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
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