Three-phase imbalance occurs when the amplitude of three-phase current (or voltage) in an electrical power system is uneven and exceeds the specified range. Three-phase equipment that is not properly matched or configured can cause three-phase imbalance. For example, if a single-phase-to-three-phase transformer were to leak energy into the other two phases, this would also be referred to as three-phase imbalance.
Three-phase power is made up of all six possible combinations of voltage and current, which means there should be balance between them at all times. Imbalance can occur because of many different reasons; for example, if one phase has more load than the others, then there will be more current in that phase. This could be due to a problem with the load or it could be due to a problem with the wiring or circuit breakers feeding power into the network.
When three-phase power is transmitted over long distances, it must be done so safely. If there is an open wire or ground path from any one conductor to another, then electricity will travel down this path and could cause damage to other parts of the network or even destroy other property. Transformers used to transform three-phase power into single-phase power for distribution to consumers must be designed to prevent leakage currents into the other two phases.
The phase voltages in a balanced three-phase system should be equal or very near to equal. Unbalance, often known as imbalance, is a measurement of the inequity of phase voltages. A voltage imbalance is the difference in voltage between the phases of a three-phase system. Voltage imbalance can occur because some phases are connected to hot wires while others are not. This is called a single-phased circuit. Or, voltage imbalance may occur because one pair of phases is longer than the other. This would make one pair of phases have more resistance than the others, causing it to carry less current.
In an ideal situation, there would be no voltage imbalance in a balanced system. However, in practice this is difficult if not impossible to achieve. The main cause of voltage imbalance is usually due to unequal lengths of wire connecting each phase pair together. If these wires are not equal in length, then they will have different resistances and thus drive the phase currents into balance or unbalance depending on which pairs of wires are shorter/longer. Also, any nonlinear elements such as transformers will affect the balance of the system. For example, if one side of a transformer has higher primary voltage than the other, then it will also drive the secondary voltages out of balance.
There are two types of voltage imbalances: positive and negative. These terms refer to which phase carries more current.
An unbalanced load is defined as a variation from perfect sinusoidal voltage and current waveforms. Any load flaws produce a current imbalance at the distribution level, which can go to a transformer and cause a three-phase voltage imbalance. This could cause equipment failures or damage to unprotected circuits.
The term "load imbalance" refers to two different but related issues: 1 a lack of balance between currents drawn by a group of parallel-connected loads; and 2 a lack of balance between the amounts of power consumed by a group of parallel-connected loads.
In both cases, the problem arises because some loads are not being treated equally by a circuit. If some loads are delivering more current than others, then they're said to have an excessive current burden. If some loads are using more electricity than others, then they have an excessive power burden.
Loads that draw more current than their connected peers will have their voltage dropped across their internal resistance instead of dropping it directly into the next load in line. This causes all of the currents to be unequal, so it's called an "current imbalance".
Loads that use more electricity than their connected peers will heat up more than their peers, which could lead to failure by burning out thermal sensors or causing electrical arcs with subsequent destruction of the load.