A wealth of benefits
Digital Instrument Transformers offer many benefits compared to conventional instrument transformers (oil, SF6), including:
Wide dynamic range
1 A to 4800 A. One current transformer can cover a wide dynamic range through the same output. The protective current is up to 216 kA (peak value) and the bandwidth is DC to 20 kHz.
Smart Grid ready
COSI products deliver direct digital output according to IEC 61850-9.2 or 1 A for metering applications.
System Cost savings
Drastic reduction of cabling and cubicle costs in substation compared to conventional system.
Standard optical fiber
All signals are transmitted through a standard fiber optic cable (same cable as used in Telecom). By using a globally-available fiber optic cable to connect all electronic equipment, we offer our customers substantial savings and global maintenance.
Lightweight
Typically, an optical sensor represents only 10% of the weight of a oil filled transformer. As transportation costs and ease of installation depend on the weight and volume, the benefits are immediately apparent. There is no need for special transportation to protect the equipment against vibrations (truck and hard road). Moreover, the support structure also depends on weight and dimensions. So, global installations costs are also reduced.
Installation flexibility
Bus mounting is possible, as well as horizontal mounting or assembly directly on the circuit breakers. All these configurations are possible with Digital Instrument Transformers, but not with oil filled equipment. The total substation footprint can be reduced by as much as 15 to 25%.
Increased safety for people, substation equipment and the environment
COSI range is explosion proof. No oil and no SF6 mean no environmental costs on end-of-life disposal and no leakage problems. Moreover, horizontal transport and (long-term) storage is possible without risk and there are no ferro-resonance or dangerous open secondary concerns.
Near zero maintenance
Time is money, and the optical sensors dramatically reduce the number of outages for maintenance. No oil sampling or DGA are needed. Optical sensors offer remote monitoring for preventive maintenance without tripping.
A seismic solution
Digital Instrument Transformers offer retrofitting flexibility without concern for seismic withstand. Also, they are constructed with a composite line post insulator for maximum seismic endurance.
Secondary circuit saving and "Forgiving secondaries"
In oil filled and SF6 technology, a magnetic current transformer requires two (or more) wires for each core. Losses in the secondary loop can either dramatically increase the cores sizes or require greater wire selections. The wide dynamic range of sensor and the Ethernet connection limits the number of “secondaries” and makes most of the secondary wiring obsolete. In oil filled current transformers, eventual modifications are either very costly or impossible. Moreover, it is often impossible to add more secondaries or modify key characteristics once production of CT is in progress. With digital current transformers, additional secondaries or last-minutes changes in specifications can be handled by the electronics. The turns ratio is user-selectable on site.
Flexibility and inventories reduction
Ratio can be modified any time (via computer connection). This results in very short delivery time (from stock). Moreover, the CT ratio can be adapted according to CT location and there is a significant reduction of customers stock as there is no CT needs for every ratio.
Software evolution
It is possible to update or enhance the software throughout the life of the equipment.
Interchangeability
In the case of an (exceptional) failure in the electronics, all that is needed is a very simple box change. No recalibration is required.