Capacitive Grading Layers: Temperature Range -40°C to +105°C

Component Specifications

Definition

Capacitive grading layers are concentric cylindrical or conical conductive layers embedded within the insulation of high-voltage bushings. They function as a series of capacitors connected in parallel with the main insulation, creating a controlled voltage gradient along the bushing's length. This prevents excessive electric field concentration at either end, which could cause partial discharges or complete insulation failure. These layers are typically made of conductive foil or metallized paper and are precisely spaced to achieve linear voltage distribution.

Working Principle

The working principle is based on capacitive voltage division. Multiple conductive layers are inserted at specific intervals within the dielectric material. Each layer acts as an electrode, forming capacitors with adjacent layers and the central conductor/ground. This creates a capacitive ladder network that forces the voltage to drop uniformly across the insulation, rather than concentrating at stress points. The capacitance values are designed to be inversely proportional to the distance from the high-voltage end, ensuring equal voltage steps between layers.

Materials

Aluminum foil (10-50 μm thickness), copper foil, metallized paper (kraft paper with vapor-deposited aluminum), semiconductor coatings (carbon-loaded polymers), epoxy-impregnated materials. Dielectric spacers: oil-impregnated paper, resin-bonded paper, epoxy resin, silicone rubber.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Layer Count	10-100 layers depending on voltage
Layer Spacing	1-10 mm (graded)
Voltage Rating	Up to 1200 kV AC, ±1100 kV DC
Partial Discharge	<5 pC at rated voltage
Temperature Range	-40°C to +105°C
Dielectric Strength	>15 kV/mm
Capacitance Per Layer	100 pF to 10 nF

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

IEC 60137, IEEE C57.19.00, DIN 42523, ISO 9001

Parent Products

This component is used in the following industrial products

Bushings

Insulating devices that provide electrical connection and mechanical support for conductors passing through grounded transformer enclosures.

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Engineering Analysis

Risks & Mitigation

Partial discharge inception
Dielectric breakdown
Thermal runaway
Moisture ingress
Mechanical damage during installation

FMEA Triads

Trigger: Manufacturing defect in layer alignment
Failure: Uneven voltage distribution
Mitigation: Automated optical inspection during winding, capacitance testing of each layer

Trigger: Moisture absorption in dielectric
Failure: Reduced dielectric strength, increased leakage current
Mitigation: Hermetic sealing, moisture barriers, regular dielectric loss testing

Trigger: Thermal cycling stress
Failure: Delamination between layers
Mitigation: CTE-matched materials, stress-relief designs, thermal cycling qualification testing

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Layer spacing ±0.1 mm, capacitance tolerance ±5%, concentricity <0.5 mm TIR

Test Method

Capacitance and dissipation factor measurement (tan delta), partial discharge test (>1.5x rated voltage), power frequency withstand voltage test, impulse voltage test

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

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Inspection readiness

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Supplier transparency

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Manufacturers of Capacitive Grading Layers

Manufacturer profiles associated with Capacitive Grading Layers.

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Frequently Asked Questions

Why are capacitive grading layers necessary in bushings?

Without grading layers, the electric field would concentrate at the ends of the bushing, exceeding the dielectric strength of the insulation and causing failure. The layers distribute voltage evenly.

What happens if a grading layer fails?

Layer failure creates localized high electric stress, leading to partial discharges, insulation degradation, thermal runaway, and eventual bushing explosion.

Can grading layers be repaired?

No, damaged grading layers require complete bushing replacement as they are embedded within solid insulation during manufacturing.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Capacitive Grading Layers