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Cable Feeder Unit(D)

The ASNA cable feeder unit (symbol: D) from 

HM Power, a professional Ring Main Unit Manufacturer, 

is designed to connect cables to the horizontal busbars of adjacent switchgear. It consists of a cable compartment and a busbar compartment.


This unit is also known as an incoming cable feeder unit or outgoing cable feeder unit. A three-position disconnector is supplied as an optional accessory.

Cable Feeder Unit(D)

The ASNA cable feeder unit(symbol: D) is designed to connect cables to the horizontal busbars of adjacent switchgears. It consists of a cable compartment and a busbar compartment. This unit is also known as an incoming cable feeder unit or outgoing cable feeder unit. A three-position disconnector is supplied as an optional accessory.

Introduction

Core functions

Connection Function
Maintenance & Protection Function
Monitoring Function
Extended Functions

Connection Function

It enables reliable interconnection between feeder cables and the main busbars of adjacent switchgears. The unit can act as either a power incoming feeder or load outgoing feeder to complete power transmission.

HM Power, a professional Ring Main Unit Manufacturer

Maintenance & Protection Function

Where a three-position disconnector is fitted in the D unit, the earthing switch shall be closed during circuit de-energized maintenance to solidly earth the cable terminal, so as to avoid personal injury caused by accidental energization.

Monitoring Function

The voltage presence indicator (VPIS) provides a visual indication of the energized status of the circuit.

When a D unit fitted with a three-position switch is coupled with circuit breaker switchgear (D+B), an interlock mechanism shall be fitted to prevent the disconnector from being operated under load. Operating logic: The disconnector shall be closed prior to closing the circuit breaker; the circuit breaker shall be opened prior to opening the disconnector.

Lightning arresters may be supplied as optional components for suppression of circuit switching overvoltages and lightning surges. 

Temperature sensors can be installed optionally to enable real-time temperature monitoring within the cable compartment.

Parameter List

Parameter list of 24kV D Unit
Parameter list of 12kV D Unit
Name Unit Parameter
Rated voltage(Ur) kV 24
Rated frequency(fr) Hz 50
Rated current(lr) A 630 1250
Rated Short-duration power-frequency withstand voltage(Ud) Common value kV 50
Across the isolating distance 60
Rated Lightning impulse withstand voltage(up) Common value kV 125
Across the isolating distance 145
Rated short-time withstand current(lk) kA 20 25
Rated short-time duration(tk) s 4
Rated peak withstand current(lp) kA 50 63
Rated short-circuit breaking current(lsc) kA 20 25
Rated short-circuit making current(lma) Three-position disconnector kA 50 63
Mechanical endurance Three-position disconnector time 3000
Electrical endurance Earthing Switch class E2
Degree of protection by enclosure   IP4X
Degree of protection by Fully Sealed tank   IP65
Dimension Low voltage chamber not included W(mm) 550 600
D(mm) 850
H(mm) 1890,17001) 1940

1) 1700mm is the solution for the low cable room.

Name Unit Parameter
Rated voltage(Ur) kV 12
Rated frequency(fr) Hz 50
Rated continuous current(lr) A 630 1250
Rated short-duration power-frequency withstand voltage(Ud) Common value kV 28
Across the isolating distance 32
Rated lightning impulse withstand voltage(Up) Common value kV 75
Across the isolating distance 85
Rated short-time withstand current(Ik) kA 20 /25 20/25/31.5
Rated short-time of short-circuit(tk) s 4
Rated peak withstand current(Ip) kA 50 / 63 50/63/80
Rated short-circuit breaking current(Isc) kA 20 / 25 20/25/31.5
Rated short-circuit making current(Ima) Three-position disconnector kA 50 / 63 50/63/80
Mechanical endurance Three-position disconnector time 3000
Electrical endurance Earthing Switch class E2
Degree of protection by enclosure   IP 4X
Degree of protection by fully sealed tank   IP 65
Dimensions
Low voltage chamber not included
W(mm) 460 550
D(mm) 800 900
H(mm) 1640 1810

1) and 2): The 900mm and 1810mm are the sizes used to be match the 1250A switchgear.

Application

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Italy PCS Energy Storage Integrated Unit Power Distribution Project
Italy has witnessed rapid growth in installed capacity of wind and solar new energy, with steadily rising demand for energy storage on both grid-side and commercial & industrial sides. By charging and discharging to implement peak shaving and valley filling, energy storage systems effectively smooth grid fluctuations and reduce power consumption costs. As a critical component for grid connection, the medium-voltage switchgear supporting energy storage power stations is subject to growing attention on environmental compliance. Relevant EU greenhouse gas control regulations impose mandatory constraints on equipment selection. The EU F-Gas Regulation (EU) 2024/573 clearly stipulates that SF₆ greenhouse gas shall be prohibited for new medium-voltage switchgear with rated voltage ≤24kV starting from 1 January 2026.
Power Distribution Project of Tanzania Sapphire Float Glass Industrial Park
The Tanzania Sapphire Float Glass Industrial Park is a benchmark project under China’s Belt and Road Initiative. The glass manufacturing process imposes extremely stringent requirements on power supply continuity, power quality and voltage stability. Meanwhile, the park features complex operating conditions including high temperature, high humidity, dust and tin fog corrosion, which pose severe challenges to the corrosion resistance and long-term operational reliability of power distribution equipment.
Smart City Distribution Project in Stockholm, Sweden
Stockholm, Sweden, is a benchmark for smart city and green low-carbon urban development in Northern Europe. It was awarded the world’s first "European Green Capital" title in 2010. As a key supporting initiative for the grid intelligence and urban low-carbon transition of Stockholm, this smart city power distribution project comprehensively improves the stability and environmental performance of urban public power supply and serves as an important pillar for long-term sustainable development.
Tesla Supercharger Station Power Distribution Project, Sweden
In 2014, the first batch of Tesla Superchargers in Västerås, Sweden, supporting this project was completed and put into operation. It serves as a highly representative energy replenishment infrastructure for new energy vehicles in Northern Europe. As a high-power dynamic electrical load scenario, the supercharger station imposes stringent requirements on the 10kV distribution system in terms of power supply reliability, equipment stability, fault handling capability and low-carbon compliance.
Power Distribution Project of Hainan Wenchang Space Launch Site
The commercial Wenchang Space Launch Site is located on the coast of Hainan, featuring year-round high humidity and salt spray. Its core power distribution room supports uninterrupted critical services including launch telemetry & control, command communication and data computation. It imposes aerospace-grade stringent requirements far exceeding ordinary industrial standards on the safety level of the power distribution system, power supply continuity, environmental weather resistance and long-period maintenance-free performance.
Haikou Meilan International Airport Phase II Expansion · ATC Station Room Renovation Project
As the core aviation hub of the Hainan Free Trade Port, Haikou Meilan International Airport undertakes key functions including passenger and cargo transportation as well as air traffic control (ATC) navigation support. The ATC station room renovation required an upgrade of the power distribution system under non-stop flight and uninterrupted ATC service conditions. The project demands absolutely continuous and secure power supply, while the equipment must adapt to on-site conditions featuring densely arranged devices and complex electromagnetic environments.
Tencent Data Center Power Distribution Project, Guizhou
Tencent Data Center in Guizhou is China’s first large-scale cave-type data center, undertaking core services including data storage and AI training. Power outages may result in data loss and computing capacity loss, so extremely high reliability requirements are imposed on power supply. Its unique geographic location also raises stringent requirements for anti-condensation performance and maintenance-free operation.
Qualification

Certification And Qualification

Questions and answered

1
Q:  Why is an interlock mechanism required when a D unit fitted with a three-position disconnector is coupled with a circuit breaker switchgear to form a D+B combination?
A: Disconnectors possess no arc extinction capability. Performing switching operations under load will create severe electric arcs. An interlock mechanism is therefore installed to prohibit opening or closing the disconnector under loaded conditions.
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