HVDC Test System
Precision Instrument Transformers: CTs & PTs for Grid Monitoring & Protection
*IEC 61869 / IEEE C57.13 Compliant | 69kV–800kV | Metering & Protection Grades*
Core Functions
| Type | Function | Critical Applications |
|---|---|---|
| CT (Current Transformer) | Steps down high current (kA) to standardized outputs (1A/5A) | Relay protection, energy metering, fault recording |
| PT (Potential Transformer) | Steps down high voltage (kV) to standardized outputs (110V/120V) | Synchronization, voltage regulation, revenue metering |
Technical Specifications
Current Transformers (CTs)
| Parameter | Metering CT | Protection CT | Transient Performance CT |
|---|---|---|---|
| Accuracy Class | 0.2S, 0.5S (IEC 61869-2) | 5P, 10P (IEC 60044-1) | TPX, TPY (IEC 61869-6) |
| Burden | ≤5 VA | 15–30 VA | Dynamic burden compensation |
| Rated Primary | 100A–6000A | 300A–63kA | Up to 80kA (fault current) |
| Rated Short-Time Current | - | 10–50 kA/1s or 3s | 63kA/120ms (C&O cycles) |
| Core Material | Nanocrystalline | Grain-oriented silicon steel | Hybrid amorphous/silicon |
Voltage Transformers (PTs)
| Type | Electromagnetic PT | Capacitive VT (CVT) | GIS Integrated |
|---|---|---|---|
| Voltage Range | 72.5kV–245kV | 123kV–800kV | 72.5kV–550kV (SF6 insulated) |
| Accuracy Class | 0.1, 0.2 (IEC 61869-3) | 0.2, 0.5 | 0.2S |
| Frequency Range | 15–100Hz | 15–150Hz (harmonics) | DC–500Hz |
| Dielectric Medium | Oil/SF6 | Oil-impregnated paper | SF6 gas |
| Resonance Control | Ferro-resonance suppression | Damping filters | Active electronic damping |
Critical Design Features
CT Innovations
✅ Anti-Saturation Core Design
Transient-tolerant cores for fault currents >40kA
Remanence <10% (TPY class)
✅ Hybrid Insulation SystemsRIP (Resin-Impregnated Paper) for 245kV+
Silicone composite sheds for coastal pollution
✅ Optical Sensing OptionsRogowski coils (0.2% accuracy)
Faraday effect sensors (345kV+)
PT/CVT Advancements
✅ Zero-Ferroresonance Circuits
Active damping for grid switching transients
✅ HVDC-Ready CVTsDC-bias tolerant up to ±1200kV
✅ Seismic ResilienceIEC 60255-21-3 compliance (Zone 4 seismic)
Application Matrix
| Grid Segment | Recommended CT | Recommended PT | Key Standard |
|---|---|---|---|
| Distribution (≤36kV) | Low-Burden 0.5S Metering CTs | Dry-Type Electromagnetic PT | IEEE C57.13.6 |
| Transmission (110–500kV) | TPY Protection CTs | CVT with Harmonics Filter | IEC 61869-5 |
| HVDC Stations | Optical DCCTs (0.1%) | Resistive DC Dividers | IEC 61869-11 |
| Renewables | Dual-core (Metering+Protection) | Wideband RIP PTs (15–150Hz) | IEC 60044-8 |
Compliance & Testing
Type Tests:
• Power frequency withstand (IEC 60060-1)
• Lightning impulse (1.2/50μs) & chopped wave
• Temperature rise (IEC 60076-2)Routine Tests:
• Ratio/polarity verification
• Burden accuracy validation
• Partial discharge <5pC @ 1.2Ur
