技術リソース · 技術解説
Current Transformer Ratio Selection: Primary Current and Secondary Output
Specify a current transformer ratio from the primary circuit, secondary measurement input and exact burden and accuracy evidence. A useful buyer review connects the project requirement to one exact orderable product and preserves the evidence used for approval.
This guide explains the evidence chain for a current-transformer ratio. It does not calculate a project ratio, declare compatibility with a meter or protection relay, or provide secondary wiring or safety instructions.
意思決定の入力要素の概要
| レビュー欄 | 購入者は以下を定義しなければならない | 提出を求める証拠 |
|---|---|---|
| Primary current | Normal, maximum and relevant operating range | Project load study |
| 二次出力 | Exact input required by the receiving meter or relay | Receiving-device manual |
| 比率 | Declared primary-to-secondary relationship | Exact CT model row |
| Measurement performance | Accuracy and burden under documented conditions | Manufacturer data and system calculation |
| 機械的嵌合 | Window, conductor, mounting and installation constraints | Drawing and installation review |
Start With the Real Primary Current Range
The primary side should be described by the expected operating current, maximum normal condition and any meaningful variation that affects measurement. Selecting from conductor ampacity or protective-device frame size alone can place normal readings in an unsuitable part of the measurement range.
Record how the current estimate was obtained and whether future operating modes change it. The buyer does not need to force a final ratio before the receiving-device input and measurement objective are known.
Match the Secondary Output to the Receiving Device
A current transformer and a meter form an interface. The CT secondary declaration must match the exact input expected by the meter, transducer or relay. A familiar ratio notation is not enough to establish that relationship. Request both documents and review them together.
Do not use a product family page to infer input compatibility. Neighboring meter variants may accept different sensors or secondary signals. The approval record must name the exact receiving device and its terminal documentation.
Understand What the Ratio Expresses
The ratio states the declared relationship between primary current and secondary output under the product's defined conditions. It does not by itself establish accuracy across the required operating range, available burden, saturation behavior or suitability for protection. Those are separate evidence fields.
When quotations offer different ratios, compare the resulting measurement use rather than treating the values as catalog alternatives. Each proposal should explain how the ratio aligns with the project's primary-current range and receiving input.
Review Burden and Accuracy as a System
The connected input, lead path and terminals contribute to the secondary circuit seen by the transformer. The responsible engineer should calculate and verify that complete circuit against the exact CT and receiving-device documents. Procurement should preserve the inputs rather than guessing from a headline accuracy class.
Ask where accuracy is declared, at which conditions and for which order code. Never combine the ratio of one model, burden data from another and dimensions from a third. If the system calculation is missing, mark the proposal incomplete.
Confirm Frequency, Purpose and Operating Context
State whether the measurement supports indication, energy monitoring, control, protection or another purpose. These uses can demand different evidence. Also record the system frequency and waveform context that the manufacturer requires for its declaration.
This guide deliberately avoids treating a measurement CT as a protection CT or vice versa. The proposed device must be documented for the intended role, and any special behavior must be evaluated by the system designer.
Verify Window Size and Installation Constraints
The primary conductor, bar arrangement, insulation, bending space and access determine whether the CT can be installed. A ratio match does not prove mechanical fit. Request the exact outline drawing and confirm that the window accommodates the real conductor without unsupported modification.
For retrofit work, a split-core construction may change installation access, but it does not remove the need to review ratio, output, burden, accuracy and environmental conditions. Keep construction choice separate from electrical approval.
正確なモデルの証拠ファイルを作成する
Create one approval record for the proposed Current Transformer order code. Put each project requirement beside the supplier document that answers it. Preserve the exact datasheet, drawing, table, instruction or selection output used, including its revision or retrieval date. A category page can establish family context, but it cannot prove an exact rating, terminal arrangement or system combination.
承認されたすべての明細が、同一の注文可能品目を記述していることを確認してください。外観が類似している製品であっても、回路、電源、端子、付属品、または機能が異なる場合があります。あるバリエーションの「ファミリー最大値」、別のバリエーションの「図面」、さらに別のバリエーションの「オプション機能」を組み合わせて使用しないでください。未解決の項目については、商業レビューでも確認できるよう、明確にマークを付けておいてください。.
プロジェクトのインプットと成果物の根拠は区別しておく
The project team defines the application: source, load, duty, environment, controls, mechanical limits and required functions. The supplier identifies an exact Current Transformer and supports it with exact documents. Neither side should fill a gap by inference from appearance, a shared family name or one matching headline value.
見積書の比較中は、申請記録を凍結してください。トポロジー、電源、負荷、環境、筐体、または必要な出力が変更された場合は、改訂版記録を発行し、各サプライヤーに候補品の再確認を依頼してください。そうしないと、一見比較可能な見積書であっても、実際には異なる技術要件に対応している可能性があるからです。.
調達におけるよくあるミス
Avoid selecting a Current Transformer from one headline value while the application context remains incomplete. Do not use a circuit, curve, terminal drawing or performance claim from a neighboring model. A product photograph and a family page can support discovery, but neither is exact technical evidence.
また、見積書や正確なモデル仕様書に記載されていない限り、付属品、通信機能、保護機能、または連携による成果が含まれていると想定しないようにしてください。代替品については、当初の候補品と同様に、トポロジー、定格、取り付け方法、および証拠資料の審査が必要です。.
サプライヤーの提案を比較する方法
Normalize every Current Transformer offer to the same application record. Keep document revisions, stated conditions, included accessories and open questions beside each value. This makes differences in delivered scope visible and prevents a lower-cost but narrower offer from appearing equivalent to a complete solution.
重要なアプリケーションの入力値が不明な場合、引用されたモデルが曖昧な場合、必要な主張が他のメーカーや注文コードによってのみ裏付けられている場合、あるいは設置条件が利用可能な証拠の範囲外である場合は、比較を中止してください。これらは編集上の細部ではなく、技術的な不備です。.
改訂および置換の管理
Give the approved Current Transformer record a revision identifier and keep it with the project file. If the supplier changes the order code, accessory, firmware, drawing or stated operating condition, identify the change before accepting it. A substitution is a new technical proposal even when its price, housing or product-family name looks familiar.
影響を受けたチェック項目のみ再実施し、それらを免除してはならない。改訂後の候補が依然として「凍結済み」の申請に対応していること、参照されているすべての文書がその申請に属していること、および未解決の例外事項すべてに担当者が割り当てられていることを確認すること。この小さな変更管理の手順により、技術的な審査を経た選定が、審査を受けていない商業的な代替品に置き換えられることを防ぐことができる。.
意思決定ワークフロー
- カタログコードを選択する前に、アプリケーションとシステムの記録を凍結してください。.
- 証拠を必要とする正確な関数と、すべてのインターフェースを特定する。.
- 1件の完全な注文コードと、それに付随する最新のデータシートおよび図面を1セットご提供ください。.
- 各プロジェクト要件を、特定のメーカーの声明と対応付けます。.
- 逸脱事項、付属品、文書の改訂、および未解決の疑問点を記録してください。.
- アプリケーションや提案された製品に変更があった場合は、その都度、見直しを行ってください。.
Use this workflow as a procurement and evidence discipline. It does not replace qualified design, installation instructions or the responsible engineer's approval for the Current Transformer application.
見積依頼書（RFQ）作成チェックリスト
A practical current transformer ratio selection should be concise enough for a supplier to answer and complete enough to prevent silent assumptions. Identify unknown values as questions rather than allowing them to become undocumented selections.
- Primary current: Normal, maximum and relevant operating range.
- Secondary output: Exact input required by the receiving meter or relay.
- Ratio: Declared primary-to-secondary relationship.
- Measurement performance: Accuracy and burden under documented conditions.
- Mechanical fit: Window, conductor, mounting and installation constraints.
- 正確な製品コード、同梱付属品、およびドキュメントの改訂版
- 数量、仕向地、必要な承認、および商業的範囲
分類、互換性、調整、または性能に関する主張については、その正確な範囲を明示するよう求めてください。技術的な仕様の後に数量と仕向地を明記し、商取引上の条件によって未解決の技術的な問題が覆い隠されないようにしてください。.
よくある質問
Can CT ratio be selected from breaker size alone?
No. Use the real current range, receiving-device input and measurement objective.
Does a matching secondary value prove compatibility?
No. Burden, accuracy, frequency, terminals and the exact interface still require review.
Can a current transformer secondary be treated as an ordinary signal?
No. Follow qualified design practices and the exact manufacturer safety instructions.
関連するRITOKS製品およびガイダンス
これらのリンクは、製品ファミリーに関する背景情報を提供するのみです。こうしたリンクは、互換性や適合性、あるいは承認されたシステムの組み合わせを保証するものではありません。.
Current Transformer product category
BH-0.66-60I current transformer family
GTA20L precision current transformer
技術資料
これらのメーカーの情報は、以下に説明する一般的な技術概念のみを裏付けるものです。それらの製品の定格、回路図、認証、および調整結果は、RITOKS製品には適用されません。.
シュナイダーエレクトリック、PowerLogic 多機能電力計
Supports treating the meter input and measurement architecture as part of the complete system record. Schneider meter inputs do not establish compatibility with RITOKS CTs.
正確なモデルに関するレビューを依頼する
申請要件、書類に関する具体的な質問、数量、および配送先を、RITOKSのお問い合わせフォームから送信してください。RFQ（見積依頼）では、正確なモデルの確認が求められます。本ガイドでは、回路、設置、または自動的な代替品の承認は行いません。.