Events || News

World Class Reliability


Motor and Generator Monitoring

rmmDynamic Ratings offers several monitoring technologies for motors and generators. The primary diagnostic technology is monitoring for partial discharges (PD). PD is usually a symptom of a key problem such as loose coils, poor impregnation, coil spacing and reduction of gradient materials. Some of these types of problems are slow in developing and others can occur quite rapidly.

Depending on the application, additional monitoring technologies are part of the overall monitoring system, including:

  • Six temperature inputs for winding temperature
  • Four vibration Inputs
  • Six 4 -20 mA inputs
  • One ambient temperature input
  • One humidity input
  • Three load current inputs
  • Three voltage inputs
  • Current Signature Analysis for broken rotor bars on Induction Machines
  • Many new options coming soon

No other monitor in the market has the capabilities that the Rotating Machine Monitor (RMM) offers.

Portable Partial Discharge Analyzer

DRPD-15The DRPD-15 is a lightweight, portable, 15 channel electrical partial discharge (PD) analyser. The DRPD-15 can be operated from a 90 – 265 VAC power source or from the integrated battery. Typically battery life is 8 hours.

The unit is versatile and can be used to test for partial discharges on generators, motors, cables, transformers, bus ducts and switchgear. It can be used with most partial discharge sensors, whether they are installed permanently or on a temporary basis.

Time of flight, pulse polarity, gating, pulse shape analysis and multi-channel signal acquisition makes the DRPD-15 the most versatile portable PD analyser on the market. There is no need for a different analyser for each type of application as you do with many other suppliers. With its advanced noise cancellation features, the uses are almost unlimited.

The DRPD-15 features 48 phase windows (7.5 Deg resolution) and 32 magnitude windows, with a single dynamic range of 75dB. All PD channels have identical isolated input circuitry, protection and input high pass filters. There is also a dedicated noise channel, as well as a power frequency reference channel.

The DRPD-15 interfaces with a laptop computer via a USB port. The dedicated software allows the user to easily configure each object being tested and analyse the data. All common PD quantities are recorded such as Magnitudes, Pulse Counts and PD Intensity/Power. Trends, N-Q distribution and full phase resolved data are standard features.

Rotating Machine Monitor

rmmThe RMM (Rotating Machine Monitor) is a microprocessor-based device that continuously monitors the insulation system for partial discharges of motors and generators. Applications are available for motors, hydro generators, and turbine generators.

Operating characteristics such as ambient temperature, ambient humidity, vibration, load current, voltage and hydrogen pressure can also be monitored and correlated with the recorded PD activity. These correlations assist in the diagnostics and determining the type of defect. Trending of all common PD quantities such as magnitudes, pulse counts and PD Power are measured and recorded as well as N-Q distributions and full phase resolved data are standard features.

One additional key built in feature for induction motors is current signature analysis. Analysis of the current signature will provide indication of possible broken rotor bars.

Typical PD sensors used with the RMM include Coupling Capacitors, RTD PD Modules and the Ground PD Current Sensor. If you already have other manufacturers coupling capacitors installed, the RMM is capable of utilizing these sensors, thus there is no lost investment. The basic standalone unit consists of three modules: Power Supply, Main Module and one Electrical PD Module.


A large variety of sensors are offered depending on the application. Contact your representative for assistance in proper selection of the sensors for your application and review our Literature and Application Notes for additional information.

sensor_aCoupling Capacitors (CC)

A full complement of 80 pF Epoxy Mica coupling capacitors are available. Typically the coupling capacitors are connected at the line terminal of motors and generators and switchgear. Three voltage levels are available: 8, 16 and 28 kV. The epoxy resin used in the capacitors is specifically designed for high voltage applications. This material provides excellent insulation properties, high mechanical properties and superior resistance to chemicals including concentrated acids. The epoxy has superior arc resistance as compared to standard electrical grade epoxy materials and meets UL 94/V-0 requirements.

Download Literature

RFCT 1Radio Frequency Current Transformers (RFCTs)

Radio Frequency Current Transformers (RFCT) are installed in the ground circuits of a variety of electrical equipment to measure Partial Discharges (PD). The RFCT is made from a special ferrite core which is molded into a plastic/epoxy covering. Typical applications include: cable terminations, splices, motors, neutral connections and external core ground connections on large power transformers.

Download Literature

BAU Sensor 3Bushing Sensors (BAU)

The Type BAU bushing sensor provides both a power frequency and high frequency signals to the EDI monitoring equipment. These signals are used for the monitoring of the bushing insulation as well as for partial discharges that may be occurring in the bushings or windings. The BAU Bushing Sensors are installed in the bushing test/capacitance tap that are found on all High Voltage Bushings.

Download Literature

High Voltage Current Transformer (BAU-HVCT)

The BAU-HVCT is a sensor which is used on high voltage current transformers. This sensor is installed in series with the grounding wire in the HVCT junction box. The BAU-HVCT is used to monitor the power factor and the capacitance of a set of 3 HVCTs. This sensor also has the ability to provide a partial discharge signal to an appropriate partial discharge monitor or analyzer.

RTD Sensor Module (RTD-M)

Typically RTDs are embedded in the wining of motors and generators to monitor winding temperature. It has been proven that the use of just coupling capacitors installed at the line terminals of a machine is not adequate to monitor partial discharges that may be occurring deeper in the winding. The high frequency pulses caused by a PD event will attenuate quite quickly, therefore limit the effectiveness or “Zone of Sensitivity) of the coupling capacitors. By utilizing the existing RTD as a PD sensor additional coverage of the winding can be achieved. The RTD-M is a passive device and is installed in series with the existing RTD wiring at the machine and will not affect the operation of any installed temperature monitoring equipment The RTD and RTD wiring act as an antenna and any nearby PD events will be coupled to the RTD and its wiring. The RTD-M decouples the high frequency signals from the RTD wiring where they are connected to the analyzer for signal processing. Each RTD-M can be connected to 6 RTDs. The resistance value of the RTDs is of no consequence.

Download Literature

sensor_cRogowski Coil (RC)

Rogowski Coils (RC) are an air core high frequency current transformer. Partial Discharges and many noise signatures are found in the high frequency range. Typically RCs are used on high voltage Large Power Transformer applications. The RCs are installed around the base of all high voltage bushings, and are used in conjunction with BAU bushing sensors, to determine if the detected signal is internal or external to the transformer.

Acoustic PD Sensor (APS)

Partial discharges (PD) will emit an acoustical wave when they occur. This Acoustic Emission (AE) can then be detected by sensors mounted on the external area of the transformer tank. According to IEEE documents, if the PD is occurring near the surface of the core and coil assembly there is a good opportunity to detect these signals. If the PD is buried in the internal parts of the core and coil assembly, there will be little chance to detect these signals. The AE sensor is fixed to the transformer tank wall by the use of strong rare earth magnets.