TMEICA ARND-3620

Description

Technical Specifications:

• Model: ARND-3620
• Type: Static Excitation Controller — Thyristor Bridge Controller
• Application: Slip-ring (static) excitation for synchronous generators
• Input Signals: Generator PT voltage, generator CT current, field current (shunt), field voltage, frequency, start/stop
• Output: Firing pulses for 6-pulse or 12-pulse thyristor bridge
• Voltage Regulation Accuracy: ±0.5% (steady state)
• Response Time: < 30 ms
• Field Current Range: 0–6000 A (external thyristor bridge rating determines max — controller itself handles up to 2000 A field via 6-pulse)
• Firing Angle Range: 0°–150° (limited vs. brushless due to field time constant)
• Communication: RS-485 Modbus RTU, optional Ethernet
• Power Supply: 110/220 VAC, 50/60 Hz, or 24 VDC
• Operating Temperature: -10°C to +50°C
• Dimensions: 1/4 DIN or panel-mount
• Weight: Approximately 2.0 kg
• Compliance: IEC 60034, IEEE 421.5

Functional Features:

• Field current feedback control (closes the loop on actual field current, not just terminal voltage)
• Field flash protection: detects loss of field and initiates emergency flash from auxiliary source
• Overvoltage protection:crowbar circuit coordination
• Underexcitation limiter (UEL) with adaptive settings
• Stator current limiter (SCL)
• Soft starter function for controlled field buildup
• Field discharge resistor control

Structural Characteristics:

• Enclosure: Metal panel-mount or DIN-rail, IP20
• Terminals: Screw terminals for all I/O, shunt input for field current (mV range)
• PCB: 4-layer, conformal coated
• Display: 4-digit LED for setpoint and actual field current

Working Principle: The ARND-3620 regulates the generator terminal voltage by controlling the DC field current. It measures terminal voltage (PT) and compares it to the setpoint. The error is processed by a PI controller. The controller output sets the firing angle of the thyristor bridge. The thyristor bridge rectifies AC power and delivers controlled DC current to the field winding via slip rings. A field current shunt (mV signal) provides closed-loop feedback on actual field current, ensuring accurate regulation even with varying field resistance (temperature-dependent). The field flash function uses a separate auxiliary thyristor bridge to rapidly discharge the field winding in case of excitation failure, preventing loss of synchronism.

Advantages:

• Field current feedback provides superior regulation accuracy compared to open-loop brushless systems
• Compatible with existing slip-ring generators — no need to convert to brushless
• Built-in field flash eliminates need for separate flash protection relay
• Proven technology in hydro generators with slip rings worldwide

Applicable Industries: Hydroelectric generators (large Francis/Kaplan turbines with slip rings), thermal generators with static excitation, industrial synchronous motors, synchronous condensers

Installation Requirements:

• Field current shunt: installed on field circuit, rated for max field current, mV output (typically 75 mV or 50 mV full scale)
• PT and CT: same as brushless systems
• Firing pulse cables to thyristor bridge: shielded, max 50 m
• Crowbar circuit: must be coordinated with ARND-3620 protection settings — contact TMEIC for coordination study
• Ground: < 1 Ohm

Usage Precautions:

• Field flash coordination is critical — incorrect crowbar settings can destroy the thyristor bridge
• Verify field current shunt polarity before energizing — reverse polarity causes uncontrolled field current
• Slip ring maintenance schedule must be followed — carbon dust can cause field ground faults
• Do not exceed 150° firing angle — this is the maximum for safe commutation in static excitation
• Annual calibration of field current shunt required (drift affects regulation accuracy)