Voltage Imbalance Study

Electrical equipment like motors will not function consistently on unbalanced voltages in systems. Usually, the variance between the maximum and the minimum voltages must not surpass four percent of the lowest voltage. Larger unbalances may lead to overheating of components, particularly motors.

• A three phase equipment such induction motor with unbalance in its windings.
• Any large single phase load, or a number of small loads connected to only one phase cause more current to flow from that particular phase causing voltage drop on line.
• Switching of three phase heavy loads results in current and voltage surges which cause unbalance in the system.
• Unequal impedances in the power transmission or distribution system cause differentiating current in three phases.

Why is Voltage Imbalance Study Important?

The effects of extensive voltage imbalances on power systems and equipment are broad and serious. A severe imbalance might dramatically decrease the equipment life cycles, considerably speed up the replacement cycle of equipment, and significantly increase system operation and maintenance costs. Furthermore, for a 3 phase 4 wire system, voltage imbalance leads to bigger neutral wire current and cause relay malfunction.

Voltage imbalances will create extra power loss, reduce system efficiency, decrease motor life cycles, etc. Also few abnormal functioning and maintenance circumstance also causes voltage imbalance and result in negative effects on equipment and systems. These conditions include such problems as bad electrical contacts, unsuitable shunt capacitor bank installation, single-phase operation of a motor, etc. These kinds of operation and maintenance conditions may not occur frequently. However, if they do occur they will bring about very serious problems for systems or equipment

The major effects of voltage imbalance are described as follows:

• Extra power loss
• Safety deficiency
• Motor failure
• Life cycle decrease
• Relay malfunction
• Inaccurate Measurement
• Transformer failure

What is Done During Voltage Unbalance Study?

Because voltage unbalance can be very harmful to electrical equipment, the source of the problem should be thoroughly investigated and corrected. By tallying the voltage it can assist put aside money and energy by improving gear efficiency and possibly avoiding costly facility interruption because of its failure. Proper testing and communication with the utility can help locate and resolve the problem.

Main objective of this study is:

• To determine the causes and effects of voltage unbalance on the distribution system and in user facilities.
• To determine the accepted definitions for calculating voltage unbalance and to clarify the related standards.
• To identify mitigation techniques for the distribution system and for industries.

Voltage imbalance percentage can be calculated using this formula:

% Unbalance= [Maximum deviation from average / Average of 3 phase to phase voltages]\100

To calculate the percentage deviation in three phases:

[Max (Im-Ir)(Im-Iy)(Im-Ib)\100] / Im

Where, Im is mean of currents in three phases

Im= (Ir+Iy+Ib)/3

Ir, Iy, Ib are phase currents.

Besides, an unbalance can also be measured by matching the strength of positive sequence currents in comparison to the negative sequence currents. The permissible limit in terms of percentage of negative phase sequence current over positive sequence current is 1.3% ideally but acceptable upto 2%.

How is Voltage Imbalance Study Done?

This study performed a comprehensive analysis of the issue of voltage unbalance on the power system. It will help utilities and industries understand the causes, effects, and definitions of voltage unbalance, identify mitigation techniques, and interpret related standards.

Several practical cases are taken into account to deal with voltage imbalances. The simulation results with problem defined and improvement measures will be later carried out based on the results from these cases. Few examples of these cases are:

• Bad connection of neutral wire
• Neutral wire broken
• Operation of three-phase motor under voltage imbalance
• Unsuitable capacitor bank installation
• Effects of Voltage Unbalance on Machines
• Effects of Voltage Unbalance on Power Electronic Converters and Drives

Such cases will be used to confirm the impacts of voltage imbalance on systems and equipment. Voltage imbalance not only causes extra energy loss, but also causes safety problems for a system. To prevent voltage imbalance, the balance problem should be taken into account through all the planning, design, installation and operation stages. This study will provide details, with theoretical analysis and explanation, to make it easy to grasp the impacts of voltage imbalance on systems and equipment. The results are of value to engineers for better design, operation and maintenance of power distribution systems

Mitigation Techniques for Facilities:.