Power Quality and Harmonics

Power Quality Overview

Power quality determines the suitability of electric power for consumer devices. There are three main contributors to low voltage and poor power quality problems:

● Harmonic Pollution causes extra stress on a power supply system and reduces reliability.

● Reactive Power loads the power supply system unnecessarily.

● Load Imbalance increases neutral current and neutral to earth voltage.

Harmonics

Normally, power system generators produce a clean sinusoidal voltage waveform at their terminals. However, a lot of modern electronic equipment such as VFDs, UPSs, LEDs, battery chargers, and other equipment powered

by switched-mode power supply (SMPS) equipment, generates non-sinusoidal current injected into the power system, which causes electrical harmonic pollution.

Reactive Power

In most cases, reactive power is the power that magnetic equipment such as transformers, motors, and relays, needs to produce magnetizing flux, which is inductive. In some cases, long-distance power cables and some loads generate capacitive reactive power. Both inductive and capacitive reactive power will increase the apparent power (kVA), demanding larger transformers and cable size.

Load Imbalance

Every three-phase current can be divided into positive, negative and zero sequences. Negative and zero sequences cause load imbalance.

CoEpo Power Quality Solution

CoEpo power quality solution consists of the Active Power Filter (APF) and Static VAR Generator (SVG). Both

provide an active compensation solution based on power electronics technology.

Compared with conventional passive compensation solutions such as capacitor banks, an active compensation solution improves the reliability and quality of the power distribution system.

CoEpo APF Principle

CoEpo APF is connected in parallel with non-linear loads, and uses one set of current transformers (CT) to detect the load current. It calculates each order harmonic current by FFT algorithms in its DSP microchips, and then generates a compensating current with the same amplitude but opposite phase angles to the detected harmonic current, which cancels out the original load harmonics.

CoEpo APF not only eliminates harmonic current from the load side, but it also mitigates harmonic voltage caused by harmonic currents. The APF system can also improve power factor (PF) and correct load imbalances in the power system.

Note: CT is a critical part of the APF system, and it can be purchased by users themselves, following CoEpo’suggestions on CT specification.

CoEpo APF Compensation Performance

CoEpo APF can perfectly mitigate harmonic current, and suppress harmonic voltage caused by the harmonic

current. When the APF capacity is sufficient and background harmonic voltage is low, the APF ensures excellent

compensation performance at full load condition, as below.

● THDu (Total Harmonic Distortion of Voltage) < 3%

● THDi (Total Harmonic Distortion of Current) < 5%

● PF (Power Factor) ≥ 0.99 (improves both leading and lagging PF)

● Neutral Current Attenuation Ratio ( )>95%

CoEpo APF Features

● Multifunctional: Harmonic, reactive power and imbalance compensation

● High harmonic filtering rate: Up to 98%

● Excellent reactive compensation: High speed, Precise (-0.99≤PF≤0.99), Step-less, Bi-directional (capacitive and inductance) compensation

● Excellent imbalance correction: Both negative and zero sequence, mitigates neutral current

● Wide input voltage & frequency range, adapts to tough electrical environments

● Low thermal loss (≤3% of rated APF kVA), efficiency ≥ 97%

● High stability: Infinite impedance to grid, avoids harmonic resonance problems

● Flexible application: Modular design, embedded in standard or customized cabinet

● Easy installation and maintenance: Plug-in installation for APF module replacement and expansion

● Wide capacity range: 30A~600A for a single cabinet,

● Environmental adaptability: -10~50°C temperature, compatible with diesel generator

● Complete protection: Grid Over/Under voltage, APF over current, over temperature, and more. All faults are recorded in the event log, which is convenient for failure analysis

CoEpo SVG Principle

The principle of the SVG is very similar to that of Active Power Filter, as demonstrated in the picture below. When the load is generating inductive or capacitive current, it makes load current lagging or leading the voltage. SVG detects the phase angle difference and generates leading or lagging current into the grid, making the phase angle of current almost the same as that of voltage on the transformer side, which means fundamental power factor is unit.

CoEpo SVG is also capable of correcting load imbalance.

Note: CT is a critical part of the SVG system, and it can be purchased by users themselves, following CoEpo’s suggestions on CT specification.

CoEpo SVG Compensation Performance

CoEpo SVG can rapidly and continuously compensate both inductive and capacitive reactive power, and correct load imbalance. With sufficient capacity, the SVG ensures excellent fundamental power factor improvement performance.

● Fundamental Power Factor (Cosφ) ≥ 0.99 (improves both leading and lagging PF)

CoEpo SVG Features

● Multifunctional: Reactive power and imbalance compensation

● Excellent reactive compensation: High speed, Precise (-0.99≤Cosφ≤0.99), Step-less, Bi-directional (capacitive and

inductance) compensation

● Excellent imbalance correction: Both negative and zero sequence, mitigates neutral current

● Wide input voltage & frequency range, adapts to tough electrical environment

● Low thermal loss (≤3% of rated SVG capacity), efficiency ≥ 97%

● High stability: Infinite impedance to grid, avoids harmonic resonance problem

● Flexible application: Modular design, embedded in standard or customized cabinet

● Easy installation and maintenance: Easy installation for APF module replacement and expansion

● Wide capacity range: 30kvar~500kvar for a single cabinet

● Environmental adaptability: -10~50°C temperature, compatible with diesel generators

● Complete protection: Grid over/under voltage, SVG over current, over temperature, and others. All faults recorded in event log, convenient for failure analysis

Comparison between Capacitor Bank, SVG and APF

AHF can solve 2nd-51th harmonic,but above 30th is very difficult to solve for any brand. And above

30th is very rare.

SVG can solve 2nd-13th harmonic.

it can also resolve even order harmonic

Item	Capacitor Bank	SVG	APF
Harmonic Filtering	Unavailable	Eliminate 2nd~13th harmonics(selectable)	Eliminate 2nd~50th harmonics(selectable)
Reactive Power Compensation	Only compensate inductive reactive power	Steplessly compensate both inductive and capacitive reactive power	Steplessly compensate both inductive and capacitive reactive power
Imbalance Correction	Unavailable	Available	Available
Response Speed	slow, can’t track dynamic reactive power (20ms~5s)	fast, can track dynamic reactive power (<0.1ms)	fast, can track dynamic harmonic & reactive loads (<0.1ms)
Harmonic Resonance Problem	Potential resonance between capacitor and transformer sabotages power system stability	Active compensation technology avoids harmonic resonance from the principle.	Active compensation technology avoids harmonic resonance from the principle.
Output Ability	Actual output capacity is less than the rated capacity	Actual output capacity is the same as rated capacity	Actual output capacity is the same as rated capacity.