GB/T 32288-2020Electrical steel cores for power transformers (English PDF)

5.1 Core insulation

5.1.1 Under the condition that the relative humidity of the air is lower than 85%, the insulation value of the core with a voltage level of 35kV and below shall meet the following requirements:

a) Dry-type transformer >= 5Mohm;

b) Oil-immersed transformer >= 1Mohm.

5.1.2 Under the condition that the relative humidity of the air is lower than 85%, the insulation value of the core with a voltage level of 35kV above shall meet the following requirements:

a) Core-to-ground insulation >= 0.5Mohm;

b) The insulation between the core oil channels is >=0.5Mohm.

5.2 No-load loss, no-load current and sound level

The no-load loss, no-load current and sound level of the core shall meet the technical […]

6.3.4 Roughness

Firstly, cut a section of 2m-long strip material with waves; and place it freely on the measuring platform. Use a plug gauge to measure the value h value; use a steel ruler to measure the L value; and calculate the roughness lambda according to Formula (1).

Where:

lambda - roughness; h - maximum height of the rough area, in mm; L - maximum length of the rough area, in mm.

6.3.5 Burr

Use a micrometer to measure the burr value at any three points on the same shearing surface of the electrical steel sheet; and take the average value.

6.3.6 Residual curvature

The residual curvature of electrical steel sheet shall comply with the provisions of GB/T 2521.2.

6.3.7 White edge

The white edge of the fixed-length electrical steel strip (sheet) shall be observed by a 20 times magnifying glass with a scale; and the width of the white edge shall be measured.

6.3.8 Metal hair

Visually measure the edge of the longitudinal shearing to check whether there are tiny hair-like metal strips at the cut.

6.4 Transverse shearing

6.4.1 Deviation

The sheet length deviation, consistency deviation, angle deviation, hole position deviation, aperture deviation, and V-notch deviation of the transverse shearing are measured by general measuring tools that meet the corresponding accuracy requirements.

6.4.2 Mechanical loss

The mechanical loss of the transverse shearing shall be inspected visually.

6.5 Others

Inspection methods for other items shall comply with the provisions in Tables 1, 2, and 3.

8.1 Marking

The product marking shall have the following content:

--- The name or trademark of the manufacturer;

--- Transformer model;

--- Core assembly drawing number and core lamination drawing number;

--- product number;

--- Inspection date, etc.

8.2 Packaging and transportation

It shall be properly packaged according to the transportation requirements to ensure that the core shall not be deformed, loose, cracked, damaged on the end face, rusted or otherwise damaged during transportation.

8.3 Storage

The core shall be stored in a ventilated, dry and non-corrosive gas space. […]