PWM Harmonic Line Distortion
Software Estimator
Introduction | Job Data | System Data | Drive Data | Results | Warning | Support/Comments
Introduction
This document provides a brief operation explanation of the file PWMHARM.EXE program. The setup program will install all required files including the Visual Basic Run files.
Download
Application:(413KB)  Save the downloaded file d8308b.exe to a folder on your hard drive (create a new folder if needed). Navigate to the folder and double-click the downloaded executable file. It should extract the contained files into the same directory. Install the software by double-clicking the file SETUP.EXE and follow the instructions. |
PWMHARM is a
harmonics estimating program which requires
Microsoft' Windows V 3.1 to be resident on
your computer. The program allows entry of power
distribution system data and calculates 5th, 7th, 1 1 th,
and 13th voltage and current harmonics for standard PWM
AC drives. The calculations are based on an IEEE paper
and Laboratory Report prepared by Bob Schieman and Suang
Khuwatsamrit of Reliance titled "AC Line
Current Variations on a Three-Phase PWM Drive with AC
Impedance".
This program is
intended for estimating purposes only. This program has
been prepared by Reliance Industrial Company and
may be copied freely, provided that no changes are made
and credit is given to Reliance.
Job
Data
The first several lines in the program
ask for "JOB NAME", "ANALYSIS BY",
and "SYSTEM #". These lines are for your use in
identifying the data calculated when you have multiple
spreadsheets printed or saved in memory. Automatic date
and time stamping are provided. These will be correct if
your computer's real-time clock is correct.
System
Data
A system is defined as a single source
transformer feeding a single point of common coupling
(PCC). The source transformer is your customer's utility
transformer, not an isolation transformer. The PCC should
be defined by the customer, not you. If no PCC
information is available a "worst case" PCC
would be the point where all VFD electrical feeds meet.
In general the PCC is also the connection point of other
potentially harmonic sensitive loads.
The calculated outputs from the program
are usually the Total Current and Total Voltage Harmonic
Distortion at the PCC. The PCC is usually a panel board,
switchboard, or motor control center that serves as a
distribution point for power from a single source
transformer. Pan of that power is sent to PWM drives,
causing harmonic distortion at the PCC.
The "SOURCE XFMR KVA" is
the base-rated capacity of your customer's source
transformer. If the transformer rating is given as 2000
t725OOKVA, use the lower number, called the "base
rating". "SOURCE TRANSFORMER Z%" is
also known as the impedance of the source transformer. It
is usually listed on the transformer nameplate. If this
data is not known, assume an impedance of 4% and enter
the value "4" in this block.
"SOURCE TO PCC, FT" refers
to the distance, in feet, from the source transformer to
the panel board, cm, or switchboard that is defined as
the point of common coupling (PCC).
"UFT, SOURCE TO PCC" is the inductance per foot of the conductor (cable or
low-impedance bus duct) that carries power from the source transformer to the PCC. If the system uses busway, enter a value of 0.03 here. If the current is carried by cables use the actual cable inductance as listed by the manufacturer. If this information is not known, use the value of 0.3 as typical.
"SOURCE SECONDARY VOLTS" is the system voltage at the PCC.
"SOURCE FREQUENCY, HZ" is
the system frequency.
"NUMBER OF DRIVES" is
the number of drives connected to the same PCC.
Drive Data
The data that must be entered for each drive is as follows:
- "HP": Enter the HP of the PWM drive.
- "VOLTS": Enter the PWM Drive input AC voltage. (The default entry is assumed to be the PCC voltage)
- "DIST. (FT) TO PCC": Enter the distance from the PCC to drive in feet.
- "CONDUCTOR uH/FT": Enter the inductance per foot to the conductor that carries the power from the PCC to the PWM drive. If not known enter ".3" for cable or ".03" for bus duct.
- "XFRM KVA": If an isolation transformer is used, enter the KVA. If not, enter zero.
- "XFRM %Z": If an isolation transformer is used, enter the impedance of the transformer in %. If it is not known, enter "4.00"
- "REACTOR KVAR": If a line reactor is added, or is part of the drive from the factory, enter the KVAR value of the reactor. If the KVAR value is not known, enter a value of [0.03 X HP =KVAR]. For example, the value of the factory-installed line reactor in a 1OOHP Reliance GP2000 is about [0.03 X 1 00 = 3.00 KVAR].
Results
"% V_ DIST" is
the % Total Voltage Distortion at the PCC for the system
described during the data entry process. IEEE-519-1992
calls for this value to be less than 5% for
..general" systems.
"% C _ DIST" is the %
Total Current Harmonic Distortion at the PCC. Current
Distortion values are usually higher than Voltage
Distortion. This percentage is based on the FLA of the
distribution transformer specified. If your customer has
a specified Demand Current, you should divide this by the
transformer FLA and multiply the resultant fraction by
your %C - DIST to obtain the current distortion as a
percentage of demand current. IEEE-519-1992 has a sliding
scale for this measurement from 5 to 20 % depending on
the Short circuit to Load Current Ratio.
Warning!
This spreadsheet is for PWM drives with
a six-pulse diode bridge input only. Do not use for VVI
or CSI drives, or for DC drives. The results are for
estimating purposes only. General references in this
manual to IEEE standards
are for examples only. For a complete copy of the
complete standard please contact the IEEE at:
IEEE Corporate
Office
345 East 47 Street
New York, NY 1001 7-2394