Tech Tip 10
Complying With Harmonic Standard IEEE 519
This Tech Tip briefly describes harmonic limits recommended by the recently revised standard IEEE 519. If you have questions regarding harmonic problems or for assistance in applying IEEE 519, please contact Power Quality.
IEEE 519 was upgraded from a Guideline to Recommended Practice in 1992 and is now available from IEEE. IEEE 519 was developed to establish goals for the design of power systems which include linear and non-linear, or harmonic, loads. It defines acceptable voltage quality and limits distortion current users may demand. The recommended limits are applied at the interface between sources and loads (the Point of Common Coupling or PCC).
CURRENT DISTORTION LIMITS
IEEE 519 current distortion limits are based upon the ratio of the size of the supply system to the customer load. This ratio, the Short Circuit Ratio, is calculated at the PCC between the consumer and utility. Loads that are small when compared to supply capacity may require higher distortion.
Table I contains limits for total harmonic distortion (THD) and individual harmonics. The letter h represents the individual harmonic number. For example, h equals 5 for current at 300 Hertz (5 x 60 Hertz). Note as plant load increases on a given supply system, the ratio will decrease and the limits may tighten.
Table I: IEEE 519 Current Distortion Limits
To illustrate, consider the following data:
Short circuit capacity: 108 MVA (5000A @ 12.47 kV) Customer Load: 1.50 MV Short Circuit Ratio: 108/1.50 = 72
For ratios between 50 and 100, the total harmonic distortion (THD) limit is 12%.
VOLTAGE DISTORTION LIMITS
IEEE 519 establishes maximum voltage distortion at the PCC with each consumer. Supply voltage quality should stay within limits provided the current limits are satisfied. Table II shows the voltage distortion limits.
Table II: IEEE 519 Voltage Distortion Limits
COMMUTATION VOLTAGE NOTCHING LIMITS
Voltage notching is common on many industrial power systems, especially those with large dc drives. When rectifying ac to dc, current is transferred from one phase to another. Since current does not transfer instantly, there is an overlap period during which two devices are conducting. During the overlap, a transient ac short circuit occurs through the two conducting devices causing a voltage notch. Six short circuits, or voltage notches, occur per 60 Hertz cycle or 360 notches per second.
IEEE 519 notch limits are divided into two parts: notch depth and notch area. These are illustrated in Figure 1.
Figure 1: Notch Depth and Notch Area
Table III contains recommended limits, where Special Applications include hospitals and airports, and a Dedicated System is exclusively dedicated to the converter load.
Table III: IEEE 519 Commutation Notching Limits
The information and diagrams presented herein are for general educational purposes only, and should not be relied upon as instructions for customer self-wiring. Customers should at all times seek the assistance of qualified electricians or utility personnel for all wiring projects.