Power And Distribution Transformer Operation Regulations

Core Operational & Compliance Foundations

Protection, Measurement & Cooling Systems

Mandatory Device Requirements

• Equip transformers with protection and measurement devices that meet industry standards. For oil-immersed models, safety protection systems, cooling units, oil protection components, temperature gauges, tanks, and accessories must comply with GB6451. Dry-type transformers should adhere to their respective technical specifications.
• If using fuses for protection: Ensure the fuse’s performance matches the system’s short-circuit capacity, sensitivity, and selectivity. For transformers with graded insulation, the neutral point must be directly grounded.

Gas Relay Installation (Oil-Immersed Transformers)

• If the transformer’s top cover lacks a natural slope, install it with a 1%–1.5% incline toward the gas relay to ensure proper gas collection and reliable operation.

Cooling System Specifications

• Install all cooling components per the manufacturer’s instructions.
• For forced oil circulation systems: Equip two independent power sources with automatic switching. Trigger audible and visual alarms if the primary power fails, and activate the backup supply immediately.
• When a faulty cooler is isolated, trigger alarms and automatically (or manually, for water-cooled systems) start standby coolers.
• Protect fan, water pump, and oil pump motors against overload, short circuits, and phase loss. Add monitors to verify oil pump rotation direction.
• Mount water cooler oil pumps on the cooler’s oil inlet side. Maintain oil pressure 0.05MPa higher than water pressure (unless specified otherwise by the manufacturer) and install a drain cock on the water outlet.
• For forced oil-water cooled transformers: Add check valves to each cooler’s submersible oil pump outlet.
• Enable cooler switching based on temperature and/or load for forced oil circulation transformers.

Temperature Measuring Devices

• Install top-oil thermometers (pole-mounted transformers are exempt). Unattended substations require thermometers that indicate peak top-oil temperature.
• Connect signal thermometers to remote monitoring for: Oil-immersed transformers ≥1000kVA, oil-immersed transformers ≥800kVA (specific applications), and dry-type factory transformers ≥630kVA.
• Equip transformers ≥8000kVA with remote temperature measurement systems.
• Add temperature gauges at cooler inlets and outlets for forced oil-water cooled models.
• Fill thermometer tube bases with transformer oil for accurate readings.
• Install temperature measuring devices on dry-type transformers as specified by the manufacturer.

Unattended Substation Special Requirements

• For transformers ≥20000kVA: Install remote monitors for load current and top-oil temperature.
• For forced oil circulation transformers in unattended sites: Implement reliable measures to prevent overheating if the cooling system loses power (document these in on-site protocols).

Additional Operational Requirements

Physical & Safety Infrastructure

• Equip large and medium-sized transformers with temporary lifting facilities and adequate workspace for maintenance.
• Position pressure relief devices to ensure unobstructed oil discharge—avoid directing spray toward cable trenches, busbars, or other equipment. Use shields if necessary.
• Attach nameplates with operation numbers and phase marks. Number transformers in rooms, platforms, or poles, and post warning signs.

Accessibility & Monitoring

• Design installations to allow safe inspection of oil conservator/bushing oil levels, top-oil temperature, gas relays, and gas sampling. Install fixed ladders if needed.

Ventilation (Indoor/Underground Transformers)

• Ensure sufficient ventilation to prevent overheating. For rooms with mechanical ventilation, trigger remote alarms if the system stops. Avoid connecting transformer ventilation to other building systems.

Transformer Room Safety

• Use fire-retardant or non-combustible materials for doors, which must be lockable. Mark doors with the transformer’s name and operation number, and post “High Voltage—Danger” warning signs externally.

Fire & Environmental Protection

• Equip oil-immersed transformer installations with fire-fighting equipment and accident oil storage facilities (per design regulations) and maintain them regularly.

Anti-Vibration Measures (Seismic Zones ≥Magnitude 7)

• Secure transformer chassis to rails.
• Use appropriately slack soft wires or extended transitional soft connections for bushing connections (avoid rigid wire stress).
• Connect separate coolers to transformers via valves, flexible joints, and pipes.
• Install shock-resistant gas relays.
• Fasten pole-mounted transformer chassis to brackets and secure the upper section to the pole.

Short-Circuit Protection

• If the system’s actual short-circuit apparent capacity exceeds GB1094.5 Table 2 limits, implement short-circuit current limiting measures. Ensure transformer protection triggers faster than the short-circuit heat resistance duration.

On-Line Monitoring

• For insulation condition monitoring devices: Ground sensors reliably and ensure oil-dissolved gas sampling devices have tight seals.

Required Technical Documentation

Pre-Commissioning Handover (Construction to Operation Unit)

New Equipment Installation

• Manufacturer-provided manuals, drawings, and factory test reports.
• Handover test reports for the transformer body, cooling system, and accessories (bushings, instrument transformers, tap changers, gas relays, pressure relief valves, etc.). Include lifting/inspection records for the body.
• Complete installation records (per GBJ148 and manufacturer guidelines).
• As-built drawings for cooling systems and on-load voltage regulator control/protection circuits.
• Oil quality test and chromatographic analysis reports.
• Spare parts list.

Post-Overhaul Handover

• Overhaul reasons and full process records.
• Test reports for the transformer and accessories.
• Drying records (if applicable).
• Oil test, chromatographic analysis, and oil treatment records.

Permanent Technical Files (Per Transformer)

• Transformer resume card.
• Post-installation handover documents.
• Post-overhaul handover documents.
• Preventive test records.
• Calibration records for protection and measurement devices.
• Oil treatment and refueling logs.
• Other test and inspection reports.
• Accident and abnormal operation records (e.g., overheating, gas relay activation, short circuits, overcurrent).

Documentation Handover

General Operating Conditions

Voltage Limits

• Operate transformers at voltages ≤105% of the rated tap voltage (standard use). For special cases (e.g., bidirectional active power flow), voltages up to 110% of rated are permitted.
• If no specific voltage-current constraints apply, limit overvoltage duration based on load current (K, where K ≤1) using industry-standard formulas. For shunt reactors, arc suppression coils, and voltage regulators, follow manufacturer-specified overvoltage limits.

Tap Changer Capacity Adjustments

• Non-excitation voltage regulators: Rated capacity remains unchanged for taps within ±5% of rated voltage. For 7.5% and 10% taps, reduce capacity by 2.5% and 5% respectively (unless the manufacturer specifies otherwise).
• On-load voltage regulators: Follow manufacturer ratings for each tap position.

Top-Oil Temperature Limits (Oil-Immersed Transformers)

• Adhere to temperature limits specified by the manufacturer (or industry standards if unspecified). For natural circulation cooling, avoid frequent top-oil temperatures exceeding 85℃. Lower ambient temperatures allow proportionally lower top-oil temperatures.