AI-generated concept illustration of substation transformer bushing CT components and a terminal cabinet. Not an actual HEAKOR product or project, an approved design or evidence of the supplied CT configuration.
Substation transformer bushing CTs should be specified by location, core and purpose, with an agreed secondary-terminal handover point. For a liquid-immersed transformer that requires bushing current transformers, the purchase schedule should identify each core's ratio, rated secondary current, applicable accuracy and burden requirements, and supporting documents. The quotation should also state where the supplier's secondary wiring ends. “CTs included” does not define either the electrical configuration or the complete supply boundary.
This guide is for EPC protection engineers and procurement teams preparing IEC-based industrial substation enquiries. It supports specification and bid review, not protection settings, secondary-circuit work or permission to energize equipment.
Build the CT schedule around each location and core
Give every required CT core an identifiable duty and a traceable position on the proposed drawing. Identify the winding side, phase or neutral location, as applicable, and distinguish metering, protection and any other specified function. Do not merge several duties into a single line simply because the cores share a bushing location.
Use the following comparison fields for each scheduled core. These are suggested procurement fields, not a universal standard form. Add columns for the project requirement, offered value, document reference, deviation and responsible reviewer.
| Review item | Information to request | Question to close |
|---|---|---|
| Location and identity | Transformer tag, winding side, phase or neutral position, core identifier and drawing reference. | Which physical CT core does this entry describe? |
| Purpose | Assigned metering, protection or other duty and receiving equipment. | Who defines and approves the duty? |
| Ratio and secondary current | Rated primary and secondary currents in amperes; available ratios and the selected tap where applicable. | Which ratio is actually being offered for use? |
| Accuracy and burden | Applicable accuracy designation, rated burden and stated conditions for the selected ratio. | Does the declaration cover this core and configuration? |
| Protection-specific evidence | Engineer-specified performance data, such as excitation characteristics or secondary resistance where required. | Does the evidence address the intended protection scheme? |
| Secondary terminals | Terminal identifiers, connection drawing, included boxes, cables and specified terminal accessories. | Where does the transformer supplier's work end? |
| Documents and status | CT data sheet, required curves and test records, revisions, exclusions and open items. | What remains to be accepted before release? |
For a multi-ratio offer, request the declared performance for the selected ratio rather than assuming every available tap has identical characteristics. Keep unused or future requirements separately identified so that procurement does not substitute an available option for the engineer's selected configuration.
Review burden with the actual secondary circuit
The stated CT burden needs a project circuit behind it. Assign the protection or metering engineer responsibility for reviewing the connected inputs, secondary leads and other applicable circuit components. The transformer supplier and panel or cable package supplier should identify the information each will provide.
For protection duties, the review should address the relevant fault conditions, protection objective and CT performance evidence. A nominal ratio alone is insufficient information for that assessment. Do not select a class or burden from another project's schedule, or treat a larger catalogue burden as automatic confirmation of suitability.
Keep the review specific to the protection scheme. Evidence appropriate to a non-directional overcurrent application should not be assumed to settle a differential or restricted-earth-fault requirement. Procurement's role is to obtain the requested data and retain the engineer's disposition, not calculate relay settings.
Name the exact secondary-terminal handover point
Describe the wiring boundary as identifiable connection points, not “wired complete.” Ask the offer and drawing to distinguish:
- The CT leads and any terminal box near the bushing.
- Connections from that box to the transformer marshalling cabinet, including the supplied cables and terminations.
- The outgoing interface from the agreed cabinet terminals to the customer's protection or metering panel.
For each applicable section, name the supplier, installation responsibility and drawing reference. Confirm whether the price includes the specified shorting-terminal facilities, terminal identification and cable accessories. These are scope questions, not instructions for manipulating a CT secondary circuit.
A concrete purchasing example is POWERGRID's June 2021 transformer specification. Section 17.3 describes a terminal box near each bushing and separate cables for each core to a common marshalling box; Sections 12.3.10–12.3.11 address cabinet termination arrangements. Those requirements belong to that specification. They demonstrate a definable procurement boundary, not a standard accessory package for every HEAKOR transformer.
Agree the standard and submission basis
Record the applicable standard edition and project requirements separately from the CT schedule. The official scope of IEC 61869-2:2012 covers newly manufactured inductive current transformers for measurement or protection at rated frequencies from 15 Hz to 100 Hz. This scope statement does not establish compliance of an offered CT or approve its application.
Ask the responsible engineer to confirm the applicable standards package and required evidence. Agree which data sheets, connection drawings, curves and test records must accompany the offer or follow at an identified review milestone. The HEAKOR document centre helps frame a request; it is not evidence that a particular CT report is already available.
Carry changes back into the approved schedule
A revised CT, selected ratio or wiring endpoint needs an identifiable review outcome. Require the supplier to flag affected data sheets, drawings and scope lines when proposing a change. Keep the accepted revision and any remaining conditions with the purchase record. Approval of the CT schedule does not replace the project's protection review or authorize site work.
Frequently asked questions
Are bushing CTs included with every substation transformer?
No inclusion should be assumed. Ask whether CTs are required and offered for the specific transformer, then confirm their locations, duties, quantities and documentation scope.
Can a neutral CT be treated as another bushing CT entry?
Identify the neutral arrangement separately before deciding how to schedule it. The proposed design may have a different location or assembly; the connection drawing and engineer's requirements should define the entry.
Does a metering-core declaration also establish protection suitability?
Do not assume that it does. Record each intended duty and have the responsible engineer confirm the required performance evidence for that duty.
What if the relay panel or cable route is not finalized?
Mark the affected inputs as preliminary or TBC and assign an owner and review milestone. Ask the engineer which decisions can proceed conditionally and which depend on the final secondary-circuit information.
Does an IEC reference replace a utility specification?
No. Record both the applicable standard editions and the project's utility requirements, including deviations requiring acceptance. A standards reference alone does not establish project approval.
Prepare a focused HEAKOR enquiry
For a HEAKOR substation transformer enquiry, provide the liquid-immersed transformer duty, phase, MVA or kVA, full winding voltages, frequency, destination and applicable specification. Add the per-location and per-core CT schedule, intended receiving equipment, secondary-terminal handover point and required documents. Mark unknown inputs TBC.
Submit Your Project Specification and request a quotation response identifying the proposed CT configuration, wiring boundary, exclusions and unresolved requirements. CT availability, ratios, accuracy classes, documentation and any engineering service require confirmation for the specific HEAKOR offer.