Failures in dry-type transformers for offshore applications

Failures in dry-type transformers for offshore applications

Special Edition - Dry-type Transformers
  1. Introduction

The consequences of transformer failures in offshore applications can be much more serious than similar failures in industrial and commercial applications. Failures may result in significant costs associated with lost production and transformer repair or replacement costs. Additionally, such failures will involve serious safety issues, such as the possibility of fire, explosion, smoke emission and toxic fume emission.

Due to concerns regarding leaks from liquid-filled transformers and the need to contain the leaking liquid in order to prevent pollution and minimize the risk of fire – a major concern for offshore applications – dry-type transformers, either VPI (vacuum pressure impregnated) or cast coil (cast resin) are the preferred option for offshore applications.

This article will examine the possible causes of failure, describe the modes of failure and provide recommendations to specifiers and end-users for reducing the occurrence of failures.

 

  1. Causes of failure

Below is a selection of common causes of failure, specific to offshore and marine applications.

 

2.1 Environmental

  • Salt – Offshore equipment spends its life operating in a salt-laden atmosphere. This can cause corrosion of the copper or aluminium used for the conductors of the winding and the terminals, and also of the silicon steel core and the carbon steel used for the clamping structure.
  • Moisture – Moisture is the enemy of any electrical equipment, and the effects of moisture are obviously a much greater threat in offshore applications. Moisture reduces the dielectric properties of the insulation, which is especially problematic for the transformer coils. Surface moisture can lead to tracking over insulation surfaces, particularly in the case of medium voltage transformers.
  • Chemical contamination – Many different chemicals are in use on drilling rigs and ships, and these chemicals can be damaging to the transformer insulation and conductors. For example, exhaust gases from engine-driven generators may enter the transformer enclosure, where they can leave carbon deposits on coils which will lead to tracking and eventual damage to the transformer insulation system.
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