What is Voltage Imbalance Study?
Electric voltage imbalance study is an activity to conduct a comprehensive analysis of the voltage unbalance problem in an electrical power system. Voltage unbalance analysis studies help utility and industrial managers to understand the definition of a voltage imbalance, causes, effect or impact, and identify suitable mitigation techniques. This study is also an aspect of the Load Flow Study & Analysis and Electrical Power Quality Study — Omazaki Engineering is a consultant who serves voltage unbalance studies and analysis consulting services. If you are looking for voltage imbalance analysis and study consultants for your electrical system projects or existing facilities in Indonesia and Southeast Asia, please contact us by sending an email to cs@omazaki.co.id or filling in the form at contact.
Voltage imbalance can be very dangerous for electrical equipment. The source of the problem must be thoroughly investigated and corrected. With voltage imbalances calculated or measured, this can help save money and energy by increasing efficiency and possibly avoiding costly facility outages due to failure.
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Basic Knowledge
Definition of Voltage Unbalance
Voltage unbalance or imbalance is defined by IEEE as the ratio of the negative or zero sequence component to the positive sequence component. In simple terms, it is a voltage variation in a power system in which the voltage magnitudes or the phase angle differences between them are not equal. It follows that this power quality problem affects only polyphase systems (e.g. three-phase).
In three phase systems, voltage unbalance or voltage imbalance occurs when the phase or line voltages differ from the nominal balanced condition. Normal balanced condition is when the three phase voltages are identical in magnitude and phase angles are displaced 120 degree vectorially. The unbalance could be caused due to the difference in magnitude of the voltage or the phase angle or both. From a reliability and power quality aspect having a good voltage balance in the system is paramount.
Causes of Voltage Unbalance
Following are some of the factors that could contribute to voltage unbalance:
- Electricity source voltage (either public grid or own generation) which is not balanced
- The unequal impedance of a three-phase distribution system
- Unbalanced loading of power factor correction capacitors [such as a blown fuse in one phase]
- Uneven distribution of single-phase loads
- The load is unbalanced even though it is connected in three phases
- Incorrect transformer tapping
Effect of Voltage Imbalance
Like voltage drop, voltage imbalance is undeniable. The problem is when the difference of magnitude and the angle of the voltage exceeds the tolerance limits or allowable percentage set by the applicable standards.
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.
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
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Why is Voltage Imbalance Study Important?
The impact of excessive voltage unbalance on power systems and equipment is extensive and serious. Severe imbalances can dramatically decrease equipment life-time, greatly speed up equipment replacement cycles, and significantly increase system operating and maintenance costs. For 3 phase 4 wiring systems, voltage imbalance results in larger neutral wire currents and causes relay failure.
Voltage unbalances will cause extra power loss, reduce system efficiency, reduce motor life cycle, etc. Also some abnormal functioning and maintenance conditions also cause voltage imbalance and result in negative impacts on equipment and systems. These conditions include problems such as poor electrical contact, improper installation of capacitor banks, operation of single-phase motors, etc. These operating and maintenance conditions may not occur frequently. However, if it happens, it will cause very serious problems for the system or equipment.
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Objective of Voltage Imbalance Studies
- To determine the magnitude of the existing voltage imbalance and compare it with related standards.
- To determine the causes and consequences of unbalanced stresses in distribution systems and user facilities.
- To identify mitigation techniques for distribution systems and for industry.
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Mitigation of Voltage Unbalance
Making a zero voltage imbalance in a distribution system clearly impossible. Due to, (a) randomness of connection and termination of single-phase loads (b) uneven distribution of single-phase loads over three phases and (c) inherent asymmetry of the power system. However, there are utility system level mitigation techniques as well as industry level (load) mitigation techniques that can be used to correct excessive voltage imbalances.
Utility Level Techniques
- Redistribution of single-phase loads equally to all phases.
- Reduction of the system unbalance that arise due to system impedance such as those due to transformers and lines.
- Single-phase regulators have been suggested as devices that can be used to correct the unbalance but care must be exercised to ensure that they are controlled carefully not to introduce further unbalance.
- Passive network systems and active power electronic systems such as static var compensator and line conditioners also have been suggested for unbalance correction. Compared to passive systems, active systems are able to dynamically correct the unbalance.
Plant Level Techniques
- Load balancing.
- Use of passive networks and static var compensator.
- Equipment that is sensitive to voltage unbalance should not be connected to systems which supply single-phase loads.
- Effect of voltage unbalance on ac variable speed drives can be reduced by properly sizing ac side and dc link reactors.
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Contact Omazaki Engineering if you are looking for voltage imbalance or unbalance study analysis or evaluation consultant who serves related consulting services using ETAP software for your new project or for other purposes related to your existing electrical system.
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Related Articles
- Power System Study & Analysis
- Load Flow Study & Analysis
- Protection Coordination Study
- Motor Starting Study and Analysis
- Power System Transient Stability Study
- Harmonic Study and Analysis
- Arc Flash Study & Assessment
- Power Quality Study & Assessment
- Voltage Drop Study & Analysis
References
- IEEE Std 1459 IEEE Standard Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Nonsinusoidal, Balanced, or Unbalanced Conditions
- IEEE Std 1159 IEEE Recommended Practice for Monitoring Electric Power Quality
- IEC/TR 61000-3-14 : 2010 Assessment of emission limits for harmonics, interharmonics, voltage fluctuations and unbalance for the connection of disturbing installations to LV power systems
- Power Quality Issues – Part 4 – Voltage Imbalance, EM Magazine, 8 June 2019
- Voltage Unbalance – Power Quality Centre, School of Electrical, Computer and Telecommunications Engineering at the University of Wollongong, Australia
- Voltage Unbalance – http://voltage-disturbance.com/voltage-quality/voltage-unbalance/
- Effect of Unbalanced Voltage on End Use Equipment Performance, EPRI, June 2000
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