AMORPHOUS-METAL FOR DISTRIBUTION TRANSFORMER APPLICATIONHow does amorphous distribution transformers help in reducing losses in a distribution system?
For example, the core loss for a new 50-kVA amorphous-core transformer might be only 30 watts instead of the 100 watts typical for a 50-kVA unit of conventional low-loss design. Winding losses and impedance are about the same for amorphous-core transformers and silicon-core transformers. The purchase price of a amorphous-core transformer is approximately 25% higher than a conventional-design transformer of the same size and type.
From a loss-economics point of view, each distributor should evaluate the equivalent first cost of reduced core losses for each size and type of transformer and compare this with the purchase price premium.
This discussion provides a detailed procedure for such an economic evaluation, which includes evaluation of winding losses as well. Amorphous-core transformers may be evaluated economically in the same manner as any other type of transformer design. Consideration of amorphous-core distribution transformers is imperative for distributors because of the high cost of core losses resulting from the TVA Distribution Loss Charge formula.
A few negatives associated with amorphous-core transformers have been reported. First, an amorphous-core distribution transformer (including tank and oil) will be physically larger and heavier than a silicon-steel-core transformer of the same kVA size. For most installations this extra physical size should not present special problems.
Second, amorphous-core distribution transformer design reported in engineering literature tend to border more closely on core saturation than low-loss silicon-steel-core designs. When excitation voltage is increased above nominal on an amorphous-core distribution transformer; the core losses increases at approximately the 3.3rd power of the voltage increase. This means that a transformer with quoted core losses of 30watts would incur approximately 35 watts when operated at 126 volts on a 120-volt base. However, the core losses are substantially less than for silicon-steel-core units even operated at 5% above nominal voltage. Nevertheless, distributors can guard against high voltage core loss increases by having manufacturers quote core losses for all transformers at 105% of nominal voltage as well as at 100% voltage.
Third, the still-unanswered question about amorphous-core transformers is whether or not they can maintain adequate reliability over several decades in actual service, as has come to be expected from conventional-design transformers. The fact that the first ten years of service for amorphous-core transformers have demonstrated an excellent reliability record is encouraging.
Nevertheless, each distributor should be cautious about installing a very large number of amorphous-core transformers on its system until that distributor obtains a service-reliability record for this type of transformer in its own service territory. However, the loss savings that will accrue should encourage each distributor to consider purchasing amorphous-metal transformers to begin experience record with this promising improvement in system efficiency.
Distribution transformers with amorphous-metal cores were introduced in the early 1980s and have now accumulated many years of in-service time. The amorphous-metal core design results in transformer core losses approximately 70% less than silicon-steel core designs.
For example, the core loss for a new 50-kVA amorphous-core transformer might be only 30 watts instead of the 100 watts typical for a 50-kVA unit of conventional low-loss design. Winding losses and impedance are about the same for amorphous-core transformers and silicon-core transformers. The purchase price of a amorphous-core transformer is approximately 25% higher than a conventional-design transformer of the same size and type.
From a loss-economics point of view, each distributor should evaluate the equivalent first cost of reduced core losses for each size and type of transformer and compare this with the purchase price premium.
This discussion provides a detailed procedure for such an economic evaluation, which includes evaluation of winding losses as well. Amorphous-core transformers may be evaluated economically in the same manner as any other type of transformer design. Consideration of amorphous-core distribution transformers is imperative for distributors because of the high cost of core losses resulting from the TVA Distribution Loss Charge formula.
A few negatives associated with amorphous-core transformers have been reported. First, an amorphous-core distribution transformer (including tank and oil) will be physically larger and heavier than a silicon-steel-core transformer of the same kVA size. For most installations this extra physical size should not present special problems.
Second, amorphous-core distribution transformer design reported in engineering literature tend to border more closely on core saturation than low-loss silicon-steel-core designs. When excitation voltage is increased above nominal on an amorphous-core distribution transformer; the core losses increases at approximately the 3.3rd power of the voltage increase. This means that a transformer with quoted core losses of 30watts would incur approximately 35 watts when operated at 126 volts on a 120-volt base. However, the core losses are substantially less than for silicon-steel-core units even operated at 5% above nominal voltage. Nevertheless, distributors can guard against high voltage core loss increases by having manufacturers quote core losses for all transformers at 105% of nominal voltage as well as at 100% voltage.
Third, the still-unanswered question about amorphous-core transformers is whether or not they can maintain adequate reliability over several decades in actual service, as has come to be expected from conventional-design transformers. The fact that the first ten years of service for amorphous-core transformers have demonstrated an excellent reliability record is encouraging.
Nevertheless, each distributor should be cautious about installing a very large number of amorphous-core transformers on its system until that distributor obtains a service-reliability record for this type of transformer in its own service territory. However, the loss savings that will accrue should encourage each distributor to consider purchasing amorphous-metal transformers to begin experience record with this promising improvement in system efficiency.
Comments
Post a Comment