STER PMU portable phasor measurement unit is the integral part of the WAMSTER synchrophasor system.

STER PMU is an easy to use, portable (handheld) synchrophasor measurement unit (PMU) with a rechargeable battery backup and SD flash memory for more than 4 months of synchrophasor data. Contrary to a classic PMU unit, it needs no additional infrastructure to operate - it can use GPRS/UMTS to send data to a cloud server, or integrate with existing IEEE C37.118 equipment.

Portable PMU unit: Key features

  • Small, lightweight (only 1.45 lb / 0.66 kg without accessories), easy to install, low-cost PMU device
  • Battery backup for up to 5h of autonomy during power blackouts (or 8h if not communicating during the blackout)
  • 4.5 months of full-speed synchrophasor measurements (with 32 GB SD cards), and 8 MB of installed flash memory for more than 1 hour of synchrophasor measurements during SD card replacement (up to 64 GB SD cards supported on demand)
  • 10-min. harmonic/THD aggregates (min/max/avg)
  • Up to 4 days of continuous waveform recording (3.2kHz, 8 channels)
  • Base of the device is the handheld IEC 61000-4-30 A/S class analyzer
  • Two 4-channel 16-bit A/D converters
  • Three voltage ranges (150, 300 and 1000V), with configurable current/voltage transformer ratios
  • Backlit 3.5" LCD display for configuration, measurements and diagnostics
  • No additional infrastructure (no concentrator equipment, no cabling): data is sent over GPRS/UMTS to a cloud storage location
  • Magnetic baseplate allows quick mounting of the device and accessories to the existing switchboard equipment
  • No on-site configuration necessary
  • Available as a single product (with IEEE C37.118 or other specific communication protocols on demand), or integrated with the WAMSTER service

Easy startup

Data is visible on the web in less than 15 minutes from arrival on site.

For the end user, all the equipment necessary to start recording synchrophasors is included in a soft carrying bag: It takes only a couple of minutes to setup the wiring and signal ranges, as well as configure the SIM card settings and connect to the Internet. STER PMU can also be attached to the (optional) magnetic baseplate which is designed to pre-wire the device to the GPRS modem using as little area as possible, allowing instant attachment to switchboard doors and backplanes.

Simple setup

All measurement and communication settings can be configured on the device.

Equipped with a 3.5" backlit LCD display, all settings are easily visible and adjustable using the graphical user interface. This makes it simple to configure voltage and current transmission ratios, monitor real-time voltage and current synchrophasor measurements as well as diagnose and troubleshoot problems.

Battery operated

More than 4 hours of autonomy during blackout conditions.

Wamster system is ideal for analyzing synchrophasor data during blackout conditions. Rechargeable battery can keep the portable PMU device operating for more than 4 hours without supply, including the supply for the GPRS modem. If the communication also breaks, device will continue storing measurements locally and report them to server when the connection is restored.

Up to 32 GB of SD flash memory

More than 5 months of data can be stored locally.

Without the SD card, internal flash memory is sufficient for storing around 2 hours of 4-phase synchrophasor data cyclically (at full reporting speed, 60Hz). If a 32 GB SD memory card is used, more than 4 months of synchrophasor measurements can be stored locally. This makes it even possible to use the device for offline scenarios and analyze data by retrieving it directly from the memory card.

Continuous Waveform Recording

Continuous waveform data stored locally.

Using a 32GB SD card, device can store 4 days of oscillograms (waveforms) for all channels, along with synchrophasor measurements at synchronous frequency. Additionally, the device records 10-min harmonic/THD aggregates (min/max/avg). Grouping multiple PMU devices into a single campaign using the WAMSTER system enables automatic retrieval of synchronized oscillograms from multiple locations in case of events, allowing detailed insight into the system operation.

Standard equipment

A single STER PMU measurement set (Fig. 3) includes:

PMU unit1
3 phase 5A/1V measuring transformer1
Test probe, red3
Test probe, black1
Crocodile clip, red3
Crocodile clip, black1
Voltage measurement lead, red3
Voltage measurement lead, black1
Voltage measurement lead, green1
Power supply adapter1
GPRS class 10 modem with connection cable1
GPS unit1
1.2 V NiMH rechargeable battery6
Soft carrying bag1
Instruction manual1
Calibration certificate1

Technical specifications

Measurement inputs
  • 4 voltage inputs (3 phases, earth), 3 ranges: 150V, 300V, 1000V
  • 4 current inputs: xx A /1V, 2 ranges: 100%, 10%
  • default current sensor: 5A/1V A1037 measurement transformer
  • optional current sensors: current clamps with nominal currents from 5A to 3000A, measurement class: 1 (high currents) or 2 (low currents).
Basic measurement accuracy
  • Voltage RMS accuracy: 0.2% of reading
  • Current RMS accuracy: 0.5% of reading (using default current sensor)
Synchronized phasor measurements
  • Measurement result tagging according to C37.118 specification
  • Accuracy: TVA < 1% with default current sensor
  • Max. reporting rate: synchronous (50/60 synchrophasors frames per second)
Power quality measurements
  • 8 channel 3.2kHz continuous waveform recorder, circular buffer (4 days with 32GB card)
  • 10-min voltage and current harmonic/THD aggregates (min/max/avg)
Local non-volatile memory autonomy
  • 32 GB, sufficient for 4.5 months of measurement results saved at synchronous reporting rate, or
  • 32 GB, sufficient for 4 days of synchrophasor measurements and 4 days of waveforms, or
  • 64 GB, sufficient for up to 9 months of measurement results saved at synchronous reporting rate, or
  • Other capacities can be used on request, disabling certain channels can also increase max. capacity.
Communication reporting rates
  • 50 Hz (1-2-5-10-25-50 fps)
  • 60 Hz (1-2-5-10-12-15-20-30-60 fps)
Safety standards
  • EN 61010-1: 2001 Safety requirements for electrical equipment for measurement, control and laboratory use
Overvoltage protection
  • 1000 V / CAT III; 600 V / CAT IV
Protection class
  • double insulation
EMC standard
  • EN 61326-2-2: 2006 Electrical equipment for measurement, control and laboratory use
  • Emission: Class A equipment (for industrial purposes)
  • Immunity for equipment intended for use in industrial locations
Communication link
  • GPRS modem class 10
Time source
  • GPS PPS – error < 3µs
  • internal clock – error < 2s/day
  • monochrome LCD, 320x200 with backlight
Battery backup
  • > 8 hours as a standalone device
  • > 5 hours if supplying GPRS modem with power
Auxiliary power
  • 80-260V, 50/60 Hz
  • 220 x 115 x 90 mm
  • 0.65 kg

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