RFQ Template for Transformer Accessory Projects

A complete transformer accessory RFQ requires: transformer nameplate data (kVA, HV/LV voltage, vector group, cooling type), highest system voltage Um in kV, BIL in kVp, site conditions (altitude, pollution class, ambient temperature), quantity with spare ratios per family, and accessory-specific parameter fields for all seven families LV/MV bushings, bushing well inserts, Bay-O-Net fuses, current limiting fuses, loadbreak switches, and off-circuit tap changers.

Procurement teams routinely underestimate how much specification detail a transformer accessory order requires. A nameplate provides kVA rating and voltage ratio it does not specify bushing BIL, fuse coordination thresholds, tap changer current rating, or contamination class. When those parameters are missing, the supplier guesses, requests clarification, or ships the nearest available configuration. Field data consistently points to incomplete RFQs as the primary driver of accessory mismatches not counterfeit product, not manufacturing defect.

Two procurement failure scenarios illustrate the cost:

Scenario A — Missing BIL Triggers a Three-Week Delay

A project specified “35 kV class bushings” without confirming BIL. The supplier shipped 170 kVp units; the insulation coordination study required 200 kVp. Replacement units required re-manufacturing. Commissioning shifted by 23 days.

Scenario B — Fuse Coordination Threshold Left Unspecified

A Bay-O-Net fuse link was selected at 65 A against a transformer with an 83 A full-load primary current at 15 kV. The coordination margin was negative before the transformer was energized. Both fuse accessories required replacement.

The sections below structure specification into required, conditional, and optional fields across all seven transformer accessory families available through ZeeyiElec’s transformer accessories range.

What This RFQ Template Covers: Scope, Accessory Families, and How to Use It

This template addresses seven transformer accessory families in the 10–35 kV range. Before completing any section, confirm transformer nameplate data is available attempting to size fuse links or tap changer steps without a confirmed nameplate introduces specification errors that propagate through every downstream field.

Accessory Families Covered

• Низковольтные втулки — 1.2 kV to 3.0 kV class, 600 A to 5,000 A+
• Проходные изоляторы среднего напряжения — 12 kV to 52 kV class, ANSI / DIN / epoxy interface
• Bushing well inserts — 15/25 kV and 15/25/35 kV classes, 200 A continuous
• Сборки предохранителей Bay-O-Net — 15/25 kV, sidewall-mounted expulsion protection
• Токоограничивающие предохранители — high-fault interruption, coordinated with Bay-O-Net
• Loadbreak switches — 15/25 kV and 38/40.5 kV, 630 A rated
• Off-circuit tap changers — 15/25/35 kV, 63 A and 125 A current ratings

How to Navigate the Template

Each section uses REQUIRED, CONDITIONAL, and OPTIONAL field designations. REQUIRED fields must be completed before submission; CONDITIONAL fields apply only when a specific configuration is selected; OPTIONAL fields improve quotation accuracy but will not block a valid supplier response. On-load tap changers, protection relays, transformer oil, and cable accessories fall outside this template’s scope.

Universal Header Fields: Project-Level Parameters Every Accessory RFQ Must Include

Every RFQ requires a completed header block before any accessory-specific fields are addressed. Suppliers use it to confirm compatibility across the full accessory scope and flag configuration conflicts before manufacturing begins.

Transformer Nameplate Parameters

System and Site Condition Fields

Highest system voltage Um must be stated separately from nominal voltage. For a 22 kV nominal system, Um typically reaches 24 kV this value directly governs bushing creepage distance and BIL selection.

Basic insulation level (BIL) must be stated in kV_p. For 24 kV U_m class, standard BIL values are 125 kV_p or 145 kV_p depending on the insulation coordination study. Confirm which applies before completing bushing and fuse sections. [VERIFY STANDARD: IEC 60071-1 insulation coordination confirm BIL table for U_m = 24 kV]

Additional required site fields: installation altitude in metres dielectric derating applies above 1,000 m; maximum ambient temperature (°C) typical range 40°C to 50°C for tropical and desert sites; pollution level per IEC classes I–IV; and installation environment (indoor / outdoor / pad-mounted / pole-mounted).

Altitude and contamination class are the two site parameters most frequently omitted from first-draft transformer accessory RFQs. Both directly determine whether a standard-catalogue bushing is acceptable or whether an upgraded creepage configuration is required.

Quantity and Delivery Fields

Specify spare ratios per accessory family: 10–15% for consumable fuse links; 5% or one spare unit per project for non-consumables such as bushings and tap changers. Confirm export documentation requirements at header stage test reports, certificate of origin, packing list, and HS code classification are standard minimums. The IEC specification and procurement cheat sheet provides a parallel reference for standards alignment across these header fields.

[Expert Insight]

• Um and nominal voltage diverge by 5–15% depending on system design always use Um for bushing and fuse specification, never nominal voltage alone
• Pollution class IV (very heavy) requires creepage distances of 53 mm/kV or greater catalogue bushings rated for class II (25 mm/kV) will track and fail within one wet season at coastal industrial sites

Bushing RFQ Fields: LV Bushings, MV Bushings, and Bushing Well Inserts

Bushings require simultaneous confirmation of electrical class, mechanical interface, insulation material, and terminal configuration. A bushing that is electrically correct but dimensionally incompatible with the tank flange cannot be installed. One that fits mechanically but carries insufficient creepage for the site pollution class will fail within its first wet season.

LV Bushing Parameters

For a 1,000 kVA transformer with LV winding at 0.4 kV, secondary current reaches approximately 1,443 A per phase (I = S ÷ (√3 × U_LV)). A bushing rated at 1,250 A continuous would be undersized specify 1,600 A minimum with a 10% thermal margin confirmed by the supplier.

MV Bushing Parameters

The applicable standard for bushing performance testing is IEC 60137, which defines impulse withstand, power frequency withstand, and thermal current rating test requirements for bushings in liquid-filled transformers.

For projects bridging ANSI and IEC supply chains common in Middle East and Southeast Asian utility tenders confirm interface standard explicitly. ANSI and DIN porcelain MV bushings are not interchangeable at the transformer flange; field substitution is not feasible without adapter hardware.

Bushing Well Insert Parameters

Confirm elbow manufacturer compatibility at RFQ stage. Dimensional differences at the elbow interface that prevent full seating are only detectable during energization preparation — not during visual inspection after delivery.

Protection & Switching RFQ Fields: Bay-O-Net Fuses, Current Limiting Fuses, and Loadbreak Switches

Fuse coordination must be resolved before either fuse family is sized. Switch voltage class must be confirmed against Um, not nominal voltage. These three families are interdependent — an incomplete specification in any one affects the validity of the other two.

Bay-O-Net Fuse Assembly Fields

In pad-mounted installations with restricted enclosure clearances, confirm the expulsion arc path is unobstructed before specifying an open-expulsion Bay-O-Net assembly.

Current Limiting Fuse Fields

Per IEC 60282-1, current limiting fuses for transformer protection must be characterized by rated voltage, continuous current, and maximum interrupting current all three are required RFQ fields without exception.

The let-through energy of a current limiting fuse is expressed as I²t in units of A²s. For transformer protection coordination, the fuse I²t at maximum fault current must remain below the transformer’s withstand I²t derived from short-circuit impedance Z_k % and winding thermal time constant. Omitting this field prevents the supplier from confirming the protection margin.

Сайт Bay-O-Net vs current limiting fuse coordination guide provides the technical basis for completing both fuse sections in a coordinated submission.

Loadbreak Switch Fields

Stored-energy mechanisms are preferred over direct manual operation at 15 kV and above interruption speed is consistent regardless of operator technique, directly reducing contact erosion rate across the switch’s service life.

[Expert Insight]

• Never size a Bay-O-Net fuse link from transformer kVA alone full-load primary current must be calculated, then multiplied by an inrush margin of 8–12× FLA for 0.1 s to avoid nuisance operation during energization
• Let-through I²t must be confirmed against the transformer’s short-circuit withstand rating before fuse selection procurement teams frequently omit this field, treating it as a supplier responsibility when it is not

Off-Circuit Tap Changer RFQ Fields and Voltage Adjustment Specification Logic

Off-circuit tap changers adjust transformer turns ratio across a discrete set of positions typically five, spaced at 2.5% intervals giving ±5% adjustment around the nominal voltage ratio. The transformer must be fully de-energized before any position change; this constraint governs every parameter in this section.

Electrical and Mechanical Parameter Fields

Tap step voltage must be calculated before RFQ submission. For a transformer with HV winding rated at 22 kV and a standard 5-position tap arrangement, each 2.5% step equals 550 V. The full adjustment range spans 20,900 V (position –2) to 23,100 V (position +2) a total window of 2,200 V_AC. Specifying only “22 kV, 5-position” without step voltage confirms nothing about winding compatibility.

Rotation Type Selection Logic

Confirming rotation type requires the transformer OEM drawing or direct manufacturer confirmation, it cannot be inferred from kVA rating or voltage class alone. In one documented field case, a replacement tap changer ordered on electrical parameters alone required 40% more linear travel clearance than the tank interior allowed; installation was not possible without internal transformer modification.

Conditional Field: Motor Operator

Every tap changer RFQ should request the supplier’s recommended interlock labeling specification. Field incidents involving tap changers operated under load consistently trace to inadequate lockout/tagout labeling or personnel confusion between this device and a loadbreak switch.

Supplier Assessment Fields and RFQ Submission Checklist

Supplier Qualification Parameters

RFQ Submission Readiness Gate

Before submitting, confirm all eight points are resolved:

1. Transformer nameplate data complete
2. Highest system voltage Um confirmed
3. BIL stated in kVp
4. Fuse coordination threshold documented
5. Quantity per accessory family stated with spare ratio
6. Delivery terms and port confirmed
7. Inspection requirement stated
8. Dimensional drawing or datasheet attached where applicable

A single missing item is sufficient grounds for a supplier clarification request resetting the quotation clock by days or weeks.

ZeeyiElec supports technical RFQ responses across all seven transformer accessory families in this template. Submit project parameters and nameplate data via the project inquiry form. For a parallel field-by-field procurement reference with IEC standard alignment notes, the Аксессуары для трансформаторов Контрольный список RFQ covers the same accessory families. For cable accessory procurement on the same project, the cable accessories series provides a parallel selection and RFQ framework.

Часто задаваемые вопросы

What is the minimum information needed to start a transformer accessory RFQ?

At minimum, you need transformer nameplate data (kVA, HV/LV voltage, vector group, cooling type, and applicable standard), highest system voltage Um, BIL in kVp, installation altitude, and site pollution class without these, no accessory family can be correctly specified without supplier assumption filling the gaps.

How do I calculate the correct fuse link current rating for a Bay-O-Net assembly?

Calculate the transformer’s full-load primary current using kVA ÷ (√3 × HV kV), then apply an inrush margin of 8 to 12 times FLA for 0.1 seconds to identify a fuse link rating that carries normal load without operating while clearing overload faults below the Bay-O-Net interrupting limit of approximately 2,500–3,500 A.

What is the difference between nominal voltage and Um in transformer accessory specification?

Nominal voltage is the network’s design reference; Um is the maximum voltage the system sustains under normal operating conditions typically 5–15% higher and bushing creepage distance, BIL, and flashover requirements are all governed by Um, not nominal voltage.

Why does rotation type matter when specifying an off-circuit tap changer?

Linear and rotary tap changer mechanisms have different internal travel geometry and tank clearance requirements, meaning a unit specified on electrical parameters alone may need more internal clearance than the transformer allows making installation physically impossible without transformer modification.

When should a loadbreak switch be specified instead of an off-circuit tap changer?

Specify a loadbreak switch when the application requires making or breaking load current while the transformer remains energized; specify an off-circuit tap changer when voltage ratio adjustment is needed only during planned de-energization despite similar external appearance, these devices are not operationally interchangeable.

What spare ratio should be included in a transformer accessory RFQ?

Consumable accessories such as fuse links warrant 10–15% spare allowance per project; non-consumable mechanical components such as bushings, tap changers, and loadbreak switches are commonly held at 5% or one spare unit per project, with higher ratios justified for remote sites where replacement lead times exceed four weeks.

Can a single RFQ cover multiple transformer accessory families from one supplier?

Yes, and consolidating into one submission reduces coordination effort but each accessory family must occupy a separate section with its own parameter fields, since bundling undifferentiated specifications into one block is the most common cause of misquotation and wrong shipment on multi-family transformer accessory orders.