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Dynamic Feeder Rating System

A Dynamic Feeder Rating (DFR) system configured to link several remote terminal units (RTU) positioned at strategic locations along the cable route.

Data Acquisition System

The Dynamic Feeder Rating system is controlled by the CPU, typically an industrial grade unit which maintains continuous service. Hardware is powered by an uninterruptible power supply with provision for safe shutdown protocols in case of extended power outages. To overcome possible malfunction of the Dynamic Feeder Rating (DFR) system and maintain remote operation capability, the CPU is restarted at will, by a simple telephone command.

The key performance characteristics of the RTUs provide reliable acquisition and storage of cable and ambient temperatures and load current data. This data is transferred at regular intervals to the CPU under typical field conditions, including transient potential rises.

Alternatively, cable and soil temperature data can be acquired by a distributed fiber optic measurement system capable of collecting temperature information along the entire cable route.

RTU Capabilities

The distributed RTU units are commercial data acquisition units requiring a power supply and a link for communication to the CPU. To enable an uninterrupted collection of data, the units are capable of long-term operation (1-2 weeks) based solely on battery power. The units have sufficient memory to retain upwards of 500k points of data.

To overcome possible malfunction of the remote system and maintain continuous operation, the RTUs are restarted directly by the CPU. The RTUs have a broad operating range, typically from -40 degrees C to +70 degrees C. The technology has proven highly reliable in monitoring the mechanical performance of transmission equipment for over 10 years outdoors in Northern Ontario.

RTU power is provided from a conventional ac source or, where appropriate, from a solar battery pack to minimize installation costs. To minimize telephone installation costs, the communications link can be established via cellular phone or dedicated wireless transmitter.  Depending on requirements, RTUs can accommodate over 100 thermocouple inputs.

DFR Software

The DFR software program performs calculations of cable conductor temperature, steady state and emergency ratings in real-time. The user specifies the relevant maximum operating temperatures and the duration of the emergency. The DFR software computes the maximum current that the cable can carry for the specified conditions.

Calculation of the steady-state rating is performed in two modes. In one case, standard Neher/McGrath or IEC 287 calculations are performed with the user-specified load-loss factor.  In the second case, the program evaluates recorded load variations over a 24-hour period and assumes the same variations during the following period. Duration of this period is such that the steady-state conditions are achieved.

Time-dependent ratings are based on the method described in the IEC Standards 853-1 and 2.  Similarly, as in the steady-state case, two modes of load representation are considered during the emergency period: (1) a step function is applied, or (2) the load curve from the last 24 hours is scaled.

During the steady state and time-dependent calculations, the thermal and electrical parameters of the model are continuously adjusted so that the computed and measured cable surface temperatures match.

Enhanced Capacity 

DFR systems are used to enhance current-carrying capacity of power cables and to eliminate the risk of overheating. They allow utilization of cable systems to their maximum capabilities and are particularly useful when a deferment of costly capital programs is desirable.