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D2233-86 – Standard Test Method Technical Guide
ASTM D2233-86 (Reapproved 1997) defines the standard specification for synthetic nonflammable electrical insulating liquids of the chlorinated aromatic hydrocarbon type, known as askarels. These fluids are specifically formulated for use as an electrical insulating and cooling medium in capacitors. This specification covers liquids that were previously available and remain in service in existing apparatus.
Regulatory Note: Current governmental regulations prohibit the manufacture and sale of polychlorinated biphenyls (askarels). This standard is maintained exclusively for the reference, testing, and maintenance of capacitor units that are still in active service.
📜 Scope and Application
The scope of this standard encompasses synthetic nonflammable electrical insulating liquids of the chlorinated aromatic hydrocarbon type. The standard specifies the physical, chemical, and electrical properties these liquids must meet to be suitable for use in capacitors. It includes formulations that were previously available and are still operational in existing apparatus.
The specification formally defines four types of askarels. While these descriptions reflect historical formulations, the binding requirements of the specification are founded entirely upon the physical and chemical properties prescribed in Table 1 of the standard.
🧪 Chemical Composition and Types
Askarels covered by this specification are classified into four distinct chemical types. Type A is biphenyl chlorinated to a chlorine content of 42 weight percent. Type B is biphenyl chlorinated to a chlorine content of 54 weight percent. Type C is a mixture of approximately 75% Type B and 25% trichlorobenzene. Type D is the same as Type A, except the higher boiling homologs have been removed to a maximum level of 0.4%.
| 🟦 Type | 📏 Description | 🎯 Chlorine Content | ⚡ Key Characteristics |
|---|---|---|---|
| Type A | Chlorinated Biphenyl | 42 weight % | Standard general-purpose capacitor fluid. |
| Type B | Chlorinated Biphenyl | 54 weight % | Higher fire resistance due to increased chlorine content. |
| Type C | 75% Type B + 25% Trichlorobenzene | ~40.5 weight % | Blended formulation for specific viscosity and electrical parameters. |
| Type D | Low Homolog Biphenyl | 42 weight % | Refined Type A with reduced higher boiling homologs (max 0.4%). |
Safety Characteristic Under Arcing: Askarels possess a unique property where, under arcing conditions, the gases produced consist predominantly of noncombustible hydrogen chloride with lesser amounts of combustible gases (Section 3.1.1). However, arcing of insulation systems combining these fluids with cellulosic or organic materials may produce moderately flammable gaseous mixtures.
⚙️ Testing and Key Measured Properties
Conformance to ASTM D2233-86 is verified through a comprehensive suite of standard test methods. The detail requirements mandate that askarels for use in capacitors conform to the limits established in Table 1 of the standard. These properties are evaluated using rigorous ASTM protocols to ensure reliable performance in capacitor applications.
Electrical integrity is assessed through dielectric breakdown voltage (ASTM D877), dissipation factor and relative permittivity (ASTM D924), and specific resistance (ASTM D1169). Physical properties such as viscosity (ASTM D88), pour point (ASTM D97), flash and fire points (ASTM D92), specific gravity (ASTM D1810), and coefficient of thermal expansion (ASTM D1903) are critical for design. Chemical stability is confirmed via tests for acid number (ASTM D664 or D974), water content (ASTM D1533), hydrolyzable chlorine (ASTM D1820), inorganic chlorides (ASTM D1821), and thermal stability (ASTM D1936).
❓ Frequently Asked Questions
🔍 What is an askarel?
Askarel is a generic term for a group of synthetic, fire-resistant, chlorinated aromatic hydrocarbons used as electrical insulating liquids. Their defining characteristic is that under arcing conditions, the gases produced consist predominantly of noncombustible hydrogen chloride.
💡 Why does this standard exist if PCBs are banned?
Current governmental regulations prohibit the manufacture and sale of polychlorinated biphenyls. ASTM D2233-86 is maintained as a reference document for the continued safe operation, testing, and maintenance of thousands of installed capacitors that remain in service.
⚡ What are the four types of askarels specified?
The standard specifies Type A (42% chlorine biphenyl), Type B (54% chlorine biphenyl), Type C (a mixture of 75% Type B and 25% trichlorobenzene), and Type D (42% chlorine biphenyl with higher boiling homologs removed to max 0.4%).
📌 How is sampling for these fluids conducted?
Sampling of askarels for conformance testing must be performed in accordance with ASTM D923. This ensures representative samples are taken for the battery of electrical, physical, and chemical tests required by the specification.