ABB Relion 670 Series Applications Manual page 512

Section 17
Monitoring
17.14 Voltage harmonic monitoring VHMMHAI(VTHD)
17.14.1 Identification
Function description
Voltage harmonic monitoring
17.14.2 Application
In order to maintain the power quality for better supply, harmonics in the system must be
monitored. Due to the nonlinear loads connected to the system, harmonics (apart from
fundamental frequency component) are generated and thereby the system voltage is distorted.
Voltage distortion appears to have a little effect on operation of nonlinear loads connected, either
phase-to-phase or phase-to-neutral. Current distortion is limited at the point of common coupling
PCC to control the harmonic current from the utility to the consumer. Thereby, the voltage
distortion must be limited in order to prevent it from spreading to other facilities.
Voltage harmonic distortion levels can vary drastically, depending on the configuration of system.
These voltage harmonics can damage the equipment as they are designed to operate for certain
range of voltage inaccuracy.
Moreover, in four-wire distribution systems (three-phase and neutral), the currents in the three
phases will return via the neutral conductor, a 120 degree phase shift between corresponding
phase currents that causes the currents to cancel out in the neutral, under balanced loading
conditions. When nonlinear loads are present, any 'Triplen' (3
currents does not cancel out. However, they will be added cumulatively in the neutral conductor,
which can carry up to 173% of phase current at a frequency of predominately 180 Hz (3
harmonic).
In case of electric traction systems, it generates various power quality problems that have an
important impact on its distribution network. DC traction loads, fed through AC/DC rectifiers,
generates non-linear voltages and currents on the AC system, that will result in harmonic voltage
distortion of the power supply system. Traction power supply system creates power quality
problems to the corresponding grid, which can cause:
• Poor power quality
• Increase in operational cost due to less productivity
• Damage to sensitive equipment in nearby facilities.
In general, harmonics can cause reduced equipment life if a system is designed without
considering the harmonics and if the equipment is not designed to withstand harmonics. Hence, it
is important to measure and monitor harmonics in power systems. Harmonic voltage distortions
on 161 kV power system and above is limited to 1.5% of total harmonic distortion (THD), in with
each individual harmonic is limited to 1.0%.
17.14.3 Setting guidelines
The recommended limits for total harmonic distortion and individual harmonic distortion are
available in the IEEE 519 standard. The limits are based on measurements which are done at the
506
IEC 61850
identification
VHMMHAI
© Copyright 2017 ABB. All rights reserved
IEC 60617 ANSI/IEEE C37.2
identification device number
UTHD VTHD
rd th
, 9 ...) harmonics in the phase
1MRK 511 401-UUS F
GUID-B2F24353-AAEA-4520-BB1C-5FD5FFCFC67B v1
GUID-BF90E93F-C0F4-43F7-BDD5-F3C289B5535B v1
GUID-987BCB6C-C559-42EE-9AAB-5F71189A58C6 v2
rd
GUID-45A6724C-1FF0-4910-9878-01518111EB26 v1
GUID-57719753-00C3-43F6-97B5-AA3B22618A3F v1
Bay control REC670
Application manual