CHAPTER 5: HARMONIC MITIGATION TECHNIQUES AND SYSTEM STABILITY
5.9. Harmonic standards
The importance of standards to limit high emissions is reflected in the creation of working international association and standardization committees, such as the IEEE, IEC 61000-3- 2, and the C4.24 (CIGRE /CIRED). The interest in the distortion in the considered frequency range is due to an increasing number of sources of emission, including energy‐efficient lighting and generation (such as DERs) and some other electrical equipment within the LV sector of the electricity distribution network (Zavoda et al., 2016).
111 5.9.1. IEEE 519-1992
The recommendation described in this document attempts to reduce the harmonic effects at any point in the entire system by establishing limits on certain harmonic indices (currents and voltages) at the point of common coupling (PCC), a point of metering, or any point as long as both the utility and the consumer can either access the point for direct measurement of the harmonic indices meaningful to both, or can estimate the harmonic indices at the point of interface (POI) through mutually agreeable methods.
5.9.2. IEEE 519- 2014
The limits in this recommended practice are the intended for application at a point of common coupling (PCC) between the system owner or operator and a user, where the PCC is usually taken as the point in the power system closest to the user where the system owner or operator could offer service to another user.
IEEE 519-1992, known as the “Recommended Practices and Requirements for Harmonic Control in Electric Power Systems”, established limits for harmonic currents and voltages at the point of common coupling (PCC), or point of metering in 1981 as a guide for harmonic control and reactive compensation of static power converters (Franquelo et al., 2007).
The limits of IEEE 519 are intended to:
Assure that the electric utility can deliver relatively clean power to all of its customers.
Assure that the electric utility can protect its electrical equipment from overheating, loss of life from excessive harmonic currents, and excessive voltage stress due to excessive harmonic voltage.
To protect the voltage integrity of the utility grid system
Each table from IEEE 519 lists the limits for harmonic distortion at the point of common coupling (PCC) or metering point with the utility. The voltage distortion limits are 3% for individual harmonics and 5% THD.
Maximum harmonic current distortions limits that can be contained at the PCC as per IEEE- 519 requirement (Standard, 2014)
112 Table 5.1: Maximum harmonic current distortions limits that can be contained at the PCC as per IEEE-519 requirement (Standard, 2014)
ISC/IL
<11 11≤h<17 17≤h<23 23≤h<35 35≤h≤50 %TDD
<20 4.0 2.0 1.5 0.6 0.3 5.0
20<50 7.0 3.5 2.5 1.0 0.5 8.0
50<100 10.0 4.5 4.0 1.5 0.7 12.0
100<1000 12.0 5.5 5.0 2.0 1.0 15.0
>1000 15.0 7.0 6.0 2.5 1.4 20.0
Table 5.2 from IEEE 519-2014 defines the voltage distortion limits that can be reflected back onto the utility distribution system.
Table 5.2: Voltage Distortion limits (Standard, 2014)
PCC Voltage Individual Harmonic Magnitude (%) HD%
Total harmonic distortion
THD%
≤69 3.0 5.0
69-161 1.5 2.5
>161 1.0 1.5
The harmonics in the electric power distribution system combine with the fundamental current (60 Hz) to create distortion. All of the harmonic frequency currents combine with the fundamental current to form the total harmonic distortion. The THD value is expressed as a percentage of the fundamental current and any THD values over 10% are significant enough for concern. Usually if the industrial user controls the overall combined current distortion according to Table 5.1, this will help meet the limitations set forth in the guidelines.
Therefore, IEEE standard 519-1992 is a guidance document for utilities and electric power users which specifies both the maximum distortion levels and recommends correction levels.
113 The harmonic distortion limit of 5% is proven to be the point where harmonics begin to have a detrimental effect on the electrical distribution system.
5.9.3. IEC 61000-3-2 (1995-03), IEC 61000-3-6, IEC 61000-4-7, & IEC 61000-4-30
The study of renewable generation technologies harmonic emission is an important issue when connecting these power plants to the national grid. Requirements set by power system operators have to be fulfilled and the harmonic emission is part of these requirements. For example, IEC 61400-21, IEC 61000-3-6, IEC 61000-4-7, and IEC 61000-4-30, are the standards that guide the limits, measurement procedures and assessment of power quality related to renewable technologies, in particular wind plants (Schwanz, 2016).
The IEC 61000-3-2 harmonic emissions standards which were first published as IEC 55-2 1982 and applied only to household appliances specified limits for harmonic current emissions applicable to electrical and electronic equipment having an input current up to and including 16A per phase, and intended to be connected to public low-voltage distribution systems (Schwanz, 2016).
The objective of IEC 61000-3-2 (harmonics) is to test the equipment under the conditions that will produce the maximum harmonic amplitudes under normal operating conditions for each harmonic component. For the purpose of this research the IEE 519-1992 harmonic limitation standards are used for the harmonic study analysis presented later in this Chapter (Schwanz, 2016).
5.9.4. CIGRE and CIRED (C4.24) Standard
The- International Council on Large Electric Systems-(in French: Conseil International des Grands Réseaux Électriques and abbreviated as (CIGRÉ) is a global organization in the field of high voltage electricity (Zavoda et al., 2016). It was founded in Paris, France in 1921. The scope of its activities includes the technical and economic aspects of the electrical grid, as well as the environmental and regulatory aspects (Zavoda et al., 2016).
CIGRE and CIRED is a joint working group of C4.24 for “Power Quality and EMC Issues associated with future electricity networks” (Bollen et al., 2015). The mandate Working group
114 C4.24 obtained its mandate in 2012 and it should, according to its scope, address the following issues:
• The study of new emissions from equipment connected to the low-voltage network which includes integration of renewable generation system to the LV grid network. The emissions (harmonic and unbalance) by new types of devices connected to the distribution network as production (DG) or consumption (load), especially devices with active power-electronics interface including equipment connected to low voltage and installations connected to higher voltage levels (Bollen et al., 2015).
• This might require the evaluation of new measurement techniques, including a closer look at the frequency response of existing instrument transformers and sensors. The main question is whether this will require new ways of considering power quality in the design (Bollen et al., 2015)?
• The positive and negative impact of new smart distribution technologies applications such as Volt &VAR control, as well as feeder reconfiguration on the power quality (voltage unbalance and harmonic flow) in the distribution system (Bollen et al., 2015). The question here is in terms of how these power quality issues at the distribution level may impact the transmission system.