Indian Railways employs various equipment in PSI & OHE to keep the 25kV AC single-phase, 50Hz traction supply system working efficiently. Significant numbers of PSI & OHE failures are due to component failure and lack of maintenance from non-availability of power block — modern condition-based maintenance (CBM) instruments are intended to reduce maintenance time, improve quality of work with least block time, and improve system reliability and availability.
- Reduction of un-planned outage.
- Predictable maintenance schedule.
- Prevention of costly failure.
- Minimize the severity of damages.
- Increase the system stability.
- Helps to plan future renovation.
- Use of equipment for maximum economical efficiency.
The full range of equipment monitored under this CBM programme: Transformers, Circuit Breakers/Interrupters, Current Transformers, Surge Arresters, Relays, Electrical connections, Earth pits, Batteries, Cables, Machines, Contact wire, and Insulators.
Why Monitor Each Parameter — The Educational Rationale
- Winding Resistance: DC resistance measurement verifies manufacturer test readings, checks winding health during regular maintenance, and locates defects such as loose connections/open circuits.
- Winding Insulation Resistance: predicts insulation failure between winding-to-core (earth), winding-to-winding, and of bushings/internal connections.
- Capacitance & Tan Delta: Tan Delta gives the TRUE picture of insulation health, revealing contamination, fracture, or puncture from manufacturing defects, plus field ageing effects.
- Transformer Turn Ratio & Phase Angle Deviation: HV-to-LV winding turns ratio, plus the phase relationship between applied and extracted voltage signals — used as a low-cost method to accurately verify PT/CT class at zero burden.
- DGA (Dissolved Gas Analysis) of Transformer Oil: thermal/electrical stresses from short circuits, overloads, and over-voltages produce dissolved gases in oil — DGA detects growing faults not always revealed by established routine tests.
- Oil Break Down Voltage: reveals extent of physical pollution by water/suspended matter, predicting the need for drying-out/filtration treatment.
Transformer Winding Resistance Meter
- Application: measures winding resistance of transformers, inductors, generators, motors, tap changers.
- Test current ranges: 10A, 5A, 1A, 0.1A DC. Resistance range: 1 milli-ohm to 199.99 ohms. Accuracy: ±0.5% (1-1999 µΩ), ±1.0% (20-999 mΩ), ±1.5% (1-200Ω) — accuracy tiers roughly match measurement range order of magnitude.
- Open circuit voltage: 30V DC. Operating temperature: -10°C to 50°C. Built-in discharge circuit safely discharges the specimen if leads are accidentally disconnected or power is lost — a real safety feature.
Winding Insulation Resistance Meter
- Application: measures IR of transformer winding, CTs, PTs, bushings, cables, motor windings.
- Test voltage: 500V to 5000V DC. IR range: 0-5 TΩ (tera-ohms). Short-circuit current limited to <2mA for user safety. Accuracy per IS 2992.
- LED-based visual indication for discharge condition — glows after HT switch-off until the test object voltage drops below ~50V, warning against premature handling.
- Also provides Polarization Index and Dielectric Absorption Ratio, plus internal discharge of the test object and memory/PC data transfer capability.
Capacitance & Tan Delta Test Kit
| Parameter | Range | Accuracy |
|---|---|---|
| Capacitance | 1 pF – 1.1 µF (up to 2.6 µF with extension CT) | ±0.2% of reading ±1pF |
| Tan Delta | 0% – 100% (infinity) | ±1% of reading ±0.05% |
| Voltage measurement | 0 – 12 kV | ±1%, ±1 digit |
| Current measurement | 0 – 2000 mA | ±1%, ±1 digit |
| Power factor | 0.01% – 100% | ±1.0% of reading ±0.05% |
Suitable for testing transformers, bushings, cables, insulators, switchgear, rotating machines, capacitors, and lightning arresters. Notably suitable for extraneous conditions in a 400kV switch yard under heavy induction — measurement can be taken at line frequency OR a fixed generated frequency, so output frequency stays independent of input frequency changes. Provides auto-balancing measurement and data logging with graph of voltage vs Tan Delta.
Transformer Turn Ratio Meter
| Ratio Range | Resolution | Accuracy |
|---|---|---|
| 1 – 9.999 (ratio 10) | 0.001 | ±0.2% for ratio 5 to 1000 |
| 10 – 99.99 (ratio 100) | 0.01 | ±0.2% for ratio 5 to 1000 |
| 100 – 999.9 (ratio 1000) | 0.1 | ±1.5% for ratio beyond 1000 |
| 1000 – 10000 (ratio 10000) | 1 | ±1.5% for ratio beyond 1000 |
| 10000 – 14000 (ratio 14000) | 1 | ±1.5% for ratio beyond 1000 |
Microprocessor-based, for automatic measurement of voltage/turn ratio, current, and phase displacement of power transformers, CTs, and PTs. Test voltage: 4.8V, 48V AC, or 110V AC on request. Fully protected against wrong connections, remote controllable, works in the presence of high interference/high voltage. Quickly indicates partial shorted turns and core faults from phase deviation of primary vs. secondary.
Transformer Oil Multiple Gas Extraction System (DGA)
- Method: sampling, extraction, and analysis of incipient fault gases at PPM levels from a small transformer oil sample, per ASTM 3612 and IEC 567.
- Direct-drive rotary vacuum pump, displacement capacity 250 litre/min, particle discharge pressure 5×10⁻⁴ m bar. Digital Pirani gauge, range 0.999 to 0.001 m bar. Gas extractor holds vacuum of 0.1 m bar with MINIMUM 97% GAS EXTRACTION EFFICIENCY (some models exceed 98%).
M2 Fault Gas & Moisture Monitor (HYDRAN)
- A COMBINED, permanently-installed early-warning device — two products in one: a fault monitor reading composite gas value in PPM (H2, CO, C2H2/acetylene, C2H4/ethylene), and a moisture-level sensor detecting bubbling risk, temperature, and insulation ageing rate.
- Measurement range: moisture 0-100% RH (accuracy ±2% RH), gas 0-2000 ppm (accuracy ±10% reading ±25 ppm). Response time: moisture 5 minutes, gas 10 minutes (both at 90% of step change).
- Requires only a SINGLE VALVE for both fault gas and moisture monitoring — installed with no additional oil lines, no pumps or moving parts, for maximum long-term reliability.
Oil Tan Delta Test Kit
- Tests dielectric dissipation factor and resistivity of oil. Test voltage: adjustable 0-3000V AC, accuracy ±1.0%. Test frequency: 50Hz.
- Dielectric constant range 1.0-13.0 (accuracy ±0.2%±0.001), Dielectric Tan Delta range 10⁻⁵ to 10 (accuracy ±1%±0.3% full scale). Resistance range 10⁶-10¹² Ω, Resistivity range 10⁹-10¹⁵ Ω-cm.
- Oil test cell: 3-terminal configuration, stainless steel with Teflon spacers, 2mm electrode spacing, 55pF±1pF cell capacitance, 45ml volume — heated, adjustable 20°C (room) to 150°C (accuracy ±0.5%).
Automatic Oil Break Down Voltage (BDV) Tester
- Determines dielectric strength of insulating oils in transformers, switchgear, other electrical apparatus. Voltage range: 0-100kV AC. Trip current: 10mA, shut-down sensitivity 5mA, shut-down time <20 milliseconds.
- Fully automatic microprocessor control: adjustable stand time, stir time, rate of voltage rise (0.005-5.0 kV, adjustable), and test count per selected standard. Oil test cell: transparent acrylic, 36mm removable mushroom-head electrodes, gap gauge 2.5mm.
- Safety: interlock on HV test chamber, zero-start protection, double ground protection, overload/short-circuit protection.
Sweep Frequency Response Analyser (SFRA)
Detects internal MECHANICAL displacements without extended downtime — problems it can identify include: winding deformations/displacements, shorted turn/open winding, loosened or broken clamping structure, core connection problems, partial winding collapse, faulty core ground, core movements, and hoop buckling.
- Method: sweep frequency. Frequency range: 0.1Hz – 25MHz, user-selectable. Default 1046 points (user-selectable up to 32,000). Default measurement time 64s (fast setting 37s for 20Hz-2MHz). Accuracy: ±0.3dB down to -105dB (10Hz-10MHz).
- The measurement is easy to perform and captures a unique 'FINGERPRINT' of the transformer, compared against a reference fingerprint — DEVIATIONS indicate geometrical/electrical changes within the transformer. PC communication via Bluetooth and USB.