1. Introduction
In modern high-voltage transmission and substation projects, communication systems are a critical part of power system operation. They support:
- Protection signaling
- SCADA and control
- Teleprotection
- Monitoring and data transfer
To achieve reliable communication over long distances and within substations, optical fiber communication is widely used. The most common arrangement includes:
- Overhead optical fiber (OPGW)
- Underground optical fiber (UGNMFOC)
- Indoor fiber management systems
2. Overall Communication System Concept
The communication network in a power transmission project is divided into three main zones:
- Transmission line communication
- Substation outdoor–indoor connectivity
- Internal substation communication
All these zones are interconnected using single-mode optical fiber, usually compliant with ITU-T G.652.D, ensuring:
- Low attenuation
- High bandwidth
- Long-distance signal transmission
- Compatibility across different cable types
3. Overhead to Underground Fiber Interface
3.1 Purpose
Overhead transmission lines use Optical Ground Wire (OPGW), which combines:
- Ground wire for lightning protection
- Optical fibers for communication
Inside substations, overhead fiber cannot be routed directly into buildings. Therefore, underground non-metallic fiber optic cables (UGNMFOC) are used to bridge the connection.
3.2 Underground Fiber Characteristics
Typical underground fiber cables used in substations have the following features:
- Single Mode fiber
- 96 cores (for redundancy and future expansion)
- Non-metallic construction (to avoid induced currents)
- Suitable for duct or trench installation
The underground fiber must have matching optical parameters with the overhead fiber to ensure:
- Low splice loss
- Stable communication
- Long-term reliability
4. Communication Works from Substation Gantry to Communication Room
4.1 Scope of Work
Communication works include:
- Supplying underground fiber optic cables
- Installing cables in HDPE or PVC ducts
- Routing cables from the substation gantry to the communication room
- Splicing underground fiber with overhead fiber
- Terminating fibers on optical racks
4.2 Duct and Cable Installation
Key installation practices include:
- Use of multi-way ducts with spare sub-ducts for future use
- Fire-rated ducts inside buildings
- Proper bending radius to avoid fiber damage
- Pull ropes installed in unused ducts
This ensures safe installation, easy maintenance, and future expandability.
5. Splicing and Termination System
5.1 Fiber Splicing
Fiber splicing is carried out in joint boxes installed at:
- Substation gantries
- Cable transition points
Types of splicing:
- Overhead fiber to underground fiber
- Underground fiber to indoor fiber
Splicing must be performed using fusion splicing to achieve minimal loss.
5.2 Fiber Termination
Inside the communication room, fibers are terminated on:
- Optical Fiber Management Racks (OFMR)
- Fiber Splice Termination Panels (FSTP)
Each fiber core is:
- Properly labeled
- Neatly dressed
- Individually accessible
This allows easy testing, fault isolation, and future modifications.
6. Communication Between Substation Rooms
6.1 Purpose
Within a substation, communication links are required between:
- Communication Room
- Control Room
- Relay Room
- Customer or utility interface rooms
These links support:
- Protection relays
- Control panels
- Data concentrators
6.2 Internal Fiber Cabling
Internal communication is typically achieved using:
- Underground or indoor fiber optic cables
- Installation through ducts or cable trays
- Termination at both ends using OFMR and FSTP
Sufficient fiber cores are provided to:
- Separate protection and control systems
- Maintain redundancy
- Allow future system upgrades
7. Fiber Core Management and Color Coding
To manage large fiber counts, standard practices are followed:
- Fibers grouped in sets of 12 cores
- Standard color coding for easy identification
- Repeated color sequence for higher core counts
This system helps engineers quickly identify fibers during:
- Testing
- Splicing
- Maintenance
8. Testing and Commissioning
After installation, the communication system must be tested to ensure proper performance.
Common Tests Include:
- Optical Time Domain Reflectometer (OTDR) testing
- Insertion loss testing
- Continuity and polarity checks
- End-to-end link verification
Only after successful testing is the system approved for operation.
9. Engineering Advantages of This Communication Design
This general communication design offers:
- High reliability
- Low transmission loss
- Strong immunity to electrical interference
- Long service life
- Easy expansion and maintenance
Using standardized fiber types and installation practices ensures compatibility across substations and transmission networks.
10. Conclusion
Communication works in high-voltage substation projects form the backbone of power system protection and control. By integrating overhead and underground fiber optic systems and following standardized installation, splicing, and testing practices, a robust and future-proof communication network is achieved.
