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PA-9
Application Guide
TRANSFORMERS
Problems with transformers can be due to transient voltages
caused by lightning or switching operations which can result in
degradation or immediate dielectric failure. High magnitude and
fast rise time contribute to insulation breakdown in transformers.
Repeated lower magnitude application of transients can cause slow
degradation and eventual insulation failure, decreasing equipment
mean time between failures. Voltage swells can also reduce the
equipment life of transformers over time.
Voltage imbalance can also cause heating in transformers. In
general, utility supply voltage is maintained at a relatively low level
of phase imbalance since even a low level of imbalance can cause
heating effects on the generation, transmission, and distribution
system equipment. Voltage imbalance more commonly emerges in
individual customer loads due to phase load imbalances, especially
where large, single phase power loads are used, such as single
phase arc furnaces. In these cases, overheating of customer motors
and transformers can readily occur if the imbalance is not
corrected.
Waveform distortion can also cause heating in transformers.
Harmonic current injection from customer loads into the utility
supply system can cause harmonic voltage distortion to appear on
the utility system supply voltage. This harmonic current and
voltage distortion can cause overheating of rotating equipment,
transformers, and current carrying conductors. Harmonic voltage
distortion on a utility system can cause the same problems to a
customer's equipment and can cause overheating of utility
transformers, power carrying conductors, and other power
equipment.
Common Causes of harmonics include electronic loads and
SCR/Rectifier Loads.
Common causes of transients include lightning, load switching,
capacitor switching and loose wiring/arcing.
Example of distorted waveform
PA-9 Configuration
Feature Status Notes
Enable Power Calculations Enable (Select correct configuration)
Enable RMS Recording Enable
MIN, RMS and MAX MIN, RMS and MAX
Clock Hour Orientation Enabled
Enable Flicker Recording Disabled
Hysteresis 2%
Sags Enabled
This configuration is designed to
focus on Harmonic detection, as
well as sub-cycle events. Note that
the waveform capture is set to THD.
The time interval between waveform
captures should be set to the same
time interval of the storage interval.
The length of this interval should be
PA-9
Application Guide
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ISO STATEMENT
Registered to ISO 9001:1994 Reg no. Q 09250
Registered to ISO 14001 Reg no. EMS 61597
PA9_17_AG_En_V01
www.megger.com
Megger is a registered trademark
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Feature Status Notes
Sag Limit See Below
Swells Enabled
Swell Limit See Below
Sub-cycle Enabled
Sub-Cycle Limit See Below
THD Limit Disabled
THD Limit NA
Enable Waveform Capture Enabled
Waveform Trigger THD
Pre-Triggers NA
Post Triggers 5
Waveform Limit Disabled
Expected Number of Events NA
Memory Mode Stop When Full
Default Frequency 50 or 60Hz as Required
Enable Frequency Recording Enabled
MIN, AVG, MAX AVG
determined by how long the unit is
intended to record.
The unit will now capture
waveforms every storage interval
which will allow the software to
perform THD and Harmonic
trending. This is the data required to
find steady state harmonic problems.
NOTE: THD event limit is disabled.
Since the intent is to capture steady
state harmonics the event THD is
not required.
IEEE Recommendations: For a 120V / 60Hz Load
per IEEE1159.
Sag Limit = 108V (10% of Nominal)
Swell Limit = 126V (5% of Nominal)
Sub-cycle = 200V (Approx 2 times Phase to Neutral)
Unbalance = 2%
THD = 5%
European Recommendations: For a 230V / 50Hz Load
per EN50160.
Sag Limit = 207V (10% of Nominal)
Swell Limit = 253V (10% of Nominal)
Sub-cycle = None Provided
Unbalance = 2%
THD = 8%
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