CWT LF

CWT LF

Related Documents


 Datasheet PDF file opens in a new window

 Technical Notes PDF file opens in a new window

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 Power Adaptors PDF file opens in a new window

 

Need a smaller, low frequency probe?

Then take a look at the: CWT Mini

 

  • Overview
  • Performance
  • Applications
  • Get a Quote

Overview

The CWT extended Low Frequency (CWT LF) can be specified with either our standard CWT.

Like the CWT and the CWT Mini the CWT LF is a wide-band probe with high frequency bandwidth in the MHz range. However the extended low frequency bandwidth makes the CWT LF particularly suitable for the measurement of:

  • Longer duration pulses of current – such as electrolytic capacitor discharge or asymmetric short circuit testing.
  • Power measurements with very low phase shift error from 10Hz to a few 100kHz

Standards and Approvals

  • CE marked
  • Designed to comply with IEC61010-1:2001
  • PEM Ltd is an ISO9001:2008 registered company
  • Patented technology

Performance

Peak current

60A peak to 600kA peak

Output

±6.0V peak

High Frequency Bandwidth (-3dB)

6.5MHz (300mm coil),  3.0MHz (700mm coil)

Low Frequency Bandwidth (-3dB)

Varies with model type (refer to datasheet)

Accuracy (typ.)

Calibrated to ±0.2% with conductor central in the Rogowski loop

 

Typical variation with conductor position ±1.0% of reading (CWT LF)
Typical variation with conductor position ±2.0% of reading (CWT LF Mini)

Operating temperature range

0℃ to +40℃ (Integrator electronics)

 

–20℃ to +100℃ (Coil and cable)

Cable Length (coil to integrator)

2.5 or 4m (custom lengths available)

Power Supply

Option ‘B’ Battery 4 x AA (1.5V standard alkali batteries)
Plus - 2.1mm socket for 12V (±10%) DC input

 

Option ‘R’ Rechargeable Battery 4 x AA (1.2V NiMH batteries) with on-board trickle charge circuitry.
Plus - 2.1mm socket for 12V (±10%) DC input

Output load

> 100.0 k ohm (for rated accuracy)

For the CWT LF with the CWT standard coil

Coil Lengths

300, 500, 700 or 1000mm (custom lengths available)

Coil thickness

8.5mm max.

Peak coil insulation

10kV peak

Features

  • Traceable calibration (certificate included)
  • Thin, clip-around, Rogowski coil for easy insertion into circuits with restricted access
  • Non- intrusive: Loads the circuit under test by only a few pH’s
  • No magnetic materials ensures excellent linearity < 0.05% reading
  • Galvanically isolated measurement

Applications

The CWT LF has been supplied to major electrical engineering companies and leading research institutions around the world for the past 10 years. This versatile instrument has been used for a  wide variety of applications, some examples include:

Asymmetric Fault Current Measurements

Asymmetric fault currents occurring in power systems typically comprise a slow exponential decay dc component with a 50/60Hz waveform superimposed. The figure shows a typical fault current and the output from a CWT300LF probe (peak current 60.0kA).

The CWT LF range has an extended low frequency bandwidth, for example for the CWT300LF this is 0.008Hz. This limits the distortion when measuring long duration pulses. The distortion due to the low frequency bandwidth is termed ‘droop’ distortion and is discussed in the CWT Technical Notes.

A typical assymetric fault current measured by a CWT300LF
A typical assymetric fault current measured by a CWT300LF

In the waveform shown the CWT 300LF accurately measures the 50/60Hz component and DC decay with a resultant droop offset of less than 0.8% of peak current.

Due to the high tolerance to which the LF (-3dB) performance is specified the CWT LF the droop offset is predictable and can even be compensated when post processing results.

Power (Quality) measurements

Like the LFR probe probably the most common application for the CWT LF is for power measurement where the probe is often used in conjunction with a power analyser.

The CWT LF has:

  • Extremely low phase error from 10Hz up to several 100kHz
  • Very low noise floor.
  • Easy to use, clip around coils
  • Excellent linearity
  • Good accuracy with conductor position in the loop.

Thus the CWT LF is ideal for measuring current in power (quality) measurement applications

The CWT LF differs from the LFR in that it has:

  • Higher current ratings
  • Better phase error from in the range of a few kHz (higher cut-off in the MHz range)
  • Better low frequency performance at > 3000A

Power Electronic Applications – High Power  Rectifiers, Electrolytic Capacitor Discharge and Brake Choppers

The CWT LF range is capable of measuring large currents at frequencies of even less than 1Hz, PWM waveforms with ON times of a few milli-seconds or long duration single shot pulses.

Unlike current transformers or other magnetic based sensors Rogowski coils are not limited by I.t product, with no magnetic materials to saturate the CWT LF can measure large currents at low frequency such as those encountered in high power rectifiers, electrolytic capacitor discharge and brake choppers.

Other Applications Include:

  • High current very low frequency applications
  • Fault currents
  • Pulsed power applications

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