Electrical Signature Analysis (Esa) - GE 869 Instruction Manual

MONITORING

Electrical Signature Analysis (ESA)

NOTE:
4–282
Rotating machines are a critical component of many industrial processes and are
frequently integrated in commercially available equipment and industrial processes. The
condition of a rotating machine can be effectively monitored using a non-intrusive method
called Electrical Signature Analysis (ESA). The concept is to treat the electric machine as an
implicit transducer built into machine-driven equipment; the current behavior can then be
used to show various operating conditions of the machine as well as the load it is driving.
Proven ESA algorithms are implemented in the 8 Series to detect various failure modes in a
rotating machine and its assembly. Some of the proven ESA applications are described as
follows. Traditionally, machine condition can be supervised by measuring quantities such
as noise, vibration and temperature. The implementation of these measuring systems is
expensive and proves only to be economical in the case of large motors or critical
applications. A solution to this problem is to use quantities that are already measured in a
drive system e.g. the machine stator current, often required for command purposes. ESA is
the technique used to analyze and monitor the trend of dynamic energized systems.
Specifically, ESA is the monitoring of stator current or voltage (more precisely supply
current) of the machine. A single stator current or voltage monitoring system is commonly
used (monitoring only one of the three phases of the machine supply). Machine stator
windings are used as a transducer in ESA, picking the signals (induced currents and
voltages) from the rotor (but also revealing information about the state of the stator).
Various electrical and mechanical fault conditions present in the machine further
modulate machine current and/or voltage signal and contribute to additional sideband
harmonics. Faults in machine components produce corresponding anomalies in the
magnetic field and change the mutual and self-inductance of then machine and this
appears in the supply current and/or voltage spectrum as sidebands around line (supply,
grid) frequency. Based on fault signatures motor faults can be identified and their severity
can be accessed.
The technology discussed in this manual has been patented (filed) with following
disclosure numbers.
• GE 73745/316350: System, method and procedure for Industrial motor electrical
signature analysis.
• US 15/489, 228: An autonomous procedure for electrical signature analysis based
machine M&D.
The following high-level procedure describes how a motor is diagnosed:
1. ESA is part of existing Multilin 869 Protection Relay product. Hence ESA captures
current signal from the same CT sensing mechanism available in 869 relay. No
additional sensing or wiring mechanism is required to install or use ESA (M&D) with the
869 relay.
2. Stator phase A current measured by the J1 slot is used for the purpose of motor
current signature analysis.
3. Before doing analysis, a data quality check is performed to verify if the power quality
condition is good. Voltage, frequency, THD and current unbalance levels are checked
to be within satisfactory limits. Signature analysis is performed only if the data quality
check passes and an event is generated if the check fails.
4. Once the data quality check has passed, FFT is applied on J1 phase A current samples
to convert time domain data into frequency domain and obtain current magnitudes at
various frequency ranges of interest.
5. For each fault or anomaly, fault frequencies are computed based on supply
frequency, speed, harmonic factor, slip etc. depending on the fault type.
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS