Specifying China both sides grounding test on GIS factory for Wholesale and OEM Orders
Design Constraints Behind the Specification
| Parameter | Standard Range | Customisation Window | Approval Gate |
|---|---|---|---|
| Test voltage (AC withstand) | 50–420 kV rms / 1 min | ±5 % per IEC 62271-203 | Witness test protocol signed |
| Grounding switch rating | 40 kA / 3 s (peak 100 kA) | Up to 63 kA on request | Type test report review |
| Partial discharge sensitivity | ≤5 pC at 1.2 × Ur/√3 | ≤3 pC with shielded cage | Calibration certificate |
| SF6 dew point limit | ≤−36 °C (≤50 ppmv) | ≤−42 °C for coastal sites | Gas analysis log |
| Grounding resistance target | ≤0.5 Ω per bay | ≤0.2 Ω for 500 kV class | Micro-ohmmeter trace |
Most quality disputes start with a consistency gap between the test procedure the buyer approved on paper and the one the factory actually runs. A both-sides grounding test on GIS demands that each disconnecting module — line side and bus side — be earthed simultaneously before any dielectric stress is applied. The factory must demonstrate that the earthing switches close within 150 ms of the command signal, that the grounding circuit resistance stays below the agreed threshold across all three phases, and that no induced voltage from adjacent energised bays exceeds 50 V at the test point. If the test trailer's grounding mat impedance drifts above 1 Ω after rain, the whole sequence invalidates.
Specification lock point: The test procedure document (TPD) must be frozen at least 15 working days before the first unit ships. Any change after that — test voltage step, dwell time, PD background threshold — triggers a new first-article inspection and resets the delivery clock. Buyers who treat the TPD as a living document end up with split batches and contested warranty claims.
Specification Range and Customisation Limits
The test envelope is defined by the GIS voltage class, the earthing switch short-time withstand rating, and the site's seismic category. A 145 kV factory test typically runs at 275 kV AC withstand for 60 s with PD measured at 176 kV. For 245 kV the numbers shift to 460 kV / 282 kV. The customisation window is narrow: you can request a 10 % longer dwell time or a 2 pC tighter PD limit, but the factory will need a revised type-test reference and an extra calibration day on the high-voltage divider. Anything beyond that moves into a special-test quotation with a new witness-test schedule.
Standard factory package
- AC withstand at 1.1 × Ur / √3 for 60 s
- PD measurement at 1.2 × Ur / √3, ≤5 pC
- Both-sides grounding resistance ≤0.5 Ω
- Mechanical operation: 5 open/close cycles
- SF6 density and dew point check
Extended validation package
- Lightning impulse withstand (1.2/50 µs)
- PD trend logging over 30 min at rated voltage
- Grounding switch making-current test (2.5 × Ima)
- Seismic shake-table qualification report
- Thermal cycle: −40 °C to +55 °C, 5 cycles
Returns usually trace back to the same weak point: the buyer specified "both sides grounding test" in the PO but left the earthing switch rating, the test trailer grounding impedance, and the PD background level undefined. The factory then quotes the cheapest compliant configuration — often a 31.5 kA earthing switch on a 40 kA system — and the test passes on paper but fails the first site commissioning when induced voltage from the adjacent bay trips the protection relay.
How to Choose Before Requesting a Quote
| Decision Factor | Standard Test | Extended Validation | Lead-time Impact |
|---|---|---|---|
| Voltage class ≤145 kV | Default choice | Only if PD history shows defects | +0 days |
| Voltage class 245–420 kV | Minimum viable | Recommended for new designs | +3–5 days |
| Coastal / high-pollution site | Add salt-fog pre-condition | Add thermal cycle + PD trend | +7 days |
| Seismic zone 3–4 | Not covered | Mandatory shake-table | +14 days |
| Repeat order, proven design | Acceptable with prior TPD | Unnecessary cost | +0 days |
Wear shows up at the same point every season: the earthing switch contact fingers. After 2,000 operations the silver-plated tips develop micro-pitting that raises contact resistance from 20 µΩ to 120 µΩ. The factory test catches this only if the grounding resistance measurement uses a 100 A DC micro-ohmmeter with four-wire Kelvin leads — not the 10 A handheld meter some lines still keep. Specify the test current and lead configuration in the TPD or the data is meaningless.
Buying Mistakes That Lead to Returns
The most expensive mistake is accepting a factory test report that shows "PASS" without verifying the test conditions. A 145 kV GIS bay tested at 275 kV AC withstand with a PD background of 15 pC will pass the 5 pC limit on paper because the factory subtracts the background. But the same bay at site, with cleaner power, might show 8 pC genuine discharge — a fail. Insist on the raw PD waveforms and the background measurement protocol before you sign the release.
- Ordering the test without confirming the earthing switch short-time rating matches the system fault level
- Skipping the induced-voltage check on the non-tested bay during both-sides grounding
- Accepting a grounding resistance value measured at the switch terminals instead of at the test trailer connection point
- Allowing the factory to reuse the previous project's TPD without a formal deviation review
- Not requiring the SF6 gas analysis certificate from the same batch used in the test
A second pattern: the buyer approves a test voltage based on the rated voltage Ur but the GIS nameplate shows a higher maximum operating voltage Um. The test at 1.1 × Ur / √3 under-stresses the insulation by 10–15 %. The factory will not flag this unless the TPD explicitly references Um. By the time the discrepancy surfaces during site commissioning, the units are installed and the re-test requires a full SF6 evacuation.
What Gets Checked Before Shipment
Every bay that leaves the factory after a both-sides grounding test carries a shipment hold-point checklist. The inspector verifies: earthing switch position indicators show "CLOSED" on both line and bus sides; grounding circuit resistance reads ≤0.5 Ω on all three phases with the 100 A micro-ohmmeter; PD baseline at 1.2 × Ur/√3 is ≤5 pC with the raw waveform saved; SF6 density monitor reads within the green band at 20 °C reference; dew point is ≤−36 °C; all interlock keys are present and the key-exchange sequence operates mechanically; the test trailer grounding mat resistance is ≤1 Ω measured with a fall-of-potential tester. Any single fail stops the shipment.
Witness-test protocol: The buyer's representative must be on-site for the first article of each voltage class. Remote video witness is accepted only if the factory provides a live feed of the PD oscilloscope, the high-voltage divider readout, and the micro-ohmmeter display simultaneously. Recorded video without live data overlay is not a valid witness.
Packing, Marking and Freight Configuration
GIS bays tested under both-sides grounding leave the factory pressurised to 0.05–0.1 MPa gauge with SF6 (or the specified gas mixture). Each bay ships on a dedicated air-ride trailer with shock indicators set at 3 g. The earthing switches are locked in the CLOSED position with tamper-evident seals; the lock numbers are recorded on the packing list. Lifting points are marked with 50 mm yellow bands and the centre-of-gravity offset is stencilled within 100 mm of the actual CG. A gas-tight transit cover protects the bushings; the cover carries a humidity indicator card that must show <30 % RH on arrival.
- Each bay: individual crate, IP55 rated, desiccant charge per IEC 62271-1 Annex C
- Marking: voltage class, bay serial, test report number, gas type/pressure, lift points, CG
- Shock loggers: two per bay (vertical + lateral), data download at destination
- Loose items box: interlock keys, gas density monitor calibration cert, PD waveforms USB
- Freight terms: DDP to named substation gate unless EXW agreed in writing
Setup, Use and Replacement Parts
At site, the both-sides grounding test is not repeated — the factory test is the reference. Commissioning crews verify the earthing switch operation locally (five open/close cycles at rated voltage) and re-measure grounding resistance at the bay terminal pads. If the resistance exceeds 0.5 Ω, investigate the joint between the factory grounding strap and the site earth mat before touching the GIS. The earthing switch contact fingers are the only wear part; keep one complete set per three bays in the site store. Replacement requires SF6 evacuation of the affected compartment — plan a 4-hour outage window. The operating mechanism lubricant (Molykote 33 Medium or equivalent) is refreshed every 5 years or 500 operations, whichever comes first.
Serviceability note: The grounding switch shaft seal is a double-lip Viton design rated for 20 years at −40 °C to +55 °C. If the factory test shows dew point creeping above −30 °C within 12 months, the seal is the first suspect. Do not top up gas without a leak-rate calculation — IEC 62271-1 limits annual leakage to <0.1 % per gas compartment.
Packing, Marking and Freight Configuration
GIS bays tested under both-sides grounding leave the factory pressurised to 0.05–0.1 MPa gauge with SF6 (or the specified gas mixture). Each bay ships on a dedicated air-ride trailer with shock indicators set at 3 g. The earthing switches are locked in the CLOSED position with tamper-evident seals; the lock numbers are recorded on the packing list. Lifting points are marked with 50 mm yellow bands and the centre-of-gravity offset is stencilled within 100 mm of the actual CG. A gas-tight transit cover protects the bushings; the cover carries a humidity indicator card that must show <30 % RH on arrival.
- Each bay: individual crate, IP55 rated, desiccant charge per IEC 62271-1 Annex C
- Marking: voltage class, bay serial, test report number, gas type/pressure, lift points, CG
- Shock loggers: two per bay (vertical + lateral), data download at destination
- Loose items box: interlock keys, gas density monitor calibration cert, PD waveforms USB
- Freight terms: DDP to named substation gate unless EXW agreed in writing
Setup, Use and Replacement Parts
At site, the both-sides grounding test is not repeated — the factory test is the reference. Commissioning crews verify the earthing switch operation locally (five open/close cycles at rated voltage) and re-measure grounding resistance at the bay terminal pads. If the resistance exceeds 0.5 Ω, investigate the joint between the factory grounding strap and the site earth mat before touching the GIS. The earthing switch contact fingers are the only wear part; keep one complete set per three bays in the site store. Replacement requires SF6 evacuation of the affected compartment — plan a 4-hour outage window. The operating mechanism lubricant (Molykote 33 Medium or equivalent) is refreshed every 5 years or 500 operations, whichever comes first.
Serviceability note: The grounding switch shaft seal is a double-lip Viton design rated for 20 years at −40 °C to +55 °C. If the factory test shows dew point creeping above −30 °C within 12 months, the seal is the first suspect. Do not top up gas without a leak-rate calculation — IEC 62271-1 limits annual leakage to <0.1 % per gas compartment.
Ready to lock the test procedure?
Send us the single-line diagram, the GIS nameplate data, and your site fault-level study. We return a draft TPD with hold-points, witness-test dates, and a fixed-price quotation within 3 working days.
Request TPD Review & Quotation
