METHOD STATEMENT
Offline Partial Discharge Measurement of 11 kV Switchgear Using UTP-2 (TEV &
Ultrasonic) with External HV Kit
1. PURPOSE
To define the procedure for performing offline partial discharge (PD) measurement on 11
kV switchgear panels by applying 11 kV test voltage using an external HV test kit, while
monitoring PD activity using the UTP-2 PD detection kit (TEV & Ultrasonic).
2. SCOPE
This method applies to:
•
Offline PD testing of 11 kV metal-clad switchgear
•
Pre-commissioning, post-maintenance, or diagnostic inspection
•
Application of HV test voltage using external HV test kit
•
PD detection using TEV and Ultrasonic methods
3. REFERENCES / STANDARDS
•
IEC 60270 – Partial Discharge Measurement
•
IEC 62271 – 200 High-voltage switchgear
•
UTP-2 PD Kit Manufacturer Manual
•
HV Test Kit Manufacturer Manual
•
Site Electrical Safety Regulations
4. DEFINITIONS
•
PD: Partial Discharge
•
Offline PD: PD testing with equipment isolated from service
•
TEV: Transient Earth Voltage
•
UTP-2: PD detector using TEV & Ultrasonic methods
5. RESPONSIBILITIES
•
HV Testing Engineer: Apply HV and monitor PD using UTP-2
•
Authorized Electrical Person: Isolation, earthing, PTW
•
Safety Officer: HSE compliance
•
Client/Consultant: Witness testing (if required)
6. TEST EQUIPMENT
•
External AC HV Test Kit (0–15 kV)
•
UTP-2 PD Detection Kit (TEV & Ultrasonic sensors, headphones)
•
HV cables and connectors
•
Earthing leads and discharge rods
•
PPE (arc-rated clothing, gloves, helmet, shoes)
7. SAFETY PRECAUTIONS
•
PTW mandatory
•
Switchgear fully isolated from supply
•
Lock-Out / Tag-Out (LOTO) applied
•
Non-tested phases earthed
•
Barricade area with warning signage
•
No personnel inside danger zone during HV application
•
HV emergency stop verified
8. PRE-CONDITIONS
•
Circuit breakers racked out
•
Busbar and cable compartments isolated
•
External cables disconnected or earthed
•
Visual inspection completed
•
Environmental conditions recorded
•
Test setup approved by client
9. VT & CT CONDITION DURING TEST
Voltage Transformers (VTs):
•
VT primary is disconnected automatically when the breaker is racked out.
•
VT secondary circuits are shorted and earthed.
•
VT compartment remains closed and earthed.
•
No HV voltage is applied to VT primary during testing.
Current Transformers (CTs):
•
CT primaries isolated due to racked-out breaker
•
CT secondary circuits shorted and earthed
•
Protection relays and meters isolated
•
No HV voltage is applied to CT secondary
Verification Prior to HV Application:
•
Confirm VT primary isolation due to breaker racking
•
Confirm CT secondary shorting and earthing
•
Confirm earthing of all non-tested components
Rationale:
•
Protects VT and CT from HV stress
•
Ensures PD readings are not influenced by connected metering/protection circuits
•
Maintains personnel and equipment safety
10. TEST METHODOLOGY
10.1 Test Circuit Arrangement
•
Connect HV output of external HV kit to the phase under test
•
All other phases and metallic parts solidly earthed
•
Ground HV kit and switchgear properly
•
Verify correct polarity and connections
10.2 PD Detection Setup (UTP-2)
•
TEV sensor placed on panel earth bars, doors, and metal surfaces
•
Ultrasonic probes positioned at cable terminations, panel joints, and vents
•
Background noise recorded before HV application
10.3 Voltage Application
1. Confirm VT is in racked-out position and CT secondaries shorted & earthed.
2. Gradually increase test voltage from 0 kV to 11 kV using the external HV kit.
3. Hold voltage for the specified duration (e.g., 5–10 minutes).
4. Continuously monitor PD activity using UTP-2 TEV and Ultrasonic sensors.
5. Observe PD inception/extinction behavior and record readings.
6. Repeat test for each phase individually.
Notes:
•
Only the tested phase is subjected to HV; all other phases and metallic parts are
solidly earthed.
•
The VT being in the racked-out position ensures safe isolation from applied HV
voltage.
10.4 Result Interpretation (Guideline)
TEV (dBµV):
TEV Level
Condition
<20 dBµV
Normal
20–29 dBµV Low PD
30–39 dBµV Moderate PD
≥40 dBµV
Severe PD
Ultrasonic (dB):
Level
Condition
<20 dB
Normal
20–29 dB Low
30–39 dB Moderate
≥40 dB
Severe
10.5 Noise Discrimination
•
Compare readings with HV ON and HV OFF
•
Verify repeatability
•
Correlate TEV and Ultrasonic readings
•
Eliminate external interference
11. POST-TEST ACTIVITIES
•
Reduce HV to zero
•
Discharge the test object and apply earthing
•
Remove test connections
•
Restore breaker to normal or test position as per procedure
12. REPORTING
•
Switchgear identification
•
Test voltage and duration
•
TEV & Ultrasonic readings per phase
•
PD severity assessment
•
Photographs/screenshots
•
Observations and recommendations
13. LIMITATIONS
•
TEV & Ultrasonic provide qualitative PD assessment
•
Results used for condition assessment only
14. CONCLUSION
Offline PD testing of 11 kV switchgear using an external HV kit combined with UTP-2 TEV &
Ultrasonic monitoring provides an effective diagnostic approach to identify insulation
defects and potential risks prior to re-energization. The VT in rack-out position and CT
secondary earthing ensures safe application of HV during the test.