Panel meters, digital multimeters (DMMs), power monitors and other general-purpose instruments are typically limited to detecting and measuring voltages less than 1000V. Specialized instrumentation is required for AC or DC voltages above this level. Voltmeters make physical contact with the live circuit to obtain accurate readings. Non-contact devices operate by sensing the electrical field radiating from an energized circuit.
Contact Measurements
Panel meters, digital multimeters (DMMs), power monitors and other general-purpose instruments are typically limited to detecting and measuring voltages less than 1000V. Specialized instrumentation is required for AC or DC voltages above this level. Voltmeters make physical contact with the live circuit to obtain accurate readings. Non-contact devices operate by sensing the electrical field radiating from an energized circuit.
A high voltage probe can be used with other DMMs to extend the voltage measuring range. The Fluke 80K-40 is specified to 40kV DC or peak AC. This probe is a 1000:1 divider with a 1000MW input resistance. Accuracy is specified at DC & 60Hz, when used with a voltmeter having 10MW input resistance. The 80K-6 (not shown) is a smaller probe rated to 6kV DC or peak AC. It’s 1000:1 divider has a 75MW input resistance, which provides higher bandwidth (2% accuracy at 1kHz). 
This probe is also calibrated for a 10MW input meter, but a 1MW input meter can be substituted, at reduced accuracy. Both probes have an Overvoltage Category I rating, which means the probes can only be used on energy limited circuits within equipment, such as photocopy machines, not high voltages on power distribution systems.
For measuring voltages in power transmission & distribution circuits, Bierer Meters offers several products. The PD25 Phasing Voltmeter is a digital meter that measures phase-phase and phase-neutral ac voltages and dc voltages up to 25kV on overhead and underground circuits. Each probe mounts on the end of a hot stick. The meter uses a resistive divider to determine the TRMS value in 3 ranges, with 1% accuracy. 50kV and analog models are also available. The PD800W Wireless Phasing Meter (not shown) makes direct contact measurements to 69kV. Wireless communication eliminates the cable between the two probes.
The Bierer VD1000 Digital Voltage Detector measures conductor voltage to earth using a 25MW contact probe and capacitive coupling to earth ground. Maximum reading is 99.9kV on underground lines and 999kV on overhead lines. Measurement accuracy is better than 15%.
In fixed installations, a voltage transducer can convert a high voltage to a low-level process signal for connection to a panel meter, PLC or SCADA system. The NK Technologies VTU Series Transducers measure DC and AC circuit voltages to 1200 volts, and produce a DC output proportional to the input voltage. The housing can be DIN rail or panel mounted.
For AC voltages, an instrument transformer, often called a potential transformer, can be installed to reduce line voltage to a level easily measured by a panel meter. Low Voltage Instrument Transformers are commonly used to step down 240V or 480V to 120V for connecting to a panel mounted voltmeter. Although the meter may be able to read the primary voltage directly, using a transformer provides isolation and avoids routing a high energy circuit to the instrument panel. For higher voltage levels, medium voltage (MV) instrument transformers reduce the line voltage to 120V. GE PT3 Indoor Voltage Transformers (left) handle a 1-5kV primary. Models are available with or without fuses. MV outdoor units are available to 15kV (right). Digital panel meters designed for use with voltage transformers typically allow entry of transformer ratio, so the readout displays primary voltage. One example is the Weschler Power Series Plus Digital Switchboard Meters.
Non-Contact Measurements
When a precise voltage reading is not required, non-contact voltage detection is a quicker and safer way to check transmission lines, power distribution equipment, down power lines, fuses, load breaker connections, and other high voltage circuits. However, these products are more susceptible to external fields and less accurate than direct contact devices.
The Amprobe TIC 300 Pro High Voltage Detector (left) verifies the presence of ac voltages from 30 to 1500V. A flashing light and loud beeper provide the live-conductor alert. The companion TIC 410A Hot Stick extends the TIC300 range to 122kV and the reach by 57″. Also designed for use with a hot stick, the AEMC 275HVD (right) detects from 80V to 275kV in 7 ranges. The operator can make a rough estimate of voltage level by determining the distance of first detection on a range.
Many Bierer Meter products for direct contact, high voltage measurement also include non-contact capability. The VD1000P Digital Voltage Detector has the same features as the VD1000 described above, plus relative proximity voltage detection without conductor contact. The VDAO40P Analog Voltage Detector is rated 0-40kV line to ground, using proximity or direct contact. It has two ranges: 0-10kV and 0-40kV. A 5-position selector switch compensates for capacitive coupling effects on overhead and underground lines.
This article described some of the equipment available for detecting and measuring voltages above 1000V. Testing high voltage circuits requires careful selection of instrumentation for the application, a thorough understanding of the operating instructions and applicable test procedures, plus strict adherence to industry safety practices.
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