ST400‑PC / ST400‑PT Microcomputer Measurement‑Control and Protection Device

Product Overview

    The ST400‑PC and ST400‑PT are microcomputer measurement‑control & protection devices manufactured by Wanlong Electric Group. ST400‑PC is applied for PC current‑protection circuits while ST400‑PT is designed for PT voltage monitoring circuits. The device integrates protection, electrical measurement, circuit‑breaker control, alarm processing and industrial communication functions. It features local man‑machine LCD operation panel with Chinese‑English bilingual display, 4‑20 mA analog transmitter output, as well as local/remote permission management. Typical application scenarios include medium‑low voltage switchgear cabinets, distribution rooms and industrial power monitoring systems. Default user access password is 0400.

Product Models and Classification

ST400‑PC Model Coding (For PC protection circuit)

   Example model: ST400PC‑F‑2‑5A‑100V‑M1

1. Control circuit voltage type

• F: Standard type
• M: AC enhanced type (DC110V)
• H1: DC enhanced type (DC110V)
• H2: DC enhanced type (DC220V)

2. Communication protocol code

• 1: No communication
• 2: 2‑channel Profibus‑DP
• 3: 1‑channel Modbus‑RTU
• 5: 2‑channel Modbus‑RTU
• 6: 2‑channel Profibus‑DP
• 7: 1‑channel Modbus‑RTU + 1‑channel Profibus‑DP

3. Current grade: 1A, 5A (built‑in CT input range)
4. Voltage grade: 100V, 400V
5. Optional extended functions

• M1: 1‑channel analog output; M2: 2‑channel analog output
• L: Zero‑sequence current input; Uz: Zero‑sequence voltage input ‑4DI: Extended 4 digital inputs; 2DO: Extended 2 relay outputs

ST400‑PT Model Coding (For PT voltage circuit)

    Model coding rules keep consistent with ST400‑PC. The PT version removes front‑panel physical local‑remote permission switch; front‑panel close and trip buttons have no functional definition for PT units.

Core Protection Functions

    Over‑current Protection Two‑stage over‑current protection is available, including 1st‑stage over‑current and 2nd‑stage over‑current. Pick‑up value and action delay are configurable; action modes can be set as Disable, Alarm or Trip. Time resolution for protection delay is 0.02 s.

   Zero‑sequence Protection Zero‑sequence current and zero‑sequence voltage protection are supported. Users configure threshold and action mode (disable / alarm / trip) to detect earth‑related insulation faults.

   Voltage Related Protection Covers over‑voltage, under‑voltage, voltage unbalance and PT disconnection protection. Protection thresholds and action modes are adjustable for busbar voltage abnormality monitoring.

   Auto‑reclosure Three‑phase one‑shot auto‑reclosure function can be enabled or disabled according to field configuration.

   Circuit‑breaker Loop Supervision Detects close‑circuit and trip‑circuit wire break condition; function enable and external divider wiring are required for valid loop break detection.

Measurement and Metering Functions

    Analog Sampling Measurement Real‑time measuring of three‑phase current, three‑phase voltage, zero‑sequence current, zero‑sequence voltage, frequency, active/reactive/apparent power and power factor. CT primary / PT primary and secondary ratio parameters shall match with site instrument transformers for accurate reading.

    4‑20 mA Analog Transmitter Output Supports configurable AO variables, output range 4‑20 mA. Calculation formula: \(I_{out}= \frac{DisplayValue‑AO_{low}}{AO_{high}‑AO_{low}} \times16 +4\) For power‑related variables: DisplayValue = Raw reading × CT ratio × PT ratio. AO upper and lower limits are user‑configurable.

Input & Output Functions

    Digital Input (DI) DI channels accept external status signals: circuit‑breaker position feedback, spring charged status, local‑remote switching signal and general‑purpose digital input. DI status can be checked on device panel for commissioning.

   Relay Output (DO) Multiple logic relay outputs are configurable: general alarm, definite‑time over‑current output, zero‑sequence voltage output, self‑diagnostic fault output, busbar loss‑voltage output, trip output, logic outputs and general‑purpose relay outputs. DO function assignment shall be completed in parameter menu.

Operation and Maintenance Functions

   Local‑Remote Permission Switch ST400‑PC supports physical panel permission toggle switch. Permission can also be assigned via DI terminal or menu setting. PT model does not carry hardware permission switch. Improper permission setting will block local panel or remote communication control commands.

   Human‑Machine Interface LCD display supports Chinese / English language switch. Navigation keys include up / down / left / right, confirm, return, reset, close and trip buttons. LED status indicators show power status, fault, alarm and communication running status.

   Fault Diagnosis Typical diagnostic items include permission switching abnormality, measured value deviation, close/trip loop break fault and communication connection failure. The device provides menu‑based troubleshooting guidance. Event and fault information can be viewed locally on panel.

Communication Capability

   Modbus‑RTU Dual‑network A/B Modbus‑RTU interface. Device address, baud rate (4.8 / 9.6 /19.2 /38.4 kbps) are configurable. Remote close command: write register 00AF with value AAAA; remote trip: write 5555; emergency trip: write 3333.

   Profibus‑DP Requires GSD file SIDA08F4.GSD for system configuration. After entering Data‑Exchange state, send value 1000 for close, 2000 for normal trip and 8000 for emergency trip. Terminating resistor shall be correctly installed on Profibus bus. Communication documents, point tables and GSD files can be acquired from Wanlong Electric Group technical support.

Installation and Mechanical Parameters

   Panel Cut‑out Dimension: 134 mm × 134 mm Terminal blocks include relay output terminals, CT current input terminals, PT voltage input terminals, DI input terminals, communication terminals, AO analog output terminals, PE protective earth terminal and extended‑function terminals.