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What causes poor power quality?

What causes poor power quality?
As grids have been evolving towards more complex structures and consumer’s demand for reliable, secure electricity increases, the quality of power is more critical ever than before to meet these expectations. In addition, electrical equipment works in defined certain limits of voltage and frequency while operating in these tolerance limits. 

First, what good power quality means?
Hence, we can define good power quality as a power supply that is always available for everyone in safe limits. However,  poor power quality can be defined as basically the one unreliable and not always available in tolerance limits, and so causes lots of problems.  

It is better to know what causes the poor quality to solve many related issues, like economic losses, not meeting industrial standards etc. 

Why we have poor power quality? 
As power quality is quite a complex subject itself, we can’t assume only one reason for having poor quality. There could be many reasons for the poor power quality. Still, we can summarise them under main topics which are listed below, and each of these has different solutions to be addressed best practice.
Besides this, there is always a solution for each power quality problems, and some improvement strategies have been listed below.

DIPS or SAGS
Symptoms• Lighting dimming, computer lockups, relay and contactor chatter or complete dropout, equipment and system shutdowns
• Spurious and unexplained alarms and shutdowns
Potential causes• Starting large loads, especially large inductive
• Similar operations in neighboring facilities
• Short-circuit faults
• Severe weather conditions
How to Solve• Uninterruptable Power Supply (UPS)
• Dynamic Voltage Restorer (DVR)
Click to see ENDOKS DVR Solution
SWELLS
Symptoms• Overvoltage shutdowns and alarms on variable frequency drives (VFDs) and other electronic devices
• Failure and damage on equipment and loads
Potential causes• Fault on single phase of three-phase system
• Sudden load decrease
• Capacitor bank switching
How to Solve• Uninterruptable Power Supply (UPS)
• Dynamic Voltage Restorer (DVR)
Click to see ENDOKS DVR Solution
UNDERVOLTAGE / OVERVOLTAGE
Symptoms• Overheating of equipment
• Insulation failures
• Performance and life time degradation on equipment
Potential causes• Uncontrolled reactive power flow in transmission and distribution systems
• Variations in the generation of PV and wind power systems
How to Solve• Static VAR Compensator (SVC)
Click to see ENDOKS SVC Solution
• Static Synchronous Compensator (STATCOM)
Click to see ENDOKS STATCOM Solution
• Magnetically Coupled Reactor (MCR)
Click to see ENDOKS MCR Solution
• Voltage Regulator
VOLTAGE FLUCTUATIONS / FLICKER
Symptoms• Light flicker
• Nuisance tripping due to misoperation of electronic devices
Potential causes• Intermitted loads like electric arc furnaces and welding machines
• Variations in the generation of PV and wind power systems
How to Solve• Static VAR Compensator (SVC)
Click to see ENDOKS SVC Solution
• Static Synchronous Compensator (STATCOM)
Click to see ENDOKS STATCOM Solution
• Magnetically Coupled Reactor (MCR)
Click to see ENDOKS MCR Solution
• Voltage Regulator
TRANSIENTS
Symptoms• Flashover and arcing effects in distribution equipment
• Damaged insulation
• Failed electronics
• Computer lockups
Potential causes• Lightning strikes
• Switching of capacitors
• Reenergizing systems after a power failure
• Sudden stoppage of large equipment
• Dirty or worn contactors
How to Solve• Surge Arresters
• Isolation Transformers
INTERRUPTIONS
Symptoms• Equipment shutdowns
Potential causes• Momentary loss of utility power
How to Solve• Uninterruptable Power Supply (UPS)
UNBALANCE
Symptoms• Overheated three-phase motors and transformers
• Overvoltage and overloading problems in neutral conductors
Potential causes• Unbalanced loads across individual phases of three-phase panelboards
• Unbalanced utility supply
• Operation of large single-phase loads
• Open-delta transformers
How to Solve• Static Synchronous Compensator (STATCOM)
Click to see ENDOKS STATCOM Solution
HARMONICS
Symptoms• Overheated line and neutral conductors
• Overheated motors and transformers
• Spurious and unexplained alarms and shutdowns of electronic equipment
Potential causes• Nonlinear loads such as switching power supplies
• Converter sections of uninterruptible power supply (UPS), VFDs and battery chargers
• Welders
• Arc furnaces
How to Solve• Passive and Active Harmonic filters
Click to see ENDOKS Pasif and Active Harmonic Solutions

We are here to help you empower your grid or your operations in your business. We have different power quality solutions for your business need.

For more information, please, Contact Us

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What is the Dynamic Voltage Regulator and How it Works?

Electric Power Quality and Dynamic Voltage Regulator

Electric power quality is a term which importance is increasing day by day. The increasing demand for electrical energy, the change in load characteristics, and the penetration of renewable energy sources such as solar and wind power generation facilities into the electricity grid have revealed the importance of the concept of electrical power quality. Electrical power quality can be defined as a set of electrical parameters and limits that enable end-user loads or equipment connected to the electrical grid to operate as desired without a significant loss of performance and operating-life. Electrical power quality problems can be defined as power problems caused by voltage, current, and frequency changes that cause failure or malfunction of end-user loads or equipment connected to the electrical grid.

The most common power quality problems encountered in electrical grids are voltage sag, voltage swell, overvoltage, under-voltage, and voltage unbalance. These power quality events cause the trip of loads, the failure of the equipment, and the interruption of the industrial process resulting in serious economic losses. Dynamic voltage regulator (DVR) provides the most effective solution for these voltage quality problems. DVR is a power electronics-based power quality compensation system that is connected in series with the grid. DVR provides effective protection by preventing the voltage quality events occurring in the grid from being seen on the load side with its high-performance voltage compensation ability.

Basic Working Principle

The main purpose of DVR is to provide voltage quality on the load side by detecting and compensating power quality events occurring in the grid voltage in less than a half-cycle period. The block diagram showing the basic working principle of DVR is given in Figure 1. DVR basically consists of a control system and a power circuit. The control system of DVR continuously monitors the grid voltage, detects the power quality events occurring in the voltage less than a half cycle period with the help of the control and detection methods, and generates the control signals required for the compensation. The power circuit of the DVR generates the compensation voltage and inject it into the grid in series to prevent voltage quality problems on the load side. Therefore, it ensures that the loads are protected from voltage quality problems occurring in the grid.

Figure 1 – DVR Working Principle

Power Stage Topology

The single line representation of the power stage of the DVR is given in Figure 2. The DVR power stage consists of active rectifier power and serial inverter power stages connected back to back over the DC capacitor bank.


Figure 2 – DVR power stage single line circuit diagram

An active rectifier is an IGBT based rectifier type controlled by PWM signals. It has much lower current harmonic distortion (THD:<3%) than conventional diode/thyristor rectifiers. The main function of the active rectifier is to provide the constant DC voltage required for the compensation according to the switching signals from the control system. The power stage of the active rectifier consists of the inverter, the DC link capacitor bank, and the output filter. According to the switching signals sent by the inverter control system, it controls the flow of the necessary active power from the grid to provide the required fixed DC link voltage. The output filter is used to filter the switching harmonics generated by the active rectifier inverter.

The series inverter power stage consists of the inverter, output filter, protection thyristor group, and injection transformer. The inverter generates the voltage required for compensation according to the switching signals generated by the control system. The output filter is used to filter the switching harmonics generated by the series inverter, as in the active rectifier filter. The protection thyristor group consists of thyristors connected anti-parallel to each other for each phase. The protection thyristor group is activated in case of an error in the grid or DVR, ensuring the disconnection of the series inverter power stage and protection of the system. The injection transformer, on the other hand, ensures that the compensation voltage produced by the inverter is injected in series to the grid and isolation between the grid and the DVR.

The DC-link capacitor bank is used to store the energy required for the DVR to meet the expected compensation requirements within the period until the active rectifier controller reacts at the moment of compensation.

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Why is PQ so important?  

In recent years, the increasing demand for electrical energy, the change in load characteristics, and the penetration of renewable energy sources such as solar and wind power generation facilities into the electricity grid have revealed the importance of the concept of power quality. 

The demand for electrical energy increases day by day, even though the rapid increase in demand for electrical energy, electricity generation, transmission, and distribution infrastructure cannot be upgraded or renewed at the same pace. This has led to an increase in the incidence of power quality problems in electrical networks. 

With the increasing use of renewable energy systems, the electricity generation infrastructure has become a distributed structure. When the variable generation characteristics of renewable energy generation systems such as solar and wind combined with the complexity of the distributed generation structure, the load flow in electricity networks become more unpredictable, this situation causes various power quality problems to occur in transmission and distribution networks. 

What are the main power quality problems encountered in electrical networks? 

Voltage trough and peak and harmonics are among the most common power quality problems encountered in electrical networks. In addition to these, low voltage, overvoltage, voltage fluctuation, which are (flicker) caused by variable reactive power flow and voltage and current unbalance events which are caused by unbalanced loading of the lines, are also frequently seen power quality problems. 


What happens when Power quality is poor?
 

Electrical power quality problems lead to overheating and loss of life of cables and transformers, failure of capacitor banks, failure of protection equipment, failure of isolation equipment due to excessive stress, failure, or malfunction of devices connected to the network, and noise in communication lines. These impacts lead to severe economic losses for grid operators and all industrial, commercial, and residential customers. 

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What is the electrical power quality?

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It is possible to find different definitions in various sources related to electrical power quality. According to some sources, electric power quality is defined as the reliability of the electrical network systems and only voltage quality. However, these definitions are insufficient to explain the concept of electric power quality.

To make a comprehensive definition, we can say that electrical power quality can be defined as a series of electrical parameters and limits that enable end-user loads or equipment connected to the electrical network to operate in the desired manner without any significant performance and lifetime loss.

On the other hand, electrical power quality problems can be defined as power problems caused by voltage, current, and frequency changes that cause malfunction or malfunction of end-user loads or equipment connected to the mains.