Technical Guides · 2025-08-28
BSTY Three-Phase SCR AC Power Regulator: Signal Options, Sizing and Commissioning
Electrical data, control signal selection, current sizing for three-phase resistive loads, soft-start and thermal protection settings, wiring practice and commissioning steps for the BSTY three-phase SCR power regulator.
The BSTY series is a three-phase SCR AC power regulator for 380VAC industrial heating and power control. It uses phase-angle regulation to deliver a continuously variable fraction of line power, replacing the temperature ripple of on/off switching with smooth, stepless output. Ordering data is on the BSTY product page.
1. Specification
| Parameter | Specification |
| Series / type | BSTY Series three-phase SCR AC voltage regulator |
| Working voltage | 3-phase 380VAC ±5% |
| Rated current | 150A / 200A / 300A / 350A / 400A / 450A |
| Control method | Phase-angle regulation, 0–180° |
| Analog input | 1–5V, 2–10V, 4–20mA |
| Manual control | 10kΩ / 2W potentiometer |
| Soft start | 2 s default, adjustable 0–15 s |
| Protection | Over-temperature cut-off at 85°C |
| Insulation | Fully isolated control and power circuits |
| Phase sequence | No restriction |
| Mounting | Bolt installation |
| Load type | Three-phase resistive |
2. Choosing the control signal
| Parameter | Specification |
| 4–20mA | Preferred in noisy plant and for long cable runs; a broken wire reads 0 mA and is detectable. Pair with a PID controller ordered with current output. |
| 2–10V / 1–5V | Direct connection to most PLC analog output cards. Keep the cable short and screened. |
| 10kΩ potentiometer | Manual panel control of output power where no controller is used. |
Control and power circuits are fully isolated, but signal cable should still be screened and routed in separate trunking from the load cabling.
3. Sizing the regulator
- Three-phase resistive load current: I = P / (1.732 × 380). A 60 kW oven draws about 91 A per phase.
- Order the next rating up with margin — the 91 A example takes the 150A model once ambient and duty are allowed for.
- Derate for high cabinet temperature, continuous duty and restricted airflow.
- Phase-angle control generates harmonic current; confirm supply cabling and upstream protection are suitable.
- For loads below 150 A per phase, use the SCR3L (60–200A) instead.
4. Installation and wiring
- Connect the three-phase 380VAC supply to the input terminals and the heater to the output terminals; no phase sequence check is required.
- Mount vertically with unobstructed airflow over the heat sink; larger ratings require forced-air cooling in the panel.
- Fit upstream short-circuit protection sized to the module — semiconductor fuses give the best device protection.
- Torque all power terminals to specification and re-check after the first full thermal cycle.
- Set the soft-start time (0–15 s) to limit inrush on cold heating elements and transformer-coupled loads.
5. Commissioning
- With the heater isolated, apply minimum signal and confirm zero output, then ramp to maximum and confirm a smooth, step-free rise.
- Check that output tracks controller demand across the whole range, not only at the extremes.
- Measure heat sink temperature after 30 minutes at full load; if it approaches the 85°C trip point, improve cooling.
- For closed-loop operation, re-run PID auto-tune after switching from on/off control — the loop dynamics are completely different.
- Confirm the over-temperature LED and cut-off operate before handing the panel over.
6. FAQ
How is a BSTY regulator different from a solid state relay?
An SSR switches fully on or fully off. The BSTY varies the SCR conduction angle, producing continuously adjustable heating power and much tighter temperature control.
Can I use it on a single-phase heater?
No. Use the BDTY single-phase regulator, rated 10A to 400A.
Does it work with inductive loads?
The series is specified for three-phase resistive loads. Send load data before applying it to transformers or motors.
What does soft start actually do?
It ramps the conduction angle up over the set time so cold, low-resistance heating elements do not draw a large inrush current at switch-on.
Which controller should drive it?
Any PID controller with a 4–20mA output, for example a TC5 series or TC4 series ordered with current output.
Sizing help and bulk inquiries: sales@strong-ele.com.