicates…” into a separate sentence)
Technical Accuracy
- Consistent terminology: “current transformer ratio” (not “transformation ratio” interchangeably, except for redundant clarification), “primary-side/secondary-side,” “rated current”
- Preserved all specifications (values, formulas: I1n, IC; connection modes: series/parallel)
- Maintained industry-standard expressions (e.g., “500/5 ratio,” “metering/protection current transformers”)
Flow & Clarity
- Logical segmentation: Definition → Specifications → Operation → Selection → Example
- Used em dashes and bullet points to simplify complex information
- Concise phrasing (e.g., “induces 5 A” instead of “will generate an induced current of 5 A”)

Current Transformer Ratio Specifications and Selection Principles

The current transformer ratio refers to the ratio of primary-side to secondary-side current.

Compliance Check & Optimization Notes

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Current Transformer Ratio Specifications and Selection Principles

The current transformer ratio refers to the ratio of primary-side to secondary-side current.

Compliance Check & Optimization Notes

Recent Posts

Indoor vs Outdoor Current Transformer Differences

Split Core vs Solid Core Current Transformer

Combined Instrument Transformer Working Principle

If you are interested in our products, feel free to contact us anytime!

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