The Impact of Power Imbalance on Oil-Immersed Transformers
For some large electrical equipment, many people only focus on the quality. In daily life, accidents caused by power imbalance in electrical equipment are rarely heard. 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 may cause serious consequences to the oil-immersed transformer. Unbalance can cause excessive phase current (increasing by 3 times), leading to overheating of the windings and the transformer oil. Overheating of windings accelerates insulation aging; overheating of transformer oil causes oil quality deterioration, rapidly reducing the insulation performance of the transformer, shortening its lifespan (for every 8°C increase in temperature, the service life will be halved), and even burning out the windings. At the same time, under unbalanced three-phase conditions, the transformer generates zero-sequence magnetic flux, which flows through the circuit formed by the metal parts of the transformer, causing heating and affecting the safe operation of the transformer.
2. Impact on the 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 losses of the power grid lines. On the other hand, in a three-phase four-wire connection, when the three phases are balanced, the line loss is minimal; when one phase has a heavy load and two phases have lighter loads, the line loss increase is relatively small; when one phase has a heavy load, one phase has a light load, and the third phase has an average load, the line loss increase is relatively large; when one phase has a light load and two phases have heavy loads, the line loss increase will be the largest. When the three-phase loads are unbalanced, regardless of the load distribution, the greater the current unbalance, the greater the line loss increase.
3. Impact on electrical equipment.
Unbalance between phases can shorten the service life of electrical equipment, accelerate the frequency of component replacement, and thus increase equipment maintenance costs. For distribution and transformation 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 and transformation 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 on the neutral line, leading to neutral point drift, causing changes in 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 unbalance 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 unbalance also increases the reverse torque in the motor, causing the motor temperature to rise, efficiency to decrease, energy consumption to increase, vibration, output loss, and other effects. For circuit breakers, three-phase unbalance reduces the allowable current margin of the circuit breaker, making it prone to overload and short circuit when loads change or alternate.
Therefore, manufacturers must strictly control quality when producing oil-immersed transformers to ensure balanced three-phase voltage, minimizing damage to equipment and lines. Yixing Xingyi Special Transformer Co., Ltd., as a professional electrical equipment manufacturer and power engineering installation service provider, every piece of equipment undergoes strict factory inspection, and customers can rest assured when purchasing.
