Power / Imbalanced Phase Voltage

The Problem – Imbalanced Phase Voltage

Electrical equipment, especially motors and their controllers, will not operate reliably on unbalanced voltages in a 3-phase system. Generally, the difference between the highest andthe lowest voltages should not exceed 4% of the lowest voltage. Greater imbalances may cause overheating of components, especially motors and intermittent shutdown of motor controllers. Motors operated on unbalanced voltages will overheat, and many overload relays can’t sense the overheating. In addition, many solid-state motor controllers and inverters include components that are especially sensitive to voltage imbalances.

The potential impact of this scenario for many commercial and industrial companies is often related to financial losses. For instance, a production or manufacturing business might lose the operation of a critical piece of equipment for a short period. Often in these cases the equipment forms part of a production line and repairs can take time with labour and parts difficult to source quickly.

The answer…

Carrying out simple load tests as part of a power quality survey will establish the extent of any imbalances within a 3-phase supply network. If any significant imbalances are detected, these can be rectified by carrying out load sharing exercises whereby circuits are terminated equally across all 3 phases of the supply distribution boards ensuring the demand placed on each is more equally distributed.

Carrying out this work ensures that 3 phase equipment works more efficiently and accurately reducing the level of energy used and reducing heat generation in critical equipment such as motor drives and bearings. Evenly distributed loads within a 3 phase system can also reduce the presence of total harmonic distortion (THD) subsequently reducing the threat of dangerous neutral currents which can lead to damaged cables, equipment and unplanned outages.