Impact of Power Imbalance on Oil-Immersed Transformers
For some large electrical equipment, many people only focus on quality. In daily life, accidents caused by power imbalance in electrical equipment are rarely heard of. So, does power imbalance have no harm? Of course not.
1. Harm to the oil-immersed transformer itself.
Under normal circumstances, oil-immersed transformers have two types of losses: iron loss (no-load loss) and copper loss (load loss). Iron loss generally remains constant, while copper loss changes with the load. When operating with unbalanced three-phase loads, the load loss of the oil-immersed transformer can be considered as the sum of the load losses of three single-phase oil-immersed transformers. This can cause serious consequences to the transformer. Unbalance can cause excessive phase current (increasing by 3 times), leading to overheating of the windings and transformer oil. Overheating of windings accelerates insulation aging; overheating of transformer oil causes oil quality deterioration, rapidly reducing the insulation performance and lifespan of the transformer (for every 8°C increase in temperature, the service life is halved), and may even burn out the windings. At the same time, under unbalanced three-phase conditions, the transformer generates zero-sequence magnetic flux, which flows through the loop composed of metal parts of the transformer, causing heating and affecting the safe operation of the transformer.
2. Impact on lines related to the oil-immersed transformer.
As mentioned above, three-phase unbalance generates zero-sequence magnetic flux, which becomes neutral line current on the neutral line. This not only causes losses in the phase lines but also in the neutral line, thereby increasing the line losses of the power grid. On the other hand, in a three-phase four-wire connection, when the three phases are balanced, line loss is minimal; when one phase has a heavy load and two phases have lighter loads, the increase in line loss is small; when one phase has a heavy load, one phase has a light load, and the third phase has an average load, the increase in line loss is larger; when one phase has a light load and two phases have heavy loads, the increase in line loss is the greatest. When the three-phase load is unbalanced, regardless of the load distribution, the greater the current unbalance, the greater the increase in line loss.
3. Impact on electrical equipment.
Unbalance between phases can shorten the service life of electrical equipment, accelerate the frequency of component replacement, and increase equipment maintenance costs. For power distribution equipment, when operating under unbalanced three-phase loads, the output currents of each phase are unequal, leading to unequal internal three-phase voltage drops, resulting in unbalanced three-phase output voltages. At the same time, when distribution equipment operates under unbalanced three-phase loads, the output currents of the three phases are different, causing current to flow through the neutral line. This creates impedance voltage drop in the neutral line, causing neutral point drift and changing the phase voltages. The phase with a heavy load has a lower voltage, while the phase with a light load has a higher voltage. Supplying power under voltage imbalance can easily cause equipment connected to the high-voltage phase to burn out, while equipment connected to the low-voltage phase may not work properly. Therefore, unbalanced three-phase loads seriously endanger the safe operation of electrical equipment. For motors, three-phase voltage imbalance increases the reverse torque, causing the motor temperature to rise, efficiency to decrease, energy consumption to increase, vibration, and output losses. For circuit breakers, three-phase unbalance reduces the allowable current margin, making it easier to experience overload or short circuit when loads change or alternate.
Therefore, manufacturers must strictly control quality when producing oil-immersed transformers to ensure balanced three-phase voltage and minimize damage to equipment and lines. Yixing Xingyi Special Transformer Co., Ltd., as a professional electrical equipment manufacturer and power engineering installation service provider, ensures that every piece of equipment undergoes strict factory testing, so customers can purchase with confidence.
