Centre Post Isolator– Turn & Twist Design (Double Break Type)

substation control systems instead of AC

Centre Post Isolator– Turn & Twist Design (Double Break Type)

In electrical substations, safe isolation, maintenance safety, and operational reliability depend heavily on one critical equipment — the Centre Post Isolator.

Commonly known in the industry as the Turn & Twist Isolator or Center Rotating Isolator, its correct technical name as per standards is:

Double Break Centre Post Isolator

This isolator type is widely used in 33kV, 66kV, 110kV, 132kV, and 220kV substations across transmission and distribution networks.

What is a Centre Post Isolator?

A Centre Post Isolator is a double break, horizontal rotating type isolator where the moving contact rotates on its center post insulator. During operation, the top assembly turns and twists, creating a clear and visible isolation gap on both sides.

This design provides:

Positive visual isolation

Smooth mechanical operation

Balanced contact pressure

High reliability during switching

Long service life with minimal maintenance

Why It Is Called “Turn & Twist” Design?

Unlike pantograph or vertical break isolators, the centre post isolator operates with a rotational movement.

• The central post rotates

• The moving blade twists away from the fixed contacts

• Two air gaps are created (Double Break)

• Ensures higher insulation safety

This turning and twisting motion is the reason it is popularly called the Turn & Twist Isolator in substations.

Key Features of Centre Post (Turn & Twist) Isolator

Voltage Classes Where It Is Commonly Used

Centre Post Isolators are most preferred in:

Importance of Proper Contact Alignment

One of the most critical factors in centre post isolators is perfect alignment between fixed and moving contacts.

Poor alignment can lead to:

✅ Heating at contact points

✅ Reduced current carrying capacity

✅ Contact burning

✅ Failure during load conditions

At Balaji Isolators, special attention is given to:

Precise fixed and moving contact alignment, ensuring low resistance path and superior current conduction.

Applications in Substations

Centre Post Isolators are installed for:

• Line isolation

• Bus isolation

• Transformer isolation

• Maintenance safety during shutdown

• Interlocking with circuit breakers (Castle Key Interlock)

Why Centre Post Isolator is Preferred Over Other Types?

Feature	Centre Post Isolator	Other Types
Space Requirement	Compact	Larger space needed
Contact Pressure	Uniform	Uneven in some designs
Maintenance	Low	Moderate
Mechanical Stability	High	Moderate
Visual Isolation	Excellent	Good

Centre Post Isolator Manufactured by Balaji Engineers Isolators Pvt. Ltd.

Balaji Engineers Isolators Pvt. Ltd. (Balaji Isolators) is one of India’s leading manufacturers and exporters of Centre Post Isolators for substations.