Application area 
The Qualitrol STB Smart Transformer Air Dryer removes moisture from the air that enters the main compartment of oil-filled transformers or the on-load tap-changer compartment. The dehumidifier is equipped with a system for automatically restoring the silica gel moisture absorber after a user-defined period of time or when a threshold relative humidity value is reached. The alarm function and communication reduces unnecessary maintenance costs on the air dryer over time. The silica gel dehumidifier can be regenerated many times without replacement thanks to the internal heaters installed inside the dehumidifier. They remove water accumulated during the exhalation cycle.
Advantages:
- The device is made of durable materials, so you can choose a model for almost any operating conditions
- Possibility of customization and threshold values of relative humidity
- Local and remote data exchange functions allow the device to be used in various operating conditions
- Indication of the condition of the air dryer is provided by bright LED indicators and alarm functions
Specifications
| Parameter | Meaning | |
| Electrical part | Voltage/frequency | 100–240 V AC current, 50/60 Hz |
| Inrush current monitoring | Step heating in 10 seconds | |
| Conducted/radiated interference | EN 55011 | |
| Security tests | EN 61000-4-2 | |
| EN 61000-4-3 | ||
| EN 61000-4-4 | ||
| EN 61000-4-5 | ||
| EN 61000-4-6 | ||
| EN 61000-4-8 | ||
| EN 61000-4-11 | ||
| Harmonics and flicker noise testing | EN 61000-3-2 | |
| EN 61000-3-3 | ||
| Dielectric insulation | 1500 V AC current for 60 seconds to ground | |
| Power consumption | Steady state, non-recovery: < 10 W | |
| Steady state with recovery: 3 A | ||
| Recovery heater starting current: 10A | ||
| Functions | Setting the recovery rate | 10, 40, 70, 100 days |
| Humidity range | Relative humidity - 2% to 100% | |
| Status indication | LEDs - green, yellow, red | |
| Recovery rate control | Two-position DIP switch | |
| Relative humidity trigger level | Configured by the operator: default value is 50% | |
| Recovery cycle | Maximum power - 3 hours, cooling - 1 hour | |
| Monitoring recovery status | 5 A (normally open) / 3 A (normally closed) at 30 V DC current, resistive | |
| 5 A (normally open) / 3 A (normally closed) at 125/250 VAC current, resistive | ||
| Fault Detection | Relative Humidity Sensor, Heater, Solenoid | |
| Analog output signal | 4–20 mA at max. 500 ohm for recording relative humidity | |
| Data exchange | MODBUS (remote) and USB (local) | |
| terms of Use | Temperature | From – 40°C to 80°C or from – 60°C to 80°C, depending on the model |
| Relative humidity | 95% non-condensing at 80°C | |
| Housing protection | IP65 | |
| Vibration strength | 50/60 Hz at 0.1 mm (0.004 in) offset |
Suggested STB models
Qualitrol offers various models for almost any operating conditions:
Selecting the amount of desiccant STB
The standard size of STB air dryers is determined by the amount of oil contained in the system (main tank + expansion tank):
