What is the harm of three-phase unbalance in oil immersed transformer?
Yes, there are some large electrical equipment, and many people are concerned only with quality. In ordinary life, rarely heard of electrical equipment, power imbalances caused by accidents, then, is not the imbalance of electricity, there is no harm? Of course not.
1, the oil immersed transformer itself harm.
Under normal circumstances, oil immersed transformers have iron losses (no-load losses) and copper losses (load losses) two losses, iron losses are generally unchanged, copper losses will vary according to the load. When the three-phase load is unbalanced, the load loss of the oil immersed transformer can be regarded as the sum of the load losses of the three single-phase oil immersed transformers. This may cause serious consequences for oil immersed transformers, which can cause excessive phase current (3 times) when unbalanced, resulting in overheating of windings and oil immersed transformer oil.
Heating winding, insulation aging accelerated; oil immersed transformer oil overheating caused by oil deterioration, the insulation performance of rapid decrease of the oil immersed transformer, oil immersed transformer life (reduce temperature rise every 8 degrees, life will be reduced half, or even burned winding). At the same time, unbalanced three-phase oil immersed transformer condition produces zero flux, zero flux through the oil immersed transformer metal components of the circuit is oil immersed transformer fever, also affect the safe operation of oil immersed transformer.
2 、 influence on oil immersed transformer related lines.
The above mentioned three phase unbalance will produce zero flux, zero flux will become neutral line current in the neutral line, this line will not only loss, while the neutral line will also have a loss, which will increase the loss of power supply lines.
On the other hand, in the three-phase four wire connection mode, when the three-phase equilibrium line loss minimum; when a phase of heavy load, two lighter load line loss increment is small; when a heavy load, a light load, and the three-phase load is more average load line loss increase large amount when a phase; light load, load weight loss will be the largest increment under two. When the three-phase load is unbalanced, no matter what kind of load distribution, the greater the current imbalance is, the greater the line loss will be.
3, the impact of electrical equipment.
The imbalance between phases can lead to shorter service life of electrical equipment, replacement frequency of accelerating components, and increase the cost of equipment maintenance. For substation equipments, unbalanced load condition in three phase, each phase of the output current is not equal, which leads to its internal three-phase pressure drop is not equal, thus causing the output voltage unbalance. At the same time, the substation equipment runs under the unbalanced three-phase load, and the three-phase output current is different, which leads to the current passing through the neutral line. As a result, the impedance of the neutral line is suppressed, leading to a drift of the neutral point, resulting in a change in the phase voltage. The negative load phase voltage decreases while the light load phase voltage rises.
When the voltage is unbalanced, the power supply is easy to cause the user's electric equipment with a high voltage to be burned out, and the user equipment with a low voltage and a connecting belt may not be used. Therefore, the unbalanced operation of three-phase load will seriously endanger the safe operation of power equipment. For motor, three-phase voltage imbalance will cause the motor torque in the inverse increase, so that the motor temperature rise, lower efficiency, energy consumption increases, the shock occurs, the output depletion effect. For the circuit breaker, the three-phase imbalance will make the circuit breaker to allow the current margin reduction, when the load changes or alternate, prone to overloading, short-circuit and so on.