Horizontal Knee Disconnector with visible isolation point

Horizontal Knee Disconnector

Horizontal Knee Disconnector (Horizontal Knee Break Isolator) is a high-voltage disconnector used in air-insulated substations (AIS) to provide a visible isolation point for maintenance and operational safety. It employs a hinged knee-joint mechanism that folds horizontally during operation, making it suitable for substations where vertical clearance is limited.

Working Principle
The horizontal knee disconnector consists of two conducting arms connected by a hinged knee joint.
·Closed position: The arms are aligned, forming a continuous electrical path between the fixed contacts.
·Open position: The operating mechanism bends the knee joint horizontally, causing the arms to fold and creating a visible air gap between the contacts.

Since it is a disconnector, it is not capable of interrupting load current or fault current. The associated circuit breaker must first de-energize the circuit.

Normal Operating Sequence
1.Open the circuit breaker.
2.Confirm the circuit is de-energized.
3.Open the horizontal knee disconnector.
4.Close the earthing switch if maintenance is required.

Main Components
·Fixed contacts
·Upper and lower conducting arms
·Hinged knee joint
·Post insulators
·Operating linkage
·Motor-operated or manual operating mechanism
·Base frame
·Position indicator
·Auxiliary switches

Features
·Horizontal folding movement minimizes required vertical clearance.
·Provides a clear visible isolation gap.
·Robust mechanical design for outdoor environments.
·High mechanical endurance and operational reliability.
·Can be operated manually or remotely by motor drive.
·Suitable for high-voltage and extra-high-voltage applications.

Typical Voltage Ratings
·72.5 kV Distribution and sub-transmission
·110 kV Transmission substations
·132 kV Utility transmission
·145 kV High-voltage substations
·220 kV Transmission systems
·330 kV Extra-high-voltage substations
·400 kV EHV transmission

Advantages
·Requires less vertical clearance than vertical-opening designs.
·Provides reliable visible isolation.
·Well suited for substations with height restrictions.
·Long service life with relatively low maintenance.
·Reliable operation under outdoor environmental conditions.

Limitations
·Cannot interrupt load current or fault current.
·Must only be operated after the associated circuit breaker has opened.
·Mechanical linkage is more complex than simple center-break designs.

Applications
Horizontal knee disconnectors are commonly used for:
·Air-insulated substations (AIS)
·Transmission line isolation
·Power transformer isolation
·Circuit breaker isolation
·Busbar sectionalizing
·Industrial substations
·Installations with limited vertical clearance

Typical Applications by Voltage
·72.5–145 kV: Distribution and sub-transmission substations.
·220–400 kV: High-voltage transmission substations with structural height limitations.
Industrial power systems: Isolation of transformers, circuit breakers, and busbars where overhead clearance is restricted.

The Horizontal Knee Disconnector is selected when a substation requires a compact vertical profile while still providing a safe, visible isolation gap. Its horizontal folding mechanism makes it particularly useful in air-insulated substations where overhead clearance is limited but reliable isolation of high-voltage equipment is essential.