GWPR300-TD Transformer Differential Protection Relay

Protection Functions

Transformer Differential Main Protection (ANSI 87T)

•  (ANSI 87T) Instantaneous Differential Protection: Trips instantaneously when the differential current reaches or exceeds the setting value. The relay operating time is ≤35 ms at 1.2 times the setting value (excluding circuit breaker operating time), rapidly clearing severe short-circuit faults on windings and bushing terminals.
• (ANSI 87T) Percentage Restraint Differential Protection: Adopts segmented percentage restraint characteristics with built-in automatic phase correction and balance factor conversion for currents on all transformer sides. The second harmonic restraint and CT open-circuit blocking logic can be independently enabled or disabled to prevent maloperation induced by transformer inrush current and unbalanced current under external short-circuit faults.
•  (ANSI 87T) CT Open-Circuit Alarm: Monitors the operational status of CT secondary circuits in real time. An alarm signal is output with a 10-second delay after an open-circuit fault is detected. The blocking function for percentage differential protection can be independently enabled or disabled to suit diverse field operating modes.
•  (ANSI 87T) Excessive Differential Current Alarm: Triggers a 3-second delayed alarm when differential current continuously exceeds 0.5 times the pickup setting without protection tripping, delivering early warnings against CT circuit defects and three-phase load unbalance risks.

Non-Electrical Protection

The non-electrical protection circuit adopts electrically isolated independent acquisition and hardware tripping output design. Tripping signals are driven by dedicated hardware circuits without CPU logic processing, fully complying with power system anti-accident requirements to guarantee reliable operation under main transformer faults.

•  Main Tank Buchholz (Light Gas) Protection: Equipped with adjustable independent time delay, supporting two output modes: alarm or trip.
•  Main Tank Buchholz (Heavy Gas) Protection: Configurable independent time delay with selectable alarm or trip outputs.
•  On-Load Tap Changer Light Gas (Buchholz) Protection: Detects minor oil-gas generation inside tap changers and outputs alarm signals only.
• On-Load Tap Changer Heavy Gas (Buchholz) Protection: Initiates tripping for severe tap changer faults, with optional alarm or trip modes.
• (ANSI 49T) Oil Temperature Rise Warning: Sends remote alarm signals for slight oil temperature overshoot.
•  (ANSI 49T) Over-Temperature Trip Protection: Provides delayed alarm or delayed trip logic under hazardous over-temperature conditions.
•  Cooling System Fault Protection: Generates alarm signals for cooling fan shutdown failures.
• Pressure Relief Protection: Executes instantaneous tripping via independent hardware circuits when internal tank pressure spikes.
•  High / Low Oil Level Protection: Separate configurable alarm and trip logics for abnormal oil level conditions.

 Hardware Self-Diagnosis

• Continuous full-loop hardware self-diagnosis is implemented, covering memory, program storage, analog-to-digital sampling circuits, validity verification of protection settings, tripping output loops, dual Ethernet ports and RS485 communication channels. The panel fault indicator illuminates upon abnormality detection, with alarm events uploaded remotely.

Core Technical Specifications

• Power Supply: AC 100–264 V / DC 100–264 V wide-range universal power supply.
• AC Analog Input: CT secondary rated current 1 A / 5 A, selectable upon order.
• Measurement Accuracy: Class 0.2 for current; Class 0.5 for other analog quantities.
• Instantaneous Protection Operating Time: ≤35 ms at 1.2 times the setting value (excluding circuit breaker operating time).
• Timing Error of Delayed Protection: ≤±5% of delay setting or ±40 ms, whichever is larger.
• Relay Contact Capacity: 8 A @ 250 V AC / 8 A @ 30 V DC.
• Operating Ambient Temperature: -40 °C to +70 °C.
• Insulation Resistance: Each circuit to earth ≥100 MΩ, tested with a 500 V megohmmeter.
• Dielectric Strength: Power supply, sampling and output circuits withstand 2 kV for 1 min; low-voltage signal circuits withstand 500 V for 1 min, compliant with GB/T 14598 series standards.
• Mechanical Performance: Capable of withstanding Class I vibration, shock and bump tests, with stable mechanical structure for long-term operation.

Application Scenarios

• Applicable Equipment: Two-winding and three-winding oil-immersed power transformers rated up to 132 kV, including station service transformers and distribution transformers.
• Neutral Grounding Compatibility: Compatible with neutral ungrounded, resistance-earthed, arc suppression coil-earthed and solidly earthed systems. Corresponding protection logics shall be configured per power system design specifications for different voltage levels.
  Installation Methods: Embedded on-site cabinet mounting, centralized panel mounting in control rooms.
• Application Sites: Urban and rural substations, industrial and mining power distribution stations, new energy step-up substations, park power distribution facilities, digital intelligent substations (IEC 61850 module optional).

Core Product Features

• Dedicated three-side differential operation algorithm with built-in automatic phase correction for Y/Δ windings and CT ratio unbalance compensation, eliminating external balance resistors.
• Three independent anti-maloperation logics – percentage restraint differential, second harmonic restraint and CT open-circuit blocking – can be individually enabled or disabled, ensuring stable non-tripping during transformer energization and external short-circuit events.
• 10-channel non-electrical acquisition circuits with independent hardware acquisition and tripping outputs; tripping actions operate independently of CPU processing, supporting comprehensive monitoring of gas, temperature, pressure, oil level and cooling systems with superior reliability.
• Modular hardware and software architecture; all protection functions can be individually activated or deactivated for convenient on-site setting and commissioning.
• Fully sealed metal enclosure with physical isolation between power and signal wiring. Industrial wide-temperature design adapts to harsh environments such as indoor distribution rooms and outdoor cubicles.
• Multiple communication interfaces and diverse clock synchronization modes compatible with both conventional automation substations and new-generation IEC 61850 digital intelligent substations.
• Large-capacity fault recording storage and complete Sequence-of-Event (SOE) records supply full data support for fault tracing and operation and maintenance analysis.