Meter testing envolves from multi-station benches to single position systems

Because multi-station test benches could test multiple electric meters at a time, they improved many meter shops’ productivity. However, the new technologies developed by the electronics industry have enabled meter test equipment manufacturers to bring a number of single-position meter test systems to the market to rival the multi-station test benches.

A study comparing the performance of a single-position test system with a multi-station test bench found that in many cases the single-position test system was faster.

The advantage of testing multiple meters at a time disappears, because the actual time required to test a meter is reduced to a minimum with the new single-position test system.

Table 1: Meter Outputs by Hour - Multi-station Bench vs. Single-Position System

 

Single-phase
Meter Testing

Poly-phase
Meter Testing

New Single-position Test
System - Model B

75 meters / hour

40 meters / hour

Traditional 10-station Test
Bench - Model A

50 meters / hour

24 - 38 meters / hours

Modern single-position meter test systems are computer-controlled and fully automatic, with features that lead to improved speed and efficiency:

  • Automatic storage of meter test data to a database
  • Pre-programmed standard meter forms and test plans
  • Optional storage of database and meter test plans on a computer network
  • Changes to meter test plans done instantly and permanently
  • ‘Cycle’ mode that allows re-calibration of a meter ‘on the fly’
  • Built-in quick-test algorithms for both electronic and induction meters
  • One-button operation - after the meter is plugged in, pushing one key on the computer runs the test automatically.

The single-position test systems are accurate and have the capabilities of sophisticated test benches built for the shop environment. Best of all, many new single-position systems are also light in weight and can be operated reliably in the field. Electric companies in the US have installed these single-position test systems in vans and trucks, bringing the convenience, speed and accuracy of the test table into the field.

The economic benefit derived from adopting the single-position test system is significant. Furthermore, the single position systems available today offer new features and options, intended to improve meter testing operations without added cost. If a large meter shop needs more than one single-position test system, additional systems can be bought to fit the expanding needs. Some meter shops even use one computer to operate multiple single-position test systems to further optimise the operation.

True Three-phase Testing

Although small in size compared to the traditional multi-station test benches, many modern single-position test systems are true three-phase systems capable of delivering independent three-phase outputs. Since the hardware is a true three-phase test set, the firmware and software are also designed to control all three current magnitudes and phase angles, as well as all three voltages.

The true three-phase test method is generally preferred to the single-phase method (serial-parallel) for polyphase meter testing, for the following reasons:

  • Mechanical induction meters may calibrate as much as a 4% difference between single-phase and true three-phase method testing.
  • It may be difficult to satisfy some IEC provisions if the true three-phase test method is not used when testing certain polyphase meters.
  • The true three-phase test method allows testing of imbalanced load, voltage, and phase angle conditions – in other words, individual currents, voltages and phase angles can be specified, allowing field conditions to be simulated easily.
  • At full load some multi-element meters run differently under the polyphase loads than under the series-parallel (single-phase test method) conditions. These meters will be less accurate if the calibration is done using the single-phase test method.

Other convenient features and options include bar-coding (where meter nameplate data can be entered automatically with the bar code reader wand, and the test plan is selected and started without operator input); information management (using the database management tools available today, where-by all test plans, meter information, test results and report formats can easily be selected through default values or defined by users) and a DSP-based reference standard (meaning that meter shop operators no longer need to stock additional external reference standards – the calibration of the system only requires one single phase external reference standard to be connected).

The single-position meter test systems are good performers in the laboratory and in the field. A large number are in use for evaluating new incoming meters, as well as for diagnosing and re-calibrating meters. Many are also being used in the field to perform the high level test and calibration functions traditionally reserved for meter shops, as well as some meter verification functions typically done with portable test sets.

For more information contact Gary Guthrie of AVO International at gary.guthrie@avointl.com