Ieee std 1159-1995, ieee recommended Practice for Monitoring Electric Power Quality

Figure 17ÑUPS square voltage output
Figure 18ÑImpulse resulting from instrument error

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IEEE
Std 1159-1995
IEEE RECOMMENDED PRACTICE FOR
52
8.4.1 Signature analysis
Signatures are characteristic graphical representations of electromagnetic phenomena. For example, the
energization of a certain type of load may consistently generate the same waveshape disturbance. This wave-
shape would be called its signature. Seeing this signature in a monitoring situation identiÞes the presence of
that load.
Many, but by no means all, electromagnetic phenomena have signatures that can be recognized and ana-
lyzed. The more information provided by a graph, the greater the possibility that a disturbance can be identi-
Þed by its signature. Sag/swell graphs, for example, showing simultaneous voltage and current, may more
quickly lead to correct conclusions than those showing a voltage sag or swell alone.
8.4.2 Steady-state waveshape analysis
8.4.2.1 Scope
There is much that can be learned from examining the normal, steady-state waveshape of loads or the power
system. This type of analysis does not focus on disturbances, but rather on what might be happening when
Table 1ÑReference chart for problem analysis
Typical problems
Disturbance 
type
Possible causes
Subclause
Overheated neutral
Intermittent lock-ups
Frequency deviations
Steady-state
Shared neutrals 
Improper or inadequate wiring
High source impedance
SCR/RectiÞers and notching
Harmonics
8.4.2
Interruption 
Garbled data 
Random increases in harmonic levels
Utility faults
Inrush currents 
Inadequate wiring
8.4.3
Intermittent lockups 
Lights ßicker
Garbled data
Sag/swell
Source voltage variations
Inrush/surge currents 
Inadequate wiring
8.4.4
Component failure 
Dielectric breakdown 
Lock-ups 
Garbled data
Wavy CRTs
Impulses
EMI/RFI
Lightning 
Load switching 
Capacitor switching 
Static discharge 
Hand-held radios 
Loose wiring/arcing
8.4.5
Overheated transformers 
Voltage distortion 
Current distortion 
Overheated motors 
Garbled Data
Lock-ups 
Harmonics
Electronic loads 
SCR/rectiÞer 
Loads bandwidth of source impedance
8.4.6
Problems occur at the same time
Problems occur at regular intervals
All
Timed loads
Cyclical loads
8.4.7
SPS and/or automatic transfer switch 
does not work
Excessive frequency shift
Discontinuities
Switching to alternate sources
Non-synchronized power switching
8.4.8

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IEEE
MONITORING ELECTRIC POWER QUALITY
Std 1159-1995
53
there are no disturbances. Typically, waveshape analysis is more useful at the facility level or further down-
stream as opposed to the utility level.
Steady-state waveshape analysis provides information regarding the following:
a)
Type of loads
b)
Adequacy of power system
c)
VeriÞcation of wiring practices (shared vs. dedicated neutral)