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© 2011 Schneider Electric. All Rights Reserved.
63230-500-225A2 PowerLogic
TM
Series 800 Power Meter
3/2011 Chapter 9—Disturbance Monitoring (PM870)
65
Chapter 9—Disturbance Monitoring (PM870)
This chapter provides background information about disturbance monitoring and describes
how to use the PM870 to continuously monitor for disturbances on the current and voltage
inputs.
About Disturbance Monitoring
Momentary voltage disturbances are an increasing concern for industrial plants, hospitals,
data centers, and other commercial facilities because modern equipment used in those
facilities tends to be more sensitive to voltage sags, swells, and momentary interruptions.
The power meter can detect these events by continuously monitoring and recording current
and voltage information on all metered channels. Using this information, you can diagnose
equipment problems resulting from voltage sags or swells and identify areas of
vulnerability, enabling you to take corrective action.
The interruption of an industrial process because of an abnormal voltage condition can
result in substantial costs, which manifest themselves in many ways:
• labor costs for cleanup and restart
• lost productivity
• damaged product or reduced product quality
• delivery delays and user dissatisfaction
The entire process can depend on the sensitivity of a single piece of equipment. Relays,
contactors, adjustable speed drives, programmable controllers, PCs, and data
communication networks are all susceptible to power quality problems. After the electrical
system is interrupted or shut down, determining the cause may be difficult.
Several types of voltage disturbances are possible, each potentially having a different
origin and requiring a separate solution. A momentary interruption occurs when a protective
device interrupts the circuit that feeds a facility. Swells and over-voltages can damage
equipment or cause motors to overheat. Perhaps the biggest power quality problem is the
momentary voltage sag caused by faults on remote circuits.
A voltage sag is a brief (1/2 cycle to 1 minute) decrease in rms voltage magnitude. A sag is
typically caused by a remote fault somewhere on the power system, often initiated by a
lightning strike. In Figure 9–1, the utility circuit breaker cleared the fault near plant D. The
fault not only caused an interruption to plant D, but also resulted in voltage sags to plants A,
B, and C.
NOTE: The PM870 is able to detect sag and swell events less than 1/2 cycle duration.
However, it may be impractical to have setpoints more sensitive than 10% for voltage and
current fluctuations.