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Description
The PQSensor™ is a factory or field installable transducer that equips a Capacitor Voltage Transformer (CVT) with an output signal that faithfully reproduces the harmonic spectrum of the primary h.v. input. This output enables CVTs be used with any power quality monitoring device to accurately record power system harmonics and transients. The installation of the PQSensor™ on a CVT does not in any way affect the normal operation of the CVT.
To make accurate measurements of harmonics and other power quality phenomena in a transmission substation the number one requirement is to have access to a voltage signal that faithfully reflects the full harmonic spectrum of the primary system voltage. The three most common sources of voltage signals in a transmission substation are listed in the table below and the benefits and limitations of each is considered.
| Device | Pros | Cons | Summary |
| CVT | Commonly available in the majority of transmission substations | Accuracy is limited to frequencies close to nominal | Not suitable for harmonic measurements - even at lower harmonic orders |
| IVT | Higher accuracy at frequencies close to nominal | Accuracy is limited to harmonics lower than the 10th order | Not a viable option for harmonic assessment above the 10th order |
RCD | Provides accurate harmonic measurements | Not commonly available in transmission substations. Calibration and accuracy present problems | A viable solution where available; a small installed base, expense and calibration can be a problem |
It is evident from this summary that none of the above sources meet the requirement of providing a readily available voltage signal suitable for accurate harmonic measurement in a cost-effective manner.
The PQSensor™ is a transducer that can be fitted to an existing in service CVT, or supplied factory fitted with new CVTs and provides an output signal that meets this requirement.
For the first time - a unique transducer for use with CVTs providing an output signal that accurately reflects the harmonic and transient spectrum of the primary voltage.
The only solution that meets all your transmission network broadband measurement needs!
Installation
One PQSensor™ is installed on each single phase CVT. The PQSensor™ consists of two components - a Measurement Unit that is installed in the secondary terminal box of each CVT and a Signal Conditioning Module (SCM) that is mounted on the structure of the CVT. The SCM is connected to the measurement unit housed in the secondary terminal box using a cable that is supplied with the PQSensor™.
An AC or DC supply is required by the SCM and the output signal (nominal 63.5VAC) is wired to the location of the measurement equipment which is normally in the protection or metering room. Often it is convenient to wire the SCM to the local CVT marshalling box with a multicore cable. The marshalling box can provide the supply voltage for the SCM and be a convenient location where the signals from all three phases can be collected and conveniently wired back to the measurement location. The PQSensor™ can also be powered by the CVT phase to phase output voltage as it presents a small burden - less than 5VA. Sample wiring drawings are available in the Downloads section of the BVM Systems website.
Field Experience
The product has many years of field experience at voltages from 115kV - 400kV - the PQSensor™ is applicable at any system voltage where CVTs are installed. PQSensor’s™ have been field retrofitted to a variety of different designs of CVT and have also been supplied ‘factory fitted’ by all of the major manufacturers of CVTs. Applications have included power quality recording, fault and disturbance recording and monitoring of high-speed transients on transmission systems. The PQSensor™ has been used to accurately measure power quality parameters such as harmonics and flicker over a wide bandwidth from sub-synchronous harmonics to high frequencies.
For more information about the PQSensor™ power quality measurement system, please contact Fuseco.
Features
- Enables accurate harmonic and power quality measurements to be made using CVTs.
- Can be used at any voltage level where CVTs are installed.
- Accurately measures frequencies up to the 100th harmonic.
- Faithfully reproduces power system transients up to 1 MHz.
- Is compatible will all commonly used Power Quality Meters, Fault Recorders and Power System recorders.
- Allows CVTs to be used for accurate measurement of low frequency phenomena including ferro-resonance and sub synchronous resonance.
Benefits
- Eliminates the need for expensive resistor capacitor dividers when making broadband measurements on the transmission system.
- Transient measurements and studies can be carried out cost effectively using CVTs equipped with the PQSensor.
- Can be retro fitted to many existing installed CVTs.
- Can be supplied factory fitted by most of the major CVT manufacturers.
- PQSensor installation has no impact on the normal operation and measurement capabilities of the CVT.