HV Tester
A high-voltage test instrument used to perform dielectric withstand and insulation breakdown tests on AGL cables, transformers, switchgear, and other electrical equipment. HV testers apply voltages up to several kilovolts to verify insulation integrity and ensure safety under overvoltage conditions.
Image disclaimer: For identification and illustration only. It may show a product by another manufacturer and may not depict the exact item described; it is not a statement of any product’s quality, approval or performance. Third-party image and trademark rights belong to their owners. See full notice.
What Is It?
An HV Tester (High Voltage Tester), also known as a dielectric strength tester or hipot tester, is an instrument that applies a high AC or DC voltage to a device under test to assess the integrity of its insulation. In AGL systems, HV testers are used to:
- Verify dielectric strength of cables, transformers, and fixtures
- Detect insulation weaknesses that could lead to breakdown during lightning strikes or switching surges
- Perform production tests on new equipment before commissioning
- Confirm repair quality after cable splicing or transformer rewinding
- Comply with safety standards by ensuring equipment can withstand transient overvoltages
HV testers are available in portable and benchtop configurations, with output voltages ranging from a few hundred volts up to 100 kV or more, depending on the application. They are essential for ensuring the long-term reliability and safety of airfield lighting systems.
Purpose & Function
The HV tester exists to answer a question a standard low-voltage test can't: will this cable, transformer, or fixture's insulation actually hold up under the high-voltage stress of a lightning strike or switching surge, not just under normal operating conditions. Insulation that performs fine at everyday voltages can still have microscopic weaknesses that only reveal themselves under the kind of transient overvoltage an airfield's exposed, outdoor lighting infrastructure will eventually experience.
By deliberately applying that higher stress in a controlled test environment, the instrument finds those latent weaknesses before they find themselves during an actual lightning event or surge in the field — which is why it's applied both to new equipment before commissioning and to repaired cables or transformers, confirming that a splice or rewind hasn't introduced a new insulation vulnerability.
Where Is It Used?
HV testers are used in various phases of AGL system lifecycle management:
- Factory Acceptance Testing (FAT): Testing newly manufactured cables, transformers, and fixtures before shipment.
- Installation Commissioning: Verifying insulation integrity after installation, especially for underground cables and transformers.
- Preventive Maintenance: Periodic high-voltage testing to detect insulation aging, moisture ingress, or mechanical damage.
- Fault Diagnosis: Identifying insulation breakdown that causes earth faults or circuit failures.
- Post-Repair Verification: Confirming that repairs have restored insulation strength.
- Type Testing: Qualifying new equipment designs to meet ICAO, FAA, and IEC requirements.
Testing is performed on de-energized circuits, with strict safety protocols including lockout/tagout, grounding, and barrier protection.
Storage & Handling
Because the instrument generates hazardous voltages, it is stored in a locked case or cabinet when not in use, with high-voltage leads and probes kept separate from other test equipment to avoid an inadvertent live connection. Before the instrument is packed away, any device under test is fully discharged and the tester's own output is confirmed at zero, since HV testers can retain a stored charge on internal capacitors after a test is complete. Leads are coiled loosely to avoid stressing the high-voltage insulation, and safety accessories such as interlocks, warning barriers, and grounding leads are stored and inventoried alongside the instrument so a complete safety setup is available for the next test. Calibration and safety interlock function are checked on the schedule set by the manufacturer, and any lead or probe showing insulation damage is taken out of service immediately rather than used until the next scheduled inspection.
How Does It Work?
An HV tester generates a high voltage (AC or DC) and applies it between the conductor(s) under test and ground (or between conductors). The tester monitors the leakage current that flows through the insulation. The test is typically performed for a specified duration (e.g., 1 minute) at a specified test voltage (e.g., 2× rated voltage + 1000V). If the leakage current exceeds a preset threshold, the tester indicates a failure (breakdown). Key operating principles include:
- Voltage Generation: A step-up transformer or voltage multiplier circuit generates the required high voltage from a low-voltage supply.
- Current Monitoring: The tester measures the leakage current and compares it to the allowable limit (typically 5-10 mA for most AGL equipment).
- Ramp-Up Control: Most testers apply the voltage gradually to avoid transient stresses and allow for accurate measurement of insulation properties.
- Automatic Discharge: After the test, the equipment automatically discharges the capacitive charge stored in the cable or device under test.
- Fail/Pass Indication: Visual and audible alarms indicate whether the test passed or failed, with detailed data logging for traceability.
AC hipot tests are common for cables, while DC hipot tests are often used for transformers and high-capacitance loads. Some advanced testers also perform partial discharge measurements to detect microscopic insulation defects.
System Architecture & Control Logic
Safety, not the voltage generator, is what drives the internal architecture of a hipot tester. The MCU commands a controlled ramp on the HV transformer or multiplier stage rather than switching full voltage on directly, both to protect the device under test from transient stress and so the current-sense circuit can watch the rising leakage current for an early sign of impending breakdown. A fast comparator continuously checks the sensed current against a pre-set trip threshold on every cycle of the ramp and, independently of the main control loop, can cut the high-voltage output within milliseconds if the threshold is exceeded — this trip path is typically hardware-latched rather than firmware-only, so a locked-up MCU cannot leave the output energised. Once the test voltage is reached and the dwell timer completes (or a trip occurs), the MCU switches from generation to a controlled discharge path that bleeds down the capacitive energy stored in the cable or device under test through a bleed resistor, and only releases the "test complete" interlock once the discharge circuit confirms the output has decayed to a safe residual voltage. The pass/fail decision and all measured values are then latched to the display and, on logging-capable models, written to memory with a timestamp.
Dielectric Withstand Test Sequence
Physical Construction
The tester's high-voltage generation stage, comprising a step-up transformer or voltage multiplier, is housed in a heavily insulated, high-dielectric-strength enclosure separated from the low-voltage control and display section by an internal barrier to protect the operator from the generated test voltage. Output terminals are recessed behind interlocked, high-voltage-rated shrouds, and a physical safety interlock disables the high-voltage output the moment an access panel or test compartment is opened. An emergency-stop button and a visible, illuminated high-voltage-present indicator are mounted prominently on the control panel, with the enclosure itself constructed from flame-retardant, impact-resistant material rated to contain internal arcing. Portable units are built into a rugged case with wheels or a carry handle and a compartment for high-voltage test leads and safety grounding equipment, while bench units use a rack- or trolley-mount chassis with forced-air ventilation to dissipate heat from sustained high-voltage testing.
Technical Parameters
| Parameter | Typical Value |
|---|---|
| Output Voltage (AC) | 0 – 5 kV, 10 kV, 20 kV, up to 100 kV |
| Output Voltage (DC) | 0 – 6 kV, 12 kV, 24 kV, up to 120 kV |
| Leakage Current Range | 0 – 20 mA (AC); 0 – 10 mA (DC) |
| Accuracy | ±2% of reading ± 2 digits (voltage & current) |
| Test Duration | 1 second to 99 minutes (programmable) |
| Ramp Time | 0.1 – 999.9 seconds (programmable) |
| Display | LCD with backlight, voltage, current, time, and status indicators |
| Data Storage | Internal memory (100+ tests) with USB/SD export |
| Power Supply | 230V AC ±10% or battery-powered (portable) |
| Protection | Overcurrent, overvoltage, and short-circuit protection |
| Safety Rating | CAT III 600V, with safety interlock and emergency stop |
| Operating Temperature | 0°C to +40°C |
| Standards Compliance | IEC 61010-1, IEC 61180, IEEE 400, EN 50191 |
Electrical Requirements
| Requirement | Typical Value |
|---|---|
| Circuit Type | Mains or battery-powered test instrument generating high test voltages — isolated from the mains input once applying test voltage |
| Power Supply | 230VAC ±10% or battery-powered (portable) |
| Test Output | Up to 100kV AC / 120kV DC (model dependent) — hazardous test output, isolated from the supply input |
| Protection | Overcurrent, overvoltage, and short-circuit protection; safety interlock and emergency stop |
| Safety Rating | CAT III 600V |
| Cable Type | High-voltage rated test leads with safety-shrouded terminations |
| Earthing/Grounding | Chassis and test-object return path bonded to a dedicated safety earth during test |
| Standards | IEC 61010-1, IEC 61180, IEEE 400, EN 50191 |
Applicable Standards
IEC 61010-1
Safety requirements for electrical test and measurement equipment
IEC 61180
High-voltage test techniques for low-voltage equipment
IEEE 400
Guide for field testing and evaluation of shielded power cable systems
EN 50191
Safety requirements for high-voltage test equipment
Setup Requirements
Storage & Access Check
Pre-UseConfirm the instrument and its high-voltage leads have come from secure storage undamaged, since abuse or unauthorised access is the main risk to this class of instrument.
Calibration Currency Check
Pre-UseConfirm the instrument's calibration certificate is current before relying on the readings.
Device Under Test De-Energisation & Discharge
Pre-UseConfirm the device under test is fully de-energised and discharged before connecting test leads.
Safety Interlock & E-Stop Check
Pre-UseTest the safety interlock and emergency-stop function before applying any test voltage.
Exclusion Zone & PPE Setup
Pre-UseEstablish an exclusion zone around the test area and confirm appropriate PPE is in place before energising the tester.
Testing & Commissioning
Safety Interlock & Emergency-Stop Function Test
AcceptanceConfirm the access-panel interlock disables high-voltage output immediately when triggered, and verify the emergency-stop button cuts output instantly.
Calibration Certificate Verification
AcceptanceConfirm the tester's calibration certificate is current before it is used for dielectric withstand or leakage current testing.
Output Voltage Accuracy Check
AcceptanceVerify the generated AC/DC output voltage against a calibrated high-voltage reference across the tester's working range.
Leakage Current Measurement Verification
AcceptanceCheck the leakage current measurement function against a known reference load to confirm accuracy before field use.
Documentation & Sign-off
AcceptanceLog the interlock test, voltage accuracy, and calibration due date against the instrument's serial number.
Inspection & Maintenance
Calibration Check
AnnualSend the tester for calibration against a traceable high-voltage standard to confirm test voltage accuracy.
Discharge Function Test
QuarterlyVerify the automatic discharge function fully dissipates capacitive charge after DC testing before each maintenance cycle.
Test Lead & Guard Terminal Inspection
QuarterlyCheck test leads and guard terminals for damage or contamination that could introduce leakage current errors.
Safety Interlock Check
QuarterlyTest safety interlocks and warning indicators to confirm they function correctly before high-voltage testing resumes.
Battery / Power Check
QuarterlyVerify internal battery or power supply condition to ensure reliable test voltage generation.
Common Field Issues
Incorrect Test Voltage Selection
Applying a test voltage higher than the equipment's rated insulation level can cause catastrophic failure. Always refer to the manufacturer's specifications or relevant standards (e.g., 2× rated voltage + 1000V for cables).
Leakage Current from Surface Contamination
Dust, moisture, or dirt on the surface of insulators or cable terminations can cause leakage currents that falsely indicate failure. Ensure test surfaces are clean and dry, and use guard terminals to eliminate surface leakage effects.
Insufficient Discharge After DC Testing
DC high-voltage tests leave a capacitive charge on the cable. Failing to discharge adequately can result in electric shock. Always use the tester's automatic discharge function and verify zero voltage before handling.
Troubleshooting Guide
Test Trips Out Immediately on Insulation That Should Be Healthy
Inconsistent Readings Between Repeat Tests
Residual Voltage or Shock Risk After a DC Test
Failure Modes & Root Causes
Incorrect Test Voltage or Surface Leakage
Surface Contamination or Environmental Variation
Incomplete Discharge After DC Test
Safety & Operational Notes
Treat as a Lethal Hazard
Electrical SafetyAn HV/hipot tester deliberately generates dangerous voltages; only trained, authorised personnel should operate it, and the test area must be barricaded and clear of unauthorised personnel before energising.
Establish a Clear Test Area
Personnel SafetyPost a second person as a safety watch where required, use warning barriers or signage, and confirm no one is in contact with the device under test before applying voltage.
Discharge and Ground After Every Test
Electrical SafetyAlways discharge and short the device under test to ground after a test, particularly after a DC hipot test, since cable and equipment capacitance can retain a dangerous charge well after the voltage source is removed.
Never Touch the DUT During or Immediately After Test
Personnel SafetyDo not touch test leads, terminals, or the device under test while voltage is applied or before confirming discharge, even if the display indicates the test has ended.
PPE for High-Voltage Testing
Personnel SafetyUse insulated gloves and tools rated for the test voltage, and follow the instrument's interlock and ramp-up/ramp-down procedures rather than bypassing them for speed.
Avoid Testing in Wet or Contaminated Conditions
OperationalDo not perform HV testing in rain, high humidity, or on visibly contaminated insulation surfaces, since surface leakage can produce a false failure or an unsafe flashover.
Restore Isolation Before Leaving Live
ComplianceRemove all test connections and confirm the circuit is restored to its normal, safe configuration before re-energising it for service.
Engineering & Expert Notes
Cable Temperature and Humidity Bias the Result on the Day
Field TechniqueInsulation resistance and dielectric withstand readings on buried cable are meaningfully affected by soil temperature and moisture on the day of the test, so a cable that passes comfortably in dry summer conditions can show a markedly different result after weeks of rain. Record ambient conditions alongside every HV test result so later trend comparisons account for this rather than mistaking weather variation for genuine degradation.
A Pass at Test Voltage Isn't a Margin Guarantee
TestingCable or transformer insulation that just barely passes a proof test at the specified voltage may have very little remaining margin, and a straight pass/fail result on its own hides how close to the edge the insulation actually is. Where the test method allows, record the actual breakdown or leakage current trend rather than only the pass/fail outcome.
Trend Test Results Year Over Year on the Same Cable Run
DiagnosticsA single HV test result tells you whether a cable passed today; a sequence of results on the same run over several maintenance cycles tells you whether it's degrading, and how fast. Insulation that's trending steadily downward toward the threshold, even while still passing, deserves closer attention than a result that's stable year to year.
Never Assume a Discharged Cable Stays Discharged
Electrical SafetyLong cable runs and cables with significant capacitance can regain a dangerous residual charge after being discharged, particularly if the discharge step was rushed. Re-verify zero charge immediately before handling conductors, even on a cable that was properly discharged minutes earlier.
Verify the Tester's Own Calibration Before a Compliance Campaign
CalibrationCommitting to a full-airfield HV test campaign on an instrument whose own calibration is close to expiring risks having to repeat significant portions of the work if a later calibration check shows the instrument had drifted. Confirm calibration currency with margin before scheduling large testing programmes, not just before individual tests.
A Marginal Pass After Splicing Work Warrants a Retest, Not a Sign-Off
QualityA repaired splice that passes an HV test but noticeably closer to the threshold than the surrounding healthy cable often indicates workmanship that will degrade faster than the rest of the run. Treat a marginal post-repair result as a prompt to inspect the splice technique, not simply a pass to close out the work order.
Frequently Asked Questions
Short answers about HV testers (hipot testers) in AGL maintenance: purpose, use, safety, standards and maintenance.
Q1What is an HV tester?
An HV (high voltage) tester, also called a dielectric strength or hipot tester, applies a high AC or DC voltage to a device under test to check the integrity of its insulation. In AGL it is used on cables, transformers and fixtures.
Q2When are HV tests done on AGL equipment?
During factory acceptance testing, installation commissioning (especially for underground cables), preventive maintenance to detect insulation ageing or moisture ingress, and fault diagnosis when insulation breakdown causes earth faults or circuit failures.
Q3How does an HV tester work?
A step-up transformer or voltage multiplier generates the test voltage, applied gradually between the conductor and ground or between conductors. The tester measures leakage current and compares it with an allowable limit, typically 5 to 10 mA for most AGL equipment.
Q4Why is it important to select the correct test voltage?
Applying a test voltage higher than the equipment's rated insulation level can itself damage the insulation. Always use the voltage specified for the equipment and the test type.
Q5Why must cables be discharged after DC high-voltage testing?
DC tests leave a capacitive charge on the cable, which can be dangerous to personnel. The tester's automatic discharge function should fully dissipate the charge before anyone touches the cable.
Q6Which standards apply to HV testers?
The main references are IEC 61010-1 (safety of test and measurement equipment), IEC 61180 (high-voltage test techniques for low-voltage equipment), IEEE 400 (field testing of shielded power cable systems) and EN 50191 (safety of high-voltage test equipment).
Q7How often should an HV tester be maintained?
Annual calibration against a traceable high-voltage standard, and quarterly checks of the discharge function and of the test leads and guard terminals.
Q8What are the common problems when using an HV tester?
Incorrect test voltage selection, leakage current from surface contamination such as dust or moisture on insulators, and insufficient discharge after DC testing.
Related Components
Go Beyond the Component. Understand the Complete AGL System.
You have explored the component. Now understand how it works within the complete Airfield Ground Lighting system.
Learn AGL from fundamentals to design, installation, testing, photometry, commissioning, maintenance and troubleshooting through structured technical training at Precision AGL Academy.
Build practical knowledge. Understand the circuit. Read the standards. Troubleshoot with confidence.
Your next step in AGL starts here.
Need expert guidance on HV tester selection or high-voltage testing procedures?
Precision AGL Academy provides advice on test voltages, safety protocols, and interpretation of test results for AGL equipment.
Follow the Academy
Important Notice, Disclaimer & Limitation of Liability
Please read before relying on any content on this page.
- Purpose and intended users. This page on HV Tester is an independent educational and informational reference for competent, suitably trained and authorised airfield ground lighting (AGL) and aerodrome electrical personnel. It is not professional engineering, legal or regulatory advice, and using it does not create any professional or client relationship.
- Safety. Work on series circuits, constant current regulators (CCRs), isolating transformers, cables, connectors and lighting equipment can be fatal. Always apply the aerodrome’s permit-to-work and isolation/LOTO procedures, prove dead, use correctly rated instruments and PPE, and follow the manufacturer’s instructions. Nothing here authorises work on live equipment or the bypassing of any safety device or interlock.
- Aviation operations. Nothing here authorises installation, modification, energisation, adjustment, return to service, a change of operating category (CAT I/II/III), a NOTAM or any aerodrome certification or approval decision. These rest with the aerodrome operator, the air navigation service provider and the competent regulator.
- Specifications, ratings and typical values. Descriptions, parameters, ratings, dimensions, photometric values, wattages, service lives, maintenance tasks and intervals, failure modes, certifications (for example CE, FCC, UL or IEC marks) and part or type designations are general, typical and indicative. They may not match any particular product, make, model or version, and they are not a datasheet, design, specification, selection, sizing, procurement or acceptance criterion. The manufacturer’s current documents, the approved design and the project specification prevail.
- Standards and regulations. References to ICAO, FAA, IEC, IEEE, ISO, BIS, DGCA and other standards are paraphrased summaries for orientation only. They may be incomplete or out of date, and standards are revised from time to time. Consult the current official editions. Following this content does not guarantee compliance with any law, standard or regulatory approval, and the regulator’s requirements always prevail.
- No warranty. Content is provided “as is” and “as available”, without warranty of any kind, express or implied, including accuracy, completeness, currency or fitness for a particular purpose. Real installations differ in design, equipment make and model, age and condition.
- Limitation of liability. To the fullest extent permitted by applicable law, Precision AGL Academy, Precision AGL Solutions and their owners, authors and contributors are not liable for any injury, death, loss, damage, downtime, penalty or regulatory consequence, whether direct or indirect, arising from the use of, reliance on, or inability to use this content. Nothing in this notice excludes or limits any liability that cannot lawfully be excluded or limited.
- Independence, brands and no endorsement. This is an independent publication. It is not affiliated with, sponsored by or endorsed by ICAO, the FAA, the IEC, DGCA, AAI, any airport, regulator, supplier or equipment manufacturer. Third-party names, product designations, standard designations and trademarks (including Megger®, Siemens, Eaton, Crouse-Hinds, ADB SAFEGATE, Fluke, ABB and Honeywell) belong to their respective owners and are used only for identification and description. Mention of a brand, product or supplier is not a recommendation, and we do not sell, supply or quote for any component described.
- Images and third-party content. Images and illustrations are shown to help identify the type of component. They may show products of various manufacturers, may not depict the exact item described, and are not a statement about any product’s quality, approval or performance. Copyright and trademarks in third-party images, logos and photographs belong to their respective owners and are not claimed as ours. If you are a rights holder and want an image removed, replaced or credited, email precisionaglsolutions@gmail.com with the page address and we will act promptly.
- Training and services. Mentions of training, courses, consultation, advice, selection, installation, calibration or other support, including the “Learn…Certify” pathway, describe learning stages and are not an offer, quotation, tender or promise of any result. Contacting us or our replying creates no engagement or duty of care; an engagement exists only under a written agreement. We are not a regulator or certification body, and completing any course or reading this content is not a certification, accreditation or authorisation to work on any aerodrome.
- Copyright, privacy and corrections. © 2026 Precision AGL Academy. All rights reserved. Text, structure, compilations and diagrams may be viewed for personal reference and internal training only; any other copying, republication or commercial use needs our written permission. If you email, telephone or message us, we use your details only to respond and handle your matter, in line with applicable Indian law including the Digital Personal Data Protection Act, 2023; please do not send confidential or security-sensitive information. To display this page your browser requests fonts, icons and images from third-party servers, which receive your IP address and browser details under their own policies. Content is reviewed periodically with no obligation to update. To report an error, safety concern or rights issue, write to precisionaglsolutions@gmail.com.