Model Interpretation

SR745: 745 series transformer protection relay

W2: 2‑winding transformer configuration

P5: 5 A CT secondary phase current input

G5: 5 A ground CT input

HI: High‑impedance control power (70–265 VAC / 90–300 VDC, 48–62 Hz)

Technical Parameters

Input & Power

CT Input: 5 A phase (2 windings); 5 A ground

VT Input: 60–120 V phase‑neutral

Control Power: 70–265 VAC / 90–300 VDC, 48–62 Hz

Power Consumption: ≤12 VA typical

Protection Functions

Differential: 2‑winding restrained differential, high‑speed (≤8 ms trip)

Overcurrent: Phase/ground, IEC inverse/definite time, 0.1–20×In

Thermal: Winding/iron core overload, RTD‑based overtemperature

Voltage/Frequency: Over/undervoltage, over/underfrequency, overexcitation blocking

Ground Fault: Restricted earth fault (REF), high‑Z ground fault

Trip Time: ≤8 ms (differential); ≤15 ms (overcurrent)

I/O & Interfaces

Analog Inputs: 4 RTD (3‑wire; Pt100, Ni100/120, Cu10)

Analog Outputs: 4 × 4–20 mA, isolated, 600 Ω burden max

Digital Inputs: 16 opto‑isolated (dry/wet, ≤1 ms)

Relay Outputs: 8 Form C (5 A / 250 VAC)

Communication: RS‑232 (front), RS‑485 (Modbus RTU), Ethernet (IEC 61850, DNP3)

Display & User Interface

Display: 40‑character backlit LCD

Indicators: 12 LED (RUN, TRIP, ALARM, FAULT, SERVICE)

Keypad: Numeric/navigation for local programming

Mechanical & Environmental

Dimensions: 228.6 mm H × 177.8 mm W × 180.9 mm D (9”×7”×7.125”)

Mounting: Panel mount (19” rack compatible)

Enclosure: Flame‑retardant plastic; IP50 (front), IP20 (overall)

Operating Temp: -40°C to +60°C

Storage Temp: -40°C to +85°C

Humidity: 5–95% non‑condensing

Certifications: UL, CE, CSA, IEC 60255, ATEX

Metering & Diagnostics

Metering: 3‑phase current/voltage, power, energy, frequency, PF, demand (0.2% accuracy)

Diagnostics: Event log (1024 events), fault recorder (256‑cycle oscillography), pre‑trip data

Thermal Modeling: RTD biasing, load loss cooling curves, hot‑spot estimation

Core Functions

High‑Speed Differential Protection: Detects internal winding faults in <10 ms to prevent catastrophic failure.

Comprehensive Thermal Protection: Monitors winding/bearing temps via RTDs and models thermal stress.

Wide‑Range HI Power: Operates from 70–265 VAC / 90–300 VDC for flexible substation integration.

Advanced Communications: Ethernet IEC 61850 for grid‑wide SCADA and Modbus for legacy systems.

Robust Fault Diagnostics: Captures oscillography and event logs for root‑cause analysis.

Applications

Power Utilities: Transmission/distribution transformers, substations

Oil & Gas: Step‑up/down transformers, offshore platforms

Metallurgy: Furnace transformers, heavy‑duty process units

Petrochemical: Refinery transformers, corrosive environments

Renewables: Wind/solar farm grid‑intertie transformers

Usage & Maintenance

Installation: Panel‑mount; wire CT/VT, HI control power, RTDs, and communications.

Programming: Use front keypad or connect to EnerVista 745 software via RS‑232/Ethernet.

Configuration: Set CT/VT ratios, differential slopes, protection curves, and RTD types.

Maintenance: Inspect terminals annually; update firmware; verify settings after system changes.