Low-Power Voltage Transformers (LPVT / ePT)

Voltage sensing without ferroresonance or core polarization.

A low-power voltage transformer (LPVT) replaces the wound inductive VT with a divider-based sensor. The inductive VT's two classic failure modes go with it: ferroresonance against network capacitance, and core polarization after a switching event. The output is a conventional 115/√3 V or 115 V signal, so the relay, meter and SCADA gateway downstream do not need to change.

The measuring range holds from 10% to 190% of rated voltage, which is what lets one sensor serve revenue metering, protection and power quality at the same point instead of three separate devices. Burden is 0.1 VA, with amplified versions available, and accuracy is offered in 0.2%, 0.3% and 3% classes. The secondary is intrinsically limited to 180 V. Ratings cover 17.5, 24 and 36 kV maximum voltage (15, 25 and 38 kV classes) at 34 / 50 / 70 kV power-frequency withstand and 95 / 125 / 170 kV BIL.

Why it matters

• Ferroresonance stops being a design risk. There is no core to enter the nonlinear region, so you do not need damping resistors or a study to prove the network will not oscillate.

• One sensor covers three jobs. Linearity from 10% to 190% of rated voltage means metering, protection and power quality read from the same point.

• 0.1 VA burden ends the burden argument. Panel design and cable sizing stop being driven by the VT's VA demand.

• An open secondary is safe, and the intrinsic 180 V limit keeps a fault on the secondary side from propagating into the relay.

• Compact and light, so a 36 kV sensing point fits inside a cubicle that could not take a wound VT.

Ratings

• Maximum voltage: 17.5 / 24 / 36 kV

• Power-frequency withstand: 34 / 50 / 70 kV

• BIL: 95 / 125 / 170 kV

• Secondary output: 115/√3 V or 115 V

• Burden: 0.1 VA (amplified versions available)

• Accuracy classes: 0.2% · 0.3% · 3%

• Measuring range: Consistent from 10% to 190% of rated voltage

• Secondary protection: Intrinsic limit at 180 V

• Frequency: 60 Hz (50 Hz available)

Standards

• IEC 61869-11

• IEC 60529

• EMC per IEC 61000 series

Applications

• Digital MV switchgear

• Ring main units and compact substations

• Power quality monitoring points

• Ferroresonance-prone networks

Questions engineers ask

Why does an LPVT not suffer from ferroresonance?Ferroresonance needs a saturable iron core resonating against network capacitance, typically after a switching operation on an ungrounded or lightly damped system. An LPVT senses voltage through a divider rather than a wound core, so the nonlinear inductance that sustains the oscillation is not present. No damping resistor or ferroresonance study is required.

Can one LPVT feed metering, protection and power quality at the same time?Yes. The measuring range is consistent from 10% to 190% of rated voltage, so a single sensor stays accurate at the low end for metering and does not clip during overvoltage events that protection and power quality analysis care about. Choose the 0.2%, 0.3% or 3% class against the most demanding function on that point.

Technical documentation

Download HVEX / Brasformer Low-Power Voltage Transformer (ePT) datasheet (English, PDF)