Calculator #006 IEC 61869 IEEE / ANSI switch Protection + Metering Vendor database DOCX report

CT Secondary Windings — professional verification

Multi-winding current transformer checker for protection and metering cores. Includes IEC/IEEE voltage class selector, CT execution and catalogue-family selection, relay/meter burden database, multiple connected devices per winding, multiple cable segments, analog-input thermal withstand screening, saturation curve and professional report package.

Developed by the ieccalc.com engineering team

Questions and corrections — forum

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1 — CT assembly and catalogue selection

Voltage standard Voltage class CT execution Max secondary cores physically allowed Current transformer — shared IECcalc database No catalogue transformer selected — the check runs on the values you enter below. Manufacturing feasibility method Internal diameter [mm] Window width [mm] Window height [mm] Available CT height / depth [mm] Maximum load current through CT [A] Primary Ith [kA] Ith duration [s] Primary Idyn peak [kA] System frequency [Hz]Sets the primary time constant Tp = (X/R)/ω used for the transient factor. Continuous thermal factor KthRated continuous thermal current is Kth × Ipr; the load-current check uses it.

Dimension fields are enabled only where they are physically relevant. Ring/window and split-core types use internal diameter/window data; cast-resin, oil, SF6, GIS/bushing and wound-primary types use catalogue envelope screening.

2 — Selected CT parameters for all secondary windings

Core	Application	Class	Ratio	Sr/Vk/ALF	Connected burden	Margin	Scenario	Analog input I²t	Verdict

3 — Overall CT manufacturability and recommendations

4 — Automatic improvement proposals

2 — Required fault scenarios for CT saturation and thermal checks

Professional saturation verification is not performed with default demonstration values. At least one real project fault scenario shall be entered: maximum primary fault current through the CT, network X/R ratio and the relevant clearing / required no-saturation time. Each secondary winding then selects the applicable scenario(s).

ID	Scenario	Fault type	Use	Ik primary [kA]	X/R	Clearing time [s]	No-saturation time [ms]	DC offset

For transient checks: Ktd = 1 + X/R. Vtransient-required = If-secondary × (Rct + Zb) × Ktd ÷ (1 − Kr) × 1.20.

Enter separate fault scenarios for 3-phase, phase-to-phase and single-phase-to-earth faults. The governing scenario is not assumed to be the 3-phase fault: in solidly earthed systems, near transformers or generators, the single-phase earth-fault current may be higher and shall be checked separately. Secondary cable resistance is calculated from the actual CT secondary circuit loop; for a normal dedicated S1-S2 pair the loop multiplier remains 2 for any primary fault type. If a residual/common-return circuit is used, model it as a separate cable segment with the actual loop multiplier.

2 — Secondary winding tabs

Core name Accuracy class Core application Secondary current Is [A] Primary current Ip [A] Rated burden Sr [VA] ALF / FS / NProtection: ALF. Metering: FS or N as diagnostic factor. Rct at 75 °C [ohm] Knee point voltage Vk [V] Excitation current Ie at Vk [A] Applicable fault scenariosSelect one or more real project scenarios from the Fault scenarios tab. Max values are used for ALF, Vk, transient and analog-input I²t checks. Residual flux Kr [%] Secondary loop time constant Ts [s]0 = not stated, treated as a non-gapped core (conservative). Gapped TPY/TPZ cores state Ts in the datasheet. Transient safety margin MKtd = Ktf × M per IEC TR 61869-100, 6.1.3. Required no-saturation basis

Applicable methods for this class

3 — Connected devices for active winding

Brand	Device / input module	Qty	Burden VA	Input I²t A²s	Function check	Note

Burden is selected automatically from the reference database using the active secondary current. Manual values are allowed for project-specific devices and should be backed by manufacturer datasheet.

4 — Cable segments and terminals for active winding

Segment	Length one-way [m]	Wire [mm²]	Loop multiplier	Terminal pairs	Terminal mΩ	Test switch mΩ	Aging

5 — Active winding calculation

6 — Active winding recommendations

Reference database — relays, meters, terminals and CT families

Kind	Manufacturer	Country / region	Family / model	1A burden	5A burden	Input I²t	Cont. A	Source note

The database contains factory-value templates and user-provided corrected values. For IFC/approval, each value must be locked to exact manual revision, order code, input card and manufacturer datasheet.

Method references used in the report: IEC 61869-1 and IEC 61869-2 for instrument/current transformer requirements and accuracy-class framework; IEC 60044 legacy classes where project documentation still references them; IEEE C57.13 / ANSI C57.13 class selection mode for North American voltage-class input; IEC 60949-style I²t calculation logic for thermal withstand screening; manufacturer-specific rule packs for relay/meter input burden and analog input thermal withstand. Vendor database rows are editable and shall be verified against exact manuals before final issue.